test: lock in the app readiness gate with static, deterministic and real-stack probes (E00-S03-T06)

tests/compose-config.test.mjs

@@ -509,15 +509,20 @@ test('docker compose up -d starts the database and application containers', { sk
       `the "app" container must stay running after "docker compose up -d" (state: "${appState}") — since T03 the server serves the health endpoint and must not exit`,
     );
 
-    // T03: the app serves the health endpoint — HTTP smoke test against the
-    // endpoint inside the app container (no host-port dependency), polling
-    // until it answers or times out.
+    // T03 + E00-S03-T06: the app serves the health endpoint — HTTP smoke test
+    // against the endpoint inside the app container (no host-port dependency),
+    // polling until it answers or times out. Since T06 the endpoint is the
+    // readiness probe: it answers 503 {"status":"not ready"} while the startup
+    // migration run is in flight and 200 {"status":"ok"} only after it
+    // completes, so the probe treats a 503 (and a connection failure) as
+    // "still starting — retry" and fail-fasts only on a definitive non-2xx
+    // answer.
     let healthOutput = '';
     let healthOk = false;
     for (let attempt = 0; attempt < 30 && !healthOk; attempt += 1) {
       const probe = run('docker', ['compose', 'exec', '-T', 'app', 'node', '-e', `
         fetch('http://127.0.0.1:3000/health')
-          .then(async (res) => { console.log(res.status, await res.text()); process.exit(res.ok ? 0 : 1); })
+          .then(async (res) => { console.log(res.status, await res.text()); process.exit(res.ok ? 0 : res.status === 503 ? 2 : 1); })
           .catch(() => process.exit(2));
       `], { cwd: REPO_ROOT, timeout: 15_000 });
       const output = String(probe.stdout ?? '') + String(probe.stderr ?? '');