fix(tp): import BackendStorage trait for CudaStorage methods

Stage 7b-iii (1/2) introduced AllReduce with `s.device()` and
`s.dtype()` calls on `&CudaStorage`. Both come from the
`candle_core::backend::BackendStorage` trait, which wasn't imported —
fine on CPU builds (the cuda_fwd block was cfg-gated out) but the
prerelease cuda build hit E0599.

Also drop the unused `cudarc::driver::DeviceSlice` import inside
cuda_fwd — `CudaSlice::len()` is an inherent method on cudarc 0.19,
not a trait method.

Caught by run 2894 (build-neuron-{blackwell,ampere}); CPU clippy +
tests stay green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-prerelease.yml

@@ -0,0 +1,342 @@
+name: build-prerelease
+
+# Manually-dispatched workflow that builds CUDA-flavoured neuron binaries
+# (and a single cortex binary), packages each as a Fedora RPM, signs
+# them, and publishes to the `unstable` channel at rpm.lair.cafe.
+#
+# Trigger from the Gitea UI: Actions → build-prerelease → Run workflow.
+# Optionally provide a `ref` to build from a non-default branch.
+#
+# The published packages are versioned as e.g.
+#   helexa-neuron-blackwell-0.1.16-0.1.20260518T140530.gitabcdef0.fc43.x86_64
+#                                       ^^^^^^^^^^^^^^^^^^ ^^^^^^^^
+#                                       commit time (s)    commit sha
+# so they sort BELOW the eventual 0.1.16-1 stable release, and so two
+# commits on the same day are still strictly ordered by their commit
+# timestamps (rather than by RPM-vercmp's alpha-vs-digit precedence
+# on the SHA fragment).
+
+on:
+  # Auto-build on every push to main so the unstable channel tracks
+  # head without a manual dispatch step.
+  push:
+    branches: [main]
+  # Manual dispatch still available to build from a non-main ref.
+  workflow_dispatch:
+    inputs:
+      ref:
+        description: "Git ref to build (branch / tag / commit). Defaults to the workflow's branch."
+        required: false
+        default: ""
+
+concurrency:
+  # Share the group with ci.yml so the two workflows can't run
+  # concurrently on the same `rust` runner (act reuses the workspace
+  # cache and races destroy each other's build files mid-compile).
+  # cancel-in-progress=false → workflows queue; if a newer push lands,
+  # the older run is still picked up by ci.yml's own ref-keyed
+  # concurrency (same group, queued).
+  group: cortex-runner-pool-${{ github.ref }}
+  cancel-in-progress: false
+
+env:
+  CARGO_INCREMENTAL: "0"
+
+jobs:
+  prepare:
+    name: Resolve version stamps
+    runs-on: rust
+    outputs:
+      version: ${{ steps.info.outputs.version }}
+      release: ${{ steps.info.outputs.release }}
+      short_sha: ${{ steps.info.outputs.short_sha }}
+      commit_timestamp: ${{ steps.info.outputs.commit_timestamp }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.ref }}
+          fetch-depth: 0
+
+      - id: info
+        run: |
+          set -eux
+          VERSION=$(awk -F\" '/^version[[:space:]]*=/ { print $2; exit }' Cargo.toml)
+          SHORT_SHA=$(git rev-parse --short=7 HEAD)
+          # Second-precise commit timestamp gives the release stamp a
+          # strictly monotonic numeric prefix. The earlier %Y%m%d-only
+          # form let same-day builds be ordered by RPM's rpmvercmp
+          # rules over the SHA, which is non-chronological — e.g.
+          # "git602e8e1" sorts newer than "gitf9f5fa4" purely because
+          # rpmvercmp ranks digit-prefixed segments above alpha ones.
+          # The SHA stays only as a debug identifier; sort order is
+          # decided entirely by the timestamp.
+          COMMIT_TIMESTAMP=$(git log -1 --format=%cd --date=format:%Y%m%d%H%M%S HEAD)
+          RELEASE="0.1.${COMMIT_TIMESTAMP}.git${SHORT_SHA}"
+          echo "version=${VERSION}" >> "$GITHUB_OUTPUT"
+          echo "release=${RELEASE}" >> "$GITHUB_OUTPUT"
+          echo "short_sha=${SHORT_SHA}" >> "$GITHUB_OUTPUT"
+          echo "commit_timestamp=${COMMIT_TIMESTAMP}" >> "$GITHUB_OUTPUT"
+
+  build-cortex:
+    name: Build cortex binary
+    needs: prepare
+    # runner-rust image already provides rust/cargo/clippy/rustfmt via
+    # dnf — no rustup install step needed.
+    runs-on: rust
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.ref }}
+
+      - name: Build cortex (release)
+        run: cargo build --release -p cortex-cli
+
+      - name: Stage binary
+        run: |
+          mkdir --parents artifacts
+          cp target/release/cortex artifacts/cortex
+          ./artifacts/cortex --version || true
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: cortex-fc43
+          path: artifacts/cortex
+          retention-days: 1
+
+  build-neuron:
+    name: Build neuron-${{ matrix.flavour }}
+    needs: prepare
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - flavour: ampere
+            compute_cap: "86"
+            runner: cuda-13.0
+            cuda_home: /usr/local/cuda-13.0
+            build_jobs: 8
+            nvcc_threads: 4
+            cargo_features: "cuda cudnn flash-attn"
+          - flavour: ada
+            compute_cap: "89"
+            runner: cuda-13.0
+            cuda_home: /usr/local/cuda-13.0
+            build_jobs: 8
+            nvcc_threads: 4
+            cargo_features: "cuda cudnn flash-attn"
+          - flavour: blackwell
+            compute_cap: "120"
+            runner: cuda-13.0
+            cuda_home: /usr/local/cuda-13.0
+            build_jobs: 8
+            nvcc_threads: 4
+            cargo_features: "cuda cudnn flash-attn"
+    runs-on: ${{ matrix.runner }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.ref }}
+
+      - name: Build neuron with CUDA (${{ matrix.flavour }})
+        run: |
+          set -eux
+          export PATH="${{ matrix.cuda_home }}/bin:${PATH}"
+          export LD_LIBRARY_PATH="${{ matrix.cuda_home }}/targets/x86_64-linux/lib:${{ matrix.cuda_home }}/lib64:${LD_LIBRARY_PATH:-}"
+          export LIBRARY_PATH="${{ matrix.cuda_home }}/targets/x86_64-linux/lib:${{ matrix.cuda_home }}/lib64:${LIBRARY_PATH:-}"
+          cargo build --release -p neuron --features "${{ matrix.cargo_features }}"
+        env:
+          CUDA_COMPUTE_CAP: ${{ matrix.compute_cap }}
+          CARGO_BUILD_JOBS: ${{ matrix.build_jobs }}
+          NVCC_THREADS: ${{ matrix.nvcc_threads }}
+
+      - name: Stage binary
+        run: |
+          mkdir --parents artifacts
+          cp target/release/neuron artifacts/neuron-${{ matrix.flavour }}
+          file "artifacts/neuron-${{ matrix.flavour }}"
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: neuron-${{ matrix.flavour }}-fc43
+          path: artifacts/neuron-${{ matrix.flavour }}
+          retention-days: 1
+
+  package-cortex:
+    name: Package cortex RPM
+    needs: [prepare, build-cortex]
+    runs-on: rpm
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.ref }}
+
+      - uses: actions/download-artifact@v3
+        with:
+          name: cortex-fc43
+          path: artifacts/
+
+      - name: Build RPM
+        run: |
+          set -eux
+          rm -f ~/.rpmmacros
+          rpmdev-setuptree
+          cp artifacts/cortex ~/rpmbuild/SOURCES/
+          cp data/cortex.service ~/rpmbuild/SOURCES/
+          cp data/cortex-sysusers.conf ~/rpmbuild/SOURCES/
+          cp data/cortex-firewalld.xml ~/rpmbuild/SOURCES/
+          cp cortex.example.toml ~/rpmbuild/SOURCES/
+          cp models.example.toml ~/rpmbuild/SOURCES/
+          cp LICENSE ~/rpmbuild/SOURCES/
+          rpmbuild -bb rpm/cortex-prerelease.spec \
+            --define "cortex_version ${{ needs.prepare.outputs.version }}" \
+            --define "cortex_prerelease ${{ needs.prepare.outputs.release }}" \
+            --undefine dist \
+            --define "dist .fc43"
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: rpm-cortex-fc43
+          path: ~/rpmbuild/RPMS/x86_64/*.rpm
+          retention-days: 7
+
+  package-neuron:
+    name: Package helexa-neuron-${{ matrix.flavour }} RPM
+    needs: [prepare, build-neuron]
+    runs-on: rpm
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - flavour: ampere
+          - flavour: ada
+          - flavour: blackwell
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.ref }}
+
+      - uses: actions/download-artifact@v3
+        with:
+          name: neuron-${{ matrix.flavour }}-fc43
+          path: artifacts/
+
+      - name: Build RPM
+        run: |
+          set -eux
+          rm -f ~/.rpmmacros
+          rpmdev-setuptree
+          cp artifacts/neuron-${{ matrix.flavour }} ~/rpmbuild/SOURCES/
+          cp data/neuron.service ~/rpmbuild/SOURCES/
+          cp data/neuron-sysusers.conf ~/rpmbuild/SOURCES/
+          cp data/neuron-firewalld.xml ~/rpmbuild/SOURCES/
+          cp neuron.example.toml ~/rpmbuild/SOURCES/
+          cp LICENSE ~/rpmbuild/SOURCES/
+          rpmbuild -bb rpm/helexa-neuron-prerelease.spec \
+            --define "neuron_version ${{ needs.prepare.outputs.version }}" \
+            --define "neuron_flavour ${{ matrix.flavour }}" \
+            --define "neuron_prerelease ${{ needs.prepare.outputs.release }}" \
+            --undefine dist \
+            --define "dist .fc43"
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: rpm-neuron-${{ matrix.flavour }}-fc43
+          path: ~/rpmbuild/RPMS/x86_64/*.rpm
+          retention-days: 7
+
+  publish:
+    name: Publish to rpm.lair.cafe (unstable)
+    needs: [package-cortex, package-neuron]
+    runs-on: rpm
+    concurrency:
+      group: rpm-publish
+      cancel-in-progress: false
+    env:
+      RPM_REPO_HOST: oolon.kosherinata.internal
+      FEDORA_VERSION: "43"
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.ref }}
+
+      - name: Download all built RPMs
+        uses: actions/download-artifact@v3
+        with:
+          path: rpms/
+          pattern: rpm-*-fc43
+
+      - name: Flatten RPM artifacts
+        run: |
+          set -eux
+          find rpms/ -name '*.rpm' -exec mv --target-directory=rpms/ {} +
+          find rpms/ -mindepth 1 -type d -empty -delete
+          ls -la rpms/
+
+      - name: Check for sequoia-sq
+        run: |
+          if ! command -v sq &> /dev/null; then
+            echo "ERROR: sequoia-sq is not installed. Install with: sudo dnf install sequoia-sq"
+            exit 1
+          fi
+
+      - name: Import signing key
+        env:
+          # Pass secrets via env so values stay out of the rendered shell
+          # script (which Gitea includes in step logs). Template
+          # expansion of ${{ secrets.X }} inside `run:` writes the literal
+          # value into the script and depends on Gitea's log masker to
+          # scrub it — fragile for multi-line keys.
+          RPM_SIGNING_KEY: ${{ secrets.RPM_SIGNING_KEY }}
+          RPM_SIGNING_KEY_ID: ${{ secrets.RPM_SIGNING_KEY_ID }}
+        run: |
+          echo "$RPM_SIGNING_KEY" | gpg --batch --import
+          fpr=$(gpg --batch --with-colons --list-keys "$RPM_SIGNING_KEY_ID" | awk -F: '/^fpr:/ { print $10; exit }')
+          echo "${fpr}:6:" | gpg --batch --import-ownertrust
+          sed "s/@GPG_NAME@/$RPM_SIGNING_KEY_ID/" rpm/rpmmacros > ~/.rpmmacros
+
+      - name: Sign RPMs
+        run: |
+          set -eux
+          for rpm in rpms/*.rpm; do
+            echo "signing ${rpm}..."
+            rpm --addsign "${rpm}"
+          done
+
+      - name: Set up SSH for rsync
+        run: |
+          install --directory --mode 700 ~/.ssh
+          echo "${RSYNC_SSH_KEY}" | install --mode 600 /dev/stdin ~/.ssh/id_ed25519
+        env:
+          RSYNC_SSH_KEY: ${{ secrets.RSYNC_SSH_KEY }}
+
+      - name: Test SSH connectivity
+        run: |
+          ssh -o StrictHostKeyChecking=accept-new "gitea_ci@${RPM_REPO_HOST}" exit
+
+      - name: Ensure unstable repo directory exists
+        run: |
+          ssh "gitea_ci@${RPM_REPO_HOST}" \
+            "mkdir --parents /var/www/rpm/fedora/${FEDORA_VERSION}/x86_64/unstable"
+
+      - name: Sync RPMs to unstable repo
+        run: |
+          rsync \
+            --archive \
+            --verbose \
+            --chmod D755,F644 \
+            rpms/*.rpm \
+            "gitea_ci@${RPM_REPO_HOST}:/var/www/rpm/fedora/${FEDORA_VERSION}/x86_64/unstable/"
+
+      - name: Update unstable repo metadata
+        run: |
+          ssh "gitea_ci@${RPM_REPO_HOST}" \
+            "cd /var/www/rpm/fedora/${FEDORA_VERSION}/x86_64/unstable && createrepo_c --update ."
+
+      - name: Generate packages.json manifest
+        run: |
+          scp script/generate-packages-json.py "gitea_ci@${RPM_REPO_HOST}:/tmp/"
+          ssh "gitea_ci@${RPM_REPO_HOST}" \
+            "python3 /tmp/generate-packages-json.py \
+              --repodata-dir /var/www/rpm/fedora/${FEDORA_VERSION}/x86_64/unstable/repodata \
+              --output /var/www/rpm/fedora/${FEDORA_VERSION}/x86_64/unstable/packages.json \
+              --base-url https://rpm.lair.cafe/fedora/${FEDORA_VERSION}/x86_64/unstable"

.gitea/workflows/ci.yml

@@ -7,7 +7,18 @@ on:
   pull_request:
     branches: [main]
 
+# Share a concurrency group with build-prerelease.yml so the two
+# workflows don't race on the same `rust` runner workspace (act's
+# /root/.cache/act/<hash>/hostexecutor/ is shared across concurrent
+# jobs and one job's checkout step nukes another's in-flight build
+# files). cancel-in-progress=false → they queue; same-ref pushes
+# coalesce per workflow via cancel-in-progress on each.
+concurrency:
+  group: cortex-runner-pool-${{ github.ref }}
+  cancel-in-progress: false
+
 env:
+  CARGO_INCREMENTAL: "0"
   RUSTC_WRAPPER: sccache
   SCCACHE_BUCKET: sccache
   SCCACHE_ENDPOINT: http://caveman.kosherinata.internal:9000
@@ -15,46 +26,47 @@ env:
   SCCACHE_S3_USE_SSL: "false"
   AWS_ACCESS_KEY_ID: ${{ secrets.SCCACHE_S3_ACCESS_KEY }}
   AWS_SECRET_ACCESS_KEY: ${{ secrets.SCCACHE_S3_SECRET_KEY }}
+  # fmt, clippy, and test all run in parallel on the same `rust` runner
+  # and would otherwise share /root/.cache/act/<hash>/hostexecutor/target/,
+  # racing each other's cargo temp files (.tmpXXXXXX) and failing builds
+  # mid-compile. Give each job its own target directory so the invocations
+  # don't collide. sccache still backs the actual rustc cache, so the
+  # rebuild penalty is small.
+  CARGO_TARGET_DIR: target-${{ github.job }}
 
 jobs:
-  check:
+  fmt:
-    name: Format, lint, build, test
+    name: Format
-    runs-on: fedora
+    runs-on: rust
     steps:
       - uses: actions/checkout@v4
+      - run: cargo fmt --check --all
 
-      - name: Ensure sccache with S3 support
+  clippy:
-        env:
+    name: Clippy
-          RUSTC_WRAPPER: ""
+    runs-on: rust
-        run: |
+    steps:
-          if sccache --version 2>/dev/null && sccache --show-stats 2>/dev/null; then
+      - uses: actions/checkout@v4
-            echo "sccache with S3 support already installed"
+      - run: cargo clippy --workspace -- -D warnings
-          else
+      - run: sccache --show-stats
-            cargo install sccache --features s3 --locked
-          fi
 
-      - name: Check formatting
+  test:
-        run: cargo fmt --check --all
+    name: Test
-
+    runs-on: rust
-      - name: Clippy
+    steps:
-        run: cargo clippy --workspace -- -D warnings
+      - uses: actions/checkout@v4
-
+      - run: cargo test --workspace
-      - name: Build
+      - run: sccache --show-stats
-        run: cargo build --workspace
-
-      - name: Test
-        run: cargo test --workspace
-
-      - name: Show sccache stats
-        run: sccache --show-stats
 
   srpm-cortex:
     name: Build cortex SRPM
-    runs-on: fedora
+    runs-on: rpm
-    needs: check
+    needs: [fmt, clippy, test]
     if: startsWith(github.ref, 'refs/tags/v')
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
       - name: Determine version
         id: version
@@ -68,6 +80,12 @@ jobs:
           sed -i '/\[workspace\.package\]/,/\[/{ s/^version = ".*"/version = "'"${VERSION}"'"/ }' Cargo.toml
           sed -i "s/^Version:.*/Version:        ${VERSION}/" cortex.spec
 
+      - name: Generate changelog entry
+        uses: https://git.lair.cafe/actions/rpm-changelog@v1
+        with:
+          spec: cortex.spec
+          version: ${{ steps.version.outputs.VERSION }}
+
       - name: Generate source tarball
         run: |
           set -ex
@@ -102,11 +120,13 @@ jobs:
 
   srpm-neuron:
     name: Build neuron SRPM
-    runs-on: fedora
+    runs-on: rpm
-    needs: check
+    needs: [fmt, clippy, test]
     if: startsWith(github.ref, 'refs/tags/v')
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
       - name: Determine version
         id: version
@@ -118,31 +138,37 @@ jobs:
         run: |
           VERSION="${{ steps.version.outputs.VERSION }}"
           sed -i '/\[workspace\.package\]/,/\[/{ s/^version = ".*"/version = "'"${VERSION}"'"/ }' Cargo.toml
-          sed -i "s/^Version:.*/Version:        ${VERSION}/" neuron.spec
+          sed -i "s/^Version:.*/Version:        ${VERSION}/" helexa-neuron.spec
+
+      - name: Generate changelog entry
+        uses: https://git.lair.cafe/actions/rpm-changelog@v1
+        with:
+          spec: helexa-neuron.spec
+          version: ${{ steps.version.outputs.VERSION }}
 
       - name: Generate source tarball
         run: |
           set -ex
           VERSION="${{ steps.version.outputs.VERSION }}"
-          tar czf /tmp/neuron-${VERSION}.tar.gz \
+          tar czf /tmp/helexa-neuron-${VERSION}.tar.gz \
-            --transform "s,^\.,neuron-${VERSION}," \
+            --transform "s,^\.,helexa-neuron-${VERSION}," \
             --exclude='./target' \
             --exclude='./.git' \
             --exclude='*.tar.gz' \
             --exclude='*.src.rpm' \
             .
-          mv /tmp/neuron-${VERSION}.tar.gz .
+          mv /tmp/helexa-neuron-${VERSION}.tar.gz .
 
       - name: Vendor Rust dependencies
         run: |
           VERSION="${{ steps.version.outputs.VERSION }}"
           cargo vendor vendor/
-          tar czf neuron-${VERSION}-vendor.tar.gz vendor/
+          tar czf helexa-neuron-${VERSION}-vendor.tar.gz vendor/
           rm -rf vendor/
 
       - name: Build SRPM
         run: |
-          rpmbuild -bs neuron.spec \
+          rpmbuild -bs helexa-neuron.spec \
             --define "_sourcedir $(pwd)" \
             --define "_srcrpmdir $(pwd)"
 
@@ -154,7 +180,7 @@ jobs:
 
   copr-cortex:
     name: Publish cortex to COPR
-    runs-on: fedora
+    runs-on: fedora-43
     needs: srpm-cortex
     steps:
       - name: Download SRPM
@@ -162,17 +188,16 @@ jobs:
         with:
           name: srpm-cortex
 
-      - name: Configure copr-cli
+      - name: Publish to COPR
-        run: |
+        uses: https://git.lair.cafe/actions/copr-publish@v1
-          mkdir -p ~/.config
+        with:
-          echo "${{ secrets.COPR_CONFIG }}" > ~/.config/copr
+          project: helexa/helexa
-
+          srpm: "*.src.rpm"
-      - name: Submit build to COPR
+          copr-config: ${{ secrets.COPR_CONFIG }}
-        run: copr-cli build helexa/cortex *.src.rpm
 
   copr-neuron:
     name: Publish neuron to COPR
-    runs-on: fedora
+    runs-on: fedora-43
     needs: srpm-neuron
     steps:
       - name: Download SRPM
@@ -180,35 +205,56 @@ jobs:
         with:
           name: srpm-neuron
 
-      - name: Configure copr-cli
+      - name: Publish to COPR
-        run: |
+        uses: https://git.lair.cafe/actions/copr-publish@v1
-          mkdir -p ~/.config
+        with:
-          echo "${{ secrets.COPR_CONFIG }}" > ~/.config/copr
+          project: helexa/helexa
-
+          srpm: "*.src.rpm"
-      - name: Submit build to COPR
+          copr-config: ${{ secrets.COPR_CONFIG }}
-        run: copr-cli build helexa/neuron *.src.rpm
 
   bump-version:
     name: Bump version in source
-    runs-on: fedora
+    runs-on: rust
     needs: [copr-cortex, copr-neuron]
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
-      - name: Stamp version and push
+      - name: Determine version
+        id: version
+        run: echo "VERSION=${GITHUB_REF#refs/tags/v}" >> "$GITHUB_OUTPUT"
+
+      - name: Stamp version
+        run: |
+          VERSION="${{ steps.version.outputs.VERSION }}"
+          sed -i '/\[workspace\.package\]/,/\[/{ s/^version = ".*"/version = "'"${VERSION}"'"/ }' Cargo.toml
+          sed -i "s/^Version:.*/Version:        ${VERSION}/" cortex.spec
+          sed -i "s/^Version:.*/Version:        ${VERSION}/" helexa-neuron.spec
+          cargo check --workspace 2>/dev/null || true
+
+      - name: Generate cortex changelog entry
+        uses: https://git.lair.cafe/actions/rpm-changelog@v1
+        with:
+          spec: cortex.spec
+          version: ${{ steps.version.outputs.VERSION }}
+
+      - name: Generate helexa-neuron changelog entry
+        uses: https://git.lair.cafe/actions/rpm-changelog@v1
+        with:
+          spec: helexa-neuron.spec
+          version: ${{ steps.version.outputs.VERSION }}
+
+      - name: Commit and push
         env:
           GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
         run: |
-          VERSION="${GITHUB_REF#refs/tags/v}"
+          VERSION="${{ steps.version.outputs.VERSION }}"
-          sed -i '/\[workspace\.package\]/,/\[/{ s/^version = ".*"/version = "'"${VERSION}"'"/ }' Cargo.toml
-          sed -i "s/^Version:.*/Version:        ${VERSION}/" cortex.spec
-          sed -i "s/^Version:.*/Version:        ${VERSION}/" neuron.spec
-          cargo check --workspace 2>/dev/null || true
           git config user.name "Gitea Actions"
           git config user.email "actions@git.lair.cafe"
-          git add Cargo.toml Cargo.lock cortex.spec neuron.spec
+          git add Cargo.toml Cargo.lock cortex.spec helexa-neuron.spec
           if git diff --cached --quiet; then
-            echo "Version already at ${VERSION}"
+            echo "Nothing to commit for ${VERSION}"
           else
             git commit -m "chore: bump version to ${VERSION}"
             git remote set-url origin "https://gitea-actions:${GITEA_TOKEN}@git.lair.cafe/helexa/cortex.git"

CLAUDE.md

@@ -125,7 +125,8 @@ automatically. Clippy warnings must be resolved, not suppressed with
   - One or more GPU nodes running mistral.rs on port 8080
   - Optionally a metrics-only node (no GPU) for Prometheus/Grafana
 - Each node runs `mistralrs serve` on port 8080
-- Gateway listens on port 8000 (API) and 9100 (metrics)
+- Gateway listens on port 31313 (API) and 31314 (metrics)
+- neuron listens on port 13131 on each GPU host
 - TLS terminated at gateway or via nginx; internal traffic is plaintext over WireGuard
 
 ## Conventions
@@ -380,7 +381,7 @@ processes (one process per loaded model, each on its own port).
 
 ## neuron API
 
-neuron exposes an HTTP API on port 9090 that cortex polls and calls.
+neuron exposes an HTTP API on port 13131 that cortex polls and calls.
 
 ```
 GET  /discovery
@@ -424,8 +425,8 @@ endpoint. cortex.toml shrinks to:
 
 ```toml
 [gateway]
-listen = "0.0.0.0:8000"
+listen = "0.0.0.0:31313"
-metrics_listen = "0.0.0.0:9100"
+metrics_listen = "0.0.0.0:31314"
 
 [eviction]
 strategy = "lru"
@@ -433,15 +434,15 @@ defrag_after_cycles = 50
 
 [[neurons]]
 name = "beast"
-endpoint = "http://beast.hanzalova.internal:9090"
+endpoint = "http://beast.hanzalova.internal:13131"
 
 [[neurons]]
 name = "benjy"
-endpoint = "http://benjy.kosherinata.internal:9090"
+endpoint = "http://benjy.hanzalova.internal:13131"
 
 [[neurons]]
 name = "quadbrat"
-endpoint = "http://quadbrat.hanzalova.internal:9090"
+endpoint = "http://quadbrat.hanzalova.internal:13131"
 ```
 
 On startup and periodically, cortex calls `GET /discovery` and
@@ -521,7 +522,7 @@ cortex/
 │   │       └── metrics.rs      # prometheus exporter (unchanged)
 │   ├── neuron/                 # node plane (replaces cortex-agent)
 │   │   └── src/
-│   │       ├── main.rs         # binary entrypoint, axum server on :9090
+│   │       ├── main.rs         # binary entrypoint, axum server on :13131
 │   │       ├── discovery.rs    # nvidia-smi, device enumeration
 │   │       ├── health.rs       # runtime GPU polling
 │   │       ├── api.rs          # HTTP handlers for /discovery, /models, etc.
@@ -595,70 +596,65 @@ placement matching can be added incrementally.
 Completed. Both packages have RPM specs, systemd units, and example configs.
 CI builds parallel SRPMs on tag push and publishes to separate COPR repos.
 
-- `cortex.spec` → `helexa/cortex` COPR: binary, systemd unit, config files
+- `cortex.spec` — installs the `cortex` binary. Package name keeps the
-- `neuron.spec` → `helexa/neuron` COPR: binary, systemd unit, config
+  short `cortex` because no Fedora package collides with it.
+- `helexa-neuron.spec` — installs the `neuron` binary under package name
+  `helexa-neuron`. Renamed from bare `neuron` to avoid collision with
+  Fedora's NEURON neural-simulation package
+  (https://src.fedoraproject.org/rpms/neuron); binary, systemd unit,
+  system user, and config dir all stay named `neuron` since those are
+  project-local contexts.
 - `data/cortex.service`, `data/neuron.service` — systemd units
 - `cortex.example.toml`, `neuron.example.toml`, `models.example.toml`
-- CI: parallel `srpm-cortex` + `srpm-neuron` jobs, then parallel COPR publish
+- CI: parallel `srpm-cortex` + `srpm-neuron` jobs, then parallel COPR
+  publish to a single project `helexa/helexa` hosting both packages.
 
 Install:
 ```sh
-dnf copr enable helexa/cortex && dnf install cortex    # gateway host
+dnf copr enable helexa/helexa
-dnf copr enable helexa/neuron && dnf install neuron    # GPU nodes
+dnf install cortex                # gateway host
+dnf install helexa-neuron         # GPU nodes
 ```
 
-### Phase 11: llama.cpp harness stub
+## 2026-05-18 addendum: candle-native pivot
 
-**Goal:** Prove the harness abstraction works with a second engine.
+Phases 11 (llama.cpp harness) and 12 (mistral.rs COPR) below are
+**superseded**. The project no longer treats mistral.rs or llama.cpp as
+dependencies — both are conceptually out of scope. neuron becomes a
+candle-native inference daemon, with `Harness` retained as an
+internal seam for adding future engines (vision/audio/diffusion) but
+its only implementation being in-process candle.
 
-**Steps:**
+The full staged plan for this pivot lives at
-1. `crates/neuron/src/harness/llamacpp.rs` — implement the `Harness`
+`~/.claude/plans/create-a-more-aggressive-calm-naur.md`. Summary:
-   trait for llama.cpp's `llama-server`.
-   - `start()` — launch `llama-server` with the correct model path,
-     `--port`, `--n-gpu-layers`, `--tensor-split` args. Track the
-     child process.
-   - `stop()` — send SIGTERM to the child process.
-   - `list_models()` — llama-server serves one model per process, so
-     return a single-element list.
-   - `load_model()` — start a new llama-server process for this model.
-   - `unload_model()` — stop the process.
-   - `inference_endpoint()` — return `http://localhost:{assigned_port}`.
-2. Port allocation: neuron assigns ports from a range (e.g. 8100-8199)
-   to llama-server instances.
-3. Register in `HarnessRegistry` when configured:
-   ```toml
-   [[harnesses]]
-   name = "llamacpp"
-   binary = "/usr/local/bin/llama-server"
-   port_range = [8100, 8199]
-   ```
-4. Tests: mock llama-server (simple HTTP server returning canned
-   responses), test load/unload/endpoint lifecycle.
 
-**Done when:** A model with `harness = "llamacpp"` in `models.toml` can
+- **Stage 1 (this commit):** delete `mistralrs.rs` and `llamacpp.rs`,
-be loaded and served through cortex. Tests pass with mock llama-server.
+  scaffold inert `CandleHarness`, drop `endpoint`/`systemd_unit` from
+  `HarnessConfig`, default no-op `start`/`stop` on the `Harness` trait.
+- **Stages 2–4:** wire up candle model load/unload (quantized Qwen3
+  first), add OpenAI-compatible inference endpoint in neuron, then SSE
+  streaming.
+- **Stages 5–6:** load-on-activation (default models in config) and
+  unload-on-deactivation (graceful shutdown).
+- **Stages 7–8:** multi-GPU tensor parallelism and broader model/quant
+  coverage.
 
-### Phase 12 (lower priority): mistral.rs COPR packaging
+Sections of this document that describe mistral.rs HTTP behaviour
+("mistral.rs API gotchas") are retained as historical context for
+Phases 1–10 — they document what was true while the project depended
+on mistral.rs. They do not describe current behaviour.
 
-**Goal:** Fedora RPMs for mistral.rs built against specific CUDA versions.
+---
 
-**Steps:**
+### Phase 11 (superseded): llama.cpp harness stub
-1. `mistralrs-cuda.spec` — RPM spec that clones a pinned mistral.rs git
-   tag, builds with `--features cuda`, links against the system CUDA
-   toolkit. Produces `mistralrs-cuda13-server` (CUDA 13.x / sm_120) and
-   `mistralrs-cuda12-server` (CUDA 12.x / sm_89). Install binary to
-   `/usr/local/bin/mistralrs`.
-2. COPR build config: enable the NVIDIA CUDA repo as a build dependency.
-   Pin the CUDA toolkit version in `BuildRequires`.
-3. Gitea Actions or manual workflow: bump the mistral.rs tag in the spec,
-   trigger COPR rebuild.
-4. neuron's mistralrs harness config references which binary/package
-   provides the mistral.rs binary. neuron could warn at startup if the
-   installed mistral.rs CUDA version doesn't match the discovered driver.
 
-**Done when:** `dnf install mistralrs-cuda13-server` on beast provides a
+~~Originally planned as a second engine to prove the harness
-working `mistralrs` binary built for Blackwell GPUs. `dnf install
+abstraction.~~ Replaced by the candle harness work in the 2026-05-18
-mistralrs-cuda12-server` on benjy provides one built for Ada GPUs.
+addendum above. llama.cpp's any-model/any-hardware breadth is no
+longer in scope for helexa.
 
-This is a separate repo/spec — not part of the cortex workspace — but
+### Phase 12 (superseded): mistral.rs COPR packaging
-tightly coupled operationally. Track it as a sibling project.
+
+~~Originally planned to ship CUDA-versioned mistral.rs RPMs.~~ Replaced
+by the candle harness work in the 2026-05-18 addendum above. With
+mistral.rs out of the dependency tree, there is nothing to package.

Cargo.toml

@@ -8,7 +8,7 @@ members = [
 ]
 
 [workspace.package]
-version = "0.1.0"
+version = "0.1.16"
 edition = "2024"
 license = "GPL-3.0-or-later"
 repository = "https://git.lair.cafe/helexa/cortex"
@@ -27,7 +27,7 @@ serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 toml = "0.8"
 
-# http client (for proxying to mistralrs backends)
+# http client (for proxying to neuron backends)
 reqwest = { version = "0.12", features = ["json", "stream"] }
 
 # observability

README.md

@@ -1,22 +1,23 @@
 # cortex
 
-A Rust reverse-proxy and fleet management layer for multi-node
+A Rust reverse-proxy and fleet management layer for multi-node GPU inference
-[mistral.rs](https://github.com/EricLBuehler/mistral.rs) inference clusters.
+clusters. Cortex sits in front of one or more `neuron` daemons (each running
+candle-based inference on a local GPU host) and presents a unified OpenAI +
+Anthropic compatible API surface.
 
 ## Problem
 
 Running local LLMs across multiple GPU nodes (different VRAM tiers, different
 model affinities) requires a unified API surface that:
 
-- Presents a **single `/v1/models` catalogue** merging every model across every
+- Presents a **single `/v1/models` catalogue** merging every model that can be
-  node.
+  served by any neuron in the fleet.
-- **Routes requests** to the correct node based on where a model is loaded (or
+- **Routes requests** to the correct node based on where a model is loaded
-  *can* be loaded).
+  (or can be loaded), handling cold-load and eviction transparently.
-- Manages **model lifecycle** — unload cold models, reload on demand, pin
+- Manages **model lifecycle** — load on demand, unload cold models, pin
-  critical ones — using the mistral.rs
+  critical ones — by calling each neuron's `/models/{load,unload}` API.
-  `/v1/models/{unload,reload,status}` HTTP API (PR #1828+).
 - Translates between **OpenAI and Anthropic** request/response envelopes so
-  every client in the homelab speaks whichever dialect it prefers.
+  every client speaks whichever dialect it prefers.
 - Captures **per-request metrics** (tokens, tok/s, TTFT, latency) and exposes
   them as Prometheus counters/histograms.
 
@@ -38,10 +39,9 @@ model affinities) requires a unified API surface that:
                     └──┬──────┬────────┬──┘
                        │      │        │
             ┌──────────▼┐  ┌──▼─────┐  ┌▼──────────┐
-            │ gpu-large │  │gpu-med │  │ gpu-small │
+            │  neuron   │  │ neuron │  │  neuron   │
-            │ mistralrs │  │mistral │  │ mistralrs │
+            │  :13131   │  │ :13131 │  │  :13131   │
-            │ serve     │  │rs serve│  │ serve     │
+            │  candle   │  │ candle │  │  candle   │
-            │ :8080     │  │ :8080  │  │  :8080    │
             └───────────┘  └────────┘  └───────────┘
                   private network (.internal)
 ```
@@ -50,70 +50,48 @@ model affinities) requires a unified API surface that:
 
 | Crate | Purpose |
 |---|---|
-| `cortex-core` | Shared types: config, node/model state, metrics, OpenAI/Anthropic request/response envelopes |
+| `cortex-core` | Shared types: config, node/model state, metrics, OpenAI/Anthropic envelopes, harness trait, discovery types |
-| `cortex-gateway` | Axum HTTP server: proxy, router, evictor, metrics exporter |
+| `cortex-gateway` | Axum HTTP server: proxy, router, evictor, poller, metrics exporter |
-| `cortex-agent` | Per-node sidecar: polls local mistralrs, reports to gateway, handles restart/defrag |
+| `neuron` | Per-node daemon: GPU discovery, in-process candle inference, model lifecycle API |
 | `cortex-cli` | CLI entrypoint (`cortex serve`, `cortex status`, etc.) |
 
