Surface desktop daemon gate failures instead of silent no-op

The async settings gate added in f0d96f8e called
shouldStartDaemon() inside Promise.resolve(...).then(...) with no
catch. If loadDesktopSettings() rejects (corrupted JSON, FS error),
the daemon never starts, no error renders on the splash, and the
retry button repeats the same silent path.

Add a recordError method to DaemonStartService and an onGateError
callback to startDaemonIfGateAllows / startHostRuntimeBootstrap.
_layout.tsx wires it through so a gate rejection populates
lastError, the splash shows the failure, and retry has signal.

packages/app/src/runtime/daemon-start-service.test.ts

@@ -188,6 +188,21 @@ describe("DaemonStartService", () => {
     expect(service.getLastError()).toBeNull();
   });
 
+  it("recordError surfaces an external error and notifies subscribers", () => {
+    const fake = createFakeStore();
+    const service = new DaemonStartService({
+      store: fake.store,
+      startDesktopDaemon: async () => makeStatus(),
+    });
+    const notifications = vi.fn();
+    service.subscribe(notifications);
+
+    service.recordError("settings file unreadable");
+
+    expect(service.getLastError()).toBe("settings file unreadable");
+    expect(notifications).toHaveBeenCalledTimes(1);
+  });
+
   it("stops notifying after a subscriber unsubscribes", async () => {
     const fake = createFakeStore();
     let notifications = 0;

packages/app/src/runtime/daemon-start-service.ts

@@ -53,6 +53,10 @@ export class DaemonStartService {
     return this.lastError;
   }
 
+  recordError(message: string): void {
+    this.setLastError(message);
+  }
+
   isRunning(): boolean {
     return this.inFlightCount > 0;
   }