refactor(app): reshape session store reads around narrow hook surface

Eliminate sidebar re-render cascades by fixing both sides of the
subscription contract:

- Session-store writes preserve identity: setWorkspaces, mergeWorkspaces,
  removeWorkspace, and patchWorkspaceScripts return the previous Map/entry
  reference when content is unchanged.
- HostRuntimeController.updateSnapshot only notifies when a patched field
  actually changed; idle probe ticks no longer replace the snapshot.
- New canonical hook surface in stores/session-store-hooks.ts
  (useWorkspace, useWorkspaceFields, useWorkspaceStructure,
  useWorkspaceKeys, useResolveWorkspaceIdByCwd,
  useWorkspaceStatusesForBadges, useWorkspaceExecutionAuthority,
  useRecommendedProjectPaths, useHasWorkspaces). These are the only
  place to subscribe to workspaces.
- 15 greedy subscribers migrated to the hook surface. The sidebar is now
  driven by useWorkspaceStructure for identity/ordering; each row
  hydrates its own descriptor via useWorkspaceFields, so a workspace
  update re-renders only its row. Archive-redirect callbacks switched to
  event-time useSessionStore.getState().
- Deleted dead code: use-session-directory.ts, workspace-fetch-debug.ts,
  and the unused SidebarProjectEntry aggregates (activeCount,
  totalWorkspaces, aggregated statusBucket).

No user-visible behavior change. Targeted tests green (79 tests across
host-runtime, session-store, session-store-hooks, sidebar list, sidebar
row model, sidebar shortcuts, workspace source of truth).

packages/app/src/utils/sidebar-project-row-model.test.ts

@@ -31,9 +31,6 @@ function project(overrides: Partial<SidebarProjectEntry> = {}): SidebarProjectEn
     projectName: "paseo",
     projectKind: "git",
     iconWorkingDir: "/repo",
-    statusBucket: "done",
-    activeCount: 0,
-    totalWorkspaces: 1,
     workspaces: [workspace()],
     ...overrides,
   };

packages/app/src/utils/sidebar-shortcuts.test.ts

@@ -33,9 +33,6 @@ function project(projectKey: string, workspaces: SidebarWorkspaceEntry[]): Sideb
     projectName: projectKey,
     projectKind: "git",
     iconWorkingDir: workspaces[0]?.workspaceDirectory ?? "",
-    statusBucket: "done",
-    activeCount: 0,
-    totalWorkspaces: workspaces.length,
     workspaces,
   };
 }

packages/app/src/utils/workspace-fetch-debug.ts

@@ -1,104 +0,0 @@
-type WorkspaceLike = {
-  id: string;
-  projectId: string;
-  projectDisplayName?: string;
-  name: string;
-  status: string;
-  workspaceKind: string;
-};
-
-type SidebarWorkspaceLike = {
-  workspaceId: string;
-  name: string;
-  statusBucket: string;
-  workspaceKind: string;
-};
-
-type SidebarProjectLike = {
-  projectKey: string;
-  projectName: string;
-  statusBucket: string;
-  activeCount: number;
-  totalWorkspaces: number;
-  workspaces: SidebarWorkspaceLike[];
-};
-
-function countByValue(values: Iterable<string>): Record<string, number> {
-  const counts = new Map<string, number>();
-  for (const value of values) {
-    counts.set(value, (counts.get(value) ?? 0) + 1);
-  }
-  return Object.fromEntries(counts);
-}
-
-export function summarizeWorkspaceCollection(
-  workspaces: Iterable<WorkspaceLike> | null | undefined,
-): {
-  count: number;
-  projectIds: string[];
-  statusCounts: Record<string, number>;
-  workspaces: Array<{
-    id: string;
-    projectId: string;
-    projectDisplayName: string | null;
-    name: string;
-    status: string;
-    workspaceKind: string;
-  }>;
-} {
-  const entries = Array.from(workspaces ?? [], (workspace) => ({
-    id: workspace.id,
-    projectId: workspace.projectId,
-    projectDisplayName: workspace.projectDisplayName?.trim() || null,
-    name: workspace.name,
-    status: workspace.status,
-    workspaceKind: workspace.workspaceKind,
-  }));
-
-  return {
-    count: entries.length,
-    projectIds: [...new Set(entries.map((workspace) => workspace.projectId))],
-    statusCounts: countByValue(entries.map((workspace) => workspace.status)),
-    workspaces: entries,
-  };
-}
-
-export function summarizeSidebarProjects(
-  projects: Iterable<SidebarProjectLike> | null | undefined,
-): {
-  count: number;
-  projectKeys: string[];
-  projects: Array<{
-    projectKey: string;
-    projectName: string;
-    statusBucket: string;
-    activeCount: number;
-    totalWorkspaces: number;
-    workspaces: Array<{
-      workspaceId: string;
-      name: string;
-      statusBucket: string;
-      workspaceKind: string;
-    }>;
-  }>;
-} {
-  const entries = Array.from(projects ?? [], (project) => ({
-    projectKey: project.projectKey,
-    projectName: project.projectName,
-    statusBucket: project.statusBucket,
-    activeCount: project.activeCount,
-    totalWorkspaces: project.totalWorkspaces,
-    workspaces: project.workspaces.map((workspace) => ({
-      workspaceId: workspace.workspaceId,
-      name: workspace.name,
-      statusBucket: workspace.statusBucket,
-      workspaceKind: workspace.workspaceKind,
-    })),
-  }));
-
-  return {
-    count: entries.length,
-    projectKeys: entries.map((project) => project.projectKey),
-    projects: entries,
-  };
-}