 ## Node setup
 
-Each GPU node runs `mistralrs serve` with a multi-model config. Models are
+Each GPU node runs `neuron` (listening on `:13131`). Neuron uses
-declared but start **unloaded** — mistral.rs lazy-loads on first request and
+huggingface/candle for in-process inference — there is no external
-the gateway can explicitly unload/reload via the HTTP API.
+inference subprocess to manage.
 
-Example node systemd unit:
+The neuron RPM (`helexa-neuron`) ships a systemd unit:
 
-```ini
+```sh
-# /etc/systemd/system/mistralrs.service
+dnf copr enable helexa/helexa
-[Unit]
+dnf install helexa-neuron
-Description=mistral.rs inference server
+systemctl enable --now neuron
-After=network-online.target
-Wants=network-online.target
-
-[Service]
-Type=simple
-ExecStart=/usr/local/bin/mistralrs serve \
-    --from-config /etc/mistralrs/config.toml \
-    --port 8080
-Restart=on-failure
-RestartSec=5
-Environment=CUDA_VISIBLE_DEVICES=0,1
-
-[Install]
-WantedBy=multi-user.target
 ```
 
 ## Gateway config
 
 ```toml
-# cortex.toml
+# /etc/cortex/cortex.toml
 [gateway]
-listen = "0.0.0.0:8000"
+listen = "0.0.0.0:31313"
-metrics_listen = "0.0.0.0:9100"
+metrics_listen = "0.0.0.0:31314"
 
 [eviction]
 strategy = "lru"        # lru | priority
 defrag_after_cycles = 50
 
-[[nodes]]
+[[neurons]]
-name = "gpu-large"
+name = "beast"
-endpoint = "http://gpu-large.internal:8080"
+endpoint = "http://beast.internal:13131"
-vram_mb = 49_152        # e.g. 2x RTX 4090
-pinned = ["your-org/large-model"]
 
-[[nodes]]
+[[neurons]]
-name = "gpu-medium"
+name = "benjy"
-endpoint = "http://gpu-medium.internal:8080"
+endpoint = "http://benjy.internal:13131"
-vram_mb = 24_576        # e.g. RTX 4090
-pinned = ["your-org/medium-model"]
-
-[[nodes]]
-name = "gpu-small"
-endpoint = "http://gpu-small.internal:8080"
-vram_mb = 12_288        # e.g. RTX 3060
-pinned = ["your-org/embedding-model"]
 ```
 
+Model placement profiles live in `models.toml` — see `models.example.toml`.
+
 ## Building
 
 ```sh
@@ -131,19 +109,20 @@ cargo clippy --workspace -- -D warnings   # warnings are errors
 cargo test --workspace                     # all tests must pass
 ```
 
-Tagged releases (`v*`) additionally build an SRPM and publish to COPR.
+Tagged releases (`v*`) additionally build SRPMs for both `cortex` and
+`helexa-neuron` and publish to COPR.
 
 ## Running
 
 ```sh
 # start the gateway
-cortex serve --config cortex.toml
+cortex serve --config /etc/cortex/cortex.toml
 
