Annotate nextest failures in CI

Capture nextest output in rust-ci and emit parsed FAIL/LEAK lines as annotations and step-summary text when tests fail.

Also record the isolated Linux test failure on b6e18d2e8 in the flaky-test ledger.

Co-authored-by: Codex <noreply@openai.com>

.github/workflows/rust-ci.yml

@@ -598,7 +598,42 @@ jobs:
 
       - name: tests
         id: test
-        run: cargo nextest run --all-features --no-fail-fast --target ${{ matrix.target }} --cargo-profile ci-test --timings
+        shell: bash
+        run: |
+          set -euo pipefail
+          log_file="$(mktemp)"
+          trap 'rm -f "$log_file"' EXIT
+
+          set +e
+          cargo nextest run --all-features --no-fail-fast --target ${{ matrix.target }} --cargo-profile ci-test --timings 2>&1 | tee "$log_file"
+          status=${PIPESTATUS[0]}
+          set -e
+
+          if [[ $status -ne 0 ]]; then
+            summary_lines="$(grep -E '^(FAIL|LEAK)([[:space:]]|$)' "$log_file" || true)"
+            if [[ -n "$summary_lines" ]]; then
+              {
+                echo "### nextest failure summary"
+                echo '```text'
+                printf '%s\n' "$summary_lines"
+                echo '```'
+              } >> "$GITHUB_STEP_SUMMARY"
+
+              while IFS= read -r line; do
+                echo "::error::$line"
+              done <<< "$summary_lines"
+            else
+              {
+                echo "### nextest failure tail"
+                echo '```text'
+                tail -n 200 "$log_file"
+                echo '```'
+              } >> "$GITHUB_STEP_SUMMARY"
+              echo "::error::nextest failed without a parsable FAIL/LEAK line; inspect the tail in the step summary"
+            fi
+          fi
+
+          exit $status
         env:
           RUST_BACKTRACE: 1
           NEXTEST_STATUS_LEVEL: leak