fix(docker): let dumb-init forward the stop signal in the shipped compose file

The compose file drops every capability and adds back CHOWN, SETUID and
SETGID. dumb-init runs as root and node as the node user, and signalling a
process of another user needs KILL, so docker stop never reached node and
always ended in SIGKILL (exit 137). KILL only reaches processes inside the
container's own PID namespace. CI starts the image with the same set and now
checks that docker stop exits 0 after a logged SIGTERM.

Closes #2790

.github/workflows/test.yml

@@ -1161,7 +1161,7 @@ jobs:
           docker run -d --name trek-ci -p 127.0.0.1:3000:3000 \
             --read-only --tmpfs /tmp:noexec,nosuid,size=128m \
             --security-opt no-new-privileges:true \
-            --cap-drop ALL --cap-add CHOWN --cap-add SETUID --cap-add SETGID \
+            --cap-drop ALL --cap-add CHOWN --cap-add SETUID --cap-add SETGID --cap-add KILL \
             -v "$RUNNER_TEMP/trek/data:/app/data" \
             -v "$RUNNER_TEMP/trek/uploads:/app/uploads" \
             -e ENCRYPTION_KEY="$(openssl rand -hex 32)" \
@@ -1194,6 +1194,17 @@ jobs:
           curl -sf http://127.0.0.1:3000/ | grep -q '<div id="root">' \
             || { echo "::error::/ does not serve the client"; exit 1; }
 
+      # Same capabilities as the shipped compose file: dumb-init has to be able
+      # to pass the stop signal on to node, or docker stop ends in SIGKILL (137).
+      - name: Stop gracefully
+        run: |
+          set -euo pipefail
+          docker stop -t 30 trek-ci >/dev/null
+          code="$(docker inspect -f '{{.State.ExitCode}}' trek-ci)"
+          [ "$code" = "0" ] || { echo "::error::docker stop ended with exit code $code, not a graceful shutdown"; exit 1; }
+          docker logs trek-ci 2>&1 | grep -q 'SIGTERM received' \
+            || { echo "::error::the server never saw SIGTERM"; exit 1; }
+
       - name: Container log
         if: always()
         run: docker logs trek-ci 2>&1 || true