ci(arm64): add ADVISORY Mac arm64 fast-check lane (Pilot ②, internal#418 relief)

Additive, non-gating lane that offloads the genuinely
container-independent fast checks (Go build/vet/golangci-lint,
shellcheck, Python compile/ruff) onto the Mac arm64 self-hosted
runner so developers get a fast arm64 signal without adding load to
the queue-contended amd64 pool (internal#418).

PRIME DIRECTIVE — required-check contract is provably preserved:
ci.yml is byte-for-byte untouched; the `CI / all-required` sentinel
and its 5 polled contexts are unchanged; the emitted context
`ci-arm64-advisory / fast-checks (pull_request)` is NOT added to
branch_protections.status_check_contexts (DB-verified pb 86/75 stay
exactly the 2 existing contexts), NOT added to audit-force-merge.yml
REQUIRED_CHECKS, NOT in the sentinel's hardcoded required[] list.
Branch protection never waits on this context, so a missing/offline
Mac runner cannot hang any merge. `continue-on-error: true` +
`github.event_name` if-gate keep it advisory and out of
ci-required-drift F1. Rollback = delete this one file (no BP/ci.yml/
REQUIRED_CHECKS edit was made to roll forward).

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

.gitea/workflows/ci-arm64-advisory.yml

@@ -0,0 +1,186 @@
+# ci-arm64-advisory — Mac arm64 self-hosted ADVISORY fast-check lane.
+#
+# === WHY ===
+#
+# The amd64 Gitea runner pool (molecule-runner-1..20) is queue-contended
+# (internal#418). This lane offloads the *genuinely container-independent*
+# fast checks (Go build/vet/lint, shellcheck, Python lint) onto the Mac
+# arm64 self-hosted runner so developers get a fast arm64 signal WITHOUT
+# adding load to the starved amd64 pool — capability-honestly, as an
+# additive pilot. Pilot ② of the Mac-CI strategy (CTO-delegated 2026-05-17).
+#
+# === NON-NEGOTIABLE SAFETY CONTRACT (the prime directive) ===
+#
+# This lane is **ADVISORY ONLY**. It is provably incapable of hanging a
+# merge. Concretely:
+#
+#   1. It is a SEPARATE workflow file. `ci.yml` is byte-for-byte
+#      untouched by this PR. The `CI / all-required` aggregator sentinel
+#      and the five contexts it polls
+#      (`CI / Detect changes|Platform (Go)|Canvas (Next.js)|
+#      Shellcheck (E2E scripts)|Python Lint & Test (pull_request)`)
+#      are unchanged. The canonical required gate stays 100% on the
+#      existing amd64 pool.
+#
+#   2. The context this workflow emits is
+#      `ci-arm64-advisory / fast-checks (pull_request)`. That string is
+#      DELIBERATELY NOT present in, and this PR does NOT add it to:
+#        - branch_protections/{main,staging}.status_check_contexts
+#          (DB-verified pb 86/75 = exactly
+#           ["CI / all-required (pull_request)",
+#            "sop-checklist / all-items-acked (pull_request)"])
+#        - audit-force-merge.yml REQUIRED_CHECKS env
+#        - ci.yml `all-required` sentinel's hardcoded `required[]` list
+#      Branch protection therefore never waits on this context. If the
+#      Mac runner is absent / offline / removed, this workflow's status
+#      simply never appears — and because nothing requires it, every
+#      merge proceeds exactly as it does today. There is no path by
+#      which a missing/red arm64 status blocks a merge.
+#
+#   3. `continue-on-error: true` on the job — even a genuine arm64-only
+#      failure (toolchain drift, arch-specific test flake) is surfaced
+#      as information, never as a merge blocker, for the duration of
+#      the pilot.
+#
+#   4. The job carries a `github.event_name` `if:` gate. Beyond its
+#      functional purpose this also keeps the job OUT of
+#      `ci-required-drift.py:ci_job_names()` (which excludes
+#      `github.event_name`/`github.ref`-gated jobs), so the hourly
+#      ci-required-drift sentinel's F1 ("job not under sentinel needs")
+#      cannot ever flag this advisory job. F2/F3 are untouched because
+#      this context is absent from BP and from REQUIRED_CHECKS.
+#      `lint-bp-context-emit-match` only fails on BP→emitter gaps; an
+#      emitter without a BP context is explicitly informational there.
+#
+# === RUNNER TARGETING ===
+#
+# The Mac runner is `hongming-pc-runner-1`. The bare `self-hosted`
+# label is POLLUTED in this Gitea instance: molecule-runner-1..20
+# (the contended amd64 pool) also advertise `self-hosted`. Targeting
+# bare `self-hosted` would route back onto the very pool we are trying
+# to relieve — and onto amd64 hardware. We therefore require an
+# AND-set of labels that ONLY the Mac satisfies. `macos-self-hosted`
+# is Mac-exclusive (the amd64 pool does not carry it). Until the
+# label-install burst (a10862b2) lands `self-hosted`+`macos-self-hosted`
+# on the Mac, the runner's current unique label `hongming-pc-laptop`
+# is also listed; AND-semantics over the labels a runner advertises
+# means a job requiring [self-hosted, macos-self-hosted] can ONLY be
+# claimed once the Mac advertises both. If neither label set is yet