 # check fleet status
 cortex status
 
 # list all models across nodes
-curl http://localhost:8000/v1/models
+curl http://localhost:31313/v1/models
 ```
 
 ## License

asset/manifest.yml

@@ -0,0 +1,30 @@
+# Helexa fleet manifest.
+#
+# Drives rolling deploys via script/deploy.sh and serves as the source
+# of truth for which hosts run cortex vs neuron, and which CUDA
+# compute-capability flavour each neuron host needs.
+#
+# Flavour ↔ NVIDIA generation ↔ compute cap:
+#   ampere    sm_86   (RTX 30 series — e.g. 3060)
+#   ada       sm_89   (RTX 40 series — e.g. 4090)
+#   blackwell sm_120  (RTX 50 series — e.g. 5090)
+#
+# The flavour determines which RPM is installed on a given neuron host:
+# helexa-neuron-<flavour>. Only one flavour may be installed at a time
+# (the packages Conflict: with each other).
+
+cortex:
+  host: hanzalova.internal
+
+neurons:
+  - host: beast.hanzalova.internal
+    flavour: blackwell
+    gpu: "2x RTX 5090"
+
+  - host: benjy.hanzalova.internal
+    flavour: ada
+    gpu: "RTX 4090"
+
+  - host: quadbrat.hanzalova.internal
+    flavour: ampere
+    gpu: "RTX 3060"

cortex.example.toml

@@ -3,22 +3,22 @@
 # Copy to cortex.toml and adjust for your environment.
 #
 # Environment variable overrides use CORTEX_ prefix with __ separators:
-#   CORTEX_GATEWAY__LISTEN=0.0.0.0:9000
+#   CORTEX_GATEWAY__LISTEN=0.0.0.0:31313
 
 [gateway]
-listen = "0.0.0.0:8000"
+listen = "0.0.0.0:31313"
-metrics_listen = "0.0.0.0:9100"
+metrics_listen = "0.0.0.0:31314"
 
 [eviction]
 strategy = "lru"
-# Restart mistralrs after this many load/unload cycles to defragment VRAM.
+# Restart neurons after this many load/unload cycles to defragment VRAM.
 # Set to 0 to disable.
 defrag_after_cycles = 50
 
 # -- Nodes ---------------------------------------------------------------
-# Each [[nodes]] entry declares a mistral.rs instance in the fleet.
+# Each [[nodes]] entry declares a neuron daemon in the fleet.
-# Models are discovered by polling the node's /v1/models endpoint.
+# Models are discovered by polling the neuron's /models endpoint.
-# Pinned models are never evicted.
+# Pinned models (see models.toml) are never evicted.
 
 [[nodes]]
 name = "gpu-large"

cortex.spec

@@ -1,5 +1,5 @@
 Name:           cortex
-Version:        0.1.0
+Version:        0.1.16
 Release:        1%{?dist}
 Summary:        Inference gateway for multi-node GPU clusters
 
@@ -13,9 +13,24 @@ ExclusiveArch:  x86_64
 BuildRequires:  rust >= 1.85
 BuildRequires:  cargo
 BuildRequires:  gcc
+BuildRequires:  gcc-c++
+BuildRequires:  cmake
+BuildRequires:  perl-interpreter
+BuildRequires:  pkgconfig(openssl)
 BuildRequires:  systemd-rpm-macros
 
 Requires(pre):  shadow-utils
+Requires:       systemd
+Requires:       firewalld-filesystem
+
+# systemd-rpm-macros ships a unit dep generator that parses User=/Group=
+# from our .service file and emits Requires: user(cortex)/group(cortex).
+# rpm's sysusers provides-generator emits the unversioned form for groups
+# but only a versioned user(cortex) = <base64> for users with GECOS/home/
+# shell. Provide the unversioned user(cortex) explicitly so dnf can resolve
+# the auto-generated Requires. Without this, dnf5 silently filters the
+# package and reports "Nothing to do".
+Provides:       user(cortex)
 
 %description
 Cortex is a Rust reverse-proxy that sits in front of multiple inference
@@ -41,13 +56,14 @@ cargo build --release -p cortex-cli
 %install
 install -Dm755 target/release/cortex %{buildroot}%{_bindir}/cortex
 install -Dm644 data/cortex.service %{buildroot}%{_unitdir}/cortex.service
-install -dm750 %{buildroot}%{_sysconfdir}/cortex
+install -Dm644 data/cortex-sysusers.conf %{buildroot}%{_sysusersdir}/cortex.conf
-install -Dm640 cortex.example.toml %{buildroot}%{_sysconfdir}/cortex/cortex.toml
+install -Dm644 data/cortex-firewalld.xml %{buildroot}%{_prefix}/lib/firewalld/services/cortex.xml
-install -Dm640 models.example.toml %{buildroot}%{_sysconfdir}/cortex/models.toml
+install -dm755 %{buildroot}%{_sysconfdir}/cortex
+install -Dm644 cortex.example.toml %{buildroot}%{_sysconfdir}/cortex/cortex.toml
+install -Dm644 models.example.toml %{buildroot}%{_sysconfdir}/cortex/models.toml
 
 %pre
-getent group cortex >/dev/null || groupadd -r cortex
+%sysusers_create_compat %{_builddir}/%{name}-%{version}/data/cortex-sysusers.conf
-getent passwd cortex >/dev/null || useradd -r -g cortex -d /var/lib/cortex -s /sbin/nologin cortex
 
 %post
 %systemd_post cortex.service
@@ -63,10 +79,22 @@ getent passwd cortex >/dev/null || useradd -r -g cortex -d /var/lib/cortex -s /s
 %doc README.md
 %{_bindir}/cortex
 %{_unitdir}/cortex.service
-%dir %attr(750,root,cortex) %{_sysconfdir}/cortex
+%{_sysusersdir}/cortex.conf
-%config(noreplace) %attr(640,root,cortex) %{_sysconfdir}/cortex/cortex.toml
+%{_prefix}/lib/firewalld/services/cortex.xml
-%config(noreplace) %attr(640,root,cortex) %{_sysconfdir}/cortex/models.toml
+%dir %{_sysconfdir}/cortex
+%config(noreplace) %{_sysconfdir}/cortex/cortex.toml
+%config(noreplace) %{_sysconfdir}/cortex/models.toml
 
 %changelog
-* Tue Apr 15 2026 Rob Thijssen <grenade@rob.tn> - 0.1.0-1
+* Thu Apr 16 2026 Gitea Actions <actions@git.lair.cafe> - 0.1.16-1
+- chore: ignore local deploy script
+- chore: move default ports out of common-collision ranges
+- ci: drop actions/cache for cargo registry and target
+
+* Thu Apr 16 2026 Gitea Actions <actions@git.lair.cafe> - 0.1.14-1
+- ci: publish both packages to a single helexa/helexa COPR project
+- fix(rpm): rename neuron package to helexa-neuron
+- ci: commit generated %changelog entries back to main
+
+* Wed Apr 15 2026 Rob Thijssen <grenade@rob.tn> - 0.1.0-1
 - Initial package

crates/cortex-cli/src/main.rs

@@ -5,7 +5,7 @@ use tracing_subscriber::EnvFilter;
 
 #[derive(Parser)]
 #[command(name = "cortex")]
-#[command(about = "Unified inference gateway for multi-node mistral.rs clusters")]
+#[command(about = "Unified inference gateway for multi-node GPU clusters")]
 #[command(version)]
 struct Cli {
     #[command(subcommand)]
@@ -23,7 +23,7 @@ enum Commands {
     /// Print the fleet status (models, nodes, health).
     Status {
         /// Gateway API endpoint to query.
-        #[arg(short, long, default_value = "http://localhost:8000")]
+        #[arg(short, long, default_value = "http://localhost:31313")]
         endpoint: String,
     },
 }

crates/cortex-core/src/anthropic.rs

@@ -2,7 +2,7 @@
 //!
 //! These mirror the `/v1/messages` format used by the Anthropic API.
 //! The gateway accepts these, translates to OpenAI format, proxies to
-//! mistral.rs, then translates the response back.
+//! the inference backend (neuron), then translates the response back.
 
 use serde::{Deserialize, Serialize};
 use serde_json::Value;

crates/cortex-core/src/config.rs

@@ -22,9 +22,9 @@ fn default_models_path() -> String {
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct GatewaySettings {
-    /// Address to listen on for API requests (e.g. "0.0.0.0:8000")
+    /// Address to listen on for API requests (e.g. "0.0.0.0:31313")
     pub listen: String,
-    /// Address to listen on for Prometheus metrics (e.g. "0.0.0.0:9100")
+    /// Address to listen on for Prometheus metrics (e.g. "0.0.0.0:31314")
     pub metrics_listen: String,
 }
 
@@ -50,7 +50,7 @@ pub enum EvictionStrategy {
 pub struct NeuronEndpoint {
     /// Human-readable node name (e.g. "beast")
     pub name: String,
-    /// Base URL of the neuron daemon (e.g. "http://beast.internal:9090")
+    /// Base URL of the neuron daemon (e.g. "http://beast.internal:13131")
     pub endpoint: String,
 }
 
@@ -70,8 +70,8 @@ impl Default for GatewayConfig {
     fn default() -> Self {
         Self {
             gateway: GatewaySettings {
-                listen: "0.0.0.0:8000".into(),
+                listen: "0.0.0.0:31313".into(),
-                metrics_listen: "0.0.0.0:9100".into(),
+                metrics_listen: "0.0.0.0:31314".into(),
             },
             eviction: EvictionSettings {
                 strategy: EvictionStrategy::Lru,

crates/cortex-core/src/harness.rs

@@ -9,13 +9,13 @@ use async_trait::async_trait;
 use serde::{Deserialize, Serialize};
 
 /// Configuration for a harness instance on a neuron.
+///
+/// All current harnesses are in-process (candle); per-harness tuning
+/// (cache paths, device policies, etc.) lives in dedicated config
+/// blocks rather than on this struct.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct HarnessConfig {
     pub name: String,
-    /// Base URL of the harness (e.g. "http://localhost:8080" for mistral.rs).
-    pub endpoint: Option<String>,
-    /// Systemd unit name, if the harness is managed via systemd.
-    pub systemd_unit: Option<String>,
 }
 
 /// Health status of a harness process.
@@ -47,16 +47,24 @@ pub struct ModelInfo {
 }
 
 /// What an inference harness must do, from neuron's perspective.
+///
+/// All current harnesses are in-process — they share neuron's address
+/// space and lifecycle. `start`/`stop` therefore default to no-ops; a
+/// future process-supervising harness would override them.
 #[async_trait]
 pub trait Harness: Send + Sync {
-    /// Human-readable name (e.g. "mistralrs", "llamacpp", "comfyui").
+    /// Human-readable name (e.g. "candle").
     fn name(&self) -> &str;
 
-    /// Start the harness process if it is not already running.
+    /// Start the harness. Default no-op for in-process harnesses.
-    async fn start(&self, config: &HarnessConfig) -> Result<()>;
+    async fn start(&self, _config: &HarnessConfig) -> Result<()> {
+        Ok(())
+    }
 
-    /// Stop the harness process gracefully.
+    /// Stop the harness. Default no-op for in-process harnesses.
-    async fn stop(&self) -> Result<()>;
+    async fn stop(&self) -> Result<()> {
+        Ok(())
+    }
 
     /// Health check. Returns the harness process status.
     async fn health(&self) -> HarnessHealth;

crates/cortex-core/src/node.rs

@@ -6,7 +6,7 @@ use std::collections::HashMap;
 #[derive(Debug, Clone)]
 pub struct NodeState {
     pub name: String,
-    /// Base URL of the neuron daemon (e.g. "http://beast.internal:9090").
+    /// Base URL of the neuron daemon (e.g. "http://beast.internal:13131").
     pub endpoint: String,
     pub healthy: bool,
     pub models: HashMap<String, ModelEntry>,

crates/cortex-core/src/openai.rs

@@ -3,7 +3,7 @@
 //! These are a subset sufficient for chat completions (streaming + non-streaming).
 //! Fields not relevant to proxying are captured as `serde_json::Value` via
 //! `#[serde(flatten)]` so we forward them without needing to enumerate every
-//! extension field mistral.rs supports.
+//! extension field a backend might support.
 
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
@@ -22,7 +22,7 @@ pub struct ChatCompletionRequest {
     pub max_tokens: Option<u64>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub stream: Option<bool>,
-    /// All other fields (tools, response_format, mistral.rs extensions, etc.)
+    /// All other fields (tools, response_format, backend extensions, etc.)
     #[serde(flatten)]
     pub extra: Value,
 }

crates/cortex-gateway/src/proxy.rs

@@ -1,4 +1,4 @@
-//! Streaming HTTP reverse proxy to mistral.rs backends.
+//! Streaming HTTP reverse proxy to neuron backends.
 //!
 //! For streaming requests, SSE chunks are forwarded as they arrive.
 //! The proxy captures timing information for metrics but does not

crates/cortex-gateway/tests/common/mod.rs

@@ -22,6 +22,7 @@ use tokio::net::TcpListener;
 /// - GET /models/:id/endpoint (returns the inference URL)
 /// - POST /models/unload (accepts unload requests)
 /// - GET /v1/chat/completions + POST /v1/chat/completions (inference)
+///
 /// Returns the neuron base URL.
 pub async fn spawn_mock_neuron() -> String {
     let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
@@ -54,7 +55,7 @@ pub async fn spawn_mock_neuron() -> String {
 
 async fn mock_neuron_list_models() -> Json<Value> {
     Json(json!([
-        {"id": "test-model", "harness": "mistralrs", "status": "loaded", "devices": [0], "vram_used_mb": 8000}
+        {"id": "test-model", "harness": "candle", "status": "loaded", "devices": [0], "vram_used_mb": 8000}
     ]))
 }
 

crates/cortex-gateway/tests/poller.rs

@@ -12,8 +12,8 @@ use std::sync::Arc;
 async fn test_poller_discovers_models() {
     // Mock neuron reports 2 models via /models endpoint (neuron format).
     let mock_url = common::spawn_mock_neuron_with_models(json!([
-        {"id": "model-a", "harness": "mistralrs", "status": "loaded", "devices": [0], "vram_used_mb": 8000},
+        {"id": "model-a", "harness": "candle", "status": "loaded", "devices": [0], "vram_used_mb": 8000},
-        {"id": "model-b", "harness": "mistralrs", "status": "unloaded", "devices": [], "vram_used_mb": null}
+        {"id": "model-b", "harness": "candle", "status": "unloaded", "devices": [], "vram_used_mb": null}
     ]))
     .await;
 
@@ -63,8 +63,8 @@ async fn test_poller_discovers_models() {
 #[tokio::test]
 async fn test_poller_updates_gateway_models_endpoint() {
     let mock_url = common::spawn_mock_neuron_with_models(json!([
-        {"id": "model-x", "harness": "mistralrs", "status": "loaded", "devices": [0], "vram_used_mb": null},
+        {"id": "model-x", "harness": "candle", "status": "loaded", "devices": [0], "vram_used_mb": null},
-        {"id": "model-y", "harness": "mistralrs", "status": "loaded", "devices": [1], "vram_used_mb": null}
+        {"id": "model-y", "harness": "candle", "status": "loaded", "devices": [1], "vram_used_mb": null}
     ]))
     .await;
 
@@ -152,8 +152,8 @@ async fn test_poller_marks_unreachable_node_unhealthy() {
 #[tokio::test]
 async fn test_poller_removes_stale_models() {
     let mock_url = common::spawn_mock_neuron_with_models(json!([
-        {"id": "keep-me", "harness": "mistralrs", "status": "loaded", "devices": [0], "vram_used_mb": null},
+        {"id": "keep-me", "harness": "candle", "status": "loaded", "devices": [0], "vram_used_mb": null},
-        {"id": "drop-me", "harness": "mistralrs", "status": "loaded", "devices": [0], "vram_used_mb": null}
+        {"id": "drop-me", "harness": "candle", "status": "loaded", "devices": [0], "vram_used_mb": null}
     ]))
     .await;
 
@@ -183,7 +183,7 @@ async fn test_poller_removes_stale_models() {
 
     // New mock with only one model.
     let new_mock_url = common::spawn_mock_neuron_with_models(json!([
-        {"id": "keep-me", "harness": "mistralrs", "status": "loaded", "devices": [0], "vram_used_mb": null}
+        {"id": "keep-me", "harness": "candle", "status": "loaded", "devices": [0], "vram_used_mb": null}
     ]))
     .await;
 

crates/cortex-gateway/tests/streaming.rs

@@ -51,18 +51,18 @@ async fn test_streaming_sse_passthrough() {
     }
 
     assert!(
-        chunks.len() >= chunk_count + 1,
+        chunks.len() > chunk_count,
-        "expected at least {} chunks (got {}): {:?}",
+        "expected more than {} chunks (got {}): {:?}",
-        chunk_count + 1,
+        chunk_count,
         chunks.len(),
         chunks,
     );
 
     assert_eq!(chunks.last().unwrap(), "[DONE]");
 
-    for i in 0..chunk_count {
+    for (i, chunk) in chunks.iter().enumerate().take(chunk_count) {
         let chunk_json: serde_json::Value =
-            serde_json::from_str(&chunks[i]).expect("chunk should be valid JSON");
+            serde_json::from_str(chunk).expect("chunk should be valid JSON");
         assert_eq!(
             chunk_json["choices"][0]["delta"]["content"],
             format!("token{i}")

crates/neuron/Cargo.toml

@@ -12,6 +12,34 @@ path = "src/lib.rs"
 name = "neuron"
 path = "src/main.rs"
 
+[features]
+default = []
+# Enables CUDA acceleration in candle and the cudarc/nccl bindings the
+# TP worker pool uses. Without this feature, candle compiles for CPU
+# only, Device::new_cuda calls fall back to CPU, and TP Init/sanity
+# requests return Error{kind="cuda_feature_not_enabled"}.
+cuda = [
+    "candle-core/cuda",
+    "candle-core/nccl",
+    "candle-nn/cuda",
+    "candle-transformers/cuda",
+    "dep:cudarc",
+]
+# Use cuDNN for convolution / attention kernels. Requires CUDA.
+cudnn = [
+    "cuda",
+    "candle-core/cudnn",
+    "candle-nn/cudnn",
+    "candle-transformers/cudnn",
+]
+# FlashAttention kernels. Requires CUDA.
+flash-attn = [
+    "cuda",
+    "candle-transformers/flash-attn",
+]
+# Reserved for GPU-only integration tests in later stages.
+cuda-integration = ["cuda"]
+
 [dependencies]
 cortex-core.workspace = true
 tokio.workspace = true
@@ -24,9 +52,25 @@ tracing-subscriber.workspace = true
 anyhow.workspace = true
 async-trait.workspace = true
 clap.workspace = true
+thiserror.workspace = true
+futures.workspace = true
+tokio-stream.workspace = true
 figment.workspace = true
 toml.workspace = true
 
+# candle for in-process inference. CUDA support is gated behind the
+# crate's `cuda` feature (default off) so the workspace builds on
+# non-CUDA hosts and CI runners.
+candle-core = "0.10.2"
+candle-nn = "0.10.2"
+candle-transformers = "0.10.2"
+# Direct dep on cudarc (matching candle's transitive version) so the
+# TP worker pool can call cudarc::nccl::{Comm, Id} directly. Gated on
+# the `cuda` feature; same toolchain requirement as candle's CUDA path.
+cudarc = { version = "0.19", optional = true, default-features = false, features = ["nccl", "cuda-version-from-build-system"] }
+tokenizers = { version = "0.22", default-features = false, features = ["onig"] }
+hf-hub = { version = "0.4", features = ["tokio"] }
+
 [dev-dependencies]
 tokio = { workspace = true, features = ["test-util"] }
 reqwest.workspace = true

crates/neuron/src/api.rs

@@ -1,23 +1,33 @@
 //! HTTP API handlers for the neuron daemon.
 
 use crate::harness::HarnessRegistry;
+use crate::harness::candle::{CandleHarness, InferenceError};
 use crate::health::HealthCache;
 use axum::Router;
 use axum::extract::{Path, State};
 use axum::http::StatusCode;
+use axum::response::sse::{Event, KeepAlive, Sse};
 use axum::response::{IntoResponse, Json};
 use axum::routing::{get, post};
 use cortex_core::discovery::{DiscoveryResponse, HealthResponse};
 use cortex_core::harness::ModelSpec;
+use cortex_core::openai::ChatCompletionRequest;
+use futures::stream::{self, StreamExt};
 use serde_json::{Value, json};
+use std::convert::Infallible;
 use std::sync::Arc;
 use tokio::sync::RwLock;
+use tokio_stream::wrappers::ReceiverStream;
 
 /// Shared state for the neuron HTTP server.
 pub struct NeuronState {
     pub discovery: DiscoveryResponse,
     pub health_cache: Arc<HealthCache>,
     pub registry: RwLock<HarnessRegistry>,
+    /// Typed handle to the candle harness for inference routes. Cached at
+    /// startup so `/v1/chat/completions` doesn't have to hold the registry
+    /// read lock or perform dyn-Trait dispatch per request.
+    pub candle: Option<Arc<CandleHarness>>,
 }
 
 /// Build the neuron API router.
@@ -29,6 +39,7 @@ pub fn neuron_routes() -> Router<Arc<NeuronState>> {
         .route("/models/load", post(load_model))
         .route("/models/unload", post(unload_model))
         .route("/models/{model_id}/endpoint", get(model_endpoint))
+        .route("/v1/chat/completions", post(chat_completions))
 }
 
 async fn discovery_handler(State(state): State<Arc<NeuronState>>) -> Json<DiscoveryResponse> {
@@ -45,7 +56,7 @@ async fn list_models(State(state): State<Arc<NeuronState>>) -> impl IntoResponse
         Ok(models) => Json(json!(models)).into_response(),
         Err(e) => (
             StatusCode::INTERNAL_SERVER_ERROR,
-            Json(json!({"error": e.to_string()})),
+            Json(json!({"error": format!("{e:#}")})),
         )
             .into_response(),
     }
@@ -58,11 +69,22 @@ async fn load_model(
     let registry = state.registry.read().await;
     match registry.load_model(&spec).await {
         Ok(()) => Json(json!({"status": "loaded"})).into_response(),
-        Err(e) => (
+        Err(e) => {
+            // Log the full anyhow chain server-side so journalctl shows
+            // the underlying failure (hf-hub timeout, permission denied,
+            // disk full, etc.) without needing to inspect the HTTP
+            // response body separately.
+            tracing::warn!(
+                model = %spec.model_id,
+                error = %format!("{e:#}"),
+                "load_model failed"
+            );
+            (
                 StatusCode::BAD_REQUEST,
-            Json(json!({"error": e.to_string()})),
+                Json(json!({"error": format!("{e:#}")})),
             )
-            .into_response(),
+                .into_response()
+        }
     }
 }
 
@@ -84,7 +106,11 @@ async fn unload_model(
     let registry = state.registry.read().await;
     match registry.unload_model(&model_id).await {
         Ok(()) => Json(json!({"status": "unloaded"})).into_response(),
-        Err(e) => (StatusCode::NOT_FOUND, Json(json!({"error": e.to_string()}))).into_response(),
+        Err(e) => (
+            StatusCode::NOT_FOUND,
+            Json(json!({"error": format!("{e:#}")})),
+        )
+            .into_response(),
     }
 }
 
@@ -102,3 +128,61 @@ async fn model_endpoint(
             .into_response(),
     }
 }
+
+/// OpenAI-compatible chat completions. Dispatches to streaming SSE when
+/// `stream: true` is set on the request; otherwise returns a single
+/// `ChatCompletionResponse`.
+async fn chat_completions(
+    State(state): State<Arc<NeuronState>>,
+    Json(req): Json<ChatCompletionRequest>,
+) -> impl IntoResponse {
+    let Some(candle) = state.candle.as_ref().map(Arc::clone) else {
+        return (
+            StatusCode::SERVICE_UNAVAILABLE,
+            Json(json!({"error": "candle harness not enabled on this neuron"})),
+        )
+            .into_response();
+    };
+
+    if req.stream.unwrap_or(false) {
+        match candle.chat_completion_stream(req).await {
+            Ok(rx) => {
+                // Each chunk → one SSE `data: {json}` line. After the
+                // channel closes, append the OpenAI [DONE] terminator.
+                let body_stream = ReceiverStream::new(rx).map(|chunk| {
+                    let body = serde_json::to_string(&chunk).unwrap_or_default();
+                    Ok::<_, Infallible>(Event::default().data(body))
+                });
+                let done_stream =
+                    stream::once(async { Ok::<_, Infallible>(Event::default().data("[DONE]")) });
+                Sse::new(body_stream.chain(done_stream))
+                    .keep_alive(KeepAlive::default())
+                    .into_response()
+            }
+            Err(InferenceError::ModelNotLoaded(id)) => (
+                StatusCode::NOT_FOUND,
+                Json(json!({"error": format!("model '{id}' not loaded on this neuron")})),
+            )
+                .into_response(),
+            Err(InferenceError::Other(e)) => (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(json!({"error": format!("{e:#}")})),
+            )
+                .into_response(),
+        }
+    } else {
+        match candle.chat_completion(req).await {
+            Ok(resp) => Json(resp).into_response(),
+            Err(InferenceError::ModelNotLoaded(id)) => (
+                StatusCode::NOT_FOUND,
+                Json(json!({"error": format!("model '{id}' not loaded on this neuron")})),
+            )
+                .into_response(),
+            Err(InferenceError::Other(e)) => (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(json!({"error": format!("{e:#}")})),
+            )
+                .into_response(),
+        }
+    }
+}

crates/neuron/src/config.rs

@@ -1,12 +1,12 @@
 //! Neuron configuration loaded from neuron.toml.
 
-use cortex_core::harness::HarnessConfig;
+use cortex_core::harness::{HarnessConfig, ModelSpec};
 use figment::{
     Figment,
     providers::{Env, Format, Toml},
 };
 use serde::{Deserialize, Serialize};
-use std::path::Path;
+use std::path::{Path, PathBuf};
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct NeuronConfig {
@@ -14,10 +14,35 @@ pub struct NeuronConfig {
     pub port: u16,
     #[serde(default)]
     pub harnesses: Vec<HarnessConfig>,
+    /// Per-harness configuration. Currently only `candle` is recognised.
+    #[serde(default)]
+    pub harness: HarnessSettings,
+    /// Models to auto-load when the neuron service activates. Each entry
+    /// is loaded sequentially before the HTTP listener binds. A failure
+    /// on any single entry logs a warning and proceeds — broken entries
+    /// don't prevent the rest of the fleet from starting.
+    #[serde(default)]
+    pub default_models: Vec<ModelSpec>,
+}
+
+/// Settings for individual harness implementations. Each harness owns
+/// its own sub-table so users only configure the harnesses they enable.
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct HarnessSettings {
+    #[serde(default)]
+    pub candle: CandleHarnessConfig,
+}
+
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct CandleHarnessConfig {
+    /// HuggingFace cache directory for model weights.
+    /// When unset, defers to hf-hub's default (~/.cache/huggingface).
+    #[serde(default)]
+    pub hf_cache: Option<PathBuf>,
 }
 
 fn default_port() -> u16 {
-    9090
+    13131
 }
 
 impl NeuronConfig {
@@ -33,8 +58,10 @@ impl NeuronConfig {
 impl Default for NeuronConfig {
     fn default() -> Self {
         Self {
-            port: 9090,
+            port: 13131,
             harnesses: vec![],
+            harness: HarnessSettings::default(),
+            default_models: vec![],
         }
     }
 }

crates/neuron/src/harness/candle.rs

@@ -0,0 +1,910 @@
+//! Candle harness — in-process inference using huggingface/candle.
+//!
+//! This is the sole `Harness` implementation. Inference runs inside
+//! the neuron process; there is no external subprocess.
+//!
+//! - Stage 2 wired GGUF (Qwen3 only) load/unload via `quantized_qwen3`.
+//! - Stage 3 (this) adds `chat_completion` — a non-streaming OpenAI
+//!   compatible chat completion routed to the loaded model's forward
+//!   pass on a per-model serialised generation loop.
+
+use anyhow::{Context, Result};
+use async_trait::async_trait;
+use candle_core::quantized::gguf_file;
+use candle_core::{DType, Device, Tensor};
+use candle_nn::VarBuilder;
+use candle_transformers::generation::{LogitsProcessor, Sampling};
+use candle_transformers::models::quantized_qwen3::ModelWeights as QuantizedQwen3Weights;
+use candle_transformers::models::qwen3 as qwen3_dense;
+use cortex_core::harness::{Harness, HarnessHealth, ModelInfo, ModelSpec};
+use cortex_core::openai::{
+    ChatCompletionChoice, ChatCompletionChunk, ChatCompletionRequest, ChatCompletionResponse,
+    ChatMessage, ChunkChoice, MessageContent, Usage,
+};
+use serde_json::json;
+use std::collections::HashMap;
+use std::path::PathBuf;
+use std::sync::Arc;
+use std::time::{SystemTime, UNIX_EPOCH};
+use tokenizers::Tokenizer;
+use tokio::sync::{Mutex, RwLock, mpsc};
+
+/// In-process candle harness. Owns the loaded model registry.
+pub struct CandleHarness {
+    models: Arc<RwLock<HashMap<String, Arc<LoadedModel>>>>,
+    hf_cache: Option<PathBuf>,
+    bind_url: String,
+}
+
+/// A loaded model with its tokenizer, device placement, and architecture-
+/// specific weights. The `arch` is `Arc<Mutex<>>` so the lock guard can be
+/// moved into `spawn_blocking` for synchronous candle forward passes.
+pub struct LoadedModel {
+    pub model_id: String,
+    pub arch: Arc<Mutex<ModelArch>>,
+    pub tokenizer: Tokenizer,
+    pub device: Device,
+    pub quant: Option<String>,
+    pub devices: Vec<u32>,
+}
+
+/// Architecture-specific weights.
+///
+/// - `Qwen3Quantized` — GGUF source, pre-quantized. Single-GPU only;
+///   TP sharding pre-quantized super-blocks is intractable. Stays the
+///   default for small models loaded via `Qwen/Qwen3-*-GGUF` and
+///   `unsloth/Qwen3-*-GGUF` repos.
+/// - `Qwen3Dense` — bf16 safetensors source. The path that supports
+///   TP (Stage 7b-ii+) because slicing dense weights by row/column
+///   under safetensors is mechanical. Used when `ModelSpec.quant` is
+///   None; intended target for Qwen3.6-27B etc.
+///
+/// Stage 8 broadens this to additional families.
+pub enum ModelArch {
+    Qwen3Quantized(QuantizedQwen3Weights),
+    Qwen3Dense(qwen3_dense::ModelForCausalLM),
+}
+
+/// Repetition penalty applied to recently-generated tokens before
+/// sampling. 1.0 disables it; >1.0 makes recently-emitted tokens less
+/// likely. mistral.rs and llama.cpp default to 1.1, which is enough to
+/// stop small quantized models from degenerating into "Wait, no, no..."
+/// loops without distorting normal output.
+const REPEAT_PENALTY: f32 = 1.1;
+
+/// Number of recently-generated tokens to feed into the repetition
+/// penalty. Matches the candle quantized-qwen3 example default.
+const REPEAT_LAST_N: usize = 64;
+
+/// Apply the repetition penalty (if any) to the prediction logits and
+/// then sample. Centralises the prefill / generation-loop call sites
+/// so they share identical sampling behaviour.
+fn sample_with_penalty(
+    logits: &Tensor,
+    history: &[u32],
+    logits_processor: &mut LogitsProcessor,
+) -> Result<u32> {
+    let penalised = if (REPEAT_PENALTY - 1.0).abs() < f32::EPSILON || history.is_empty() {
+        logits.clone()
+    } else {
+        let start = history.len().saturating_sub(REPEAT_LAST_N);
+        candle_transformers::utils::apply_repeat_penalty(logits, REPEAT_PENALTY, &history[start..])?
+    };
+    Ok(logits_processor.sample(&penalised)?)
+}
+
+impl CandleHarness {
+    pub fn new(bind_url: String, hf_cache: Option<PathBuf>) -> Self {
+        Self {
+            models: Arc::new(RwLock::new(HashMap::new())),
+            hf_cache,
+            bind_url,
+        }
+    }
+
+    /// Pick a candle `Device` for the requested indices. Without the
+    /// `cuda` feature, or if CUDA initialisation fails, falls back to CPU.
+    fn pick_device(devices: &[u32]) -> Result<Device> {
+        let _idx = devices.first().copied().unwrap_or(0) as usize;
+        #[cfg(feature = "cuda")]
+        {
+            match Device::new_cuda(_idx) {
+                Ok(d) => return Ok(d),
+                Err(e) => tracing::warn!(
+                    device = _idx,
+                    error = %e,
+                    "CUDA device unavailable, falling back to CPU"
+                ),
+            }
+        }
+        Ok(Device::Cpu)
+    }
+
+    /// Build an hf-hub API client pre-configured with the harness's
+    /// `hf_cache` (when one is set).
+    fn hf_api(&self) -> Result<hf_hub::api::tokio::Api> {
+        let mut builder = hf_hub::api::tokio::ApiBuilder::new();
+        if let Some(cache) = &self.hf_cache {
+            builder = builder.with_cache_dir(cache.clone());
+        }
+        builder.build().context("build hf-hub API")
+    }
+
+    /// Resolve a dense (bf16/fp16 safetensors) model to its local file
+    /// paths.
+    ///
+    /// Handles both sharded repos (`model.safetensors.index.json` plus
+    /// several `model-*.safetensors`) and the single-file layout
+    /// (`model.safetensors`). Returns the safetensors paths in
+    /// arbitrary order — `VarBuilder` unifies them into one tensor view.
+    async fn resolve_dense_files(
+        &self,
+        spec: &ModelSpec,
+    ) -> Result<(PathBuf, PathBuf, Vec<PathBuf>)> {
+        let api = self.hf_api()?;
+        let repo = api.model(spec.model_id.clone());
+
+        let config_path = repo
+            .get("config.json")
+            .await
+            .with_context(|| format!("fetch config.json from {}", spec.model_id))?;
+        let tokenizer_path = repo
+            .get("tokenizer.json")
+            .await
+            .with_context(|| format!("fetch tokenizer.json from {}", spec.model_id))?;
+
+        // Prefer the sharded layout (most HF dense models > 5B ship it).
+        let safetensors_paths = match repo.get("model.safetensors.index.json").await {
+            Ok(index_path) => {
+                let index_text = std::fs::read_to_string(&index_path)
+                    .context("read model.safetensors.index.json")?;
+                let index: serde_json::Value = serde_json::from_str(&index_text)
+                    .context("parse model.safetensors.index.json")?;
+                let weight_map = index
+                    .get("weight_map")
+                    .and_then(|v| v.as_object())
+                    .ok_or_else(|| {
+                        anyhow::anyhow!("safetensors index missing weight_map object")
+                    })?;
+                let unique: std::collections::BTreeSet<String> = weight_map
+                    .values()
+                    .filter_map(|v| v.as_str().map(String::from))
+                    .collect();
+                let mut paths = Vec::with_capacity(unique.len());
+                for fname in unique {
+                    let p = repo
+                        .get(&fname)
+                        .await
+                        .with_context(|| format!("fetch sharded safetensors {fname}"))?;
+                    paths.push(p);
+                }
+                paths
+            }
+            Err(_) => {
+                // Single-file fallback.
+                let p = repo
+                    .get("model.safetensors")
+                    .await
+                    .context("fetch model.safetensors (single-file layout)")?;
+                vec![p]
+            }
+        };
+        Ok((config_path, tokenizer_path, safetensors_paths))
+    }
+
+    /// Resolve + load a GGUF (pre-quantized) Qwen3. Returns the
+    /// tokenizer.json path so the caller can construct the Tokenizer
+    /// uniformly across source formats.
+    async fn load_arch_gguf(
+        &self,
+        spec: &ModelSpec,
+        device: &Device,
+    ) -> Result<(PathBuf, ModelArch)> {
+        let (gguf_path, tokenizer_path) = self.resolve_files(spec).await?;
+        let device_for_load = device.clone();
+        let gguf_path_for_load = gguf_path.clone();
+        let model_id_for_log = spec.model_id.clone();
+        let arch = tokio::task::spawn_blocking(move || -> Result<ModelArch> {
+            tracing::info!(model = %model_id_for_log, path = ?gguf_path_for_load, "loading GGUF");
+            let mut file = std::fs::File::open(&gguf_path_for_load).context("open GGUF file")?;
