Make the required Test check report on every PR

.github/workflows/test.yml

@@ -9,14 +9,8 @@ on:
       - "scripts/**"
       - "src/**"
       - "tests/**"
+      - "uv.lock"
   pull_request:
-    paths:
-      - ".github/workflows/test.yml"
-      - "examples/**"
-      - "pyproject.toml"
-      - "scripts/**"
-      - "src/**"
-      - "tests/**"
   workflow_dispatch:
 
 concurrency:
@@ -27,8 +21,49 @@ permissions:
   contents: read
 
 jobs:
+  # Decide whether the matrix needs to run. On push the trigger is already
+  # path-filtered, so this is only meaningful for pull_request, where the
+  # workflow must run on every PR (so the required Test check always reports)
+  # but the expensive matrix should only run when test-relevant files change.
+  # Uses plain git rather than a third-party changed-files action.
+  changes:
+    name: changes
+    runs-on: tenki-standard-small-2c-4g
+    outputs:
+      code: ${{ steps.filter.outputs.code }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+        with:
+          fetch-depth: 0
+
+      - name: Detect test-relevant changes
+        id: filter
+        run: |
+          set -euo pipefail
+          base='${{ github.event.pull_request.base.sha }}'
+          head='${{ github.event.pull_request.head.sha }}'
+          if [ -z "${base}" ]; then
+            # Not a pull_request (push / workflow_dispatch): the push trigger is
+            # already path-filtered, so run the matrix.
+            echo "code=true" >> "${GITHUB_OUTPUT}"
+            exit 0
+          fi
+          changed=$(git diff --name-only "${base}...${head}" -- \
+            .github/workflows/test.yml examples pyproject.toml scripts src tests uv.lock)
+          if [ -n "${changed}" ]; then
+            echo "Test-relevant files changed:"
+            echo "${changed}"
+            echo "code=true" >> "${GITHUB_OUTPUT}"
+          else
+            echo "No test-relevant files changed."
+            echo "code=false" >> "${GITHUB_OUTPUT}"
+          fi
+
   protobuf-compatibility:
     name: protobuf ${{ matrix.protobuf }}
+    needs: changes
+    if: ${{ needs.changes.outputs.code == 'true' }}
     runs-on: tenki-standard-small-2c-4g
     strategy:
       fail-fast: false
@@ -63,3 +98,32 @@ jobs:
 
       - name: Test
         run: python ${{ matrix.warning_args }} -m pytest
+
+  # Aggregate gate: this job's name is the required status check ("Test"). It
+  # runs on every PR and reports once. It passes when no test-relevant files
+  # changed (the matrix was skipped) and otherwise only when the matrix passed.
+  test:
+    name: Test
+    runs-on: tenki-standard-small-2c-4g
+    needs: [changes, protobuf-compatibility]
+    if: always()
+    steps:
+      - name: Require the matrix to pass when it ran
+        run: |
+          set -euo pipefail
+          changes_result='${{ needs.changes.result }}'
+          code='${{ needs.changes.outputs.code }}'
+          matrix_result='${{ needs.protobuf-compatibility.result }}'
+          echo "changes=${changes_result} code=${code} matrix=${matrix_result}"
+          if [ "${changes_result}" != "success" ]; then
+            echo "::error::change detection did not succeed"
+            exit 1
+          fi
+          if [ "${code}" != "true" ]; then
+            echo "No test-relevant files changed; nothing to test."
+            exit 0
+          fi
+          if [ "${matrix_result}" != "success" ]; then
+            echo "::error::protobuf compatibility matrix did not pass"
+            exit 1
+          fi