CI optimizations

- Skip CI for draft PRs and redundant master-push re-runs; membrowse nightly.
- Add smoke test (8 configs, CFLAGS=-Werror, post-merge tree, fail-fast on conflicts).
- Add wait-for-smoke composite action for downstream CI gating.
- Add check-source-text + bash -n + shellcheck workflow (script in make dist).
- Cache apt-get update in install-apt-deps composite on cache hit.

Author: dgarske

.github/actions/install-apt-deps/action.yml

@@ -54,6 +54,8 @@ runs:
 
     - name: Install packages
       shell: bash
+      env:
+        APT_CACHE_HIT: ${{ steps.apt-cache.outputs.cache-hit }}
       run: |
         export DEBIAN_FRONTEND=noninteractive
         RETRIES=${{ inputs.retries }}
@@ -62,6 +64,18 @@ runs:
         if [ "${{ inputs.no-install-recommends }}" = "true" ]; then
           NO_REC="--no-install-recommends"
         fi
+
+        # Fast path: on cache hit the .debs are already pre-seeded into
+        # /var/cache/apt/archives. Try installing directly first; if that
+        # fails (e.g. the cached .debs were superseded in the index) fall
+        # through to the regular update + install path.
+        if [ "$APT_CACHE_HIT" = "true" ]; then
+          if sudo apt-get install -y $NO_REC ${{ inputs.packages }}; then
+            exit 0
+          fi
+          echo "::warning::install from cached .debs failed, falling back to apt-get update"
+        fi
+
         for i in $(seq 1 $RETRIES); do
           if sudo apt-get update -q && \
              sudo apt-get install -y $NO_REC ${{ inputs.packages }}; then

.github/actions/wait-for-smoke/action.yml

@@ -0,0 +1,95 @@
+name: 'Wait for Smoke Test'
+description: 'Polls the Smoke Test workflow for the current commit and fails if it failed.'
+
+# Designed to be the leading job in pull_request-triggered workflows so that
+# expensive integration CI does not run unless the smoke build passes.
+#
+# Push events bypass the wait entirely (we still get smoke results for those
+# pushes, but other CI is not gated on push). For drafts, callers should
+# skip dependent jobs via `if: github.event.pull_request.draft == false` -
+# this action will still pass through if smoke is skipped or absent.
+
+inputs:
+  workflow:
+    description: 'Name of the smoke workflow file to wait on'
+    required: false
+    default: 'smoke-test.yml'
+  timeout-seconds:
+    description: 'Maximum time to wait for smoke to complete'
+    required: false
+    default: '1800'
+  poll-seconds:
+    description: 'Polling interval'
+    required: false
+    default: '20'
+  github-token:
+    description: 'GITHUB_TOKEN with actions:read permission'
+    required: true
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Wait for smoke
+      shell: bash
+      env:
+        GH_TOKEN: ${{ inputs.github-token }}
+        SMOKE_WORKFLOW: ${{ inputs.workflow }}
+        TIMEOUT: ${{ inputs.timeout-seconds }}
+        POLL: ${{ inputs.poll-seconds }}
+        REPO: ${{ github.repository }}
+      run: |
+        set -u
+        # Only gate pull_request events. Push events are not gated.
+        if [ "${{ github.event_name }}" != "pull_request" ]; then
+          echo "Not a pull_request event - skipping smoke gate."
+          exit 0
+        fi
+
+        HEAD_SHA="${{ github.event.pull_request.head.sha }}"
+        echo "Waiting for $SMOKE_WORKFLOW on $HEAD_SHA (timeout ${TIMEOUT}s)"
+
+        START=$(date +%s)
+        while :; do
+          NOW=$(date +%s)
+          ELAPSED=$((NOW - START))
+          if [ "$ELAPSED" -ge "$TIMEOUT" ]; then
+            echo "::error::Timed out after ${TIMEOUT}s waiting for $SMOKE_WORKFLOW on $HEAD_SHA"
+            exit 1
+          fi
+
+          # Look up the latest run for this workflow + head SHA.
+          RUN_JSON=$(gh api \
+            "repos/${REPO}/actions/workflows/${SMOKE_WORKFLOW}/runs?head_sha=${HEAD_SHA}&per_page=1" \
+            2>/dev/null || echo '{}')
+
+          STATUS=$(echo "$RUN_JSON"   | jq -r '.workflow_runs[0].status   // "missing"')
+          CONCLUSION=$(echo "$RUN_JSON" | jq -r '.workflow_runs[0].conclusion // ""')
+          RUN_URL=$(echo "$RUN_JSON"    | jq -r '.workflow_runs[0].html_url   // ""')
+
+          case "$STATUS" in
+            completed)
+              case "$CONCLUSION" in
+                success)
+                  echo "Smoke test passed: $RUN_URL"
+                  exit 0
+                  ;;
+                skipped|neutral)
+                  echo "Smoke test was $CONCLUSION - treating as pass: $RUN_URL"
+                  exit 0
+                  ;;
+                *)
+                  echo "::error::Smoke test concluded as '$CONCLUSION': $RUN_URL"
+                  exit 1
+                  ;;
+              esac
+              ;;
+            missing)
+              echo "[$ELAPSED s] No smoke run yet for $HEAD_SHA"
+              ;;
+            *)
+              echo "[$ELAPSED s] Smoke status=$STATUS ($RUN_URL)"
+              ;;
+          esac
+
+          sleep "$POLL"
+        done