+            let content = gguf_file::Content::read(&mut file)
+                .map_err(|e| anyhow::anyhow!("parse GGUF: {e}"))?;
+
+            let architecture = content
+                .metadata
+                .get("general.architecture")
+                .and_then(|v| v.to_string().ok().cloned())
+                .unwrap_or_default();
+            tracing::info!(architecture = %architecture, "GGUF architecture");
+
+            match architecture.as_str() {
+                "qwen3" => {
+                    let weights =
+                        QuantizedQwen3Weights::from_gguf(content, &mut file, &device_for_load)
+                            .map_err(|e| anyhow::anyhow!("from_gguf qwen3: {e}"))?;
+                    Ok(ModelArch::Qwen3Quantized(weights))
+                }
+                other => anyhow::bail!(
+                    "unsupported GGUF architecture '{other}'; quantized path only supports qwen3"
+                ),
+            }
+        })
+        .await
+        .context("blocking GGUF load task panicked")??;
+        Ok((tokenizer_path, arch))
+    }
+
+    /// Resolve + load a dense Qwen3 from safetensors. Uses
+    /// `candle-transformers::models::qwen3::ModelForCausalLM` and
+    /// builds a VarBuilder over the mmap'd safetensors files. dtype
+    /// is bf16 by default to match the HF distribution dtype for
+    /// recent Qwen3 family models; fall back to f16 if the device
+    /// doesn't support bf16.
+    async fn load_arch_dense(
+        &self,
+        spec: &ModelSpec,
+        device: &Device,
+    ) -> Result<(PathBuf, ModelArch)> {
+        let (config_path, tokenizer_path, safetensors_paths) =
+            self.resolve_dense_files(spec).await?;
+        let device_for_load = device.clone();
+        let model_id_for_log = spec.model_id.clone();
+
+        let arch = tokio::task::spawn_blocking(move || -> Result<ModelArch> {
+            tracing::info!(
+                model = %model_id_for_log,
+                shards = safetensors_paths.len(),
+                "loading dense Qwen3 from safetensors"
+            );
+            let cfg_text = std::fs::read_to_string(&config_path).context("read config.json")?;
+            let cfg: qwen3_dense::Config =
+                serde_json::from_str(&cfg_text).context("parse Qwen3 config.json")?;
+
+            // bf16 is the canonical Qwen3 distribution dtype. CUDA
+            // devices on Ada+ support it; Ampere also supports bf16
+            // natively. CPU candle handles bf16 via emulation.
+            let dtype = DType::BF16;
+            // SAFETY: VarBuilder::from_mmaped_safetensors mmaps the files;
+            // mutation of the underlying files by another process while
+            // we hold the mapping is UB. We trust that nothing else on
+            // the host modifies the HF cache files during a model's
+            // lifetime (hf-hub itself is immutable-by-design).
+            let vb = unsafe {
+                VarBuilder::from_mmaped_safetensors(&safetensors_paths, dtype, &device_for_load)
+                    .context("build VarBuilder over safetensors")?
+            };
+            let model = qwen3_dense::ModelForCausalLM::new(&cfg, vb)
+                .map_err(|e| anyhow::anyhow!("build Qwen3 dense model: {e}"))?;
+            Ok(ModelArch::Qwen3Dense(model))
+        })
+        .await
+        .context("blocking dense load task panicked")??;
+        Ok((tokenizer_path, arch))
+    }
+
+    /// Resolve a model spec to local GGUF and tokenizer file paths via
+    /// hf-hub. Downloads on first use; subsequent calls are cached.
+    async fn resolve_files(&self, spec: &ModelSpec) -> Result<(PathBuf, PathBuf)> {
+        let api = self.hf_api()?;
+        let repo = api.model(spec.model_id.clone());
+
+        let info = repo
+            .info()
+            .await
+            .with_context(|| format!("fetch HF repo info for {}", spec.model_id))?;
+
+        let quant = spec.quant.as_deref().unwrap_or("");
+        let quant_lc = quant.to_lowercase();
+        let gguf_filename = info
+            .siblings
+            .iter()
+            .map(|s| s.rfilename.as_str())
+            .filter(|name| name.to_lowercase().ends_with(".gguf"))
+            .find(|name| quant_lc.is_empty() || name.to_lowercase().contains(&quant_lc))
+            .ok_or_else(|| {
+                anyhow::anyhow!(
+                    "no GGUF file matching quant {:?} in repo {}",
+                    spec.quant,
+                    spec.model_id
+                )
+            })?
+            .to_string();
+
+        tracing::info!(
+            model = %spec.model_id,
+            file = %gguf_filename,
+            "resolving GGUF (may be cached)"
+        );
+        let gguf_path = repo
+            .get(&gguf_filename)
+            .await
+            .with_context(|| format!("fetch GGUF {gguf_filename}"))?;
+
+        // GGUF-only HF repos (unsloth/Qwen3-*-GGUF, Qwen/Qwen3-*-GGUF,
+        // etc.) ship the .gguf file but not tokenizer.json — the
+        // tokenizer.json lives in the base non-GGUF repo. Derive the
+        // base repo id by stripping a `-GGUF` / `-gguf` suffix; if
+        // there's no such suffix the same repo is used (works for
+        // non-GGUF model_ids).
+        let tokenizer_repo_id = spec
+            .model_id
+            .strip_suffix("-GGUF")
+            .or_else(|| spec.model_id.strip_suffix("-gguf"))
+            .unwrap_or(spec.model_id.as_str())
+            .to_string();
+        let tokenizer_repo = if tokenizer_repo_id == spec.model_id {
+            repo
+        } else {
+            tracing::debug!(
+                from = %spec.model_id,
+                to = %tokenizer_repo_id,
+                "tokenizer.json sourced from base repo (GGUF suffix stripped)"
+            );
+            api.model(tokenizer_repo_id.clone())
+        };
+        let tokenizer_path = tokenizer_repo
+            .get("tokenizer.json")
+            .await
+            .with_context(|| format!("fetch tokenizer.json from {tokenizer_repo_id}"))?;
+        Ok((gguf_path, tokenizer_path))
+    }
+
+    /// Run a non-streaming chat completion against a loaded model.
+    ///
+    /// Returns a typed `InferenceError` when the model isn't loaded so the
+    /// handler can map to an appropriate HTTP status without string-matching.
+    pub async fn chat_completion(
+        &self,
+        request: ChatCompletionRequest,
+    ) -> Result<ChatCompletionResponse, InferenceError> {
+        let loaded = {
+            let models = self.models.read().await;
+            models.get(&request.model).cloned()
+        };
+        let loaded = loaded.ok_or_else(|| InferenceError::ModelNotLoaded(request.model.clone()))?;
+
+        let prompt = format_qwen3_prompt(&request.messages);
+
+        let encoding = loaded
+            .tokenizer
+            .encode(prompt.as_str(), true)
+            .map_err(|e| InferenceError::Other(anyhow::anyhow!("tokenize: {e}")))?;
+        let prompt_tokens: Vec<u32> = encoding.get_ids().to_vec();
+        let prompt_len = prompt_tokens.len();
+
+        let temperature = request.temperature.unwrap_or(0.7);
+        let top_p = request.top_p;
+        let max_new = request.max_tokens.unwrap_or(512) as usize;
+        let seed = unix_subsec_nanos();
+
+        let eos_id = loaded
+            .tokenizer
+            .token_to_id("<|im_end|>")
+            .or_else(|| loaded.tokenizer.token_to_id("<|endoftext|>"));
+
+        let arch_arc = Arc::clone(&loaded.arch);
+        let device = loaded.device.clone();
+        let model_id = request.model.clone();
+
+        let (generated_ids, finish_reason) =
+            tokio::task::spawn_blocking(move || -> Result<(Vec<u32>, String)> {
+                let mut guard = arch_arc.blocking_lock();
+                run_inference(
+                    &mut guard,
+                    &device,
+                    &prompt_tokens,
+                    max_new,
+                    temperature,
+                    top_p,
+                    seed,
+                    eos_id,
+                )
+            })
+            .await
+            .map_err(|e| InferenceError::Other(anyhow::anyhow!("inference task panicked: {e}")))?
+            .map_err(InferenceError::Other)?;
+
+        let completion_text = loaded
+            .tokenizer
+            .decode(&generated_ids, true)
+            .map_err(|e| InferenceError::Other(anyhow::anyhow!("detokenize: {e}")))?;
+
+        let usage = Usage {
+            prompt_tokens: prompt_len as u64,
+            completion_tokens: generated_ids.len() as u64,
+            total_tokens: (prompt_len + generated_ids.len()) as u64,
+        };
+
+        Ok(ChatCompletionResponse {
+            id: format!("chatcmpl-{:x}", unix_subsec_nanos()),
+            object: "chat.completion".into(),
+            created: unix_now_secs(),
+            model: model_id,
+            choices: vec![ChatCompletionChoice {
+                index: 0,
+                message: ChatMessage {
+                    role: "assistant".into(),
+                    content: MessageContent::Text(completion_text),
+                    extra: serde_json::Value::Object(Default::default()),
+                },
+                finish_reason: Some(finish_reason),
+                extra: serde_json::Value::Object(Default::default()),
+            }],
+            usage: Some(usage),
+            extra: serde_json::Value::Object(Default::default()),
+        })
+    }
+
+    /// Run a streaming chat completion against a loaded model.
+    ///
+    /// Returns an `mpsc::Receiver` that yields `ChatCompletionChunk`s in
+    /// OpenAI SSE format. The first chunk carries the assistant role;
+    /// subsequent chunks carry incremental `content` deltas; the final
+    /// chunk carries `finish_reason`. The handler is responsible for
+    /// wrapping these into an SSE response and appending the `[DONE]`
+    /// terminator.
+    ///
+    /// Token-by-token decoding tracks the cumulative decoded prefix so
+    /// BPE byte-fallback boundaries don't split a UTF-8 char across
+    /// chunks.
+    pub async fn chat_completion_stream(
+        &self,
+        request: ChatCompletionRequest,
+    ) -> Result<mpsc::Receiver<ChatCompletionChunk>, InferenceError> {
+        let loaded = {
+            let models = self.models.read().await;
+            models.get(&request.model).cloned()
+        };
+        let loaded = loaded.ok_or_else(|| InferenceError::ModelNotLoaded(request.model.clone()))?;
+
+        let prompt = format_qwen3_prompt(&request.messages);
+        let encoding = loaded
+            .tokenizer
+            .encode(prompt.as_str(), true)
+            .map_err(|e| InferenceError::Other(anyhow::anyhow!("tokenize: {e}")))?;
+        let prompt_tokens: Vec<u32> = encoding.get_ids().to_vec();
+
+        let temperature = request.temperature.unwrap_or(0.7);
+        let top_p = request.top_p;
+        let max_new = request.max_tokens.unwrap_or(512) as usize;
+        let seed = unix_subsec_nanos();
+
+        let eos_id = loaded
+            .tokenizer
+            .token_to_id("<|im_end|>")
+            .or_else(|| loaded.tokenizer.token_to_id("<|endoftext|>"));
+
+        let arch_arc = Arc::clone(&loaded.arch);
+        let device = loaded.device.clone();
+        let tokenizer = loaded.tokenizer.clone();
+        let model_id = request.model.clone();
+        let id = format!("chatcmpl-{:x}", unix_subsec_nanos());
+        let created = unix_now_secs();
+
+        // Bounded channel so the producer (blocking inference) is back-
+        // pressured by the consumer (SSE writer). 32 is generous —
+        // tokens arrive one at a time and the SSE writer is async.
+        let (tx, rx) = mpsc::channel::<ChatCompletionChunk>(32);
+
+        // Lead chunk: announce the assistant role per OpenAI streaming
+        // conventions. Tools that auto-detect a streaming reply expect
+        // this before any content delta.
+        let role_chunk = ChatCompletionChunk {
+            id: id.clone(),
+            object: "chat.completion.chunk".into(),
+            created,
+            model: model_id.clone(),
+            choices: vec![ChunkChoice {
+                index: 0,
+                delta: json!({"role": "assistant"}),
+                finish_reason: None,
+                extra: serde_json::Value::Object(Default::default()),
+            }],
+            usage: None,
+            extra: serde_json::Value::Object(Default::default()),
+        };
+        // If sending the role chunk fails the receiver is already gone;
+        // bail before kicking off the heavy blocking work.
+        tx.send(role_chunk)
+            .await
+            .map_err(|_| InferenceError::Other(anyhow::anyhow!("client disconnected")))?;
+
+        tokio::task::spawn_blocking(move || {
+            let mut guard = arch_arc.blocking_lock();
+            if let Err(e) = run_inference_streaming(
+                &mut guard,
+                &device,
+                &tokenizer,
+                &prompt_tokens,
+                max_new,
+                temperature,
+                top_p,
+                seed,
+                eos_id,
+                &id,
+                created,
+                &model_id,
+                &tx,
+            ) {
+                tracing::warn!(model = %model_id, error = %e, "streaming inference failed");
+            }
+        });
+
+        Ok(rx)
+    }
+}
+
+#[async_trait]
+impl Harness for CandleHarness {
+    fn name(&self) -> &str {
+        "candle"
+    }
+
+    async fn health(&self) -> HarnessHealth {
+        HarnessHealth {
+            name: "candle".into(),
+            running: true,
+            uptime_secs: None,
+        }
+    }
+
+    async fn list_models(&self) -> Result<Vec<ModelInfo>> {
+        let models = self.models.read().await;
+        Ok(models
+            .values()
+            .map(|m| ModelInfo {
+                id: m.model_id.clone(),
+                harness: "candle".into(),
+                status: "loaded".into(),
+                devices: m.devices.clone(),
+                vram_used_mb: None,
+            })
+            .collect())
+    }
+
+    async fn load_model(&self, spec: &ModelSpec) -> Result<()> {
+        if spec.harness != "candle" {
+            anyhow::bail!("expected harness=candle, got harness={}", spec.harness);
+        }
+
+        {
+            let models = self.models.read().await;
+            if models.contains_key(&spec.model_id) {
+                anyhow::bail!("model '{}' already loaded", spec.model_id);
+            }
+        }
+
+        // Stage 7a-i scaffolds tensor-parallel worker subprocesses but
+        // does not yet route inference through them. Refuse TP loads
+        // for now with a clear marker so the request surface is honest;
+        // Stage 7b-iv replaces this bail with the TP dispatch.
+        let tp_size = spec.tensor_parallel.unwrap_or(1);
+        if tp_size > 1 {
+            anyhow::bail!(
+                "tensor_parallel={tp_size} requested for '{}': TP worker \
+                 lifecycle + NCCL handshake are in place (Stage 7a) but \
+                 TP-aware Qwen3 inference orchestration lands in Stage \
+                 7b-iv; single-GPU loads only for now",
+                spec.model_id
+            );
+        }
+
+        let devices = spec.devices.clone().unwrap_or_else(|| vec![0]);
+        let device = Self::pick_device(&devices)?;
+
+        // Dispatch by source format: GGUF (pre-quantized, single-GPU
+        // only path) vs safetensors dense (bf16/fp16; the path that
+        // grows TP support). `spec.quant` is the signal — Some means
+        // the operator picked a quantized GGUF; None means dense.
+        let (tokenizer_path, arch) = if spec.quant.is_some() {
+            self.load_arch_gguf(spec, &device).await?
+        } else {
+            self.load_arch_dense(spec, &device).await?
+        };
+
+        let tokenizer = Tokenizer::from_file(&tokenizer_path)
+            .map_err(|e| anyhow::anyhow!("load tokenizer: {e}"))?;
+
+        let loaded = Arc::new(LoadedModel {
+            model_id: spec.model_id.clone(),
+            arch: Arc::new(Mutex::new(arch)),
+            tokenizer,
+            device,
+            quant: spec.quant.clone(),
+            devices,
+        });
+
+        let mut models = self.models.write().await;
+        models.insert(spec.model_id.clone(), loaded);
+        tracing::info!(model = %spec.model_id, "model loaded");
+        Ok(())
+    }
+
+    async fn unload_model(&self, model_id: &str) -> Result<()> {
+        let mut models = self.models.write().await;
+        if models.remove(model_id).is_none() {
+            anyhow::bail!("model '{model_id}' not loaded");
+        }
+        tracing::info!(model = %model_id, "model unloaded");
+        Ok(())
+    }
+
+    async fn inference_endpoint(&self, model_id: &str) -> Option<String> {
+        let models = self.models.read().await;
+        models.contains_key(model_id).then(|| self.bind_url.clone())
+    }
+}
+
+/// Errors returned by `CandleHarness::chat_completion`. The
+/// `ModelNotLoaded` variant lets the HTTP handler map cleanly to 404
+/// without string-matching on anyhow messages.
+#[derive(Debug, thiserror::Error)]
+pub enum InferenceError {
+    #[error("model '{0}' not loaded on this neuron")]
+    ModelNotLoaded(String),
+    #[error(transparent)]
+    Other(#[from] anyhow::Error),
+}
+
+/// Apply the Qwen3 chat template:
+///
+/// ```text
+/// <|im_start|>{role}\n{content}<|im_end|>\n
+/// ...
+/// <|im_start|>assistant\n
+/// ```
+///
+/// The trailing `<|im_start|>assistant\n` cues the model to begin a turn.
+/// Non-text content parts (vision blocks) are joined as text only; full
+/// multimodal handling is out of scope for Stage 3.
+fn format_qwen3_prompt(messages: &[ChatMessage]) -> String {
+    let mut prompt = String::new();
+    for msg in messages {
+        let content = match &msg.content {
+            MessageContent::Text(s) => s.clone(),
+            MessageContent::Parts(parts) => parts
+                .iter()
+                .filter_map(|p| p.get("text").and_then(|v| v.as_str()))
+                .collect::<Vec<_>>()
+                .join(""),
+        };
+        prompt.push_str("<|im_start|>");
+        prompt.push_str(&msg.role);
+        prompt.push('\n');
+        prompt.push_str(&content);
+        prompt.push_str("<|im_end|>\n");
+    }
+    prompt.push_str("<|im_start|>assistant\n");
+    prompt
+}
+
+#[allow(clippy::too_many_arguments)]
+fn run_inference(
+    arch: &mut ModelArch,
+    device: &Device,
+    prompt_tokens: &[u32],
+    max_new: usize,
+    temperature: f64,
+    top_p: Option<f64>,
+    seed: u64,
+    eos_id: Option<u32>,
+) -> Result<(Vec<u32>, String)> {
+    let mut logits_processor = {
+        let sampling = if temperature <= 0.0 {
+            Sampling::ArgMax
+        } else {
+            match top_p {
+                Some(p) => Sampling::TopP { p, temperature },
+                None => Sampling::All { temperature },
+            }
+        };
+        LogitsProcessor::from_sampling(seed, sampling)
+    };
+
+    let mut generated: Vec<u32> = Vec::new();
+
+    let mut next_token = match arch {
+        ModelArch::Qwen3Quantized(model) => {
+            model.clear_kv_cache();
+            let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
+            let logits = model.forward(&input, 0)?;
+            let logits = logits.squeeze(0)?;
+            sample_with_penalty(&logits, &generated, &mut logits_processor)?
+        }
+        ModelArch::Qwen3Dense(model) => {
+            model.clear_kv_cache();
+            let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
+            // qwen3::ModelForCausalLM::forward returns [B, 1, V] —
+            // no final squeeze on the dense path, unlike the quantized
+            // variant which returns [B, V]. Strip both batch and seq
+            // dims to get the rank-1 logits LogitsProcessor expects.
+            let logits = model.forward(&input, 0)?.squeeze(0)?.squeeze(0)?;
+            sample_with_penalty(&logits, &generated, &mut logits_processor)?
+        }
+    };
+
+    if Some(next_token) == eos_id {
+        return Ok((generated, "stop".into()));
+    }
+    generated.push(next_token);
+
+    for index in 0..max_new.saturating_sub(1) {
+        next_token = match arch {
+            ModelArch::Qwen3Quantized(model) => {
+                let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
+                let logits = model.forward(&input, prompt_tokens.len() + index)?;
+                let logits = logits.squeeze(0)?;
+                sample_with_penalty(&logits, &generated, &mut logits_processor)?
+            }
+            ModelArch::Qwen3Dense(model) => {
+                let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
+                // Dense returns [B, 1, V]; strip both leading dims.
+                let logits = model
+                    .forward(&input, prompt_tokens.len() + index)?
+                    .squeeze(0)?
+                    .squeeze(0)?;
+                sample_with_penalty(&logits, &generated, &mut logits_processor)?
+            }
+        };
+        if Some(next_token) == eos_id {
+            return Ok((generated, "stop".into()));
+        }
+        generated.push(next_token);
+    }
+
+    Ok((generated, "length".into()))
+}
+
+/// Streaming counterpart to `run_inference`. Emits chunks via `tx` as
+/// tokens are generated and exits on EOS, max_new, or receiver drop.
+///
+/// Detokenization tracks the cumulative decoded prefix so each chunk's
+/// `content` delta is the substring appended since the last chunk —
+/// safe across BPE byte-fallback boundaries.
+#[allow(clippy::too_many_arguments)]
+fn run_inference_streaming(
+    arch: &mut ModelArch,
+    device: &Device,
+    tokenizer: &Tokenizer,
+    prompt_tokens: &[u32],
+    max_new: usize,
+    temperature: f64,
+    top_p: Option<f64>,
+    seed: u64,
+    eos_id: Option<u32>,
+    id: &str,
+    created: u64,
+    model_id: &str,
+    tx: &mpsc::Sender<ChatCompletionChunk>,
+) -> Result<()> {
+    let mut logits_processor = {
+        let sampling = if temperature <= 0.0 {
+            Sampling::ArgMax
+        } else {
+            match top_p {
+                Some(p) => Sampling::TopP { p, temperature },
+                None => Sampling::All { temperature },
+            }
+        };
+        LogitsProcessor::from_sampling(seed, sampling)
+    };
+
+    let mut all_tokens: Vec<u32> = Vec::new();
+    let mut decoded_prefix = String::new();
+    let mut finish_reason = "length".to_string();
+
+    let mut next_token = match arch {
+        ModelArch::Qwen3Quantized(model) => {
+            model.clear_kv_cache();
+            let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
+            let logits = model.forward(&input, 0)?;
+            let logits = logits.squeeze(0)?;
+            sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?
+        }
+        ModelArch::Qwen3Dense(model) => {
+            model.clear_kv_cache();
+            let input = Tensor::new(prompt_tokens, device)?.unsqueeze(0)?;
+            let logits = model.forward(&input, 0)?;
+            let logits = logits.squeeze(0)?;
+            sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?
+        }
+    };
+
+    let emit_token = |all_tokens: &[u32], decoded_prefix: &mut String| -> Result<bool> {
+        let full = tokenizer
+            .decode(all_tokens, true)
+            .map_err(|e| anyhow::anyhow!("decode: {e}"))?;
+        if full.len() > decoded_prefix.len() {
+            let delta = full[decoded_prefix.len()..].to_string();
+            *decoded_prefix = full;
+            let chunk = ChatCompletionChunk {
+                id: id.into(),
+                object: "chat.completion.chunk".into(),
+                created,
+                model: model_id.into(),
+                choices: vec![ChunkChoice {
+                    index: 0,
+                    delta: json!({ "content": delta }),
+                    finish_reason: None,
+                    extra: serde_json::Value::Object(Default::default()),
+                }],
+                usage: None,
+                extra: serde_json::Value::Object(Default::default()),
+            };
+            // blocking_send returns Err if the consumer hung up — signal
+            // the caller to stop generating.
+            if tx.blocking_send(chunk).is_err() {
+                return Ok(false);
+            }
+        }
+        Ok(true)
+    };
+
+    if Some(next_token) == eos_id {
+        finish_reason = "stop".into();
+    } else {
+        all_tokens.push(next_token);
+        if !emit_token(&all_tokens, &mut decoded_prefix)? {
+            return Ok(());
+        }
+
+        for index in 0..max_new.saturating_sub(1) {
+            next_token = match arch {
+                ModelArch::Qwen3Quantized(model) => {
+                    let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
+                    let logits = model.forward(&input, prompt_tokens.len() + index)?;
+                    let logits = logits.squeeze(0)?;
+                    sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?
+                }
+                ModelArch::Qwen3Dense(model) => {
+                    let input = Tensor::new(&[next_token], device)?.unsqueeze(0)?;
+                    // Dense returns [B, 1, V]; strip both leading dims.
+                    let logits = model
+                        .forward(&input, prompt_tokens.len() + index)?
+                        .squeeze(0)?
+                        .squeeze(0)?;
+                    sample_with_penalty(&logits, &all_tokens, &mut logits_processor)?
+                }
+            };
+            if Some(next_token) == eos_id {
+                finish_reason = "stop".into();
+                break;
+            }
+            all_tokens.push(next_token);
+            if !emit_token(&all_tokens, &mut decoded_prefix)? {
+                return Ok(());
+            }
+        }
+    }
+
+    let final_chunk = ChatCompletionChunk {
+        id: id.into(),
+        object: "chat.completion.chunk".into(),
+        created,
+        model: model_id.into(),
+        choices: vec![ChunkChoice {
+            index: 0,
+            delta: serde_json::Value::Object(Default::default()),
+            finish_reason: Some(finish_reason),
+            extra: serde_json::Value::Object(Default::default()),
+        }],
+        usage: None,
+        extra: serde_json::Value::Object(Default::default()),
+    };
+    let _ = tx.blocking_send(final_chunk);
+    Ok(())
+}
+
+fn unix_now_secs() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_secs())
+        .unwrap_or(0)
+}
+
+fn unix_subsec_nanos() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_nanos() as u64)
+        .unwrap_or(0)
+}

crates/neuron/src/harness/llamacpp.rs

@@ -1 +0,0 @@
-// llama.cpp harness implementation — Phase 11.

crates/neuron/src/harness/mistralrs.rs

@@ -1,163 +0,0 @@
-//! mistral.rs harness implementation.
-//!
-//! Wraps the mistral.rs HTTP API for model lifecycle management
-//! and optionally manages the process via systemd.
-
-use anyhow::Result;
-use async_trait::async_trait;
-use cortex_core::harness::{Harness, HarnessConfig, HarnessHealth, ModelInfo, ModelSpec};
-use reqwest::Client;
-use serde::Deserialize;
-
-pub struct MistralRsHarness {
-    endpoint: String,
-    systemd_unit: Option<String>,
-    client: Client,
-}
-
-impl MistralRsHarness {
-    pub fn new(endpoint: String, systemd_unit: Option<String>) -> Self {
-        Self {
-            endpoint,
-            systemd_unit,
-            client: Client::builder()
-                .timeout(std::time::Duration::from_secs(30))
-                .build()
-                .expect("failed to build HTTP client"),
-        }
-    }
-}
-
-/// Response from mistral.rs `GET /v1/models`.
-#[derive(Debug, Deserialize)]
-struct ModelsResponse {
-    data: Vec<ModelEntry>,
-}
-
-#[derive(Debug, Deserialize)]
-struct ModelEntry {
-    id: String,
-    #[serde(default)]
-    status: Option<String>,
-}
-
-#[async_trait]
-impl Harness for MistralRsHarness {
-    fn name(&self) -> &str {
-        "mistralrs"
-    }
-
-    async fn start(&self, _config: &HarnessConfig) -> Result<()> {
-        let Some(unit) = &self.systemd_unit else {
-            anyhow::bail!("no systemd unit configured for mistralrs harness");
-        };
-
-        let output = tokio::process::Command::new("systemctl")
-            .args(["start", unit])
-            .output()
-            .await?;
-
-        if !output.status.success() {
-            let stderr = String::from_utf8_lossy(&output.stderr);
-            anyhow::bail!("systemctl start {unit} failed: {stderr}");
-        }
-
-        // Wait for the health endpoint to respond (up to 30s).
-        let url = format!("{}/health", self.endpoint);
-        for _ in 0..30 {
-            tokio::time::sleep(std::time::Duration::from_secs(1)).await;
-            if self.client.get(&url).send().await.is_ok() {
-                tracing::info!(unit, "mistralrs started and healthy");
-                return Ok(());
-            }
-        }
-        anyhow::bail!("mistralrs started but health endpoint did not respond within 30s");
-    }
-
-    async fn stop(&self) -> Result<()> {
-        let Some(unit) = &self.systemd_unit else {
-            anyhow::bail!("no systemd unit configured for mistralrs harness");
-        };
-
-        let output = tokio::process::Command::new("systemctl")
-            .args(["stop", unit])
-            .output()
-            .await?;
-
-        if !output.status.success() {
-            let stderr = String::from_utf8_lossy(&output.stderr);
-            anyhow::bail!("systemctl stop {unit} failed: {stderr}");
-        }
-        Ok(())
-    }
-
-    async fn health(&self) -> HarnessHealth {
-        let url = format!("{}/health", self.endpoint);
-        let running = self.client.get(&url).send().await.is_ok();
-        HarnessHealth {
-            name: "mistralrs".into(),
-            running,
-            uptime_secs: None,
-        }
-    }
-
-    async fn list_models(&self) -> Result<Vec<ModelInfo>> {
-        let url = format!("{}/v1/models", self.endpoint);
-        let resp = self.client.get(&url).send().await?;
-
-        if !resp.status().is_success() {
-            anyhow::bail!("GET /v1/models returned {}", resp.status());
-        }
-
-        let models_resp: ModelsResponse = resp.json().await?;
-        Ok(models_resp
-            .data
-            .into_iter()
-            .map(|m| ModelInfo {
-                id: m.id,
-                harness: "mistralrs".into(),
-                status: m.status.unwrap_or_else(|| "loaded".into()),
-                devices: vec![],
-                vram_used_mb: None,
-            })
-            .collect())
-    }
-
-    async fn load_model(&self, spec: &ModelSpec) -> Result<()> {
-        let url = format!("{}/v1/models/reload", self.endpoint);
-        let resp = self
-            .client
-            .post(&url)
-            .json(&serde_json::json!({ "model_id": spec.model_id }))
-            .send()
-            .await?;
-
-        if !resp.status().is_success() {
-            let body = resp.text().await.unwrap_or_default();
-            anyhow::bail!("POST /v1/models/reload failed: {body}");
-        }
-        Ok(())
-    }
-
-    async fn unload_model(&self, model_id: &str) -> Result<()> {
-        let url = format!("{}/v1/models/unload", self.endpoint);
-        let resp = self
-            .client
-            .post(&url)
-            .json(&serde_json::json!({ "model_id": model_id }))
-            .send()
-            .await?;
-
-        if !resp.status().is_success() {
-            let body = resp.text().await.unwrap_or_default();
-            anyhow::bail!("POST /v1/models/unload failed: {body}");
-        }
-        Ok(())
-    }
-
-    async fn inference_endpoint(&self, _model_id: &str) -> Option<String> {
-        // mistral.rs routes internally by model name in the request body,
-        // so the inference endpoint is always the base URL.
-        Some(self.endpoint.clone())
-    }
-}

crates/neuron/src/harness/mod.rs

@@ -1,15 +1,23 @@
 //! Harness registry — maps harness names to trait implementations.
 
-pub mod llamacpp;
+pub mod candle;
-pub mod mistralrs;
+pub mod tp;
 
 use anyhow::Result;
 use cortex_core::harness::{Harness, HarnessConfig, ModelInfo, ModelSpec};
 use std::collections::HashMap;
+use std::sync::Arc;
 
 /// Registry of available harness implementations.
+///
+/// Holds an `Arc<dyn Harness>` per harness for generic lifecycle dispatch
+/// (load/unload/list_models). When a candle harness is registered, a typed
+/// `Arc<CandleHarness>` is also cached so inference routes can bypass the
+/// dyn-Trait dispatch and reach harness-specific methods (chat completion,
+/// streaming, etc.).
 pub struct HarnessRegistry {
-    harnesses: HashMap<String, Box<dyn Harness>>,
+    harnesses: HashMap<String, Arc<dyn Harness>>,
+    candle: Option<Arc<candle::CandleHarness>>,
 }
 
 impl Default for HarnessRegistry {
@@ -22,10 +30,11 @@ impl HarnessRegistry {
     pub fn new() -> Self {
         Self {
             harnesses: HashMap::new(),
+            candle: None,
         }
     }
 
-    pub fn register(&mut self, harness: Box<dyn Harness>) {
+    pub fn register(&mut self, harness: Arc<dyn Harness>) {
         self.harnesses.insert(harness.name().to_string(), harness);
     }
 
@@ -34,6 +43,12 @@ impl HarnessRegistry {
         self.harnesses.keys().cloned().collect()
     }
 
+    /// Typed handle to the candle harness, if registered. Used by inference
+    /// routes that need methods beyond the `Harness` trait surface.
+    pub fn candle(&self) -> Option<Arc<candle::CandleHarness>> {
+        self.candle.clone()
+    }
+
     /// List models from all registered harnesses.
     pub async fn list_all_models(&self) -> Result<Vec<ModelInfo>> {
         let mut all = Vec::new();
@@ -81,19 +96,25 @@ impl HarnessRegistry {
     }
 
     /// Build a registry from harness configs.
-    pub fn from_configs(configs: &[HarnessConfig]) -> Self {
+    ///
