feat(deploy): add portable external-service stack

backend/src/routes/sessions.ts

@@ -77,6 +77,9 @@ export function sessionRoutes(
       "Access-Control-Allow-Origin": origin,
       "Access-Control-Allow-Credentials": "true",
     });
+    // Send the handshake immediately. Without this, Node waits for the first event body and
+    // proxies/clients cannot establish an idle SSE subscription or inspect its headers.
+    reply.raw.flushHeaders();
     const send = (event: string, data: object) => reply.raw.write(`event: ${event}\ndata: ${JSON.stringify(data)}\n\n`);
     const off = d.hub.subscribe(id, send, rt?.bridge.pendingWidget() ?? null);
     req.raw.on("close", off);

backend/test/health.test.ts

@@ -2,9 +2,33 @@ import { test, expect } from "vitest";
 import { buildApp } from "../src/app.js";
 import { loadConfig } from "../src/config.js";
 
-test("GET /health ritorna ok", async () => {
+test("GET /health reports process readiness without external services", async () => {
   const app = buildApp(loadConfig({ THT_HARNESS_DIR: "/tmp/h" }));
   const res = await app.inject({ method: "GET", url: "/health" });
   expect(res.statusCode).toBe(200);
+  expect(res.headers["content-type"]).toContain("application/json");
   expect(res.json()).toEqual({ status: "ok" });
 });
+
+test("SSE response headers are flushed before the first event", async () => {
+  const app = buildApp(loadConfig({ THT_HARNESS_DIR: "/tmp/h" }));
+  await app.listen({ port: 0, host: "127.0.0.1" });
+  const port = (app.server.address() as { port: number }).port;
+  const controller = new AbortController();
+
+  try {
+    const response = await Promise.race([
+      fetch(`http://127.0.0.1:${port}/sessions/header-probe/events`, {
+        signal: controller.signal,
+      }),
+      new Promise<never>((_, reject) =>
+        setTimeout(() => reject(new Error("SSE headers were not flushed")), 250),
+      ),
+    ]);
+    expect(response.headers.get("content-type")).toContain("text/event-stream");
+    expect(response.headers.get("cache-control")).toBe("no-cache");
+  } finally {
+    controller.abort();
+    await app.close();
+  }
+});