ci: gate typecheck/lint/test on ref so main merge commits skip work

Forgejo Actions doesn't consistently honor `on.push.branches` as a
filter — the merge commit landing on main after a release PR was still
triggering the full CI workflow on a SHA that had already passed on
dev, burning ~1 minute of runner time for no reason.

The `build` job already had a ref guard, so no duplicate images were
being pushed, but typecheck/lint/test ran unconditionally. Add the
same guard (`refs/heads/dev` or `refs/tags/v*`) to those three so main
pushes trigger the workflow but every job skips immediately with zero
runner time.

Also tightened the build job's tag filter from `refs/tags/` to
`refs/tags/v` for consistency with the new guards and to avoid ever
building from a non-version tag.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.forgejo/workflows/ci.yml

@@ -1,8 +1,12 @@
 # CI runs first; build only proceeds if all checks pass.
 #
-# Push to any branch: typecheck + lint + test
-# Push to dev:        gates + build :dev + :<sha>
-# Tag v* (release):   gates + build :latest + :<sha> + :<version>
+# Push to dev:       typecheck + lint + test + build :dev + :<sha>
+# Tag v* (release):  typecheck + lint + test + build :latest + :<sha> + :<version>
+#
+# main pushes are NOT gated here: a merge to main only happens after
+# dev has already passed CI, and the release tag is the sole trigger
+# for a production image. Re-running CI on the merge commit just burns
+# runner time without changing the outcome.
 #
 # To cut a release:
 #   Create a release via the Forgejo UI on main with a v* tag name.
@@ -11,6 +15,13 @@
 # PRs aren't triggered on purpose — this is a solo dev→main flow, so
 # gating on branch push is already enough.
 #
+# NOTE on the `if:` guards below: Forgejo Actions does not consistently
+# honor `on.push.branches` as a filter — merge commits landing on main
+# still trigger the workflow, producing redundant runs on the same SHA
+# that was already gated on dev. Every job therefore repeats the ref
+# check so main pushes trigger the workflow but every job skips
+# immediately (no runner time, no duplicate work).
+#
 # Required secrets (repo → Settings → Secrets → Actions):
 #   REGISTRY_USER   — your Forgejo username
 #   REGISTRY_TOKEN  — Forgejo PAT with write:packages scope
@@ -18,7 +29,7 @@ name: CI & Build
 
 on:
   push:
-    branches: [dev, main]
+    branches: [dev]
     tags: ["v*"]
     paths:
       - "src/**"
@@ -51,6 +62,8 @@ env:
 jobs:
   typecheck:
     name: TypeScript typecheck
+    # Skip on main merge-commit pushes — see workflow header comment.
+    if: github.ref == 'refs/heads/dev' || startsWith(github.ref, 'refs/tags/v')
     runs-on: ci-runner
     steps:
       - uses: actions/checkout@v6
@@ -77,6 +90,7 @@ jobs:
 
   lint:
     name: Python lint
+    if: github.ref == 'refs/heads/dev' || startsWith(github.ref, 'refs/tags/v')
     runs-on: ci-runner
     steps:
       - uses: actions/checkout@v6
@@ -88,6 +102,7 @@ jobs:
 
   test:
     name: Python tests
+    if: github.ref == 'refs/heads/dev' || startsWith(github.ref, 'refs/tags/v')
     runs-on: ci-runner
     steps:
       - uses: actions/checkout@v6
@@ -118,11 +133,10 @@ jobs:
     name: Build & push image
     needs: [typecheck, lint, test]
     # Build on dev branch pushes and version tag pushes only.
-    # main branch pushes run the gates for safety but do not build —
-    # the release tag (v*) is the sole trigger for a production image.
-    if: |
-      github.event_name == 'push' &&
-      (github.ref == 'refs/heads/dev' || startsWith(github.ref, 'refs/tags/'))
+    # Mirrors the ref guard on the gate jobs above — main merge-commit
+    # pushes skip here too, so no production image is ever built from a
+    # raw main push (only from the v* tag the release creates).
+    if: github.ref == 'refs/heads/dev' || startsWith(github.ref, 'refs/tags/v')
     runs-on: ci-runner
     permissions:
       contents: read