+    /// `bind_url` is the URL where this neuron serves inference (its own
+    /// listen address). In-process harnesses (currently the only kind)
+    /// return this URL from `inference_endpoint`.
+    pub fn from_configs(
+        configs: &[HarnessConfig],
+        bind_url: &str,
+        settings: &crate::config::HarnessSettings,
+    ) -> Self {
         let mut registry = Self::new();
         for config in configs {
             match config.name.as_str() {
-                "mistralrs" => {
+                "candle" => {
-                    if let Some(endpoint) = &config.endpoint {
+                    let harness = Arc::new(candle::CandleHarness::new(
-                        registry.register(Box::new(mistralrs::MistralRsHarness::new(
+                        bind_url.to_string(),
-                            endpoint.clone(),
+                        settings.candle.hf_cache.clone(),
-                            config.systemd_unit.clone(),
+                    ));
-                        )));
+                    registry.candle = Some(Arc::clone(&harness));
-                    } else {
+                    registry.harnesses.insert("candle".into(), harness);
-                        tracing::warn!("mistralrs harness missing endpoint, skipping");
-                    }
                 }
                 other => {
                     tracing::warn!(harness = other, "unknown harness type, skipping");

crates/neuron/src/harness/tp/all_reduce.rs

@@ -0,0 +1,120 @@
+//! `AllReduce` as a candle `CustomOp1` — the bridge between candle's
+//! `Tensor` graph and `cudarc::nccl::Comm::all_reduce`.
+//!
+//! Ported from the canonical
+//! `candle-examples/examples/llama_multiprocess/model.rs` pattern.
+//! Row-parallel layers apply this op after their local matmul to sum
+//! partial outputs across NCCL ranks.
+//!
+//! Available only under `--features cuda`; on CPU builds this module
+//! is empty and row-parallel layers degenerate to local matmul only
+//! (useful for compile-checking the model code; correctness requires
+//! cuda).
+//!
+//! Thread-safety caveat: NCCL communicators are technically only
+//! safe to use from a single thread at a time
+//! (https://docs.nvidia.com/deeplearning/nccl/user-guide/docs/usage/threadsafety.html).
+//! We hold the `AllReduce` behind an `Arc<Comm>` and only issue ops
+//! against it from the dedicated `spawn_blocking` thread the inference
+//! pipeline already uses for candle's forward passes.
+
+#![cfg(feature = "cuda")]
+
+use candle_core::backend::BackendStorage;
+use candle_core::cuda_backend::WrapErr;
+use candle_core::{CpuStorage, CudaStorage, CustomOp1, DType, Layout, Result, Shape};
+use cudarc::nccl::{Comm, ReduceOp};
+use half::{bf16, f16};
+use std::sync::Arc;
+
+/// Wraps an NCCL `Comm` so it can be plugged into a candle forward
+/// graph as a custom op. Each row-parallel layer holds one of these.
+pub struct AllReduce {
+    comm: Arc<Comm>,
+}
+
+// SAFETY: `Comm` contains a raw `ncclComm_t` pointer; NCCL's docs note
+// that issuing ops against one comm from multiple threads concurrently
+// is unsafe. We serialise via the single spawn_blocking thread that
+// drives the model's forward pass. The Send/Sync impl is necessary
+// because candle's CustomOp1 trait bounds require it; the correctness
+// invariant is enforced at the call site, not the type level.
+unsafe impl Send for AllReduce {}
+unsafe impl Sync for AllReduce {}
+
+impl AllReduce {
+    pub fn new(comm: Arc<Comm>) -> Self {
+        Self { comm }
+    }
+
+    pub fn comm(&self) -> &Arc<Comm> {
+        &self.comm
+    }
+}
+
+impl CustomOp1 for AllReduce {
+    fn name(&self) -> &'static str {
+        "neuron.tp.all_reduce"
+    }
+
+    fn cpu_fwd(&self, _s: &CpuStorage, _l: &Layout) -> Result<(CpuStorage, Shape)> {
+        candle_core::bail!("AllReduce custom-op invoked on CPU storage; TP requires CUDA")
+    }
+
+    fn cuda_fwd(&self, s: &CudaStorage, l: &Layout) -> Result<(CudaStorage, Shape)> {
+        // Reject non-contiguous inputs explicitly — copying them
+        // server-side would mask shape bugs (a TP layer feeding a
+        // strided activation into all_reduce is almost certainly a
+        // model construction error).
+        fn require_contiguous<T: cudarc::driver::DeviceRepr>(
+            slice: &cudarc::driver::CudaSlice<T>,
+            l: &Layout,
+        ) -> Result<()> {
+            match l.contiguous_offsets() {
+                Some((0, n)) if n == slice.len() => Ok(()),
+                _ => candle_core::bail!(
+                    "AllReduce input is non-contiguous: layout={:?}, slice_len={}",
+                    l,
+                    slice.len()
+                ),
+            }
+        }
+
+        let elem_count = l.shape().elem_count();
+        let dev = s.device().clone();
+
+        let out = match s.dtype() {
+            DType::BF16 => {
+                let src = s.as_cuda_slice::<bf16>()?;
+                require_contiguous(src, l)?;
+                let mut dst = unsafe { dev.alloc::<bf16>(elem_count) }.w()?;
+                self.comm
+                    .all_reduce(src, &mut dst, &ReduceOp::Sum)
+                    .map_err(|e| candle_core::Error::Msg(format!("nccl all_reduce bf16: {e:?}")))?;
+                CudaStorage::wrap_cuda_slice(dst, dev)
+            }
+            DType::F16 => {
+                let src = s.as_cuda_slice::<f16>()?;
+                require_contiguous(src, l)?;
+                let mut dst = unsafe { dev.alloc::<f16>(elem_count) }.w()?;
+                self.comm
+                    .all_reduce(src, &mut dst, &ReduceOp::Sum)
+                    .map_err(|e| candle_core::Error::Msg(format!("nccl all_reduce f16: {e:?}")))?;
+                CudaStorage::wrap_cuda_slice(dst, dev)
+            }
+            DType::F32 => {
+                let src = s.as_cuda_slice::<f32>()?;
+                require_contiguous(src, l)?;
+                let mut dst = unsafe { dev.alloc::<f32>(elem_count) }.w()?;
+                self.comm
+                    .all_reduce(src, &mut dst, &ReduceOp::Sum)
+                    .map_err(|e| candle_core::Error::Msg(format!("nccl all_reduce f32: {e:?}")))?;
+                CudaStorage::wrap_cuda_slice(dst, dev)
+            }
+            dtype => candle_core::bail!(
+                "AllReduce: unsupported dtype {dtype:?}; TP path expects bf16/f16/f32"
+            ),
+        };
+        Ok((out, l.shape().clone()))
+    }
+}

crates/neuron/src/harness/tp/mod.rs

@@ -0,0 +1,372 @@
+//! Tensor-parallel inference plumbing.
+//!
+//! The leader process (the neuron daemon proper) drives one
+//! subprocess per non-zero NCCL rank — `tokio::process::Command` on
+//! `/proc/self/exe --worker --rank N --tp-size N --cuda-device N` —
+//! and talks to each over a newline-delimited JSON RPC channel on
+//! the worker's stdin/stdout (see `rpc.rs`).
+//!
+//! Sub-staging:
+//!
+//! - **7a-i (this commit):** process lifecycle. `WorkerPool::spawn`
+//!   forks N workers; `ping` round-trips every worker to confirm
+//!   they're alive; `shutdown` cleanly drains and reaps. `Init` /
+//!   `NcclSanityCheck` are stubbed.
+//! - **7a-ii:** real NCCL `Comm` setup via `Init`, sanity check via
+//!   `NcclSanityCheck`. CUDA-gated.
+//! - **7b:** TP-aware Qwen3 inference dispatched through the pool.
+//! - **7c:** crash detection, streaming SSE, graceful unload.
+
+pub mod all_reduce;
+pub mod nccl_state;
+pub mod rpc;
+pub mod tp_linear;
+pub mod tp_qwen3;
+pub mod worker;
+
+use anyhow::{Context, Result};
+use std::path::{Path, PathBuf};
+use std::process::Stdio;
+use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader, Lines};
+use tokio::process::{Child, ChildStdin, ChildStdout, Command};
+
+use rpc::{WorkerRequest, WorkerResponse};
+
+/// One worker subprocess plus its bidirectional stdio handles.
+struct Worker {
+    rank: u32,
+    /// Captured so the leader can log "spawned rank N on device M" and
+    /// future stages can re-issue Init after a CUDA reset. Unused in
+    /// the Stage 7a-i RPC paths themselves.
+    #[allow(dead_code)]
+    cuda_device: u32,
+    child: Child,
+    stdin: ChildStdin,
+    stdout: Lines<BufReader<ChildStdout>>,
+}
+
+impl Worker {
+    /// Send a request and wait for the response. Used for sequenced
+    /// ops like `Ping` / `Shutdown` where the caller doesn't need to
+    /// overlap the worker's execution with the leader's.
+    async fn request(&mut self, req: &WorkerRequest) -> Result<WorkerResponse> {
+        self.send_only(req).await?;
+        self.recv_only().await
+    }
+
+    /// Write a request without awaiting its response. Pair with
+    /// `recv_only` from the caller when leader and worker need to do
+    /// work concurrently — e.g. during `Init`, where the leader
+    /// itself calls `Comm::from_rank` on rank 0 in parallel with the
+    /// workers, then collects `InitOk` after NCCL completes.
+    async fn send_only(&mut self, req: &WorkerRequest) -> Result<()> {
+        let mut line = serde_json::to_string(req).context("serialise WorkerRequest")?;
+        line.push('\n');
+        self.stdin
+            .write_all(line.as_bytes())
+            .await
+            .with_context(|| format!("write request to rank {}", self.rank))?;
+        self.stdin
+            .flush()
+            .await
+            .with_context(|| format!("flush stdin to rank {}", self.rank))?;
+        Ok(())
+    }
+
+    async fn recv_only(&mut self) -> Result<WorkerResponse> {
+        let reply = self
+            .stdout
+            .next_line()
+            .await
+            .with_context(|| format!("read reply from rank {}", self.rank))?
+            .ok_or_else(|| anyhow::anyhow!("rank {} stdout closed before reply", self.rank))?;
+        serde_json::from_str(&reply)
+            .with_context(|| format!("parse reply from rank {}: {reply:?}", self.rank))
+    }
+}
+
+/// A live pool of worker subprocesses. Owns the `Child` handles so
+/// dropping the pool kills the children; explicit `shutdown()` is
+/// the graceful path.
+pub struct WorkerPool {
+    world_size: u32,
+    workers: Vec<Worker>,
+    /// Path to the neuron binary used to launch workers.
+    #[allow(dead_code)]
+    exe: PathBuf,
+    /// Leader's own NCCL rank-0 state. Defaults to empty; populated by
+    /// `init_nccl()`. Held here so the leader can participate in
+    /// collectives (rank 0) without spawning a fourth subprocess.
+    leader_nccl: nccl_state::NcclState,
+}
+
+impl WorkerPool {
+    /// Spawn `world_size - 1` worker subprocesses. Rank 0 is the
+    /// leader (in-process) and is *not* spawned here — the leader
+    /// holds rank 0's NCCL Comm and shard in its own address space.
+    ///
+    /// `binary` is the path to the neuron executable to run for each
+    /// worker (production passes `/proc/self/exe`; tests pass the
+    /// sibling-binary path from `env!("CARGO_BIN_EXE_neuron")`).
+    /// `cuda_devices` is one entry per rank including rank 0. Worker
+    /// `i` (rank `i`) gets `cuda_devices[i]` as its `--cuda-device`.
+    pub async fn spawn(binary: &Path, world_size: u32, cuda_devices: &[u32]) -> Result<Self> {
+        if world_size < 2 {
+            anyhow::bail!(
+                "WorkerPool::spawn called with world_size={world_size}; \
+                 use the single-process path for world_size < 2"
+            );
+        }
+        if cuda_devices.len() as u32 != world_size {
+            anyhow::bail!(
+                "expected {world_size} cuda_devices entries, got {}",
+                cuda_devices.len()
+            );
+        }
+        let exe = binary.to_path_buf();
+
+        let mut workers = Vec::with_capacity(world_size as usize - 1);
+        // Rank 0 stays in-process. Spawn ranks 1..world_size.
+        for rank in 1..world_size {
+            let cuda_device = cuda_devices[rank as usize];
+            let mut cmd = Command::new(&exe);
+            cmd.arg("--worker")
+                .arg("--rank")
+                .arg(rank.to_string())
+                .arg("--tp-size")
+                .arg(world_size.to_string())
+                .arg("--cuda-device")
+                .arg(cuda_device.to_string())
+                .stdin(Stdio::piped())
+                .stdout(Stdio::piped())
+                // Inherit stderr so worker tracing surfaces alongside
+                // the leader's journalctl stream.
+                .stderr(Stdio::inherit())
+                .kill_on_drop(true);
+
+            let mut child = cmd
+                .spawn()
+                .with_context(|| format!("spawn worker rank {rank}"))?;
+            let stdin = child
+                .stdin
+                .take()
+                .ok_or_else(|| anyhow::anyhow!("rank {rank}: no stdin handle"))?;
+            let stdout = child
+                .stdout
+                .take()
+                .ok_or_else(|| anyhow::anyhow!("rank {rank}: no stdout handle"))?;
+            let stdout = BufReader::new(stdout).lines();
+
+            workers.push(Worker {
+                rank,
+                cuda_device,
+                child,
+                stdin,
+                stdout,
+            });
+            tracing::info!(rank, cuda_device, "spawned tp worker");
+        }
+
+        Ok(Self {
+            world_size,
+            workers,
+            exe,
+            leader_nccl: nccl_state::NcclState::new(),
+        })
+    }
+
+    /// Establish the NCCL communicator across the leader (rank 0) and
+    /// every worker subprocess. Rendezvous is via a freshly-generated
+    /// `Id` broadcast over the RPC stream; the actual handshake blocks
+    /// inside `Comm::from_rank` until all `world_size` ranks check in.
+    ///
+    /// `leader_cuda_device` is the CUDA device the leader binds rank 0
+    /// to — typically the first entry of the `cuda_devices` slice
+    /// originally passed to `spawn()`.
+    ///
+    /// On the non-cuda build this immediately fails because the leader
+    /// can't generate an `Id` without libnccl. The same call works in
+    /// the worker path (returning a no-cuda error response) so the
+    /// failure surface is uniform.
+    pub async fn init_nccl(&mut self, leader_cuda_device: u32) -> Result<()> {
+        let comm_id = nccl_state::generate_comm_id_hex()
+            .map_err(|m| anyhow::anyhow!("generate NCCL id: {m}"))?;
+
+        // 1. Write Init to every worker's stdin without awaiting the
+        //    response. Workers will parse and call Comm::from_rank
+        //    concurrently with the leader below.
+        for w in &mut self.workers {
+            let req = WorkerRequest::Init {
+                comm_id: comm_id.clone(),
+            };
+            w.send_only(&req).await?;
+        }
+
+        // 2. Leader rank 0 calls Comm::from_rank on its own device.
+        //    Runs on spawn_blocking because NCCL's init blocks until
+        //    every rank has called in — that's exactly the workers
+        //    above. The leader's NcclState is moved through the
+        //    blocking task and returned to the pool.
+        let leader_cfg = worker::WorkerConfig {
+            rank: 0,
+            world_size: self.world_size,
+            cuda_device: leader_cuda_device,
+        };
+        let comm_id_for_leader = comm_id.clone();
+        // Swap out the leader's NcclState into a fresh empty one so we
+        // can move it into spawn_blocking; restore after the task
+        // returns. (NcclState isn't Clone — it owns a real NCCL Comm.)
+        let mut leader_state = std::mem::take(&mut self.leader_nccl);
+        let (returned_state, leader_resp) = tokio::task::spawn_blocking(move || {
+            let resp = leader_state.init(leader_cfg, &comm_id_for_leader);
+            (leader_state, resp)
+        })
+        .await
+        .context("leader NCCL init task panicked")?;
+        self.leader_nccl = returned_state;
+        match leader_resp {
+            rpc::WorkerResponse::InitOk => {}
+            rpc::WorkerResponse::Error { kind, message } => {
+                anyhow::bail!("leader rank 0 init failed [{kind}]: {message}");
+            }
+            other => anyhow::bail!("leader rank 0 init: unexpected {other:?}"),
+        }
+
+        // 3. Read InitOk from each worker. By now every worker has
+        //    completed its Comm::from_rank call (NCCL released them
+        //    when the leader joined the handshake) and is writing its
+        //    response.
+        for w in &mut self.workers {
+            let resp = w.recv_only().await?;
+            match &resp {
+                rpc::WorkerResponse::InitOk => {}
+                rpc::WorkerResponse::Error { kind, message } => {
+                    anyhow::bail!("worker rank {} init failed [{kind}]: {message}", w.rank);
+                }
+                other => anyhow::bail!(
+                    "worker rank {} init: expected InitOk, got {other:?}",
+                    w.rank
+                ),
+            }
+        }
+        tracing::info!(
+            world_size = self.world_size,
+            "NCCL communicator established across all ranks"
+        );
+        Ok(())
+    }
+
+    /// Validate the NCCL communicator: every rank `all_reduce`s a
+    /// sentinel `1u32` with `ReduceOp::Sum`; the expected total is
+    /// `world_size`. Confirms the handshake is live, not just
+    /// configured.
+    ///
+    /// Must be called after `init_nccl()`; before that the leader has
+    /// no Comm and the workers reply with `nccl_not_initialised`.
+    pub async fn nccl_sanity_check(&mut self) -> Result<()> {
+        // 1. Trigger the all_reduce on every worker (write-only).
+        for w in &mut self.workers {
+            w.send_only(&WorkerRequest::NcclSanityCheck).await?;
+        }
+
+        // 2. Leader's own all_reduce, in spawn_blocking. NCCL operations
+        //    block until every rank participates.
+        let mut leader_state = std::mem::take(&mut self.leader_nccl);
+        let (returned_state, leader_resp) = tokio::task::spawn_blocking(move || {
+            let resp = leader_state.sanity_check();
+            (leader_state, resp)
+        })
+        .await
+        .context("leader NCCL sanity task panicked")?;
+        self.leader_nccl = returned_state;
+
+        let expected = self.world_size;
+        let leader_sum = match leader_resp {
+            rpc::WorkerResponse::NcclSanityResult { observed_sum } => observed_sum,
+            rpc::WorkerResponse::Error { kind, message } => {
+                anyhow::bail!("leader rank 0 sanity failed [{kind}]: {message}");
+            }
+            other => anyhow::bail!("leader rank 0 sanity: unexpected {other:?}"),
+        };
+        if leader_sum != expected {
+            anyhow::bail!("leader observed_sum={leader_sum}, expected {expected}");
+        }
+
+        // 3. Read sanity result from each worker. All must match
+        //    world_size — anything else means the collective didn't
+        //    complete consistently across ranks.
+        for w in &mut self.workers {
+            let resp = w.recv_only().await?;
+            match resp {
+                rpc::WorkerResponse::NcclSanityResult { observed_sum }
+                    if observed_sum == expected => {}
+                rpc::WorkerResponse::NcclSanityResult { observed_sum } => {
+                    anyhow::bail!(
+                        "worker rank {} observed_sum={observed_sum}, expected {expected}",
+                        w.rank
+                    );
+                }
+                rpc::WorkerResponse::Error { kind, message } => {
+                    anyhow::bail!("worker rank {} sanity failed [{kind}]: {message}", w.rank);
+                }
+                other => anyhow::bail!("worker rank {} sanity: unexpected {other:?}", w.rank),
+            }
+        }
+        tracing::info!(
+            world_size = expected,
+            "NCCL sanity check OK across all ranks"
+        );
+        Ok(())
+    }
+
+    /// Ping every worker and return their Pong payloads in rank order.
+    /// Useful right after `spawn` to confirm the lifecycle plumbing is
+    /// intact before kicking off any heavier work.
+    pub async fn ping_all(&mut self) -> Result<Vec<WorkerResponse>> {
+        let mut out = Vec::with_capacity(self.workers.len());
+        for w in &mut self.workers {
+            let resp = w.request(&WorkerRequest::Ping).await?;
+            match &resp {
+                WorkerResponse::Pong { rank, .. } if *rank == w.rank => {}
+                WorkerResponse::Pong { rank, .. } => {
+                    anyhow::bail!("rank mismatch: expected {}, got {rank}", w.rank);
+                }
+                other => anyhow::bail!("expected Pong from rank {}, got {other:?}", w.rank),
+            }
+            out.push(resp);
+        }
+        Ok(out)
+    }
+
+    /// Send `Shutdown` to every worker, await each `Bye`, and reap the
+    /// children. Best-effort — individual worker failures are logged
+    /// but don't abort the rest of the sweep.
+    pub async fn shutdown(mut self) -> Result<()> {
+        for w in &mut self.workers {
+            match w.request(&WorkerRequest::Shutdown).await {
+                Ok(WorkerResponse::Bye) => {}
+                Ok(other) => tracing::warn!(
+                    rank = w.rank,
+                    response = ?other,
+                    "expected Bye on shutdown"
+                ),
+                Err(e) => tracing::warn!(rank = w.rank, error = %e, "shutdown request failed"),
+            }
+        }
+        for w in &mut self.workers {
+            match w.child.wait().await {
+                Ok(status) => tracing::info!(rank = w.rank, %status, "worker exited"),
+                Err(e) => tracing::warn!(rank = w.rank, error = %e, "wait on worker failed"),
+            }
+        }
+        Ok(())
+    }
+
+    pub fn world_size(&self) -> u32 {
+        self.world_size
+    }
+
+    pub fn binary_path(&self) -> &PathBuf {
+        &self.exe
+    }
+}

crates/neuron/src/harness/tp/nccl_state.rs

@@ -0,0 +1,243 @@
+//! NCCL state held by both the worker process and the leader's pool.
+//!
+//! Split into its own module so the worker (`tp/worker.rs`) and the
+//! leader (`tp/mod.rs`) share the same hex-encoding/decoding code and
+//! the same shape of `Option<Comm>` state machine.
+//!
+//! When the `cuda` feature is off, `NcclState` is a zero-sized
+//! placeholder that returns `Error{kind="cuda_feature_not_enabled"}`
+//! from every operation. When it's on, the same struct holds the
+//! actual `cudarc::nccl::Comm`.
+
+use super::rpc::WorkerResponse;
+use super::worker::WorkerConfig;
+
+/// Encode bytes as lowercase hex. Used for ferrying NCCL `Id::internal()`
+/// across the leader→worker RPC boundary inside a JSON string.
+pub fn encode_hex(bytes: &[u8]) -> String {
+    let mut out = String::with_capacity(bytes.len() * 2);
+    for b in bytes {
+        use std::fmt::Write;
+        let _ = write!(out, "{b:02x}");
+    }
+    out
+}
+
+/// Decode lowercase-or-uppercase hex into bytes. Errors on odd length
+/// or non-hex characters; the caller bubbles those up via the RPC's
+/// `Error{kind="bad_request"}` variant.
+pub fn decode_hex(s: &str) -> Result<Vec<u8>, String> {
+    if !s.len().is_multiple_of(2) {
+        return Err(format!("hex string has odd length {}", s.len()));
+    }
+    (0..s.len())
+        .step_by(2)
+        .map(|i| {
+            u8::from_str_radix(&s[i..i + 2], 16).map_err(|e| format!("bad hex byte at {i}: {e}"))
+        })
+        .collect()
+}
+
+#[cfg(not(feature = "cuda"))]
+pub struct NcclState;
+
+#[cfg(not(feature = "cuda"))]
+impl Default for NcclState {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(not(feature = "cuda"))]
+impl NcclState {
+    pub fn new() -> Self {
+        Self
+    }
+
+    pub fn init(&mut self, _cfg: WorkerConfig, _comm_id_hex: &str) -> WorkerResponse {
+        WorkerResponse::Error {
+            kind: "cuda_feature_not_enabled".into(),
+            message: "this neuron binary was built without --features cuda; \
+                 NCCL Init requires CUDA"
+                .into(),
+        }
+    }
+
+    pub fn sanity_check(&mut self) -> WorkerResponse {
+        WorkerResponse::Error {
+            kind: "cuda_feature_not_enabled".into(),
+            message: "NCCL sanity check requires --features cuda".into(),
+        }
+    }
+}
+
+#[cfg(feature = "cuda")]
+mod cuda_impl {
+    use super::*;
+    use cudarc::driver::CudaContext;
+    use cudarc::nccl::{Comm, Id, ReduceOp};
+    use std::sync::Arc;
+
+    /// Number of bytes in NCCL's unique-id type; matches `Id::internal()`'s
+    /// `[c_char; 128]`. Wire-encoded as 256 lowercase hex chars.
+    const NCCL_ID_BYTES: usize = 128;
+
+    pub struct NcclState {
+        comm: Option<Comm>,
+        /// Held alongside the Comm so the device isn't dropped
+        /// underneath the NCCL handle.
+        #[allow(dead_code)]
+        ctx: Option<Arc<CudaContext>>,
+    }
+
+    impl Default for NcclState {
+        fn default() -> Self {
+            Self::new()
+        }
+    }
+
+    impl NcclState {
+        pub fn new() -> Self {
+            Self {
+                comm: None,
+                ctx: None,
+            }
+        }
+    }
+
+    // SAFETY: `cudarc::nccl::Comm` contains a raw `ncclComm_t` pointer
+    // (libnccl-allocated state). NCCL requires that operations against
+    // one Comm be issued one at a time; we serialise access by storing
+    // NcclState behind a Mutex in `WorkerPool`. The Comm itself is
+    // move-safe — NCCL doesn't track the calling OS thread, only the
+    // stream the operations are dispatched against.
+    unsafe impl Send for NcclState {}
+    unsafe impl Sync for NcclState {}
+
+    /// Generate a fresh NCCL `Id` and return it hex-encoded. Used by
+    /// the leader to mint the shared communicator id which is then
+    /// broadcast to every worker via the RPC `Init` message.
+    pub fn generate_comm_id_hex() -> Result<String, String> {
+        // NcclError lacks a Display impl in cudarc 0.19.x — surface
+        // via Debug throughout this module.
+        let id = Id::new().map_err(|e| format!("Id::new(): {e:?}"))?;
+        let bytes_u8: [u8; NCCL_ID_BYTES] = std::array::from_fn(|i| id.internal()[i] as u8);
+        Ok(encode_hex(&bytes_u8))
+    }
+
+    impl NcclState {
+        pub fn init(&mut self, cfg: WorkerConfig, comm_id_hex: &str) -> WorkerResponse {
+            match try_init(self, cfg, comm_id_hex) {
+                Ok(()) => WorkerResponse::InitOk,
+                Err(msg) => WorkerResponse::Error {
+                    kind: "nccl_init_failed".into(),
+                    message: msg,
+                },
+            }
+        }
+
+        pub fn sanity_check(&mut self) -> WorkerResponse {
+            let Some(comm) = self.comm.as_ref() else {
+                return WorkerResponse::Error {
+                    kind: "nccl_not_initialised".into(),
+                    message: "sanity_check requires Init to have completed first".into(),
+                };
+            };
+            match try_sanity_check(comm) {
+                Ok(sum) => WorkerResponse::NcclSanityResult { observed_sum: sum },
+                Err(msg) => WorkerResponse::Error {
+                    kind: "nccl_sanity_failed".into(),
+                    message: msg,
+                },
+            }
+        }
+    }
+
+    fn try_init(state: &mut NcclState, cfg: WorkerConfig, comm_id_hex: &str) -> Result<(), String> {
+        let bytes = decode_hex(comm_id_hex)?;
+        if bytes.len() != NCCL_ID_BYTES {
+            return Err(format!(
+                "comm_id is {} bytes, expected {NCCL_ID_BYTES}",
+                bytes.len()
+            ));
+        }
+        let id_bytes: [std::ffi::c_char; NCCL_ID_BYTES] =
+            std::array::from_fn(|i| bytes[i] as std::ffi::c_char);
+        let id = Id::uninit(id_bytes);
+
+        let ctx = CudaContext::new(cfg.cuda_device as usize)
+            .map_err(|e| format!("CudaContext::new({}) failed: {e}", cfg.cuda_device))?;
+        let stream = ctx.default_stream();
+        let comm = Comm::from_rank(stream, cfg.rank as usize, cfg.world_size as usize, id)
+            .map_err(|e| {
+                format!(
+                    "Comm::from_rank(rank={}, world={}) failed: {e:?}",
+                    cfg.rank, cfg.world_size
+                )
+            })?;
+
+        state.ctx = Some(ctx);
+        state.comm = Some(comm);
+        Ok(())
+    }
+
+    fn try_sanity_check(comm: &Comm) -> Result<u32, String> {
+        let stream = comm.stream().clone();
+        let input = stream
+            .clone_htod(&[1u32])
+            .map_err(|e| format!("htod sentinel: {e}"))?;
+        let mut output = stream
+            .alloc_zeros::<u32>(1)
+            .map_err(|e| format!("alloc output: {e}"))?;
+        // cudarc::nccl::NcclError doesn't impl Display in 0.19.x —
+        // surface via Debug so we still see the variant + ncclResult
+        // code instead of a generic "{e}" failure.
+        comm.all_reduce(&input, &mut output, &ReduceOp::Sum)
+            .map_err(|e| format!("all_reduce: {e:?}"))?;
+        let result = stream
+            .clone_dtoh(&output)
+            .map_err(|e| format!("dtoh result: {e}"))?;
+        Ok(result[0])
+    }
+}
+
+#[cfg(feature = "cuda")]
+pub use cuda_impl::{NcclState, generate_comm_id_hex};
+
+/// Non-cuda stub for the leader: returns a clear marker error rather
+/// than letting `init_nccl` succeed vacuously.
+#[cfg(not(feature = "cuda"))]
+pub fn generate_comm_id_hex() -> Result<String, String> {
+    Err("cuda_feature_not_enabled: build with --features cuda".into())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn hex_roundtrip() {
+        let original: Vec<u8> = (0u8..=255).collect();
+        let encoded = encode_hex(&original);
+        assert_eq!(encoded.len(), 512);
+        let decoded = decode_hex(&encoded).expect("decode");
+        assert_eq!(decoded, original);
+    }
+
+    #[test]
+    fn hex_decode_rejects_odd_length() {
+        assert!(decode_hex("a").is_err());
+        assert!(decode_hex("abc").is_err());
+    }
+
+    #[test]
+    fn hex_decode_rejects_non_hex() {
+        assert!(decode_hex("zz").is_err());
+        assert!(decode_hex("ab_d").is_err());
+    }
+
+    #[test]
+    fn hex_encode_is_lowercase_padded() {
+        assert_eq!(encode_hex(&[0x0a, 0xff]), "0aff");
+    }
+}

crates/neuron/src/harness/tp/rpc.rs

@@ -0,0 +1,186 @@
+//! Wire protocol between the neuron leader process and its
+//! `--worker` subprocesses.
+//!
+//! Every frame is one newline-delimited JSON object on the worker's
+//! stdin (request) or stdout (response). Both directions are tagged
+//! sum types from the start so new ops in Stage 7b/7c slot in without
+//! breaking compatibility — no "14 message types and a version field"
+//! drift later. Adding a new variant is the canonical way to evolve
+//! the protocol; existing peers that don't recognise an op return
+//! `WorkerResponse::Error { kind: "unknown_op", .. }`.
+//!
+//! The serialised shape uses `tag = "op"` so a request looks like:
+//!     {"op":"ping"}
+//!     {"op":"init","comm_id":"a1b2..."}
+//! and a response:
+//!     {"op":"pong","rank":0,"world_size":2,"cuda_device":0}
+//!     {"op":"error","kind":"nccl_init_failed","message":"..."}
+
+use serde::{Deserialize, Serialize};
+
+/// Leader → worker. Worker handles one at a time; replies with exactly
+/// one `WorkerResponse` per request.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "op", rename_all = "snake_case")]
+pub enum WorkerRequest {
+    /// Liveness probe. Worker replies with `Pong` containing its own
+    /// identity. Used by the leader to confirm the subprocess is up
+    /// and ready before kicking off any heavier work.
+    Ping,
+
+    /// One-shot NCCL communicator setup. The leader generates the
+    /// `comm_id` once (rank 0 of NCCL), broadcasts it to every worker
+    /// via this message, then every rank (leader included) calls
+    /// `Comm::from_rank` with the same id — NCCL blocks until all
+    /// `world_size` ranks check in. The hex-encoded bytes are the
+    /// canonical `cudarc::nccl::Id::internal()` content.
+    Init {
+        /// Hex-encoded NCCL id bytes (128 bytes → 256 hex chars).
+        comm_id: String,
+    },
+
+    /// Sanity check: after Init, every rank runs an `all_reduce` over
+    /// a sentinel value (`1u32`). The expected sum is `world_size`.
+    /// Worker replies with the observed value so the leader can verify
+    /// the NCCL handshake is genuinely live, not just configured.
+    NcclSanityCheck,
+
+    /// Worker should release resources and exit. Worker replies `Bye`
+    /// and then closes stdout / exits zero. The leader reaps the
+    /// child via the `tokio::process::Child` it kept.
+    Shutdown,
+}
+
+/// Worker → leader. Always exactly one of these per `WorkerRequest`.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "op", rename_all = "snake_case")]
+pub enum WorkerResponse {
+    /// Reply to `Ping`. Carries enough identity for the leader to log
+    /// what it actually got back.
+    Pong {
+        rank: u32,
+        world_size: u32,
+        cuda_device: u32,
+    },
+
+    /// Reply to `Init`. Empty payload — success is the absence of
+    /// `Error`. NCCL's internal blocking handshake means by the time
+    /// this comes back, every other rank has also reached
+    /// `Comm::from_rank`.
+    InitOk,
+
+    /// Reply to `NcclSanityCheck`. The observed sum after a single
+    /// `all_reduce(SUM, 1u32)` across all ranks. The leader checks
+    /// this matches `world_size`.
+    NcclSanityResult { observed_sum: u32 },
+
+    /// Reply to `Shutdown`. Worker exits immediately after writing this.
+    Bye,
+
+    /// Any request can produce this instead of its dedicated success
+    /// variant. `kind` is a machine-readable category so the leader
+    /// can branch on failure mode without string-matching `message`.
+    Error {
+        /// Short tag — `nccl_init_failed`, `unknown_op`, etc.
+        kind: String,
+        /// Human-readable detail for logs.
+        message: String,
+    },
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn roundtrip<T>(value: &T) -> T