+# present on the Mac, the workflow stays queued harmlessly and is
+# garbage-collected by the normal stale-run reaper — it blocks nothing
+# (see safety contract point 2).
+#
+# === ROLLBACK ===
+#
+# Delete this single file (`git rm .gitea/workflows/ci-arm64-advisory.yml`)
+# and merge. No branch-protection edit, no ci.yml edit, no
+# REQUIRED_CHECKS edit is required to roll back, because none were made
+# to roll forward. Zero blast radius either direction.
+
+name: ci-arm64-advisory
+
+on:
+  push:
+    branches: [main, staging]
+  pull_request:
+    branches: [main, staging]
+
+# Per-ref cancel: a newer commit on the same ref supersedes the older
+# advisory run. Distinct from ci.yml's `ci-${ref}` group so this lane
+# never cancels (or is cancelled by) the canonical required CI.
+concurrency:
+  group: ci-arm64-advisory-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  GITHUB_SERVER_URL: https://git.moleculesai.app
+
+jobs:
+  fast-checks:
+    name: fast-checks
+    # AND-set: only the Mac arm64 runner advertises macos-self-hosted.
+    # See "RUNNER TARGETING" header note for why bare self-hosted is unsafe.
+    runs-on: [self-hosted, macos-self-hosted]
+    # ADVISORY: never blocks. See safety contract point 3.
+    continue-on-error: true
+    # event_name gate: functional (only meaningful on push/PR) AND keeps
+    # this job out of ci-required-drift.py:ci_job_names() so F1 can never
+    # flag it. See safety contract point 4.
+    if: ${{ github.event_name == 'push' || github.event_name == 'pull_request' }}
+    timeout-minutes: 20
+    steps:
+      - name: Provenance — advisory lane, non-gating
+        run: |
+          echo "This is the arm64 ADVISORY fast-check lane."
+          echo "It does NOT gate merges. Canonical required CI is ci.yml"
+          echo "on the amd64 pool. Arch: $(uname -m) on $(uname -s)."
+
+      - name: Checkout
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      # ---- Go: build + vet + lint (container-independent: needs only the
+      # Go toolchain; no amd64 ECR image, no docker-in-job). Race-detector
+      # unit-test + coverage gates are deliberately NOT duplicated here —
+      # those stay authoritative on amd64 ci.yml `Platform (Go)`. This lane
+      # is fast-feedback for the compile/vet/lint surface only. ----
+      - name: Setup Go
+        uses: actions/setup-go@40f1582b2485089dde7abd97c1529aa768e1baff # v5
+        with:
+          go-version: 'stable'
+      - name: Go build + vet (workspace-server)
+        working-directory: workspace-server
+        run: |
+          go mod download
+          go build ./cmd/server
+          go vet ./...
+      - name: golangci-lint (workspace-server)
+        working-directory: workspace-server
+        run: |
+          go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.12.2
+          "$(go env GOPATH)/bin/golangci-lint" run --timeout 3m ./...
+
+      # ---- Shellcheck (container-independent: shellcheck binary only).
+      # Mirrors ci.yml `Shellcheck (E2E scripts)` bulk pass scope. ----
+      - name: Install shellcheck (arm64)
+        run: |
+          if ! command -v shellcheck >/dev/null 2>&1; then
+            echo "shellcheck not preinstalled on this self-hosted runner."
+            echo "Attempting Homebrew install (Mac arm64)."
+            brew install shellcheck || {
+              echo "::warning::shellcheck unavailable on runner; advisory shellcheck skipped."
+              exit 0
+            }
+          fi
+          shellcheck --version
+      - name: Shellcheck tests/e2e + infra/scripts
+        run: |
+          command -v shellcheck >/dev/null 2>&1 || { echo "skip"; exit 0; }
+          find tests/e2e infra/scripts -type f -name '*.sh' -print0 \
+            | xargs -0 shellcheck --severity=warning
+
+      # ---- Python lint/compile (container-independent: CPython only).
+      # Lint + import-compile surface; the authoritative pytest + coverage
+      # floors stay on amd64 ci.yml `Python Lint & Test`. ----
+      - name: Setup Python
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+        with:
+          python-version: '3.11'
+      - name: Python byte-compile (workspace)
+        working-directory: workspace
+        run: |
+          python -m pip install --quiet ruff || true
+          python -m compileall -q .
+          if command -v ruff >/dev/null 2>&1; then
+            ruff check . || echo "::warning::ruff findings (advisory only)"
+          fi
+
+      - name: Advisory summary
+        if: always()
+        run: |
+          {
+            echo "## arm64 advisory fast-checks complete"
+            echo ""
+            echo "This lane is **advisory** — it does not gate merges."
+            echo "Authoritative required CI remains \`CI / all-required\`"
+            echo "on the amd64 pool (\`ci.yml\`, unchanged by this PR)."
+          } >> "$GITHUB_STEP_SUMMARY"