perf(app): keep warm workspace switching responsive (#3447)

* perf(app): reduce warm workspace switch work

Retained workspaces avoided mounts but pane activity still rerendered the full composer, message input, and agent-control presentation. Keep the activity contract intact while moving focus-sensitive behavior behind small context consumers, and add a Playwright benchmark that measures rapid retained workspace switching on one browser clock.

* perf(app): accelerate retained workspace switching

Avoid repeated retained-stream layout reconciliation and unrelated workspace structure recomputation. Use the lightweight route transition while the host is already focused, while preserving targeted root POP_TO for returns from app-wide routes where it prevents duplicate hidden decks.

* perf(app): defer composer focus during workspace switches

* perf(app): retain recently used workspaces longer

Keep up to ten workspace screens warm so normal multi-workspace navigation does not repeatedly rebuild recently used timelines. Inactive screens expire after ten minutes, while the active screen remains protected and capacity eviction stays least-recently-used.

* fix(app): reconcile retained timeline geometry

* fix(app): refresh retained reading position

packages/app/src/utils/web-focus.test.ts

@@ -52,6 +52,36 @@ describe("focusWithRetries", () => {
     expect(frameQueue).toHaveLength(0);
   });
 
+  it("can defer the first focus attempt until the next animation frame", () => {
+    const focus = vi.fn();
+
+    focusWithRetries({
+      focus,
+      isFocused: () => true,
+      deferInitialAttempt: true,
+    });
+
+    expect(focus).not.toHaveBeenCalled();
+
+    flushAnimationFrames(1);
+
+    expect(focus).toHaveBeenCalledTimes(1);
+  });
+
+  it("cancels a deferred focus before its first attempt", () => {
+    const focus = vi.fn();
+    const cancel = focusWithRetries({
+      focus,
+      isFocused: () => false,
+      deferInitialAttempt: true,
+    });
+
+    cancel();
+    flushAnimationFrames(1);
+
+    expect(focus).not.toHaveBeenCalled();
+  });
+
   it("keeps retrying on later animation frames until focus succeeds", () => {
     let focused = false;
     let attempts = 0;

packages/app/src/utils/web-focus.ts

@@ -1,6 +1,7 @@
 interface FocusWithRetriesOptions {
   focus: () => void;
   isFocused: () => boolean;
+  deferInitialAttempt?: boolean;
   timeoutMs?: number;
   onSuccess?: () => void;
   onTimeout?: () => void;
@@ -9,6 +10,7 @@ interface FocusWithRetriesOptions {
 export function focusWithRetries({
   focus,
   isFocused,
+  deferInitialAttempt = false,
   timeoutMs = 1500,
   onSuccess,
   onTimeout,
@@ -40,7 +42,11 @@ export function focusWithRetries({
     });
   };
 
-  tick();
+  if (deferInitialAttempt) {
+    requestAnimationFrame(tick);
+  } else {
+    tick();
+  }
 
   return () => {
     cancelled = true;