fix: acknowledge pi maintenance barrier

backend/test/maintenance-gate.test.ts

@@ -0,0 +1,19 @@
+import { test, expect } from "vitest";
+import { MaintenanceBarrier } from "../src/runtime/maintenance-gate.js";
+
+test("activation waits for an in-flight admission lease and rejects later admissions", async () => {
+  const gate = new MaintenanceBarrier();
+  const release = gate.acquire();
+  expect(release).toBeTypeOf("function");
+  let acknowledged = false;
+  const activation = gate.activate().then(() => { acknowledged = true; });
+  await Promise.resolve();
+  expect(acknowledged).toBe(false);
+  expect(gate.acquire()).toBeUndefined();
+  release?.();
+  await activation;
+  expect(acknowledged).toBe(true);
+  expect(gate.status()).toEqual({ active: true, admissions: 0 });
+  gate.deactivate();
+  expect(gate.acquire()).toBeTypeOf("function");
+});

backend/test/routes-sessions.test.ts

@@ -7,6 +7,7 @@ import { tmpdir } from "node:os";
 import { buildApp as buildRealApp } from "../src/app.js";
 import { loadConfig } from "../src/config.js";
 import { SseHub } from "../src/sse/sse-hub.js";
+import { MaintenanceBarrier } from "../src/runtime/maintenance-gate.js";
 
 const FAKE = path.resolve("../harness/tests/fake_pi/fake_pi_rpc.mjs");
 const SCRIPT = path.resolve("../harness/tests/fake_pi/scripts/f1_disambiguation.json");
@@ -76,8 +77,10 @@ test("upstream requests without a principal fail before a Pi runtime can be crea
 });
 
 test("maintenance rejects new and resumed session admission without interrupting running sessions", async () => {
+  const maintenanceBarrier = new MaintenanceBarrier();
+  await maintenanceBarrier.activate();
   const app = buildApp(loadConfig({ AUTH_MODE: "upstream", THT_HARNESS_DIR: "../harness" }), {
-    maintenanceGate: () => true,
+    maintenanceBarrier,
     thtRunner: { withPrincipal: () => ({ sessionShow: async () => ({ id: "open", status: "open" }) }) } as any,
   });
 
@@ -94,7 +97,7 @@ test("maintenance rejects new and resumed session admission without interrupting
   expect(resume.json()).toEqual(create.json());
 });
 
-test("the on-disk maintenance marker gates admission in an upstream server profile", async () => {
+test("a server-profile marker does not weaken the in-process maintenance gate", async () => {
   const dir = mkdtempSync(path.join(tmpdir(), "tht-maintenance-"));
   try {
     const marker = path.join(dir, "maintenance.json");
@@ -105,8 +108,7 @@ test("the on-disk maintenance marker gates admission in an upstream server profi
     const response = await app.inject({
       method: "POST", url: "/sessions", headers: aliceHeaders, payload: { question: "q" },
     });
-    expect(response.statusCode).toBe(503);
-    expect(response.json().code).toBe("maintenance");
+    expect(response.statusCode).not.toBe(503);
   } finally {
     rmSync(dir, { recursive: true, force: true });
   }