fix: finalize durable Pi lifecycle

backend/test/routes-sessions.test.ts

@@ -152,6 +152,38 @@ test.each(["none", "upstream"] as const)(
   },
 );
 
+test("maintenance endpoints report marker-derived state after post-rename and post-remove fsync failures", async () => {
+  const dir = mkdtempSync(path.join(tmpdir(), "tht-maintenance-endpoint-fsync-"));
+  const marker = path.join(dir, "maintenance.json");
+  let failSync = true;
+  try {
+    const maintenanceBarrier = new MaintenanceBarrier(marker, {
+      syncDirectory() {
+        if (failSync) throw new Error("injected maintenance fsync failure");
+      },
+    });
+    const app = buildApp(loadConfig({
+      AUTH_MODE: "none",
+      THT_HARNESS_DIR: "../harness",
+      THT_MAINTENANCE_FILE: marker,
+    }), { thtRunner: {} as any, maintenanceBarrier });
+
+    const activated = await app.inject({ method: "POST", url: "/internal/maintenance/activate" });
+    expect(activated.statusCode).toBe(500);
+    expect(activated.json()).toMatchObject({ active: true, admissions: 0 });
+
+    failSync = false;
+    expect((await app.inject({ method: "GET", url: "/internal/maintenance/status" })).json())
+      .toEqual({ active: true, admissions: 0 });
+    failSync = true;
+    const deactivated = await app.inject({ method: "POST", url: "/internal/maintenance/deactivate" });
+    expect(deactivated.statusCode).toBe(500);
+    expect(deactivated.json()).toMatchObject({ active: false, admissions: 0 });
+  } finally {
+    rmSync(dir, { recursive: true, force: true });
+  }
+});
+
 test("admin all-sessions response matches the authenticated lifecycle wire fixture", async () => {
   const fixture = JSON.parse(readFileSync(
     path.join(import.meta.dirname, "fixtures", "sessions-scope-all.json"),