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/stores/session-store-hooks/index.ts

@@ -3,6 +3,7 @@ import { useStoreWithEqualityFn } from "zustand/traditional";
 import { useSidebarOrderStore } from "@/stores/sidebar-order-store";
 import {
   composeWorkspaceStructure,
+  createWorkspaceStructureProjectsSelector,
   selectHasHydratedWorkspaces,
   selectHydratedWorkspaceServerIds,
   selectWorkspaceDirectoryServerIds,
@@ -16,7 +17,6 @@ import {
   selectWorkspaceKeys,
   selectWorkspaceOrderByScope,
   selectWorkspaceStatusesForBadges,
-  selectWorkspaceStructureProjects,
   workspaceEqualityFns,
   type WorkspaceStructure,
 } from "./selectors";
@@ -100,9 +100,13 @@ export function useWorkspaceDirectory(
 }
 
 export function useWorkspaceStructure(serverIds: string[]): WorkspaceStructure {
+  const selectProjects = useMemo(
+    () => createWorkspaceStructureProjectsSelector(serverIds),
+    [serverIds],
+  );
   const projects = useStoreWithEqualityFn(
     useSessionStore,
-    (state) => selectWorkspaceStructureProjects(state, serverIds),
+    selectProjects,
     workspaceEqualityFns.deep,
   );
   const projectOrder = useStoreWithEqualityFn(

packages/app/src/stores/session-store-hooks/selectors.test.ts

@@ -4,6 +4,7 @@ import { createProjectViewKey } from "@/projects/workspace-structure";
 import type { DaemonClient } from "@getpaseo/client/internal/daemon-client";
 import {
   composeWorkspaceStructure,
+  createWorkspaceStructureProjectsSelector,
   selectHasWorkspaces,
   selectHydratedWorkspaceServerIds,
   selectWorkspaceDirectoryServerIds,
@@ -338,6 +339,27 @@ describe("selectWorkspaceFields", () => {
 });
 
 describe("workspace structure composition", () => {
+  it("reuses structure when unrelated session state changes", () => {
+    const workspace = createWorkspace({ id: "workspace-a" });
+    const workspaces = new Map([[workspace.id, workspace]]);
+    const projects = new Map([
+      [workspace.projectId, projectDescriptorFromTestWorkspace(workspace)],
+    ]);
+    const selectProjects = createWorkspaceStructureProjectsSelector([SERVER_ID]);
+    const before = selectProjects({ sessions: { [SERVER_ID]: { workspaces, projects } } });
+    const after = selectProjects({
+      sessions: {
+        [SERVER_ID]: {
+          workspaces,
+          projects,
+          hasHydratedWorkspaces: true,
+        },
+      },
+    });
+
+    expect(after).toBe(before);
+  });
+
   function snapshotStructure(
     serverId: string,
     sidebar: SidebarOrderSnapshot,

packages/app/src/stores/session-store-hooks/selectors.ts

@@ -182,6 +182,38 @@ export function selectWorkspaceStructureProjects(
   return buildWorkspaceStructureProjects({ sessions });
 }
 
+export function createWorkspaceStructureProjectsSelector(
+  serverIds: readonly string[],
+): (state: SessionsSnapshot) => WorkspaceStructureProject[] {
+  let previousInputs: Array<{
+    workspaces: Map<string, WorkspaceDescriptor> | undefined;
+    projects: Map<string, ProjectDescriptor> | undefined;
+  }> | null = null;
+  let previousProjects: WorkspaceStructureProject[] | null = null;
+
+  return (state) => {
+    const inputs = serverIds.map((serverId) => ({
+      workspaces: state.sessions[serverId]?.workspaces,
+      projects: state.sessions[serverId]?.projects,
+    }));
+    const priorInputs = previousInputs;
+    const unchanged =
+      priorInputs !== null &&
+      inputs.every(
+        (input, index) =>
+          input.workspaces === priorInputs[index]?.workspaces &&
+          input.projects === priorInputs[index]?.projects,
+      );
+    if (unchanged && previousProjects) {
+      return previousProjects;
+    }
+
+    previousInputs = inputs;
+    previousProjects = selectWorkspaceStructureProjects(state, serverIds);
+    return previousProjects;
+  };
+}
+
 export function selectProject(
   state: SessionsSnapshot,
   serverId: string | null,