ci: add commitlint + PR-lint gate for Linear-key discipline

Conventional Commits + a Linear issue key required on release-note types
(feat/fix/perf); maintenance types exempt. Feeds Linear releases as changie
is retired (OPS-1541). Same gate as youdeploy-http-api #5981.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FAv8ZjMKaAk7v2hF3Vf4j1

Author: fhacloid

.github/workflows/pr-lint.yml

@@ -0,0 +1,48 @@
+name: PR Lint
+
+# Commit convention gate feeding Linear releases (changie retirement).
+# Validates PR commits AND the PR title (the PR title becomes the commit once we
+# squash-merge). Conventional Commits + a Linear issue key on release-note types
+# (see commitlint.config.js). No secrets, no self-hosted runner needed — runs on
+# GitHub-hosted ubuntu-latest (free for this trust-safe lint).
+
+on:
+  pull_request:
+    types: [opened, edited, synchronize, reopened]
+
+permissions:
+  contents: read
+  pull-requests: read
+
+concurrency:
+  group: pr-lint-${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  commitlint:
+    name: Commit convention
+    runs-on: ubuntu-latest
+    # Same-repo PRs only; skip dependency bots (they carry no Linear key and are
+    # exempt "Maintenance" changes). Fork PRs are skipped here (contributors have no
+    # Linear access); a maintainer re-runs from an internal branch if needed.
+    if: >-
+      github.event.pull_request.head.repo.full_name == github.repository &&
+      github.actor != 'dependabot[bot]' &&
+      github.actor != 'renovate[bot]'
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Lint PR commits
+        uses: wagoid/commitlint-github-action@v6
+        with:
+          configFile: commitlint.config.js
+
+      - name: Lint PR title (becomes the squash commit)
+        env:
+          PR_TITLE: ${{ github.event.pull_request.title }}
+        run: |
+          printf '%s\n' "$PR_TITLE" | npx --yes \
+            -p @commitlint/cli -p @commitlint/config-conventional \
+            commitlint --config commitlint.config.js

commitlint.config.js

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+// Cycloid commit convention — feeds Linear releases (changie is being retired).
+//
+// Conventional Commits + a Linear issue key on release-note-bearing commits.
+// Release-note types (feat/fix/perf) MUST reference a Linear issue key (e.g. BE-123)
+// in the subject or body, so the release pipeline can link the issue to the Linear
+// release. Maintenance types (chore/build/ci/docs/style/test/refactor/revert) are
+// exempt — they land in the "Maintenance" bucket and need no key.
+//
+// NOTE: intended to be extracted into a shared @cycloid/commitlint-config package
+// once the monorepo lands; kept inline per-repo for now.
+
+const RELEASE_NOTE_TYPES = ["feat", "fix", "perf"];
+const LINEAR_KEY = /\b[A-Z]{2,}-\d+\b/;
+
+module.exports = {
+  extends: ["@commitlint/config-conventional"],
+  plugins: [
+    {
+      rules: {
+        "linear-key-on-release-types": (parsed) => {
+          const { type, header, body } = parsed;
+          if (!type || !RELEASE_NOTE_TYPES.includes(type)) return [true];
+          const hasKey = LINEAR_KEY.test(`${header || ""}\n${body || ""}`);
+          return [
+            hasKey,
+            `a "${type}" commit must reference a Linear issue key (e.g. BE-123) ` +
+              `in the subject or body so it can be linked to the Linear release`,
+          ];
+        },
+      },
+    },
+  ],
+  rules: {
+    "linear-key-on-release-types": [2, "always"],
+  },
+};