e2e harness: refuse to run when port 8080 is already serving

The Playwright backend harness now aborts if something else (e.g. the
compose stack) is already on :8080, instead of letting reuseExistingServer
silently point every journey at the wrong backend with the wrong seed —
the failure mode that surfaced mid-restyle. Also gitignore the local
data/ blob-store artifacts.

Co-Authored-By: Claude Fable 5 <[email protected]>

.gitignore

@@ -9,3 +9,4 @@ frontend/test-results
 .env.local
 *.log
 .DS_Store
+data/

scripts/e2e-backend.sh

@@ -27,6 +27,15 @@ until curl -fsS http://127.0.0.1:54556/dex/.well-known/openid-configuration >/de
   sleep 0.5
 done
 
+# Refuse to run against someone else's 8080 (e.g. the compose stack):
+# reuseExistingServer would silently point every journey at the wrong
+# backend with the wrong seed.
+if curl -fsS -o /dev/null --max-time 2 http://127.0.0.1:8080/healthz 2>/dev/null; then
+  echo "e2e-backend: port 8080 is already serving — stop the other stack first" >&2
+  echo "  (docker compose -f deploy/compose/docker-compose.yml down)" >&2
+  exit 1
+fi
+
 cd "$ROOT"
 export CLAWMATES_MODE=e2e
 export CLAWMATES_CONFIG="$ROOT/deploy/e2e/clawmates.e2e.toml"