feat(ci): migrate to Agent-native Fast Trunk

.github/workflows/ci.yml

@@ -1,4 +1,11 @@
 name: CI
+
+# Fast Trunk (Agent-native):
+# - Aggregate source verdict: source-ci/pass
+# - CI = source correctness only; Platform builds production once
+# - Merge Queue off by default (no merge_group trigger)
+# - Concurrency cancels superseded PR/branch tip runs
+
 on:
   workflow_dispatch:
   push:
@@ -7,6 +14,11 @@ on:
     branches: [main]
 permissions:
   contents: read
+concurrency:
+  # Fast Trunk: supersede obsolete runs for the same PR or branch tip.
+  group: ci-${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   assets:
     runs-on: sylphx-linux-standard

docs/reference/fast-trunk-ci.md

@@ -0,0 +1,23 @@
+# Fast Trunk CI
+
+## Authority split
+
+| Concern | Owner |
+| --- | --- |
+| Work / claim / review | Enact |
+| Source history | Git |
+| Source correctness | This repository CI (`source-ci/pass`) |
+| Production artifact build | Sylphx Platform (once) |
+| Deploy / health / rollback | Sylphx Platform |
+
+## Paths
+
+- **Internal agents:** small-batch non-force direct-trunk to default branch.
+- **External contributors:** Pull Request presubmit feedback.
+- **Merge Queue:** default off (no `merge_group` trigger).
+
+## CI scope
+
+Blocking: lint/typecheck, affected tests, schema/migration safety, narrow security.
+
+Not in source CI: production Docker/release image builds, disposable ship binaries for ordinary tips.