fix: recover PWA after backgrounding

web/src/daemonLink.test.ts

@@ -130,6 +130,31 @@ describe("DaemonLink", () => {
     expect(link.status().state).toBe("online");
   });
 
+  it("rechecks immediately when the browser returns from the background", async () => {
+    const sched = manual();
+    let reply: DaemonInfo | null = info("aaa", "i1");
+    const link = new DaemonLink({
+      fetchInfo: async () => {
+        if (!reply) throw new Error("down");
+        return reply;
+      },
+      scheduler: sched,
+      reload: () => {},
+    });
+    await link.start();
+
+    reply = null;
+    link.noteDisconnected();
+    sched.run();
+    await Promise.resolve();
+    expect(link.status().state).toBe("down");
+
+    reply = info("aaa", "i1");
+    link.recover();
+    await Promise.resolve();
+    expect(link.status().state).toBe("online");
+  });
+
   it("reloads the page when the daemon comes back on a new commit", async () => {
     const sched = manual();
     const reload = vi.fn();

web/src/daemonLink.ts

@@ -148,6 +148,17 @@ export class DaemonLink {
     void this.probe();
   }
 
+  /**
+   * Recheck liveness after the browser resumes from the background. Mobile
+   * browsers may suspend both WebSocket events and timers while a PWA is
+   * hidden, leaving a stale `down` state after the daemon is already back.
+   */
+  recover(): void {
+    if (this.state === "updating") return;
+    this.noteDisconnected();
+    void this.probe();
+  }
+
   /**
    * One `/api/info` round-trip. Resolves `true` when the daemon answered.
    *

web/src/events.test.ts

@@ -132,6 +132,21 @@ describe("CatalogStore reducer", () => {
 });
 
 describe("CatalogStore reconnect", () => {
+  it("replaces a suspended socket immediately", () => {
+    const first = new FakeSocket();
+    const second = new FakeSocket();
+    const { store } = storeWith([first, second]);
+    store.start();
+
+    store.reconnect();
+
+    expect(first.closed).toBe(true);
+    second.open();
+    // A late close from the old socket is deliberately ignored.
+    first.drop();
+    expect(store.backoff()).toBe(INITIAL_BACKOFF_MS);
+  });
+
   it("doubles the delay per attempt and caps it", () => {
     const sockets = Array.from({ length: 8 }, () => new FakeSocket());
     const { store, scheduler } = storeWith(sockets);

web/src/events.ts

@@ -59,6 +59,23 @@ export class CatalogStore {
     this.connect();
   }
 
+  /** Replace a socket that may have gone stale while the browser was suspended. */
+  reconnect(): void {
+    if (this.reconnectTimer !== null) {
+      this.scheduler.clearTimer(this.reconnectTimer);
+      this.reconnectTimer = null;
+    }
+    if (this.ws) {
+      // A close event from the superseded socket must not schedule a second
+      // connection alongside the new one.
+      this.ws.onclose = null;
+      this.ws.onerror = null;
+      this.ws.close();
+      this.ws = null;
+    }
+    this.connect();
+  }
+
   /** Current reconnect delay, for tests asserting the backoff schedule. */
   backoff(): number {
     return this.backoffMs;

web/src/main.ts

@@ -107,6 +107,19 @@ void link.start();
 
 store.start();
 
+// Installed mobile browsers suspend timers and WebSockets in the background.
+// Replacing the socket on return avoids leaving the restart overlay up after a
+// transient lost connection has already recovered.
+function recoverFromBackground(): void {
+  if (document.visibilityState !== "visible") return;
+  link.recover();
+  store.reconnect();
+}
+
+document.addEventListener("visibilitychange", recoverFromBackground);
+window.addEventListener("pageshow", recoverFromBackground);
+window.addEventListener("online", recoverFromBackground);
+
 // Dev-only: `?mock` seeds a representative catalog so the UI can be reviewed
 // without a running daemon. Stripped from production builds by Vite.
 if (import.meta.env.DEV && location.search.includes("mock")) {