+    where
+        T: Serialize + for<'de> Deserialize<'de>,
+    {
+        serde_json::from_str(&serde_json::to_string(value).expect("serialise"))
+            .expect("deserialise")
+    }
+
+    #[test]
+    fn request_ping_round_trip() {
+        let req = WorkerRequest::Ping;
+        let wire = serde_json::to_string(&req).unwrap();
+        assert_eq!(wire, r#"{"op":"ping"}"#);
+        match roundtrip(&req) {
+            WorkerRequest::Ping => {}
+            other => panic!("expected Ping, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn request_init_carries_hex_id() {
+        let req = WorkerRequest::Init {
+            comm_id: "deadbeef".into(),
+        };
+        let wire = serde_json::to_string(&req).unwrap();
+        assert_eq!(wire, r#"{"op":"init","comm_id":"deadbeef"}"#);
+    }
+
+    #[test]
+    fn request_shutdown_round_trip() {
+        assert_eq!(
+            serde_json::to_string(&WorkerRequest::Shutdown).unwrap(),
+            r#"{"op":"shutdown"}"#
+        );
+    }
+
+    #[test]
+    fn response_pong_round_trip() {
+        let resp = WorkerResponse::Pong {
+            rank: 1,
+            world_size: 4,
+            cuda_device: 1,
+        };
+        let wire = serde_json::to_string(&resp).unwrap();
+        assert!(wire.contains(r#""op":"pong""#));
+        assert!(wire.contains(r#""rank":1"#));
+        assert!(wire.contains(r#""world_size":4"#));
+        match roundtrip(&resp) {
+            WorkerResponse::Pong {
+                rank,
+                world_size,
+                cuda_device,
+            } => {
+                assert_eq!(rank, 1);
+                assert_eq!(world_size, 4);
+                assert_eq!(cuda_device, 1);
+            }
+            other => panic!("expected Pong, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn response_error_carries_kind_and_message() {
+        let resp = WorkerResponse::Error {
+            kind: "nccl_init_failed".into(),
+            message: "could not bind device".into(),
+        };
+        let wire = serde_json::to_string(&resp).unwrap();
+        assert!(wire.contains(r#""op":"error""#));
+        assert!(wire.contains(r#""kind":"nccl_init_failed""#));
+    }
+
+    #[test]
+    fn response_sanity_result_round_trip() {
+        let resp = WorkerResponse::NcclSanityResult { observed_sum: 4 };
+        match roundtrip(&resp) {
+            WorkerResponse::NcclSanityResult { observed_sum } => {
+                assert_eq!(observed_sum, 4);
+            }
+            other => panic!("expected NcclSanityResult, got {other:?}"),
+        }
+    }
+
+    /// Unknown ops on the wire deserialise to an error rather than
+    /// silently mis-matching — confirms our `serde(tag = "op")`
+    /// configuration rejects unknowns instead of doing fuzzy matching.
+    #[test]
+    fn unknown_op_fails_to_parse() {
+        let result: Result<WorkerRequest, _> = serde_json::from_str(r#"{"op":"explode"}"#);
+        assert!(result.is_err(), "should reject unknown op, got {result:?}");
+    }
+}

crates/neuron/src/harness/tp/tp_linear.rs

@@ -0,0 +1,134 @@
+//! Tensor-parallel linear layers built on candle's `ShardedVarBuilder`
+//! and `Shard` sharding hints.
+//!
+//! candle reads only the rank's slice of each weight tensor from
+//! safetensors via `view.slice(start..stop)` — no full-tensor host
+//! materialisation. That's a memory-efficiency win over hand-rolled
+//! "load full + narrow" sharding (which the earlier
+//! `sharded_linear.rs` exploration demonstrated but didn't pay for).
+//!
+//! Two layer types:
+//!
+//! - [`ColumnParallelLinear`] — output-sharded; forward is a plain
+//!   local matmul. The downstream consumer either accepts a sharded
+//!   activation (next layer is also column-parallel) or all-gathers.
+//! - [`RowParallelLinear`] — input-sharded; forward = local matmul
+//!   then `AllReduce` `CustomOp1` to sum partials across ranks.
+//!
+//! Both assume **no bias** — every Qwen3-family weight layout we
+//! actually target (Qwen3, Qwen3-Coder, Qwen3.6 base, etc.) sets
+//! `attention_bias=false` and the MLP layers are no-bias. Adding bias
+//! support is mechanical when a future model needs it; the design
+//! choice would be: column-parallel shards the bias along dim 0;
+//! row-parallel holds the bias only on rank 0 so the post-`AllReduce`
+//! sum carries it exactly once.
+
+use anyhow::{Context, Result};
+use candle_core::{Module, Tensor};
+use candle_nn::Linear;
+use candle_nn::var_builder::{Shard, ShardedVarBuilder};
+
+#[cfg(feature = "cuda")]
+use super::all_reduce::AllReduce;
+
+/// Helper to build a [`Shard`] hint for a given dimension.
+pub(crate) fn shard(dim: usize, rank: u32, world_size: u32) -> Shard {
+    Shard {
+        dim,
+        rank: rank as usize,
+        world_size: world_size as usize,
+    }
+}
+
+/// Output-dim sharded linear (column-parallel). Holds a standard
+/// `candle_nn::Linear` whose `weight` is the rank's slice of the full
+/// `[out_features, in_features]` tensor along dim 0.
+pub struct ColumnParallelLinear {
+    inner: Linear,
+}
+
+impl ColumnParallelLinear {
+    /// Load this rank's column-parallel slice from a
+    /// `ShardedVarBuilder`. The provided `vb` must already be `pp`-ed
+    /// to the layer's path (e.g. `vb.pp("model.layers.0.self_attn.q_proj")`).
+    pub fn load(vb: &ShardedVarBuilder, rank: u32, world_size: u32) -> Result<Self> {
+        let weight = vb
+            .get_with_hints((), "weight", shard(0, rank, world_size))
+            .with_context(|| format!("load column-parallel '{}' weight", vb.prefix()))?;
+        Ok(Self {
+            inner: Linear::new(weight, None),
+        })
+    }
+}
+
+impl Module for ColumnParallelLinear {
+    fn forward(&self, x: &Tensor) -> candle_core::Result<Tensor> {
+        self.inner.forward(x)
+    }
+}
+
+/// Input-dim sharded linear (row-parallel).
+///
+/// Holds a sharded `Linear` plus an `AllReduce` op the forward chains
+/// after the local matmul to recover the full activation.
+pub struct RowParallelLinear {
+    inner: Linear,
+    #[cfg(feature = "cuda")]
+    all_reduce: AllReduce,
+    /// Whether the AllReduce should run. Column-parallel ↔ row-parallel
+    /// is a pair: the column output is sharded, the row input is
+    /// sharded, and the AllReduce gives back the full output. For
+    /// `world_size = 1` the AllReduce is a no-op so we skip it.
+    needs_reduce: bool,
+}
+
+impl RowParallelLinear {
+    /// Load this rank's row-parallel slice from a `ShardedVarBuilder`.
+    ///
+    /// Under `cuda`, `comm` is the NCCL communicator the row-parallel
+    /// `AllReduce` runs against. On CPU builds the parameter is
+    /// elided — forward returns the partial sum, which is the *wrong*
+    /// answer for inference but lets us compile-check the model.
+    #[cfg(feature = "cuda")]
+    pub fn load(
+        vb: &ShardedVarBuilder,
+        rank: u32,
+        world_size: u32,
+        comm: std::sync::Arc<cudarc::nccl::Comm>,
+    ) -> Result<Self> {
+        let weight = vb
+            .get_with_hints((), "weight", shard(1, rank, world_size))
+            .with_context(|| format!("load row-parallel '{}' weight", vb.prefix()))?;
+        Ok(Self {
+            inner: Linear::new(weight, None),
+            all_reduce: AllReduce::new(comm),
+            needs_reduce: world_size > 1,
+        })
+    }
+
+    #[cfg(not(feature = "cuda"))]
+    pub fn load(vb: &ShardedVarBuilder, rank: u32, world_size: u32) -> Result<Self> {
+        let weight = vb
+            .get_with_hints((), "weight", shard(1, rank, world_size))
+            .with_context(|| format!("load row-parallel '{}' weight", vb.prefix()))?;
+        Ok(Self {
+            inner: Linear::new(weight, None),
+            needs_reduce: world_size > 1,
+        })
+    }
+}
+
+impl Module for RowParallelLinear {
+    /// Local matmul followed by an `AllReduce` (when `cuda` and
+    /// `world_size > 1`). On CPU or single-rank, returns the partial
+    /// output directly — which is *only* correct for `world_size == 1`.
+    fn forward(&self, x: &Tensor) -> candle_core::Result<Tensor> {
+        let local = self.inner.forward(x)?;
+        #[cfg(feature = "cuda")]
+        if self.needs_reduce {
+            return local.apply_op1_no_bwd(&self.all_reduce);
+        }
+        let _ = self.needs_reduce;
+        Ok(local)
+    }
+}

crates/neuron/src/harness/tp/tp_qwen3.rs

@@ -0,0 +1,605 @@
+//! Tensor-parallel Qwen3 dense model.
+//!
+//! Mirrors `candle_transformers::models::qwen3` structurally, but with:
+//!
+//! - Attention's `q_proj` / `k_proj` / `v_proj` as
+//!   [`ColumnParallelLinear`] (output sharded along the head dimension —
+//!   per-rank `num_heads = total/world_size`, ditto for kv heads).
+//! - Attention's `o_proj` as [`RowParallelLinear`] (input sharded; the
+//!   trailing `AllReduce` recovers the full activation).
+//! - MLP's `gate_proj` / `up_proj` as [`ColumnParallelLinear`] (sharded
+//!   along `intermediate_size`).
+//! - MLP's `down_proj` as [`RowParallelLinear`].
+//! - `embed_tokens`, all `RmsNorm`s, and `lm_head` **replicated** on
+//!   every rank. The per-rank duplicate weight is bounded and lets us
+//!   skip the embedding all-gather and the lm-head column-shard +
+//!   all-gather; both are pure latency optimisations that don't change
+//!   correctness.
+//! - `kv_cache` holds the per-rank slice of K/V already (because they
+//!   came out of a column-parallel projection). No cache resharding
+//!   needed across ranks.
+//!
+//! Divisibility requirement, checked at load time:
+//!
+//! - `num_attention_heads % world_size == 0`
+//! - `num_key_value_heads % world_size == 0`
+//! - `intermediate_size  % world_size == 0`
+//!
+//! Anything else bails — the safetensors slice would lose data otherwise.
+//! This is the same divisibility-bail pattern that landed in
+//! `EricLBuehler/mistral.rs` PR #2054.
+//!
+//! Replicated tensors (norms, embedding, lm_head) are loaded by asking
+//! the `ShardedVarBuilder` for the full tensor via `vb.get(shape, name)`
+//! — which defaults to `Shard { world_size: 1 }` and falls through to
+//! the unsharded backend path.
+
+use anyhow::{Context, Result, bail};
+use candle_core::{DType, Device, IndexOp, Module, Tensor};
+use candle_nn::var_builder::ShardedVarBuilder;
+use candle_nn::{Activation, Embedding, Linear, RmsNorm, kv_cache::ConcatKvCache};
+use candle_transformers::utils::repeat_kv;
+use std::sync::Arc;
+
+#[cfg(feature = "cuda")]
+use cudarc::nccl::Comm;
+
+use super::tp_linear::{ColumnParallelLinear, RowParallelLinear};
+
+pub use candle_transformers::models::qwen3::Config;
+
+/// Replicated rotary-embedding lookup. Re-implementation of the
+/// `pub(crate)` candle equivalent — we can't reach into the upstream
+/// type, so the inv-freq / sin / cos construction lives here.
+pub(crate) struct Qwen3RotaryEmbedding {
+    sin: Tensor,
+    cos: Tensor,
+}
+
+impl Qwen3RotaryEmbedding {
+    pub(crate) fn new(dtype: DType, cfg: &Config, dev: &Device) -> Result<Self> {
+        let dim = cfg.head_dim;
+        let max_seq_len = cfg.max_position_embeddings;
+        let inv_freq: Vec<_> = (0..dim)
+            .step_by(2)
+            .map(|i| 1f32 / cfg.rope_theta.powf(i as f64 / dim as f64) as f32)
+            .collect();
+        let inv_freq_len = inv_freq.len();
+        let inv_freq = Tensor::from_vec(inv_freq, (1, inv_freq_len), dev)?.to_dtype(DType::F32)?;
+        let t = Tensor::arange(0u32, max_seq_len as u32, dev)?
+            .to_dtype(DType::F32)?
+            .reshape((max_seq_len, 1))?;
+        let freqs = t.matmul(&inv_freq)?;
+        Ok(Self {
+            sin: freqs.sin()?.to_dtype(dtype)?,
+            cos: freqs.cos()?.to_dtype(dtype)?,
+        })
+    }
+
+    fn apply(
+        &self,
+        q: &Tensor,
+        k: &Tensor,
+        offset: usize,
+    ) -> candle_core::Result<(Tensor, Tensor)> {
+        let (_, _, seq_len, _) = q.dims4()?;
+        let cos = self.cos.narrow(0, offset, seq_len)?;
+        let sin = self.sin.narrow(0, offset, seq_len)?;
+        let q_embed = candle_nn::rotary_emb::rope(&q.contiguous()?, &cos, &sin)?;
+        let k_embed = candle_nn::rotary_emb::rope(&k.contiguous()?, &cos, &sin)?;
+        Ok((q_embed, k_embed))
+    }
+}
+
+/// Helper: load a replicated tensor by asking the ShardedVarBuilder for
+/// the full tensor (world_size=1 hint falls through to SimpleBackend).
+fn load_replicated<S: Into<candle_core::Shape>>(
+    vb: &ShardedVarBuilder,
+    shape: S,
+    name: &str,
+) -> Result<Tensor> {
+    vb.get(shape, name)
+        .with_context(|| format!("load replicated '{}/{name}'", vb.prefix()))
+}
+
+fn load_rms_norm(vb: &ShardedVarBuilder, size: usize, eps: f64) -> Result<RmsNorm> {
+    let weight = load_replicated(vb, size, "weight")?;
+    Ok(RmsNorm::new(weight, eps))
+}
+
+/// TP MLP. SwiGLU = `down(silu(gate(x)) * up(x))`.
+pub(crate) struct TpQwen3MLP {
+    gate_proj: ColumnParallelLinear,
+    up_proj: ColumnParallelLinear,
+    down_proj: RowParallelLinear,
+    act_fn: Activation,
+}
+
+impl TpQwen3MLP {
+    #[cfg(feature = "cuda")]
+    pub fn load(
+        cfg: &Config,
+        vb: &ShardedVarBuilder,
+        rank: u32,
+        world_size: u32,
+        comm: Arc<Comm>,
+    ) -> Result<Self> {
+        if !cfg.intermediate_size.is_multiple_of(world_size as usize) {
+            bail!(
+                "intermediate_size {} not divisible by world_size {}",
+                cfg.intermediate_size,
+                world_size
+            );
+        }
+        Ok(Self {
+            gate_proj: ColumnParallelLinear::load(&vb.pp("gate_proj"), rank, world_size)?,
+            up_proj: ColumnParallelLinear::load(&vb.pp("up_proj"), rank, world_size)?,
+            down_proj: RowParallelLinear::load(&vb.pp("down_proj"), rank, world_size, comm)?,
+            act_fn: cfg.hidden_act,
+        })
+    }
+
+    #[cfg(not(feature = "cuda"))]
+    pub fn load(cfg: &Config, vb: &ShardedVarBuilder, rank: u32, world_size: u32) -> Result<Self> {
+        if !cfg.intermediate_size.is_multiple_of(world_size as usize) {
+            bail!(
+                "intermediate_size {} not divisible by world_size {}",
+                cfg.intermediate_size,
+                world_size
+            );
+        }
+        Ok(Self {
+            gate_proj: ColumnParallelLinear::load(&vb.pp("gate_proj"), rank, world_size)?,
+            up_proj: ColumnParallelLinear::load(&vb.pp("up_proj"), rank, world_size)?,
+            down_proj: RowParallelLinear::load(&vb.pp("down_proj"), rank, world_size)?,
+            act_fn: cfg.hidden_act,
+        })
+    }
+}
+
+impl Module for TpQwen3MLP {
+    fn forward(&self, x: &Tensor) -> candle_core::Result<Tensor> {
+        let lhs = x.apply(&self.gate_proj)?.apply(&self.act_fn)?;
+        let rhs = x.apply(&self.up_proj)?;
+        (lhs * rhs)?.apply(&self.down_proj)
+    }
+}
+
+/// TP attention. Carries per-rank head counts and the q/k per-head
+/// RmsNorms (which are replicated and operate on a flattened B*H*L
+/// axis, so the same code path works irrespective of how H was split).
+pub(crate) struct TpQwen3Attention {
+    q_proj: ColumnParallelLinear,
+    k_proj: ColumnParallelLinear,
+    v_proj: ColumnParallelLinear,
+    o_proj: RowParallelLinear,
+    q_norm: RmsNorm,
+    k_norm: RmsNorm,
+    local_num_heads: usize,
+    local_num_kv_heads: usize,
+    num_kv_groups: usize,
+    head_dim: usize,
+    local_hidden_size: usize,
+    rotary_emb: Arc<Qwen3RotaryEmbedding>,
+    kv_cache: ConcatKvCache,
+}
+
+impl TpQwen3Attention {
+    #[cfg(feature = "cuda")]
+    pub fn load(
+        cfg: &Config,
+        rotary_emb: Arc<Qwen3RotaryEmbedding>,
+        vb: &ShardedVarBuilder,
+        rank: u32,
+        world_size: u32,
+        comm: Arc<Comm>,
+    ) -> Result<Self> {
+        Self::load_inner(
+            cfg,
+            rotary_emb,
+            vb,
+            rank,
+            world_size,
+            #[cfg(feature = "cuda")]
+            comm,
+        )
+    }
+
+    #[cfg(not(feature = "cuda"))]
+    pub fn load(
+        cfg: &Config,
+        rotary_emb: Arc<Qwen3RotaryEmbedding>,
+        vb: &ShardedVarBuilder,
+        rank: u32,
+        world_size: u32,
+    ) -> Result<Self> {
+        Self::load_inner(cfg, rotary_emb, vb, rank, world_size)
+    }
+
+    fn load_inner(
+        cfg: &Config,
+        rotary_emb: Arc<Qwen3RotaryEmbedding>,
+        vb: &ShardedVarBuilder,
+        rank: u32,
+        world_size: u32,
+        #[cfg(feature = "cuda")] comm: Arc<Comm>,
+    ) -> Result<Self> {
+        if cfg.use_sliding_window {
+            bail!("sliding window is not yet supported in the TP path");
+        }
+        if cfg.attention_bias {
+            bail!("attention_bias=true is not supported by ColumnParallel/RowParallelLinear yet");
+        }
+        let ws = world_size as usize;
+        if !cfg.num_attention_heads.is_multiple_of(ws) {
+            bail!(
+                "num_attention_heads {} not divisible by world_size {}",
+                cfg.num_attention_heads,
+                world_size
+            );
+        }
+        if !cfg.num_key_value_heads.is_multiple_of(ws) {
+            bail!(
+                "num_key_value_heads {} not divisible by world_size {}",
+                cfg.num_key_value_heads,
+                world_size
+            );
+        }
+        let head_dim = cfg.head_dim;
+        let local_num_heads = cfg.num_attention_heads / ws;
+        let local_num_kv_heads = cfg.num_key_value_heads / ws;
+        let num_kv_groups = local_num_heads / local_num_kv_heads;
+        let local_hidden_size = head_dim * local_num_heads;
+
+        let q_proj = ColumnParallelLinear::load(&vb.pp("q_proj"), rank, world_size)?;
+        let k_proj = ColumnParallelLinear::load(&vb.pp("k_proj"), rank, world_size)?;
+        let v_proj = ColumnParallelLinear::load(&vb.pp("v_proj"), rank, world_size)?;
+        #[cfg(feature = "cuda")]
+        let o_proj = RowParallelLinear::load(&vb.pp("o_proj"), rank, world_size, comm)?;
+        #[cfg(not(feature = "cuda"))]
+        let o_proj = RowParallelLinear::load(&vb.pp("o_proj"), rank, world_size)?;
+
+        let q_norm = load_rms_norm(&vb.pp("q_norm"), head_dim, cfg.rms_norm_eps)?;
+        let k_norm = load_rms_norm(&vb.pp("k_norm"), head_dim, cfg.rms_norm_eps)?;
+
+        // dim=2 because we cat along the seq axis of (B, H, L, D) tensors.
+        let kv_cache = ConcatKvCache::new(2);
+
+        Ok(Self {
+            q_proj,
+            k_proj,
+            v_proj,
+            o_proj,
+            q_norm,
+            k_norm,
+            local_num_heads,
+            local_num_kv_heads,
+            num_kv_groups,
+            head_dim,
+            local_hidden_size,
+            rotary_emb,
+            kv_cache,
+        })
+    }
+
+    pub fn forward(
+        &mut self,
+        x: &Tensor,
+        attn_mask: Option<&Tensor>,
+        offset: usize,
+    ) -> candle_core::Result<Tensor> {
+        let (b, l, _) = x.dims3()?;
+
+        // 1. Projections (column-parallel → output is sharded).
+        let q = self.q_proj.forward(x)?;
+        let k = self.k_proj.forward(x)?;
+        let v = self.v_proj.forward(x)?;
+
+        // 2. Reshape: (B, L, H, D) → (B, H, L, D).
+        let q = q
+            .reshape((b, l, self.local_num_heads, self.head_dim))?
+            .transpose(1, 2)?;
+        let k = k
+            .reshape((b, l, self.local_num_kv_heads, self.head_dim))?
+            .transpose(1, 2)?;
+        let v = v
+            .reshape((b, l, self.local_num_kv_heads, self.head_dim))?
+            .transpose(1, 2)?;
+
+        // 3. Per-head RmsNorm (replicated weight, flat input).
+        let q_flat = q.flatten(0, 2)?;
+        let k_flat = k.flatten(0, 2)?;
+        let q_flat = self.q_norm.forward(&q_flat)?;
+        let k_flat = self.k_norm.forward(&k_flat)?;
+        let q = q_flat.reshape((b, self.local_num_heads, l, self.head_dim))?;
+        let k = k_flat.reshape((b, self.local_num_kv_heads, l, self.head_dim))?;
+
+        // 4. Rotary.
+        let (q, k) = self.rotary_emb.apply(&q, &k, offset)?;
+
+        // 5. Accumulate KV.
+        let (k, v) = self.kv_cache.append(&k, &v)?;
+
+        // 6. GQA repeat_kv on the rank-local K/V.
+        let k = repeat_kv(k, self.num_kv_groups)?.contiguous()?;
+        let v = repeat_kv(v, self.num_kv_groups)?.contiguous()?;
+
+        // 7. Attention scores.
+        let scale = 1.0 / (self.head_dim as f64).sqrt();
+        let mut scores = (q.matmul(&k.transpose(2, 3)?)? * scale)?;
+        if let Some(m) = attn_mask {
+            scores = scores.broadcast_add(m)?;
+        }
+        let probs = candle_nn::ops::softmax_last_dim(&scores)?;
+        let ctx = probs.matmul(&v)?;
+
+        // 8. Output projection (row-parallel → AllReduce inside).
+        ctx.transpose(1, 2)?
+            .reshape((b, l, self.local_hidden_size))?
+            .apply(&self.o_proj)
+    }
+
+    pub fn clear_kv_cache(&mut self) {
+        self.kv_cache.reset();
+    }
+}
+
+struct TpDecoderLayer {
+    self_attn: TpQwen3Attention,
+    mlp: TpQwen3MLP,
+    ln1: RmsNorm,
+    ln2: RmsNorm,
+}
+
+impl TpDecoderLayer {
+    #[cfg(feature = "cuda")]
+    fn load(
+        cfg: &Config,
+        rotary_emb: Arc<Qwen3RotaryEmbedding>,
+        vb: &ShardedVarBuilder,
+        rank: u32,
+        world_size: u32,
+        comm: Arc<Comm>,
+    ) -> Result<Self> {
+        let self_attn = TpQwen3Attention::load(
+            cfg,
+            rotary_emb,
+            &vb.pp("self_attn"),
+            rank,
+            world_size,
+            comm.clone(),
+        )?;
+        let mlp = TpQwen3MLP::load(cfg, &vb.pp("mlp"), rank, world_size, comm)?;
+        let ln1 = load_rms_norm(&vb.pp("input_layernorm"), cfg.hidden_size, cfg.rms_norm_eps)?;
+        let ln2 = load_rms_norm(
+            &vb.pp("post_attention_layernorm"),
+            cfg.hidden_size,
+            cfg.rms_norm_eps,
+        )?;
+        Ok(Self {
+            self_attn,
+            mlp,
+            ln1,
+            ln2,
+        })
+    }
+
+    #[cfg(not(feature = "cuda"))]
+    fn load(
+        cfg: &Config,
+        rotary_emb: Arc<Qwen3RotaryEmbedding>,
+        vb: &ShardedVarBuilder,
+        rank: u32,
+        world_size: u32,
+    ) -> Result<Self> {
+        let self_attn =
+            TpQwen3Attention::load(cfg, rotary_emb, &vb.pp("self_attn"), rank, world_size)?;
+        let mlp = TpQwen3MLP::load(cfg, &vb.pp("mlp"), rank, world_size)?;
+        let ln1 = load_rms_norm(&vb.pp("input_layernorm"), cfg.hidden_size, cfg.rms_norm_eps)?;
+        let ln2 = load_rms_norm(
+            &vb.pp("post_attention_layernorm"),
+            cfg.hidden_size,
+            cfg.rms_norm_eps,
+        )?;
+        Ok(Self {
+            self_attn,
+            mlp,
+            ln1,
+            ln2,
+        })
+    }
+
+    fn forward(
+        &mut self,
+        x: &Tensor,
+        mask: Option<&Tensor>,
+        offset: usize,
+    ) -> candle_core::Result<Tensor> {
+        let h = self.ln1.forward(x)?;
+        let h = self.self_attn.forward(&h, mask, offset)?;
+        let x = (x + h)?;
+        let h2 = self.ln2.forward(&x)?;
+        let h2 = h2.apply(&self.mlp)?;
+        x + h2
+    }
+
+    fn clear_kv_cache(&mut self) {
+        self.self_attn.clear_kv_cache();
+    }
+}
+
+/// Base TP Qwen3 transformer — embedding, decoder stack, final norm.
+/// The lm_head sits on top in [`TpQwen3ForCausalLM`].
+pub struct TpQwen3Model {
+    embed_tokens: Embedding,
+    layers: Vec<TpDecoderLayer>,
+    norm: RmsNorm,
+    device: Device,
+    dtype: DType,
+}
+
+impl TpQwen3Model {
+    #[cfg(feature = "cuda")]
+    pub fn load(
+        cfg: &Config,
+        vb: &ShardedVarBuilder,
+        rank: u32,
+        world_size: u32,
+        comm: Arc<Comm>,
+    ) -> Result<Self> {
+        let dtype = vb.dtype();
+        let device = vb.device().clone();
+        let rotary = Arc::new(Qwen3RotaryEmbedding::new(dtype, cfg, &device)?);
+
+        let embed_vb = vb.pp("model.embed_tokens");
+        let embed_weight = load_replicated(&embed_vb, (cfg.vocab_size, cfg.hidden_size), "weight")?;
+        let embed_tokens = Embedding::new(embed_weight, cfg.hidden_size);
+
+        let vb_l = vb.pp("model.layers");
+        let mut layers = Vec::with_capacity(cfg.num_hidden_layers);
+        for i in 0..cfg.num_hidden_layers {
+            layers.push(TpDecoderLayer::load(
+                cfg,
+                rotary.clone(),
+                &vb_l.pp(i),
+                rank,
+                world_size,
+                comm.clone(),
+            )?);
+        }
+        let norm = load_rms_norm(&vb.pp("model.norm"), cfg.hidden_size, cfg.rms_norm_eps)?;
+
+        Ok(Self {
+            embed_tokens,
+            layers,
+            norm,
+            device,
+            dtype,
+        })
+    }
+
+    #[cfg(not(feature = "cuda"))]
+    pub fn load(cfg: &Config, vb: &ShardedVarBuilder, rank: u32, world_size: u32) -> Result<Self> {
+        let dtype = vb.dtype();
+        let device = vb.device().clone();
+        let rotary = Arc::new(Qwen3RotaryEmbedding::new(dtype, cfg, &device)?);
+
+        let embed_vb = vb.pp("model.embed_tokens");
+        let embed_weight = load_replicated(&embed_vb, (cfg.vocab_size, cfg.hidden_size), "weight")?;
+        let embed_tokens = Embedding::new(embed_weight, cfg.hidden_size);
+
+        let vb_l = vb.pp("model.layers");
+        let mut layers = Vec::with_capacity(cfg.num_hidden_layers);
+        for i in 0..cfg.num_hidden_layers {
+            layers.push(TpDecoderLayer::load(
+                cfg,
+                rotary.clone(),
+                &vb_l.pp(i),
+                rank,
+                world_size,
+            )?);
+        }
+        let norm = load_rms_norm(&vb.pp("model.norm"), cfg.hidden_size, cfg.rms_norm_eps)?;
+
+        Ok(Self {
+            embed_tokens,
+            layers,
+            norm,
+            device,
+            dtype,
+        })
+    }
+
+    pub fn embed_weight(&self) -> &Tensor {
+        self.embed_tokens.embeddings()
+    }
+
+    pub fn clear_kv_cache(&mut self) {
+        for l in &mut self.layers {
+            l.clear_kv_cache();
+        }
+    }
+
+    fn causal_mask(&self, b: usize, tgt: usize, offset: usize) -> candle_core::Result<Tensor> {
+        let minf = f32::NEG_INFINITY;
+        let mask: Vec<_> = (0..tgt)
+            .flat_map(|i| (0..(tgt + offset)).map(move |j| if j <= i + offset { 0. } else { minf }))
+            .collect();
+        Tensor::from_slice(&mask, (b, 1, tgt, tgt + offset), &self.device)?.to_dtype(self.dtype)
+    }
+
+    pub fn forward(&mut self, input: &Tensor, offset: usize) -> candle_core::Result<Tensor> {
+        let (b, l) = input.dims2()?;
+        let mut h = self.embed_tokens.forward(input)?;
+
+        let causal = if l == 1 {
+            None
+        } else {
+            Some(self.causal_mask(b, l, offset)?)
+        };
+
+        for layer in &mut self.layers {
+            h = layer.forward(&h, causal.as_ref(), offset)?;
+        }
+        self.norm.forward(&h)
+    }
+}
+
+/// TP Qwen3 with a (replicated) language-model head on top.
+pub struct TpQwen3ForCausalLM {
+    base: TpQwen3Model,
+    lm_head: Linear,
+}
+
+impl TpQwen3ForCausalLM {
+    #[cfg(feature = "cuda")]
+    pub fn load(
+        cfg: &Config,
+        vb: &ShardedVarBuilder,
+        rank: u32,
+        world_size: u32,
+        comm: Arc<Comm>,
+    ) -> Result<Self> {
+        let base = TpQwen3Model::load(cfg, vb, rank, world_size, comm)?;
+        let lm_head = build_lm_head(cfg, vb, &base)?;
+        Ok(Self { base, lm_head })
+    }
+
+    #[cfg(not(feature = "cuda"))]
+    pub fn load(cfg: &Config, vb: &ShardedVarBuilder, rank: u32, world_size: u32) -> Result<Self> {
+        let base = TpQwen3Model::load(cfg, vb, rank, world_size)?;
+        let lm_head = build_lm_head(cfg, vb, &base)?;
+        Ok(Self { base, lm_head })
+    }
+
+    pub fn forward(&mut self, input: &Tensor, offset: usize) -> candle_core::Result<Tensor> {
+        let (_, l) = input.dims2()?;
+        let hidden = self.base.forward(input, offset)?;
+        hidden.i((.., l - 1.., ..))?.apply(&self.lm_head)
+    }
+
+    pub fn clear_kv_cache(&mut self) {
+        self.base.clear_kv_cache();
+    }
+
+    pub fn device(&self) -> &Device {
+        &self.base.device
+    }
+
+    pub fn dtype(&self) -> DType {
+        self.base.dtype
+    }
+}
+
+fn build_lm_head(cfg: &Config, vb: &ShardedVarBuilder, base: &TpQwen3Model) -> Result<Linear> {
+    if cfg.tie_word_embeddings {
+        Ok(Linear::new(base.embed_weight().clone(), None))
+    } else {
+        let weight = load_replicated(
+            &vb.pp("lm_head"),
+            (cfg.vocab_size, cfg.hidden_size),
+            "weight",
+        )?;
+        Ok(Linear::new(weight, None))
+    }
+}

crates/neuron/src/harness/tp/worker.rs

@@ -0,0 +1,102 @@
+//! Entry point for `neuron --worker`.
+//!
+//! The worker reads one newline-delimited JSON `WorkerRequest` from
+//! stdin per loop iteration, dispatches synchronously, and writes
+//! exactly one `WorkerResponse` JSON line to stdout. tracing goes to
+//! stderr so it doesn't collide with the RPC stream.
+//!
+//! NCCL operations (`Init`, `NcclSanityCheck`) are real when built
+//! with the `cuda` feature; without it they reply with
+//! `Error{kind="cuda_feature_not_enabled"}` so the leader can tell
+//! the difference between a misconfigured build and a genuine NCCL
+//! failure.
+
+use anyhow::Result;
+use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
+
+use super::nccl_state::NcclState;
+use super::rpc::{WorkerRequest, WorkerResponse};
+
+#[derive(Debug, Clone, Copy)]
+pub struct WorkerConfig {
+    pub rank: u32,
+    pub world_size: u32,
+    pub cuda_device: u32,
+}
+
+/// Drive the worker RPC loop until `Shutdown` or EOF on stdin.
+pub async fn run(config: WorkerConfig) -> Result<()> {
+    tracing::info!(
+        rank = config.rank,
+        world_size = config.world_size,
+        cuda_device = config.cuda_device,
+        "tp worker starting"
+    );
+
+    let mut state = WorkerState::new(config);
+    let stdin = tokio::io::stdin();
+    let mut reader = BufReader::new(stdin).lines();
+    let mut stdout = tokio::io::stdout();
+
+    while let Some(line) = reader.next_line().await? {
+        if line.trim().is_empty() {
+            continue;
+        }
+        let req: WorkerRequest = match serde_json::from_str(&line) {
+            Ok(r) => r,
+            Err(e) => {
+                let resp = WorkerResponse::Error {
+                    kind: "bad_request".into(),
+                    message: format!("parse {line:?}: {e}"),
+                };
+                write_response(&mut stdout, &resp).await?;
+                continue;
+            }
+        };
+
+        let resp = state.handle(req).await;
+        let is_bye = matches!(resp, WorkerResponse::Bye);
+        write_response(&mut stdout, &resp).await?;
+        if is_bye {
+            break;
+        }
+    }
+
+    tracing::info!(rank = config.rank, "tp worker exiting");
+    Ok(())
+}
+
+async fn write_response(stdout: &mut tokio::io::Stdout, resp: &WorkerResponse) -> Result<()> {
+    let mut line = serde_json::to_string(resp)?;
+    line.push('\n');
+    stdout.write_all(line.as_bytes()).await?;
+    stdout.flush().await?;
+    Ok(())
+}
+
+struct WorkerState {
+    config: WorkerConfig,
+    nccl: NcclState,
+}
+
+impl WorkerState {
+    fn new(config: WorkerConfig) -> Self {
+        Self {
+            config,
+            nccl: NcclState::new(),
+        }
+    }
+
+    async fn handle(&mut self, req: WorkerRequest) -> WorkerResponse {
+        match req {
+            WorkerRequest::Ping => WorkerResponse::Pong {
+                rank: self.config.rank,
+                world_size: self.config.world_size,
+                cuda_device: self.config.cuda_device,
+            },
+            WorkerRequest::Init { comm_id } => self.nccl.init(self.config, &comm_id),
+            WorkerRequest::NcclSanityCheck => self.nccl.sanity_check(),
+            WorkerRequest::Shutdown => WorkerResponse::Bye,
+        }
+    }
+}

crates/neuron/src/lib.rs

@@ -3,3 +3,4 @@ pub mod config;
 pub mod discovery;
 pub mod harness;
 pub mod health;
+pub mod startup;

crates/neuron/src/main.rs

@@ -1,21 +1,52 @@
 use anyhow::Result;
 use clap::Parser;
-use neuron::{api, config::NeuronConfig, discovery, harness::HarnessRegistry, health};
+use neuron::{
+    api,
+    config::NeuronConfig,
+    discovery,
+    harness::{HarnessRegistry, tp},
+    health, startup,
+};
 use std::sync::Arc;
 use std::time::Instant;
 use tokio::sync::RwLock;
 use tracing_subscriber::EnvFilter;
 
+/// Top-level CLI. The same binary runs as either the public neuron
+/// daemon (default) or a tensor-parallel worker subprocess (when
+/// `--worker` is set) spawned by the leader on the same host.
 #[derive(Parser)]
 #[command(name = "neuron")]
 #[command(about = "Per-node daemon for cortex inference clusters")]
 #[command(version)]
 struct Args {
-    /// Port to listen on (overrides config file).
+    /// Run in tensor-parallel worker mode. The leader process spawns
+    /// one of these per non-zero NCCL rank and drives it over
+    /// newline-delimited JSON on stdin/stdout. Worker mode skips
+    /// discovery, the HTTP listener, and the health poller — it's a
+    /// pure RPC loop.
+    #[arg(long, default_value_t = false)]
+    worker: bool,
+
+    /// NCCL rank for worker mode. Ignored when `--worker` is not set.
+    #[arg(long, default_value_t = 0)]
+    rank: u32,
+
+    /// Total NCCL world size for worker mode. Ignored when `--worker`
+    /// is not set.
+    #[arg(long, default_value_t = 1)]
+    tp_size: u32,
+
+    /// CUDA device index for worker mode. Ignored when `--worker` is
+    /// not set.
+    #[arg(long, default_value_t = 0)]
+    cuda_device: u32,
+
+    /// Port to listen on (overrides config file). Daemon mode only.
     #[arg(short, long)]
     port: Option<u16>,
 
-    /// Path to the neuron config file.
+    /// Path to the neuron config file. Daemon mode only.
     #[arg(short, long, default_value = "neuron.toml")]
     config: String,
 }
@@ -23,6 +54,7 @@ struct Args {
 #[tokio::main]
 async fn main() -> Result<()> {
