ci: share common workflow setup (#31318)

## Why

CI jobs repeat common bootstrap steps, which makes it harder to keep
Bazel and Cargo lanes aligned. Centralizing the lightweight setup gives
us one place for future runner-wide optimizations without adding Rust
toolchain or component installation to the Windows Bazel long poles.

## What

- add zero-input `.github/actions/setup-ci` to set Cargo's git
transport, install DotSlash and `just`, expose DotSlash from stable PATH
locations, and enable Windows Git long paths
- have `setup-bazel-ci` compose the common setup, then remove its
DotSlash/test-prerequisite plumbing
- migrate Bazel, Cargo CI, V8 canary, repo checks, nextest, and Windows
release call sites while keeping Rust toolchain and MSVC setup explicit
- preserve the existing nextest Dev Drive setup unchanged

## Validation

- `just test-github-scripts` (30 tests)
- parsed workflow and composite-action YAML with `yq`

.github/actions/prepare-bazel-ci/action.yml

@@ -7,10 +7,6 @@ inputs:
   cache-scope:
     description: Logical namespace used to keep concurrent Bazel jobs from reserving the same repository cache key.
     required: true
-  install-test-prereqs:
-    description: Install DotSlash for Bazel-backed test jobs.
-    required: false
-    default: "false"
 outputs:
   repository-cache-path:
     description: Filesystem path used for the Bazel repository cache.
@@ -30,7 +26,6 @@ runs:
       uses: ./.github/actions/setup-bazel-ci
       with:
         target: ${{ inputs.target }}
-        install-test-prereqs: ${{ inputs.install-test-prereqs }}
 
     - name: Compute bazel repository cache key
       id: cache_bazel_repository_key

.github/actions/run-argument-comment-lint/action.yml

@@ -16,7 +16,6 @@ runs:
     - uses: ./.github/actions/setup-bazel-ci
       with:
         target: ${{ inputs.target }}
-        install-test-prereqs: true
 
     - name: Install Linux sandbox build dependencies
       if: ${{ runner.os == 'Linux' }}

.github/actions/setup-bazel-ci/action.yml

@@ -1,13 +1,9 @@
 name: setup-bazel-ci
-description: Prepare a Bazel CI runner with shared caches and optional test prerequisites.
+description: Prepare a Bazel CI runner with shared caches.
 inputs:
   target:
     description: Target triple used for cache namespacing.
     required: true
-  install-test-prereqs:
-    description: Install DotSlash for Bazel-backed test jobs.
-    required: false
-    default: "false"
 outputs:
   repository-cache-path:
     description: Filesystem path used for the Bazel repository cache.
@@ -16,21 +12,7 @@ outputs:
 runs:
   using: composite
   steps:
-    # Some integration tests rely on DotSlash being installed.
-    # See https://github.com/openai/codex/pull/7617.
-    - name: Install DotSlash
-      if: inputs.install-test-prereqs == 'true'
-      uses: facebook/install-dotslash@1e4e7b3e07eaca387acb98f1d4720e0bee8dbb6a # v2
-
-    - name: Make DotSlash available in PATH (Unix)
-      if: inputs.install-test-prereqs == 'true' && runner.os != 'Windows'
-      shell: bash
-      run: cp "$(which dotslash)" /usr/local/bin
-
-    - name: Make DotSlash available in PATH (Windows)
-      if: inputs.install-test-prereqs == 'true' && runner.os == 'Windows'
-      shell: pwsh
-      run: Copy-Item (Get-Command dotslash).Source -Destination "$env:LOCALAPPDATA\Microsoft\WindowsApps\dotslash.exe"
+    - uses: ./.github/actions/setup-ci
 
     - name: Set up Bazel
       uses: bazel-contrib/setup-bazel@c5acdfb288317d0b5c0bbd7a396a3dc868bb0f86 # 0.19.0
@@ -124,8 +106,3 @@ runs:
       if: runner.os == 'Windows'
       shell: pwsh
       run: ./.github/scripts/compute-bazel-windows-path.ps1
-
-    - name: Enable Git long paths (Windows)
-      if: runner.os == 'Windows'
-      shell: pwsh
-      run: git config --global core.longpaths true

.github/actions/setup-ci/action.yml

@@ -0,0 +1,39 @@
+name: setup-ci
+description: Prepare common tools and environment shared by CI jobs.
+
+runs:
+  using: composite
+  steps:
+    - name: Prefer the Git CLI for Cargo git dependencies
+      shell: bash
+      run: echo "CARGO_NET_GIT_FETCH_WITH_CLI=true" >> "$GITHUB_ENV"
+
+    - name: Install DotSlash
+      uses: facebook/install-dotslash@1e4e7b3e07eaca387acb98f1d4720e0bee8dbb6a # v2
+
+    - name: Install just
+      uses: taiki-e/install-action@44c6d64aa62cd779e873306675c7a58e86d6d532 # v2.62.49
+      with:
+        tool: just@1.51.0
+
+    # Some integration tests spawn DotSlash from a stable system path rather
+    # than inheriting the action-local PATH entry.
+    - name: Make DotSlash available in PATH (Unix)
+      if: runner.os != 'Windows'
+      shell: bash
+      run: |
+        if [[ -w /usr/local/bin ]]; then
+          cp "$(which dotslash)" /usr/local/bin
+        else
+          sudo cp "$(which dotslash)" /usr/local/bin
+        fi
+
+    - name: Make DotSlash available in PATH (Windows)
+      if: runner.os == 'Windows'
+      shell: pwsh
+      run: Copy-Item (Get-Command dotslash).Source -Destination "$env:LOCALAPPDATA\Microsoft\WindowsApps\dotslash.exe"
+
+    - name: Enable Git long paths (Windows)
+      if: runner.os == 'Windows'
+      shell: pwsh
+      run: git config --global core.longpaths true