     tracing_subscriber::fmt()
+        .with_writer(std::io::stderr)
         .with_env_filter(
             EnvFilter::try_from_default_env()
                 .unwrap_or_else(|_| EnvFilter::new("info,neuron=debug")),
@@ -31,12 +63,26 @@ async fn main() -> Result<()> {
 
     let args = Args::parse();
 
+    if args.worker {
+        return tp::worker::run(tp::worker::WorkerConfig {
+            rank: args.rank,
+            world_size: args.tp_size,
+            cuda_device: args.cuda_device,
+        })
+        .await;
+    }
+
+    daemon(args).await
+}
+
+async fn daemon(args: Args) -> Result<()> {
     let cfg = NeuronConfig::load(&args.config).unwrap_or_else(|e| {
         tracing::warn!(path = %args.config, error = %e, "config not found, using defaults");
         NeuronConfig::default()
     });
 
     let port = args.port.unwrap_or(cfg.port);
+    let bind_url = format!("http://localhost:{port}");
     let start_time = Instant::now();
 
     tracing::info!("running hardware discovery");
@@ -47,9 +93,18 @@ async fn main() -> Result<()> {
         "discovery complete"
     );
 
-    // Build harness registry from config.
+    // Build harness registry from config. In-process harnesses (candle)
-    let registry = HarnessRegistry::from_configs(&cfg.harnesses);
+    // need to know neuron's own bind URL so they can return it from
+    // inference_endpoint.
+    let registry = HarnessRegistry::from_configs(&cfg.harnesses, &bind_url, &cfg.harness);
     discovery_result.harnesses = registry.names();
+    let candle = registry.candle();
+
+    // Activation: load default models before binding the listener.
+    // Each load may take tens of seconds to several minutes depending
+    // on model size and HF cache state — keep TimeoutStartSec in the
+    // systemd unit generous enough to cover the slowest entry.
+    startup::load_default_models(&registry, &cfg.default_models).await;
 
     let health_cache = Arc::new(health::HealthCache::new());
     health_cache
@@ -65,13 +120,24 @@ async fn main() -> Result<()> {
         discovery: discovery_result,
         health_cache,
         registry: RwLock::new(registry),
+        candle,
     });
 
-    let app = api::neuron_routes().with_state(state);
+    let app = api::neuron_routes().with_state(Arc::clone(&state));
     let addr: std::net::SocketAddr = format!("0.0.0.0:{port}").parse()?;
     tracing::info!("neuron listening on {addr}");
     let listener = tokio::net::TcpListener::bind(addr).await?;
-    axum::serve(listener, app).await?;
+    axum::serve(listener, app)
+        .with_graceful_shutdown(startup::shutdown_signal())
+        .await?;
+
+    // Deactivation: serve has returned (graceful shutdown signal
+    // received and connections drained). Release CUDA contexts / VRAM
+    // by unloading every model before exiting; systemd's TimeoutStopSec
+    // bounds how long this phase may take.
+    let registry = state.registry.read().await;
+    startup::unload_all_models(&registry).await;
+    tracing::info!("shutdown complete");
 
     Ok(())
 }

crates/neuron/src/startup.rs

@@ -0,0 +1,97 @@
+//! Activation- and deactivation-time orchestration.
+//!
+//! Wired from `main.rs` around the HTTP listener — activation runs
+//! before bind, deactivation runs after axum returns from its
+//! graceful-shutdown future. Kept in its own module so the logic is
+//! unit-testable without spinning up a full neuron process.
+
+use crate::harness::HarnessRegistry;
+use cortex_core::harness::ModelSpec;
+use std::time::Instant;
+use tokio::signal;
+
+/// Load each spec sequentially against the registry, treating
+/// individual failures as warnings rather than fatal errors.
+///
+/// VRAM contention makes parallel loads risky; the sequential path is
+/// boring but correct. The function logs elapsed time per load so an
+/// operator can see which model is hogging activation.
+pub async fn load_default_models(registry: &HarnessRegistry, specs: &[ModelSpec]) {
+    if specs.is_empty() {
+        return;
+    }
+    tracing::info!(count = specs.len(), "loading default models");
+    for spec in specs {
+        let start = Instant::now();
+        match registry.load_model(spec).await {
+            Ok(()) => tracing::info!(
+                model = %spec.model_id,
+                elapsed_ms = start.elapsed().as_millis() as u64,
+                "loaded default model"
+            ),
+            Err(e) => tracing::warn!(
+                model = %spec.model_id,
+                error = %e,
+                elapsed_ms = start.elapsed().as_millis() as u64,
+                "failed to load default model, continuing"
+            ),
+        }
+    }
+}
+
+/// Future that resolves on SIGINT (Ctrl-C) or SIGTERM (systemd stop).
+///
+/// Wired into `axum::serve(...).with_graceful_shutdown(shutdown_signal())`
+/// so the HTTP listener stops accepting new connections, lets in-flight
+/// requests drain, and then yields control back to main for cleanup.
+pub async fn shutdown_signal() {
+    let ctrl_c = async {
+        signal::ctrl_c().await.ok();
+    };
+    let terminate = async {
+        signal::unix::signal(signal::unix::SignalKind::terminate())
+            .expect("install SIGTERM handler")
+            .recv()
+            .await;
+    };
+    tokio::select! {
+        _ = ctrl_c => tracing::info!("received SIGINT, shutting down"),
+        _ = terminate => tracing::info!("received SIGTERM, shutting down"),
+    }
+}
+
+/// Unload every model currently registered. Called from `main.rs` after
+/// axum's graceful shutdown future resolves, so CUDA contexts and VRAM
+/// are released before the process exits rather than left to the OS to
+/// reclaim. Per-model failures are logged and skipped — keep cleanup
+/// going even when one harness is unhealthy.
+pub async fn unload_all_models(registry: &HarnessRegistry) {
+    let listed = match registry.list_all_models().await {
+        Ok(m) => m,
+        Err(e) => {
+            tracing::warn!(error = %e, "failed to list models during shutdown");
+            return;
+        }
+    };
+
+    if listed.is_empty() {
+        return;
+    }
+
+    tracing::info!(count = listed.len(), "unloading models for shutdown");
+    for model in listed {
+        let start = Instant::now();
+        match registry.unload_model(&model.id).await {
+            Ok(()) => tracing::info!(
+                model = %model.id,
+                elapsed_ms = start.elapsed().as_millis() as u64,
+                "unloaded"
+            ),
+            Err(e) => tracing::warn!(
+                model = %model.id,
+                error = %e,
+                "unload failed during shutdown"
+            ),
+        }
+    }
+}

crates/neuron/tests/activation.rs

@@ -0,0 +1,56 @@
+//! Activation-time behaviour: load_default_models continues past
+//! individual failures so a single broken catalogue entry doesn't
+//! prevent the rest of the fleet from starting.
+
+use cortex_core::harness::{HarnessConfig, ModelSpec};
+use neuron::config::HarnessSettings;
+use neuron::harness::HarnessRegistry;
+use neuron::startup;
+
+#[tokio::test]
+async fn test_load_default_models_skips_unknown_harness() {
+    let registry = HarnessRegistry::from_configs(
+        &[HarnessConfig {
+            name: "candle".into(),
+        }],
+        "http://localhost:0",
+        &HarnessSettings::default(),
+    );
+
+    // Both entries fail synchronously inside the registry — no network
+    // call escapes (the harness lookup mismatches before hf-hub is
+    // touched). The function should still return cleanly.
+    let specs = vec![
+        ModelSpec {
+            model_id: "model-a".into(),
+            harness: "no-such-harness".into(),
+            quant: None,
+            tensor_parallel: None,
+            devices: None,
+        },
+        ModelSpec {
+            model_id: "model-b".into(),
+            harness: "no-such-harness".into(),
+            quant: None,
+            tensor_parallel: None,
+            devices: None,
+        },
+    ];
+
+    startup::load_default_models(&registry, &specs).await;
+
+    let listed = registry
+        .list_all_models()
+        .await
+        .expect("list_all_models should succeed");
+    assert!(
+        listed.is_empty(),
+        "no models should be loaded after failed entries"
+    );
+}
+
+#[tokio::test]
+async fn test_load_default_models_empty_is_noop() {
+    let registry = HarnessRegistry::new();
+    startup::load_default_models(&registry, &[]).await;
+}

crates/neuron/tests/api.rs

@@ -14,6 +14,7 @@ async fn spawn_neuron(discovery: DiscoveryResponse) -> String {
         discovery,
         health_cache,
         registry: RwLock::new(registry),
+        candle: None,
     });
 
     let app = api::neuron_routes().with_state(state);
@@ -135,56 +136,30 @@ async fn test_models_empty_registry() {
     assert!(body.as_array().unwrap().is_empty());
 }
 
-/// Spawn a mock mistral.rs backend and a neuron with the mistralrs harness
+/// Verify the candle harness registers, list is empty by default, and a
-/// pointing at it, then test the full model lifecycle through neuron's API.
+/// load attempt for an obviously-bogus model id returns a 4xx error
+/// without crashing the daemon. Real load/unload exercising actual GGUF
+/// download is covered by `tests/candle_lifecycle.rs` (cuda-integration).
 #[tokio::test]
-async fn test_models_via_mistralrs_harness() {
+async fn test_candle_harness_registers_and_rejects_bogus_model() {
-    use axum::routing::{get, post};
-    use axum::{Json, Router};
     use cortex_core::harness::HarnessConfig;
-    use serde_json::Value;
+    use neuron::config::HarnessSettings;
 
-    // Mock mistral.rs backend.
+    let registry = HarnessRegistry::from_configs(
-    let mock_app = Router::new()
+        &[HarnessConfig {
-        .route(
+            name: "candle".into(),
-            "/v1/models",
+        }],
-            get(|| async {
+        "http://localhost:13131",
-                Json(json!({
+        &HarnessSettings::default(),
-                    "data": [
-                        {"id": "test-model", "status": "loaded"},
-                        {"id": "other-model", "status": "unloaded"}
-                    ]
-                }))
-            }),
-        )
-        .route(
-            "/v1/models/unload",
-            post(|Json(_body): Json<Value>| async { Json(json!({"status": "ok"})) }),
-        )
-        .route(
-            "/v1/models/reload",
-            post(|Json(_body): Json<Value>| async { Json(json!({"status": "ok"})) }),
     );
 
-    let mock_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let candle = registry.candle();
-    let mock_addr = mock_listener.local_addr().unwrap();
-    tokio::spawn(async move {
-        axum::serve(mock_listener, mock_app).await.unwrap();
-    });
-    let mock_url = format!("http://{mock_addr}");
-
-    // Build neuron with mistralrs harness pointing at mock.
-    let registry = HarnessRegistry::from_configs(&[HarnessConfig {
-        name: "mistralrs".into(),
-        endpoint: Some(mock_url.clone()),
-        systemd_unit: None,
-    }]);
-
     let health_cache = Arc::new(HealthCache::new());
     let state = Arc::new(NeuronState {
         discovery: fake_discovery(),
         health_cache,
         registry: RwLock::new(registry),
+        candle,
     });
 
     let app = api::neuron_routes().with_state(state);
@@ -197,7 +172,6 @@ async fn test_models_via_mistralrs_harness() {
 
     let client = reqwest::Client::new();
 
-    // GET /models — should return models from mock mistralrs.
     let resp = client
         .get(format!("{neuron_url}/models"))
         .send()
@@ -205,45 +179,140 @@ async fn test_models_via_mistralrs_harness() {
         .unwrap();
     assert_eq!(resp.status(), 200);
     let models: Vec<serde_json::Value> = resp.json().await.unwrap();
-    assert_eq!(models.len(), 2);
+    assert!(models.is_empty());
-    assert_eq!(models[0]["id"], "test-model");
-    assert_eq!(models[0]["harness"], "mistralrs");
-    assert_eq!(models[0]["status"], "loaded");
-    assert_eq!(models[1]["id"], "other-model");
-    assert_eq!(models[1]["status"], "unloaded");
 
-    // GET /models/test-model/endpoint — should return mock URL.
+    // Sending a wrong-harness spec should be rejected synchronously
-    let resp = client
+    // without touching the network or the model registry.
-        .get(format!("{neuron_url}/models/test-model/endpoint"))
-        .send()
-        .await
-        .unwrap();
-    assert_eq!(resp.status(), 200);
-    let body: serde_json::Value = resp.json().await.unwrap();
-    assert_eq!(body["url"], mock_url);
-
-    // POST /models/unload — should succeed.
-    let resp = client
-        .post(format!("{neuron_url}/models/unload"))
-        .json(&json!({"model_id": "test-model"}))
-        .send()
-        .await
-        .unwrap();
-    assert_eq!(resp.status(), 200);
-    let body: serde_json::Value = resp.json().await.unwrap();
-    assert_eq!(body["status"], "unloaded");
-
-    // POST /models/load — should succeed.
     let resp = client
         .post(format!("{neuron_url}/models/load"))
+        .json(&json!({"model_id": "definitely/not-real", "harness": "not-candle"}))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), 400);
+
+    // Registry still empty.
+    let resp = client
+        .get(format!("{neuron_url}/models"))
+        .send()
+        .await
+        .unwrap();
+    let models: Vec<serde_json::Value> = resp.json().await.unwrap();
+    assert!(models.is_empty());
+}
+
+/// `/v1/chat/completions` returns 503 when no candle harness is registered.
+#[tokio::test]
+async fn test_chat_completions_no_candle_harness() {
+    let registry = HarnessRegistry::new();
+    let health_cache = Arc::new(HealthCache::new());
+    let state = Arc::new(NeuronState {
+        discovery: fake_discovery(),
+        health_cache,
+        registry: RwLock::new(registry),
+        candle: None,
+    });
+    let app = api::neuron_routes().with_state(state);
+    let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let addr = listener.local_addr().unwrap();
+    tokio::spawn(async move {
+        axum::serve(listener, app).await.unwrap();
+    });
+    let url = format!("http://{addr}");
+
+    let resp = reqwest::Client::new()
+        .post(format!("{url}/v1/chat/completions"))
         .json(&json!({
-            "model_id": "test-model",
+            "model": "anything",
-            "harness": "mistralrs"
+            "messages": [{"role": "user", "content": "hi"}]
         }))
         .send()
         .await
         .unwrap();
-    assert_eq!(resp.status(), 200);
+    assert_eq!(resp.status(), 503);
-    let body: serde_json::Value = resp.json().await.unwrap();
+}
-    assert_eq!(body["status"], "loaded");
+
+/// `/v1/chat/completions` returns 404 when the requested model isn't loaded.
+#[tokio::test]
+async fn test_chat_completions_model_not_loaded() {
+    use cortex_core::harness::HarnessConfig;
+    use neuron::config::HarnessSettings;
+
+    let registry = HarnessRegistry::from_configs(
+        &[HarnessConfig {
+            name: "candle".into(),
+        }],
+        "http://localhost:0",
+        &HarnessSettings::default(),
+    );
+    let candle = registry.candle();
+    let health_cache = Arc::new(HealthCache::new());
+    let state = Arc::new(NeuronState {
+        discovery: fake_discovery(),
+        health_cache,
+        registry: RwLock::new(registry),
+        candle,
+    });
+    let app = api::neuron_routes().with_state(state);
+    let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let addr = listener.local_addr().unwrap();
+    tokio::spawn(async move {
+        axum::serve(listener, app).await.unwrap();
+    });
+    let url = format!("http://{addr}");
+
+    let resp = reqwest::Client::new()
+        .post(format!("{url}/v1/chat/completions"))
+        .json(&json!({
+            "model": "definitely/not-loaded",
+            "messages": [{"role": "user", "content": "hi"}]
+        }))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), 404);
+}
+
+/// `/v1/chat/completions` with `stream: true` returns 404 when the
+/// model isn't loaded — same surface as the non-streaming path. The
+/// streaming code only kicks in once the model lookup succeeds.
+#[tokio::test]
+async fn test_chat_completions_streaming_model_not_loaded() {
+    use cortex_core::harness::HarnessConfig;
+    use neuron::config::HarnessSettings;
+
+    let registry = HarnessRegistry::from_configs(
+        &[HarnessConfig {
+            name: "candle".into(),
+        }],
+        "http://localhost:0",
+        &HarnessSettings::default(),
+    );
+    let candle = registry.candle();
+    let health_cache = Arc::new(HealthCache::new());
+    let state = Arc::new(NeuronState {
+        discovery: fake_discovery(),
+        health_cache,
+        registry: RwLock::new(registry),
+        candle,
+    });
+    let app = api::neuron_routes().with_state(state);
+    let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let addr = listener.local_addr().unwrap();
+    tokio::spawn(async move {
+        axum::serve(listener, app).await.unwrap();
+    });
+    let url = format!("http://{addr}");
+
+    let resp = reqwest::Client::new()
+        .post(format!("{url}/v1/chat/completions"))
+        .json(&json!({
+            "model": "definitely/not-loaded",
+            "messages": [{"role": "user", "content": "hi"}],
+            "stream": true
+        }))
+        .send()
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), 404);
 }

crates/neuron/tests/candle_lifecycle.rs

@@ -0,0 +1,87 @@
+//! Real model load/unload lifecycle through the candle harness.
+//!
+//! Gated behind the `cuda-integration` feature because it downloads a
+//! real (small) GGUF from HuggingFace and materialises tensors on the
+//! configured device. Run on a host with network access and either a
+//! CUDA GPU (when built with `--features cuda`) or enough CPU RAM to
+//! hold the model.
+//!
+//! Usage:
+//!   cargo test -p neuron --features cuda-integration --test candle_lifecycle
+//!
+//! Optional environment variables:
+//!   NEURON_TEST_MODEL_ID — HuggingFace repo to load (default: a small
+//!     public Qwen3 GGUF repo).
+//!   NEURON_TEST_QUANT    — quant substring matched against GGUF
+//!     filenames (default: "Q4_K_M").
+//!   HF_HOME              — HuggingFace cache directory.
+
+#![cfg(feature = "cuda-integration")]
+
+use cortex_core::harness::{HarnessConfig, ModelSpec};
+use neuron::config::HarnessSettings;
+use neuron::harness::HarnessRegistry;
+use std::path::PathBuf;
+
+#[tokio::test]
+async fn test_candle_qwen3_load_unload_lifecycle() {
+    let _ = tracing_subscriber::fmt()
+        .with_test_writer()
+        .with_env_filter("info,neuron=debug")
+        .try_init();
+
+    let model_id = std::env::var("NEURON_TEST_MODEL_ID")
+        .unwrap_or_else(|_| "Qwen/Qwen3-0.6B-GGUF".to_string());
+    let quant = std::env::var("NEURON_TEST_QUANT").unwrap_or_else(|_| "Q4_K_M".to_string());
+
+    let mut settings = HarnessSettings::default();
+    if let Ok(home) = std::env::var("HF_HOME") {
+        settings.candle.hf_cache = Some(PathBuf::from(home));
+    }
+
+    let registry = HarnessRegistry::from_configs(
+        &[HarnessConfig {
+            name: "candle".into(),
+        }],
+        "http://localhost:13131",
+        &settings,
+    );
+
+    let spec = ModelSpec {
+        model_id: model_id.clone(),
+        harness: "candle".into(),
+        quant: Some(quant),
+        tensor_parallel: None,
+        devices: Some(vec![0]),
+    };
+
+    registry
+        .load_model(&spec)
+        .await
+        .expect("load_model should succeed");
+
+    let models = registry.list_all_models().await.expect("list_all_models");
+    assert_eq!(models.len(), 1, "expected exactly one loaded model");
+    assert_eq!(models[0].id, model_id);
+    assert_eq!(models[0].harness, "candle");
+    assert_eq!(models[0].status, "loaded");
+
+    let url = registry.inference_endpoint(&model_id).await;
+    assert_eq!(url, Some("http://localhost:13131".into()));
+
+    // Re-loading the same model should be rejected.
+    let again = registry.load_model(&spec).await;
+    assert!(again.is_err(), "second load should error");
+
+    registry
+        .unload_model(&model_id)
+        .await
+        .expect("unload_model should succeed");
+
+    let models = registry.list_all_models().await.expect("list_all_models");
+    assert!(models.is_empty(), "registry should be empty after unload");
+
+    // Unloading a model that isn't loaded should error.
+    let err = registry.unload_model(&model_id).await;
+    assert!(err.is_err(), "unload of missing model should error");
+}

crates/neuron/tests/shutdown.rs

@@ -0,0 +1,32 @@
+//! Deactivation behaviour: unload_all_models tolerates an empty
+//! registry and continues past per-model unload failures.
+
+use cortex_core::harness::HarnessConfig;
+use neuron::config::HarnessSettings;
+use neuron::harness::HarnessRegistry;
+use neuron::startup;
+
+#[tokio::test]
+async fn test_unload_all_models_empty_registry_is_noop() {
+    let registry = HarnessRegistry::new();
+    startup::unload_all_models(&registry).await;
+}
+
+#[tokio::test]
+async fn test_unload_all_models_with_no_loaded_models() {
+    let registry = HarnessRegistry::from_configs(
+        &[HarnessConfig {
+            name: "candle".into(),
+        }],
+        "http://localhost:0",
+        &HarnessSettings::default(),
+    );
+
+    startup::unload_all_models(&registry).await;
+
+    let listed = registry
+        .list_all_models()
+        .await
+        .expect("list_all_models should still succeed after shutdown cleanup");
+    assert!(listed.is_empty());
+}

crates/neuron/tests/tp_worker_lifecycle.rs

@@ -0,0 +1,145 @@
+//! Stage 7a-i: confirm the TP worker subprocess lifecycle round-trips.
+//!
+//! Spawns two worker subprocesses via the leader→worker stdio RPC,
+//! pings each, and cleanly shuts them down. No CUDA required —
+//! `Init` and `NcclSanityCheck` are stubbed in 7a-i, so this test
+//! runs on any host the workspace builds on.
+
+use neuron::harness::tp::{WorkerPool, rpc::WorkerResponse};
+
+/// Path to the neuron binary built by cargo for this test process.
+/// cargo populates `CARGO_BIN_EXE_neuron` at compile time for sibling-
+/// binary tests; production paths in main.rs use `/proc/self/exe`.
+const NEURON_BIN: &str = env!("CARGO_BIN_EXE_neuron");
+
+/// Two workers (so we spawn one subprocess: rank 0 is in-process,
+/// rank 1 is the child). Verify the spawned worker responds to Ping
+/// with its own identity, then shut it down cleanly.
+#[tokio::test]
+async fn test_spawn_ping_shutdown() {
+    // cuda_devices: rank 0 → device 0 (leader, unused here),
+    //               rank 1 → device 1 (worker; not actually opened in 7a-i).
+    let mut pool = WorkerPool::spawn(NEURON_BIN.as_ref(), 2, &[0, 1])
+        .await
+        .expect("spawn worker pool");
+
+    let pongs = pool.ping_all().await.expect("ping all workers");
+    assert_eq!(pongs.len(), 1, "expected one Pong (rank 1 only)");
+    match &pongs[0] {
+        WorkerResponse::Pong {
+            rank,
+            world_size,
+            cuda_device,
+        } => {
+            assert_eq!(*rank, 1);
+            assert_eq!(*world_size, 2);
+            assert_eq!(*cuda_device, 1);
+        }
+        other => panic!("expected Pong, got {other:?}"),
+    }
+
+    pool.shutdown().await.expect("clean shutdown");
+}
+
+/// Three workers — exercise the loop in `ping_all` / `shutdown`.
+#[tokio::test]
+async fn test_spawn_three_workers() {
+    let mut pool = WorkerPool::spawn(NEURON_BIN.as_ref(), 3, &[0, 1, 2])
+        .await
+        .expect("spawn worker pool");
+
+    let pongs = pool.ping_all().await.expect("ping all workers");
+    assert_eq!(pongs.len(), 2, "expected two Pongs (ranks 1 and 2)");
+    for (i, resp) in pongs.iter().enumerate() {
+        match resp {
+            WorkerResponse::Pong {
+                rank,
+                world_size,
+                cuda_device,
+            } => {
+                let expected_rank = (i + 1) as u32;
+                assert_eq!(*rank, expected_rank);
+                assert_eq!(*world_size, 3);
+                assert_eq!(*cuda_device, expected_rank);
+            }
+            other => panic!("expected Pong, got {other:?}"),
+        }
+    }
+
+    pool.shutdown().await.expect("clean shutdown");
+}
+
+/// 7a-ii: without the cuda feature, Init must fail with a clear
+/// `cuda_feature_not_enabled` marker rather than silently succeeding.
+/// This is the local-dev-box test; the real NCCL handshake is exercised
+/// by `tp_worker_lifecycle_cuda.rs` (gated on `cuda-integration`).
+#[tokio::test]
+async fn test_init_returns_cuda_feature_not_enabled_without_cuda() {
+    use neuron::harness::tp::rpc::WorkerRequest;
+    use std::process::Stdio;
+    use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
+    use tokio::process::Command;
+
+    // Spawn a single worker by hand to send Init directly (the pool's
+    // public API doesn't expose Init yet — that lands in 7a-ii).
+    let mut child = Command::new(NEURON_BIN)
+        .arg("--worker")
+        .arg("--rank")
+        .arg("1")
+        .arg("--tp-size")
+        .arg("2")
+        .arg("--cuda-device")
+        .arg("1")
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::null())
+        .kill_on_drop(true)
+        .spawn()
+        .expect("spawn worker");
+
+    let mut stdin = child.stdin.take().expect("stdin");
+    let stdout = child.stdout.take().expect("stdout");
+    let mut lines = BufReader::new(stdout).lines();
+
+    let req = WorkerRequest::Init {
+        comm_id: "ff".repeat(128),
+    };
+    let mut payload = serde_json::to_string(&req).unwrap();
+    payload.push('\n');
+    stdin.write_all(payload.as_bytes()).await.unwrap();
+    stdin.flush().await.unwrap();
+
+    let reply = lines
+        .next_line()
+        .await
+        .expect("read line")
+        .expect("got line");
+    let resp: WorkerResponse = serde_json::from_str(&reply).expect("parse reply");
+    match resp {
+        WorkerResponse::Error { kind, .. } => {
+            #[cfg(feature = "cuda")]
+            {
+                // With cuda enabled the response depends on whether
+                // CUDA hardware is actually present. Accept either
+                // the success contract or a real NCCL failure.
+                let _ = kind;
+            }
+            #[cfg(not(feature = "cuda"))]
+            assert_eq!(kind, "cuda_feature_not_enabled");
+        }
+        WorkerResponse::InitOk => {
+            // Real NCCL succeeded — only possible with cuda feature
+            // AND a working NCCL stack AND another rank actually
+            // joining. Don't fail; just acknowledge.
+            #[cfg(not(feature = "cuda"))]
+            panic!("InitOk without cuda feature is impossible");
+        }
+        other => panic!("expected Error or InitOk, got {other:?}"),
+    }
+
+    // Clean shutdown.
+    stdin.write_all(b"{\"op\":\"shutdown\"}\n").await.unwrap();
+    stdin.flush().await.unwrap();
+    let _ = lines.next_line().await; // Bye
+    let _ = child.wait().await;
+}

crates/neuron/tests/tp_worker_lifecycle_cuda.rs

@@ -0,0 +1,43 @@
+//! Stage 7a-ii: real NCCL handshake across the worker pool.
+//!
+//! Gated behind the `cuda-integration` feature because it requires
+//! libnccl AND multiple CUDA devices on the running host. Run on
+//! beast (2× RTX 5090) via:
+//!
+//!   cargo test -p neuron --features cuda-integration \
+//!         --test tp_worker_lifecycle_cuda
+//!
+//! Steps: spawn N-1 workers, call `init_nccl`, run `nccl_sanity_check`
+//! (every rank `all_reduce`s `1u32` with Sum; expected total =
+//! world_size), shut down cleanly.
+
+#![cfg(feature = "cuda-integration")]
+
+use neuron::harness::tp::WorkerPool;
+
+const NEURON_BIN: &str = env!("CARGO_BIN_EXE_neuron");
+
+#[tokio::test]
+async fn test_init_and_sanity_check_two_ranks() {
+    let _ = tracing_subscriber::fmt()
+        .with_test_writer()
+        .with_env_filter("info,neuron=debug")
+        .try_init();
+
+    // 2 ranks: leader = rank 0 on device 0, worker = rank 1 on device 1.
+    let mut pool = WorkerPool::spawn(NEURON_BIN.as_ref(), 2, &[0, 1])
+        .await
+        .expect("spawn worker pool");
+
+    pool.ping_all().await.expect("pong all workers");
+
+    pool.init_nccl(0)
+        .await
+        .expect("init_nccl: NCCL handshake across all ranks");
+
+    pool.nccl_sanity_check()
+        .await
+        .expect("nccl_sanity_check: observed_sum == world_size on all ranks");
+
+    pool.shutdown().await.expect("clean shutdown");
+}

data/cortex-firewalld.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<service>
+  <short>cortex</short>
+  <description>Cortex — inference gateway for multi-node GPU clusters</description>
+  <port protocol="tcp" port="31313"/>
+  <port protocol="tcp" port="31314"/>
+</service>

data/cortex-sysusers.conf

@@ -0,0 +1,3 @@
+g cortex - -
+u cortex - "Cortex inference cluster" /var/lib/cortex /sbin/nologin
+m cortex cortex

data/neuron-firewalld.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<service>
+  <short>helexa-neuron</short>
+  <description>Neuron — per-node GPU discovery and harness daemon for cortex</description>
+  <port protocol="tcp" port="13131"/>
+</service>

data/neuron-sysusers.conf

@@ -0,0 +1,3 @@
+g neuron - -
+u neuron - "Neuron GPU node daemon" /var/lib/neuron /sbin/nologin
+m neuron neuron

data/neuron.service

@@ -5,11 +5,27 @@ Wants=network-online.target
 
 [Service]
 Type=simple
-ExecStart=/usr/bin/neuron --config /etc/cortex/neuron.toml
+ExecStart=/usr/bin/neuron --config /etc/neuron/neuron.toml
 Restart=on-failure
 RestartSec=5
-User=cortex
+User=neuron
-Group=cortex
+Group=neuron
+# /var/lib/neuron is the neuron user's $HOME — hf-hub writes its
+# default cache there (~/.cache/huggingface/hub). Without this directive
+# systemd doesn't create the directory and hf-hub downloads fail with
+# "fetch GGUF <file>: failed to create cache dir".
+StateDirectory=neuron
+StateDirectoryMode=0755
+# Loading default_models from neuron.toml happens before the HTTP
+# listener binds; large models can take many minutes to download and
+# materialise on first activation. systemd's default TimeoutStartSec
+# (90s) is far too short; allow 30 minutes.
+TimeoutStartSec=1800s
+# On stop, neuron drains in-flight requests then unloads every model
+# to release CUDA contexts cleanly. Allow generous time for big-model
+# unloads; systemd will SIGKILL after this bound.
+TimeoutStopSec=120s
+KillSignal=SIGTERM
 
 [Install]
 WantedBy=multi-user.target

helexa-neuron.spec

@@ -0,0 +1,101 @@
+Name:           helexa-neuron
+Version:        0.1.16
+Release:        1%{?dist}
+Summary:        Per-node GPU discovery and harness management daemon for cortex
+# Package name disambiguates from Fedora's existing "neuron" package
+# (NEURON neural simulation environment from Yale). Binary, systemd
+# unit, and system user are still called "neuron" for brevity.
+
+License:        GPL-3.0-or-later
+URL:            https://git.lair.cafe/helexa/cortex
+Source0:        %{name}-%{version}.tar.gz
+Source1:        %{name}-%{version}-vendor.tar.gz
+
+ExclusiveArch:  x86_64
+
+BuildRequires:  rust >= 1.85
+BuildRequires:  cargo
+BuildRequires:  gcc
+BuildRequires:  gcc-c++
+BuildRequires:  cmake
+BuildRequires:  perl-interpreter
+BuildRequires:  pkgconfig(openssl)
+BuildRequires:  systemd-rpm-macros
+
+Requires(pre):  shadow-utils
+Requires:       systemd
+Requires:       firewalld-filesystem
+
+# systemd-rpm-macros ships a unit dep generator that parses User=/Group=
+# from our .service file and emits Requires: user(neuron)/group(neuron).
+# rpm's sysusers provides-generator emits the unversioned form for groups
+# but only a versioned user(neuron) = <base64> for users with GECOS/home/
+# shell. Provide the unversioned user(neuron) explicitly so dnf can resolve
+# the auto-generated Requires. Without this, dnf5 silently filters the
+# package and reports "Nothing to do".
+Provides:       user(neuron)
+
+%description
+Neuron is a per-node daemon for cortex inference clusters. It discovers
+local GPU hardware via nvidia-smi, runs in-process inference via
+huggingface/candle, and exposes an HTTP API for model lifecycle
+management (load, unload, list, inference endpoint).
+
+%prep
+%autosetup
+tar xf %{SOURCE1}
+mkdir -p .cargo
+cat > .cargo/config.toml << 'EOF'
+[source.crates-io]
+replace-with = "vendored-sources"
+
+[source.vendored-sources]
+directory = "vendor"
+EOF
+
+%build
+cargo build --release -p neuron
+
+%install
+install -Dm755 target/release/neuron %{buildroot}%{_bindir}/neuron
+install -Dm644 data/neuron.service %{buildroot}%{_unitdir}/neuron.service
+install -Dm644 data/neuron-sysusers.conf %{buildroot}%{_sysusersdir}/neuron.conf
+install -Dm644 data/neuron-firewalld.xml %{buildroot}%{_prefix}/lib/firewalld/services/helexa-neuron.xml
+install -dm755 %{buildroot}%{_sysconfdir}/neuron
+install -Dm644 neuron.example.toml %{buildroot}%{_sysconfdir}/neuron/neuron.toml
+
+%pre
+%sysusers_create_compat %{_builddir}/%{name}-%{version}/data/neuron-sysusers.conf
+
+%post
+%systemd_post neuron.service
+
+%preun
+%systemd_preun neuron.service
+
+%postun
+%systemd_postun_with_restart neuron.service
+
+%files
+%license LICENSE
+%doc README.md
+%{_bindir}/neuron
+%{_unitdir}/neuron.service
+%{_sysusersdir}/neuron.conf
+%{_prefix}/lib/firewalld/services/helexa-neuron.xml
+%dir %{_sysconfdir}/neuron
+%config(noreplace) %{_sysconfdir}/neuron/neuron.toml
+
+%changelog
+* Thu Apr 16 2026 Gitea Actions <actions@git.lair.cafe> - 0.1.16-1
+- chore: ignore local deploy script
+- chore: move default ports out of common-collision ranges
+- ci: drop actions/cache for cargo registry and target
+
+* Thu Apr 16 2026 Gitea Actions <actions@git.lair.cafe> - 0.1.14-1
+- ci: publish both packages to a single helexa/helexa COPR project
+- fix(rpm): rename neuron package to helexa-neuron
+- ci: commit generated %changelog entries back to main
+
+* Wed Apr 15 2026 Rob Thijssen <grenade@rob.tn> - 0.1.0-1
+- Initial package

models.example.toml

@@ -6,7 +6,7 @@
 
 [[models]]
 id = "your-org/large-model"
-harness = "mistralrs"
+harness = "candle"
 quant = "Q4_K_M"
 vram_mb = 19000
 min_devices = 2
@@ -15,7 +15,7 @@ pinned_on = ["gpu-large"]
 
 [[models]]
 id = "your-org/medium-model"
-harness = "mistralrs"
+harness = "candle"
 quant = "Q6_K"
 vram_mb = 12000
 min_devices = 1
@@ -23,7 +23,7 @@ pinned_on = ["gpu-medium"]
 
 [[models]]
 id = "your-org/embedding-model"
-harness = "mistralrs"
+harness = "candle"
 quant = "Q8_0"
 vram_mb = 8000
 min_devices = 1

neuron.example.toml

@@ -1,16 +1,40 @@
 # neuron.example.toml — example configuration
 #
-# Copy to /etc/cortex/neuron.toml and adjust for your environment.
+# Copy to /etc/neuron/neuron.toml and adjust for your environment.
 #
 # Environment variable overrides use NEURON_ prefix with __ separators:
-#   NEURON_PORT=9090
+#   NEURON_PORT=13131
 
-port = 9090
+port = 13131
 
 # -- Harnesses ---------------------------------------------------------------
-# Each [[harnesses]] entry declares an inference engine managed by neuron.
+# Each [[harnesses]] entry enables an inference engine. Currently only
+# "candle" is supported — it runs in-process and uses huggingface/candle
+# for inference on local CUDA devices (or CPU when CUDA is unavailable).
 
 [[harnesses]]
-name = "mistralrs"
+name = "candle"
-endpoint = "http://localhost:8080"
+
-systemd_unit = "mistralrs.service"
+# -- Candle harness settings -------------------------------------------------
+# Optional tuning for the candle harness.
+
+[harness.candle]
+# HuggingFace cache directory for model weights. When unset, hf-hub's
+# default (~/.cache/huggingface) is used.
+# hf_cache = "/var/lib/neuron/hf-cache"
+
+# -- Default models ----------------------------------------------------------
+# Models listed here are loaded automatically when the neuron service
+# activates. Loading is sequential — a slow or failing entry doesn't
+# block the rest of the fleet, but it does push out the time before
+# neuron starts serving HTTP, so keep the list short. Operators can
+# load additional models on demand via POST /models/load.
+#
+# Make sure data/neuron.service's TimeoutStartSec is generous enough to
+# cover the slowest entry's first-time download + materialisation.
+
+# [[default_models]]
+# model_id = "Qwen/Qwen3-0.6B-GGUF"
+# harness = "candle"
+# quant = "Q4_K_M"
+# devices = [0]

neuron.spec

@@ -1,69 +0,0 @@
-Name:           neuron
-Version:        0.1.0
-Release:        1%{?dist}
-Summary:        Per-node GPU discovery and harness management daemon for cortex
-
-License:        GPL-3.0-or-later
-URL:            https://git.lair.cafe/helexa/cortex
-Source0:        %{name}-%{version}.tar.gz
-Source1:        %{name}-%{version}-vendor.tar.gz
-
-ExclusiveArch:  x86_64
-
-BuildRequires:  rust >= 1.85
-BuildRequires:  cargo
-BuildRequires:  gcc
-BuildRequires:  systemd-rpm-macros
-
-Requires(pre):  shadow-utils
-
-%description
-Neuron is a per-node daemon for cortex inference clusters. It discovers
-local GPU hardware via nvidia-smi, manages inference harnesses (mistral.rs,
-llama.cpp), and exposes an HTTP API for model lifecycle management.
-
-%prep
-%autosetup
-tar xf %{SOURCE1}
-mkdir -p .cargo
-cat > .cargo/config.toml << 'EOF'
-[source.crates-io]
-replace-with = "vendored-sources"
-
-[source.vendored-sources]
-directory = "vendor"
-EOF
-
-%build
-cargo build --release -p neuron
-
-%install
-install -Dm755 target/release/neuron %{buildroot}%{_bindir}/neuron
-install -Dm644 data/neuron.service %{buildroot}%{_unitdir}/neuron.service
-install -dm750 %{buildroot}%{_sysconfdir}/cortex
-install -Dm640 neuron.example.toml %{buildroot}%{_sysconfdir}/cortex/neuron.toml
-
-%pre
-getent group cortex >/dev/null || groupadd -r cortex
-getent passwd cortex >/dev/null || useradd -r -g cortex -d /var/lib/cortex -s /sbin/nologin cortex
-
-%post
-%systemd_post neuron.service
-
-%preun
-%systemd_preun neuron.service
-
-%postun
-%systemd_postun_with_restart neuron.service
-
-%files
-%license LICENSE
-%doc README.md
-%{_bindir}/neuron
-%{_unitdir}/neuron.service
-%dir %attr(750,root,cortex) %{_sysconfdir}/cortex
-%config(noreplace) %attr(640,root,cortex) %{_sysconfdir}/cortex/neuron.toml
-
-%changelog
-* Tue Apr 15 2026 Rob Thijssen <grenade@rob.tn> - 0.1.0-1
-- Initial package

rpm/cortex-prerelease.spec

@@ -0,0 +1,106 @@
+# Prebuilt-binary spec for cortex.
+#
+# Unlike cortex.spec (which builds from source via cargo), this spec
+# wraps a pre-built `cortex` binary produced by an upstream CI job and
+# packages it for rpm.lair.cafe. The %build phase is a no-op.
+#
+# Required defines at rpmbuild time:
+#   cortex_version    e.g. "0.1.16"
+#   cortex_prerelease e.g. "0.1.20260518140530.gitabcdef0"
+#                            ^^^^^^^^^^^^^^^^^^ ^^^^^^^^
+#                            commit time (sec)  commit sha
+#                           (used as Release; the timestamp prefix
+#                            keeps same-day builds strictly ordered.)
+
+%global _build_id_links none
+%global debug_package %{nil}
+%global __strip /usr/bin/true
+
+%{!?cortex_version: %global cortex_version 0.0.0}
+%if 0%{?cortex_prerelease:1}
+%global cortex_release %{cortex_prerelease}
+%else
+%global cortex_release 1
+%endif
+
+Name:           cortex
+Version:        %{cortex_version}
+Release:        %{cortex_release}%{?dist}
+Summary:        Inference gateway for multi-node GPU clusters (prebuilt)
+
+License:        GPL-3.0-or-later
+URL:            https://git.lair.cafe/helexa/cortex
+
+Source0:        cortex
+Source1:        cortex.service
+Source2:        cortex-sysusers.conf
+Source3:        cortex-firewalld.xml
+Source4:        cortex.example.toml
+Source5:        models.example.toml
+Source6:        LICENSE
+
+ExclusiveArch:  x86_64
+
+Requires(pre):  shadow-utils
+Requires:       systemd
+Requires:       firewalld-filesystem
+
+Provides:       user(cortex)
+
+%description
+Cortex is a Rust reverse-proxy that sits in front of multiple neuron
+inference daemons and presents a unified OpenAI and Anthropic
+compatible API surface.
+
+This package wraps a binary built upstream in CI; the source-build
+spec (cortex.spec) remains available for stable releases.
+
+%prep
+cp %{SOURCE0} ./cortex
+cp %{SOURCE1} .
+cp %{SOURCE2} .
+cp %{SOURCE3} .
+cp %{SOURCE4} .
+cp %{SOURCE5} .
+cp %{SOURCE6} .
+
+%build
+# Already built in the upstream CI build job.
+
+%install
+install -Dm755 cortex %{buildroot}%{_bindir}/cortex
+install -Dm644 cortex.service %{buildroot}%{_unitdir}/cortex.service
+install -Dm644 cortex-sysusers.conf %{buildroot}%{_sysusersdir}/cortex.conf
+install -Dm644 cortex-firewalld.xml %{buildroot}%{_prefix}/lib/firewalld/services/cortex.xml
+install -dm755 %{buildroot}%{_sysconfdir}/cortex
+install -Dm644 cortex.example.toml %{buildroot}%{_sysconfdir}/cortex/cortex.toml
+install -Dm644 models.example.toml %{buildroot}%{_sysconfdir}/cortex/models.toml
+
+%pre
+getent group cortex >/dev/null || groupadd -r cortex
+getent passwd cortex >/dev/null || \
+    useradd -r -g cortex -d /var/lib/cortex -s /sbin/nologin \
+        -c "Cortex inference gateway" cortex
+
+%post
+%systemd_post cortex.service
+
+%preun
+%systemd_preun cortex.service
+
+%postun
+%systemd_postun_with_restart cortex.service
+
+%files
+%license LICENSE
+%{_bindir}/cortex
+%{_unitdir}/cortex.service
+%{_sysusersdir}/cortex.conf
+%{_prefix}/lib/firewalld/services/cortex.xml
+%dir %{_sysconfdir}/cortex
+%config(noreplace) %{_sysconfdir}/cortex/cortex.toml
+%config(noreplace) %{_sysconfdir}/cortex/models.toml
+
+%changelog
+* Mon May 18 2026 Gitea Actions <actions@git.lair.cafe> - %{cortex_version}-%{cortex_release}
+- Prerelease build from upstream CI binary.

rpm/helexa-neuron-prerelease.spec

@@ -0,0 +1,126 @@
+# Prebuilt-binary spec for helexa-neuron flavoured by CUDA compute capability.
+#
+# Unlike helexa-neuron.spec (which builds from source via cargo), this
+# spec wraps a pre-built `neuron-{flavour}` binary produced by an
+# upstream CI job and packages it for rpm.lair.cafe. The %build phase
+# is a no-op.
+#
+# Required defines at rpmbuild time:
+#   neuron_version    e.g. "0.1.16"
+#   neuron_flavour    e.g. "ada", "blackwell"  — matches the CI build
+#                     matrix's compute_cap label.
+#   neuron_prerelease e.g. "0.1.20260518140530.gitabcdef0"
+#                            ^^^^^^^^^^^^^^^^^^ ^^^^^^^^
+#                            commit time (sec)  commit sha
+#                           (used as Release; the timestamp prefix
+#                            keeps same-day builds strictly ordered.)
+#
+# One flavour can be installed at a time on a given host; flavour
+# packages Conflict with each other.
+
+%global _build_id_links none
+%global debug_package %{nil}
+%global __strip /usr/bin/true
+
+%{!?neuron_version: %global neuron_version 0.0.0}
+%{!?neuron_flavour: %global neuron_flavour blackwell}
+%if 0%{?neuron_prerelease:1}
+%global neuron_release %{neuron_prerelease}
+%else
+%global neuron_release 1
+%endif
+
+Name:           helexa-neuron-%{neuron_flavour}
+Version:        %{neuron_version}
+Release:        %{neuron_release}%{?dist}
+Summary:        Per-node GPU inference daemon (candle, %{neuron_flavour} flavour)
+
+License:        GPL-3.0-or-later
+URL:            https://git.lair.cafe/helexa/cortex
+
+Source0:        neuron-%{neuron_flavour}
+Source1:        neuron.service
+Source2:        neuron-sysusers.conf
+Source3:        neuron-firewalld.xml
+Source4:        neuron.example.toml
+Source5:        LICENSE
+
+ExclusiveArch:  x86_64
+
+# Binary links against the CUDA runtime, cuDNN, NCCL, etc. Suppress
+# auto-detected exact soname deps — users may have CUDA from various
+# sources (rpmfusion, nvidia-direct) at different compatible versions;
+# a runtime dlopen failure surfaces a clearer error than rpm dep
+# resolution would.
+%global __requires_exclude ^lib(cuda|cudart|cudnn|cublas|cublasLt|curand|nvrtc|nccl)
+
+Requires(pre):  shadow-utils
+Requires:       systemd
+Requires:       firewalld-filesystem
+
+Provides:       helexa-neuron = %{neuron_version}-%{neuron_release}
+Provides:       user(neuron)
+
+# Mutual exclusion across flavours and the source-build variant.
+Conflicts:      helexa-neuron
+Conflicts:      helexa-neuron-ada
+Conflicts:      helexa-neuron-ampere
+Conflicts:      helexa-neuron-blackwell
+# (The Conflicts: with self is filtered by rpm at install time.)
+
+%description
+Neuron is the per-node daemon for cortex inference clusters. It
+discovers local GPU hardware via nvidia-smi, runs in-process
+inference via huggingface/candle, and exposes an HTTP API for model
+lifecycle management (load, unload, list, inference endpoint).
+
+This is the %{neuron_flavour} flavour, built for that CUDA compute
+capability. Install the flavour matching the GPUs on this host.
+
+%prep
+cp %{SOURCE0} ./neuron
+cp %{SOURCE1} .
+cp %{SOURCE2} .
+cp %{SOURCE3} .
+cp %{SOURCE4} .
+cp %{SOURCE5} .
+
+%build
+# Already built in the upstream CI build job (with --features cuda).
+
+%install
+install -Dm755 neuron %{buildroot}%{_bindir}/neuron
+install -Dm644 neuron.service %{buildroot}%{_unitdir}/neuron.service
+install -Dm644 neuron-sysusers.conf %{buildroot}%{_sysusersdir}/neuron.conf
+install -Dm644 neuron-firewalld.xml %{buildroot}%{_prefix}/lib/firewalld/services/helexa-neuron.xml
+install -dm755 %{buildroot}%{_sysconfdir}/neuron
+install -Dm644 neuron.example.toml %{buildroot}%{_sysconfdir}/neuron/neuron.toml
+
+%pre
+getent group neuron >/dev/null || groupadd -r neuron
+getent passwd neuron >/dev/null || \
+    useradd -r -g neuron -d /var/lib/neuron -s /sbin/nologin \
+        -G video,render \
+        -c "Neuron GPU node daemon" neuron
+
+%post
+%systemd_post neuron.service
+
+%preun
+%systemd_preun neuron.service
+
+%postun
+%systemd_postun_with_restart neuron.service
+
+%files
+%license LICENSE
+%{_bindir}/neuron
+%{_unitdir}/neuron.service
+%{_sysusersdir}/neuron.conf
+%{_prefix}/lib/firewalld/services/helexa-neuron.xml
+%dir %{_sysconfdir}/neuron
+%config(noreplace) %{_sysconfdir}/neuron/neuron.toml
+
+%changelog
+* Mon May 18 2026 Gitea Actions <actions@git.lair.cafe> - %{neuron_version}-%{neuron_release}
+- Prerelease build from upstream CI binary (%{neuron_flavour} flavour).

rpm/rpmmacros

@@ -0,0 +1 @@
+%_openpgp_sign_id @GPG_NAME@

script/deploy.sh

@@ -0,0 +1,256 @@
+#!/bin/env bash
+#
+# Rolling deploy across the helexa fleet, driven by asset/manifest.yml.
+# Installs / upgrades cortex on the gateway host and the appropriate
+# helexa-neuron-<flavour> package on each neuron host, then restarts
+# their services.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+MANIFEST="${REPO_DIR}/asset/manifest.yml"
+
+if [[ ! -f "${MANIFEST}" ]]; then
+    echo "fatal: manifest not found at ${MANIFEST}" >&2
+    exit 1
+fi
+
+# Parse the manifest with yq. NOTE: this expects the pip-installed yq
+# (a jq wrapper using jq syntax) — `pip install yq`. The Fedora rpm
+# `yq` is mikefarah/yq and uses different (yaml-native) syntax; if a
+# host has that one instead these queries will fail.
+cortex_host=$(yq -r '.cortex.host' "${MANIFEST}")
+
+# Emit one TAB-separated 'host\tflavour' line per neuron.
+mapfile -t neuron_entries < <(
+    yq -r '.neurons[] | .host + "\t" + .flavour' "${MANIFEST}"
+)
+
+# Return the installed package's "version-release" string, or
+# "(not installed)" when rpm reports the package as absent. Capture
+# rpm's output into a variable so its "package X is not installed"
+# stdout message (rpm writes that to stdout, not stderr, when -q fails)
+# doesn't leak into the result.
+installed_nvr() {
+    local host="$1" pkg="$2"
+    local nvr
+    if nvr=$(ssh "${host}" "rpm -q --qf '%{version}-%{release}' ${pkg} 2>/dev/null"); then
+        echo "${nvr}"
+    else
+        echo "(not installed)"
+    fi
+}
+
+# Ensure the rpm.lair.cafe unstable repo is configured AND enabled on
+# the remote host.
+#
+# The upstream .repo file at https://rpm.lair.cafe/lair-cafe-unstable.repo
+# ships with `enabled=0` so a host that just fetched it won't start
+# pulling unstable packages by accident. We have to explicitly flip
+# enabled=1 via `dnf config-manager setopt`. Both addrepo and setopt
+# are idempotent.
+#
+# Non-fatal — if either step fails the subsequent `dnf install` will
+# surface a clearer diagnostic on its own.
+ensure_lair_repo() {
+    local host="$1"
+    if ! ssh "${host}" "test -f /etc/yum.repos.d/lair-cafe-unstable.repo" 2>/dev/null; then
+        echo "[${host}] adding rpm.lair.cafe unstable repo"
+        if ! ssh "${host}" sudo dnf config-manager addrepo \
+            --from-repofile=https://rpm.lair.cafe/lair-cafe-unstable.repo \
+            >/dev/null 2>&1; then
+            echo "[${host}] WARNING: failed to add lair.cafe repo file (proceeding anyway)"
+            return 0
+        fi
+    fi
+    # The .repo file ships enabled=0; flip it on. Cheap, idempotent.
+    if ! ssh "${host}" sudo dnf config-manager setopt \
+        lair-cafe-unstable.enabled=1 >/dev/null 2>&1; then
+        echo "[${host}] WARNING: failed to enable lair-cafe-unstable (proceeding anyway)"
+    fi
+}
+
+# Ensure libcudnn.so.9 is resolvable on the remote host so the
+# neuron binary (built with --features cudnn) doesn't fail at startup
+# with "cannot open shared object file: No such file or directory".
+#
+# Probes ldconfig first — if cuDNN was installed manually (.tar/.run
+# install), it'll be cached by ldconfig and we don't touch it.
+# Otherwise adds NVIDIA's RHEL9 CUDA repo (the Fedora 43 CUDA repo
+# doesn't ship cuDNN packages — only the RHEL9 one does) and installs
+# libcudnn9-cuda-13.
+ensure_cudnn_runtime() {
+    local host="$1"
+    if ssh "${host}" "ldconfig -p | grep -q libcudnn.so.9" 2>/dev/null; then
+        return 0
+    fi
+    echo "[${host}] installing cuDNN runtime"
+    if ! ssh "${host}" "test -f /etc/yum.repos.d/cuda-rhel9-x86_64.repo" 2>/dev/null; then
+        if ! ssh "${host}" sudo dnf config-manager addrepo \
+            --from-repofile=https://developer.download.nvidia.com/compute/cuda/repos/rhel9/x86_64/cuda-rhel9.repo \
+            >/dev/null 2>&1; then
+            echo "[${host}] WARNING: failed to add rhel9 CUDA repo (proceeding anyway)"
+        fi
+    fi
+    if ! ssh "${host}" sudo dnf install -y libcudnn9-cuda-13 >/dev/null 2>&1; then
+        echo "[${host}] WARNING: failed to install libcudnn9-cuda-13"
+        echo "[${host}]   neuron may fail to start; install cuDNN manually if so"
+    fi
+}
+
+# True when the named package needs to be installed or upgraded on the
+# remote host — either it's not present, or a newer version exists in
+# the repo. False only when the installed version is current.
+#
+# `dnf check-update <pkg>` returns 0 when the package isn't installed
+# at all (there's nothing to update), so we have to probe with rpm -q
+# first to distinguish "absent" from "current". Other dnf failures
+# collapse into "needs update" so the subsequent install step surfaces
+# the real diagnostic rather than this check swallowing it.
+needs_update() {
+    local host="$1" pkg="$2"
+    # Not installed → needs work.
+    if ! ssh "${host}" "rpm -q ${pkg}" >/dev/null 2>&1; then
+        return 0
+    fi
+    # Installed; ask dnf whether the repo has something newer.
+    if ssh "${host}" sudo dnf check-update --refresh -q "${pkg}" >/dev/null 2>&1; then
+        return 1
+    else
+        return 0
+    fi
+}
+
+# True if the named package is currently installed on the remote host.
+# Used to decide between `dnf install` (fresh) and `dnf upgrade` (stale):
+# dnf5's `install` is a no-op when the package is already present at
+# any version — it does NOT auto-upgrade to the latest available — so
+# the wrong command silently leaves the host on an old build.
+is_installed() {
+    local host="$1" pkg="$2"
+    ssh "${host}" "rpm -q ${pkg}" >/dev/null 2>&1
+}
+
+# Install or upgrade the named package on the remote, picking the
+# right dnf verb based on the installed-or-not state. Returns 0 with
+# dnf's combined stdout/stderr captured in __DNF_OUTPUT__ on success,
+# and 1 with the same captured output on failure.
+__DNF_OUTPUT__=""
+install_or_upgrade() {
+    local host="$1" pkg="$2"
+    local cmd
+    if is_installed "${host}" "${pkg}"; then
+        cmd="upgrade"
+    else
+        cmd="install"
+    fi
+    if __DNF_OUTPUT__=$(
+        ssh "${host}" sudo dnf "${cmd}" --refresh --allowerasing -y "${pkg}" 2>&1
+    ); then
+        return 0
+    else
+        return 1
+    fi
+}
+
+# ---------------------------------------------------------------------------
+# cortex (gateway)
+# ---------------------------------------------------------------------------
+
+ensure_lair_repo "${cortex_host}"
+cortex_nvr=$(installed_nvr "${cortex_host}" cortex)
+if needs_update "${cortex_host}" cortex; then
+    echo "[${cortex_host}] cortex update available (current: ${cortex_nvr})"
+    # Stop the service only if the unit file exists — fresh installs
+    # don't have it, and `systemctl stop` on a missing unit returns
+    # non-zero, which would otherwise short-circuit the install branch
+    # under set -e.
+    if ssh "${cortex_host}" "[ ! -f /usr/lib/systemd/system/cortex.service ] || sudo systemctl stop cortex.service"; then
+        echo "[${cortex_host}] stopped cortex service"
+        if install_or_upgrade "${cortex_host}" cortex; then
+            cortex_nvr=$(installed_nvr "${cortex_host}" cortex)
+            echo "[${cortex_host}] installed/upgraded cortex to ${cortex_nvr}"
+        else
+            echo "[${cortex_host}] failed to install/upgrade cortex:"
+            echo "${__DNF_OUTPUT__}" | sed "s/^/[${cortex_host}]   /"
+        fi
+    else
+        echo "[${cortex_host}] failed to stop cortex service"
+    fi
+else
+    echo "[${cortex_host}] cortex is up to date (${cortex_nvr})"
+    ssh "${cortex_host}" sudo systemctl stop cortex.service || true
+fi
+
+# Sync cortex.toml whether the package was upgraded or not — the config
+# can change without a package bump.
+if rsync \
+    --archive \
+    --compress \
+    --rsync-path 'sudo rsync' \
+    --chown root:root \
+    --chmod 644 \
+    "${REPO_DIR}/cortex.toml" \
+    "${cortex_host}:/etc/cortex/cortex.toml"; then
+    echo "[${cortex_host}] sync'd cortex.toml"
+else
+    echo "[${cortex_host}] failed to sync cortex.toml"
+fi
+
+ssh "${cortex_host}" sudo systemctl daemon-reload
+if ssh "${cortex_host}" systemctl is-active --quiet cortex.service; then
+    echo "[${cortex_host}] cortex service is active"
+elif ssh "${cortex_host}" sudo systemctl start cortex.service; then
+    echo "[${cortex_host}] started cortex service"
+else
+    echo "[${cortex_host}] failed to start cortex service"
+fi
+
+# ---------------------------------------------------------------------------
+# neuron (per-host, flavour from manifest)
+# ---------------------------------------------------------------------------
+
+for entry in "${neuron_entries[@]}"; do
+    IFS=$'\t' read -r neuron_host neuron_flavour <<< "${entry}"
+    package="helexa-neuron-${neuron_flavour}"
+
+    ensure_lair_repo "${neuron_host}"
+    ensure_cudnn_runtime "${neuron_host}"
+    neuron_nvr=$(installed_nvr "${neuron_host}" "${package}")
+    if needs_update "${neuron_host}" "${package}"; then
+        echo "[${neuron_host}] ${package} update available (current: ${neuron_nvr})"
+        if ssh "${neuron_host}" "[ ! -f /usr/lib/systemd/system/neuron.service ] || sudo systemctl stop neuron.service"; then
+            echo "[${neuron_host}] stopped neuron service"
+            # --allowerasing lets dnf swap out a previously-installed
+            # bare helexa-neuron or a different flavour without manual
+            # intervention. The Conflicts: clauses in the spec ensure
+            # only one flavour is ever resident.
+            if install_or_upgrade "${neuron_host}" "${package}"; then
+                neuron_nvr=$(installed_nvr "${neuron_host}" "${package}")
+                echo "[${neuron_host}] installed/upgraded ${package} to ${neuron_nvr}"
+                # Ensure firewalld allows neuron port
+                ssh "${neuron_host}" "sudo firewall-cmd --query-service=helexa-neuron --quiet 2>/dev/null || sudo firewall-cmd --add-service=helexa-neuron --permanent && sudo firewall-cmd --reload" 2>/dev/null || true
+                if ssh "${neuron_host}" "sudo systemctl daemon-reload && sudo systemctl start neuron.service"; then
+                    echo "[${neuron_host}] started neuron service"
+                else
+                    echo "[${neuron_host}] failed to start neuron service"
+                fi
+            else
+                echo "[${neuron_host}] failed to install ${package}:"
+                echo "${__DNF_OUTPUT__}" | sed "s/^/[${neuron_host}]   /"
+            fi
+        else
+            echo "[${neuron_host}] failed to stop neuron service"
+        fi
+    else
+        echo "[${neuron_host}] ${package} is up to date (${neuron_nvr})"
+        if ssh "${neuron_host}" systemctl is-active --quiet neuron.service; then
+            echo "[${neuron_host}] neuron service is active"
+        elif ssh "${neuron_host}" sudo systemctl start neuron.service; then
+            echo "[${neuron_host}] started neuron service"
+        else
+            echo "[${neuron_host}] failed to start neuron service"
+        fi
+    fi
+done

script/generate-packages-json.py

@@ -0,0 +1,154 @@
+#!/usr/bin/env python3
+"""Parse RPM repodata and emit a packages.json manifest for the UI."""
+
+import argparse
+import gzip
+import json
+import os
+import subprocess
+import sys
+import xml.etree.ElementTree as ET
+from datetime import datetime, timezone
+
+RPM_NS = "http://linux.duke.edu/metadata/common"
+OTHER_NS = "http://linux.duke.edu/metadata/other"
+REPO_NS = "http://linux.duke.edu/metadata/repo"
+
+
+def find_repodata_file(repodata_dir, data_type):
+    """Read repomd.xml and return the path to a specific data type's file."""
+    repomd_path = os.path.join(repodata_dir, "repomd.xml")
+    tree = ET.parse(repomd_path)
+    root = tree.getroot()
+
+    for data in root.findall(f"{{{REPO_NS}}}data"):
+        if data.get("type") == data_type:
+            location = data.find(f"{{{REPO_NS}}}location")
+            if location is not None:
+                href = location.get("href", "")
+                return os.path.join(os.path.dirname(repodata_dir), href)
+
+    return None
+
+
+def open_compressed(path):
+    """Open a gzip or zstd compressed file for reading."""
+    if path.endswith(".zst"):
+        result = subprocess.run(
+            ["zstdcat", path], capture_output=True, check=True
+        )
+        import io
+        return io.BytesIO(result.stdout)
+    else:
+        return gzip.open(path, "rb")
+
+
+def parse_primary(repodata_dir):
+    """Parse primary.xml.{gz,zst} and return package metadata."""
+    path = find_repodata_file(repodata_dir, "primary")
+    if not path:
+        print("error: primary metadata not found in repomd.xml", file=sys.stderr)
+        sys.exit(1)
+
+    packages = {}
+    with open_compressed(path) as f:
+        tree = ET.parse(f)
+
+    for pkg in tree.getroot().findall(f"{{{RPM_NS}}}package"):
+        if pkg.get("type") != "rpm":
+            continue
+
+        name = pkg.findtext(f"{{{RPM_NS}}}name", "")
+        version_el = pkg.find(f"{{{RPM_NS}}}version")
+        ver = version_el.get("ver", "") if version_el is not None else ""
+        rel = version_el.get("rel", "") if version_el is not None else ""
+        arch = pkg.findtext(f"{{{RPM_NS}}}arch", "")
+
+        size_el = pkg.find(f"{{{RPM_NS}}}size")
+        size = int(size_el.get("package", "0")) if size_el is not None else 0
+
+        time_el = pkg.find(f"{{{RPM_NS}}}time")
+        build_time = int(time_el.get("build", "0")) if time_el is not None else 0
+
+        location_el = pkg.find(f"{{{RPM_NS}}}location")
+        filename = os.path.basename(location_el.get("href", "")) if location_el is not None else ""
+
+        key = f"{name}-{ver}-{rel}"
+        packages[key] = {
+            "name": name,
+            "version": ver,
+            "release": rel,
+            "arch": arch,
+            "summary": pkg.findtext(f"{{{RPM_NS}}}summary", ""),
+            "size": size,
+            "buildTime": build_time,
+            "rpmFilename": filename,
+            "changelog": [],
+        }
+
+    return packages
+
+
+def parse_other(repodata_dir, packages):
+    """Parse other.xml.gz and attach changelog entries to packages."""
+    path = find_repodata_file(repodata_dir, "other")
+    if not path:
+        return
+
+    with open_compressed(path) as f:
+        tree = ET.parse(f)
+
+    for pkg in tree.getroot().findall(f"{{{OTHER_NS}}}package"):
+        name = pkg.get("name", "")
+        version_el = pkg.find(f"{{{OTHER_NS}}}version")
+        ver = version_el.get("ver", "") if version_el is not None else ""
+        rel = version_el.get("rel", "") if version_el is not None else ""
+        key = f"{name}-{ver}-{rel}"
+
+        if key not in packages:
+            continue
+
+        for entry in pkg.findall(f"{{{OTHER_NS}}}changelog"):
+            packages[key]["changelog"].append({
+                "author": entry.get("author", ""),
+                "date": int(entry.get("date", "0")),
+                "text": (entry.text or "").strip(),
+            })
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--repodata-dir",
+        required=True,
+        help="path to the repodata/ directory",
+    )
+    parser.add_argument(
+        "--output",
+        required=True,
+        help="path to write packages.json",
+    )
+    parser.add_argument(
+        "--base-url",
+        required=True,
+        help="public base URL for the repo (e.g. https://rpm.lair.cafe/fedora/43/x86_64)",
+    )
+    args = parser.parse_args()
+
+    packages = parse_primary(args.repodata_dir)
+    parse_other(args.repodata_dir, packages)
+
+    manifest = {
+        "generated": datetime.now(timezone.utc).isoformat(),
+        "baseUrl": args.base_url,
+        "packages": list(packages.values()),
+    }
+
+    with open(args.output, "w") as f:
+        json.dump(manifest, f, indent=2)
+
+    print(f"wrote {len(packages)} packages to {args.output}")
+
+
+if __name__ == "__main__":
+    main()

script/validate-neuron.sh

@@ -0,0 +1,162 @@
+#!/bin/env bash
+#
+# End-to-end smoke test for a deployed neuron.
+#
+# Confirms the daemon is reachable, loads a small public Qwen3 GGUF,
+# fires a reasoning probe at /v1/chat/completions, and prints the
+# answer. Used to validate the candle harness on a real GPU host
+# before trusting it for production traffic, and as a regression test
+# after pushing new neuron builds.
+#
+# Usage:
+#   script/validate-neuron.sh [host] [model_id] [quant]
+#
+# Defaults:
+#   host     = beast.hanzalova.internal
+#   model_id = unsloth/Qwen3-0.6B-GGUF  (official Qwen3-*-GGUF repos
+#              ship Q8_0 only; unsloth's mirror ships the full Q-spectrum
+#              including Q4_K_M)
+#   quant    = Q4_K_M
+
+set -euo pipefail
+
+HOST="${1:-beast.hanzalova.internal}"
+MODEL_ID="${2:-unsloth/Qwen3-0.6B-GGUF}"
+# `${3-Q4_K_M}` (no colon) only uses the default when the arg is
+# UNSET — passing an explicit empty string drives the dense path.
+QUANT="${3-Q4_K_M}"
+PORT="${NEURON_PORT:-13131}"
+BASE="http://${HOST}:${PORT}"
+
+# Reasoning probe — concrete, low-temperature answer that small models
+# can still get right. "Paris" is a strong signal of basic competence
+# beyond gibberish.
+PROBE_PROMPT='What is the capital of Georgia (Caucasus)? Respond with the city name only, no punctuation.'
+EXPECT_SUBSTR='Tbilisi'
+# Qwen3 prepends <think>...</think> reasoning before the answer when the
+# chat template enables thinking mode, which eats most of a small token
+# budget. 256 leaves enough room for thinking + final answer.
+MAX_TOKENS=256
+
+# /models/load is synchronous — neuron blocks the response until the
+# hf-hub download + GGUF parse + tensor materialisation is done. A
+# fresh 0.6B-Q4_K_M is ~400 MB; on a slow link or cold cache that's
+# easily a minute. Pick a generous ceiling.
+LOAD_TIMEOUT=600
+INFER_TIMEOUT=120
+
+# Status messages go to stderr so command substitutions like
+# `raw=$(run_probe)` capture only the function's intended return value
+# (an HTTP body), not the progress chatter.
+say() { printf '[%s] %s\n' "${HOST}" "$*" >&2; }
+die() { say "FAIL: $*"; exit 1; }
+
+probe_health() {
+    curl --silent --fail --max-time 5 "${BASE}/health" >/dev/null \
+        || die "neuron not reachable at ${BASE}/health"
+}
+
+list_loaded_ids() {
+    # The manifest is YAML and uses yq; HTTP responses are JSON and use
+    # jq directly. pip-yq parses input as YAML by default, which trips
+    # on JSON content that happens to look like YAML aliases (chatcmpl
+    # ids, escaped quotes inside `<think>...</think>` blocks, etc.).
+    curl --silent --fail "${BASE}/models" | jq -r '.[].id'
+}
+
+is_loaded() {
+    list_loaded_ids 2>/dev/null | grep -Fxq "${MODEL_ID}"
+}
+
+trigger_load() {
+    say "POST /models/load ${MODEL_ID} (quant=${QUANT:-<dense>}, device=[0])"
+    say "  (synchronous; may take a minute on first run while HF downloads)"
+    # Build the payload via jq so the optional `quant` field is
+    # omitted entirely when empty — that's the signal to the harness
+    # to take the dense safetensors load path rather than GGUF.
+    local payload
+    if [[ -z "${QUANT}" ]]; then
+        payload=$(jq -n -c \
+            --arg id "${MODEL_ID}" \
+            '{model_id: $id, harness: "candle", devices: [0]}')
+    else
+        payload=$(jq -n -c \
+            --arg id "${MODEL_ID}" \
+            --arg q "${QUANT}" \
+            '{model_id: $id, harness: "candle", quant: $q, devices: [0]}')
+    fi
+    # --write-out captures the response code on a separate line so we
+    # can surface a real diagnostic instead of relying on --fail.
+    local resp http_code body
+    resp=$(curl --silent --show-error --max-time "${LOAD_TIMEOUT}" \
+        --write-out '\n__HTTP__%{http_code}' \
+        -X POST "${BASE}/models/load" \
+        -H 'content-type: application/json' \
+        --data "${payload}") || die "curl /models/load failed: $?"
+    http_code=$(echo "${resp}" | grep -oP '(?<=__HTTP__)\d+$' | tail -1)
+    body=$(echo "${resp}" | sed '$ s/__HTTP__.*$//')
+    if [[ "${http_code}" != "200" ]]; then
+        die "load returned HTTP ${http_code}: ${body}"
+    fi
+    say "load returned ${http_code}: ${body}"
+}
+
+run_probe() {
+    say "POST /v1/chat/completions (probe: ${PROBE_PROMPT})"
+    local payload
+    payload=$(jq -n -c \
+        --arg model "${MODEL_ID}" \
+        --arg content "${PROBE_PROMPT}" \
+        --argjson tokens "${MAX_TOKENS}" \
+        '{
+            model: $model,
+            messages: [{role: "user", content: $content}],
+            temperature: 0.1,
+            max_tokens: $tokens
+        }')
+    local resp http_code body
+    resp=$(curl --silent --show-error --max-time "${INFER_TIMEOUT}" \
+        --write-out '\n__HTTP__%{http_code}' \
+        -X POST "${BASE}/v1/chat/completions" \
+        -H 'content-type: application/json' \
+        --data "${payload}") || die "curl /v1/chat/completions failed: $?"
+    http_code=$(echo "${resp}" | grep -oP '(?<=__HTTP__)\d+$' | tail -1)
+    body=$(echo "${resp}" | sed '$ s/__HTTP__.*$//')
+    if [[ "${http_code}" != "200" ]]; then
+        die "inference returned HTTP ${http_code}: ${body}"
+    fi
+    echo "${body}"
+}
+
+say "validating neuron at ${BASE}"
+probe_health
+say "/health OK"
+
+if is_loaded; then
+    say "${MODEL_ID} already loaded"
+else
+    trigger_load
+fi
+
+raw=$(run_probe)
+echo "---"
+# Dump the raw JSON. Don't pipe through `yq -r '.'` — yq's default
+# YAML output mode chokes on JSON strings that contain `<` (and the
+# `<think>` markers Qwen3 emits during reasoning are a perfect
+# example). The targeted `yq -r '.path'` calls below work fine
+# because jq's path filter mode bypasses the YAML re-emit.
+echo "${raw}"
+echo "---"
+
+content=$(echo "${raw}" | jq -r '.choices[0].message.content // empty')
+if [[ -z "${content}" ]]; then
+    die "no content in chat completion response"
+fi
+say "assistant said: ${content}"
+
+if echo "${content}" | grep -qiF "${EXPECT_SUBSTR}"; then
+    say "PASS — response contains expected substring '${EXPECT_SUBSTR}'"
+    exit 0
+else
+    die "response did not contain '${EXPECT_SUBSTR}'"
+fi