feat(x): sessions IPC + renderer data layer with testable stores (stage 5a)

The wire and state layer for the UI cutover; App.tsx integration follows
separately.

- shared/ipc.ts: eleven sessions:* invoke channels + the sessions:events
  push feed (SessionBusEvent via z.custom, like runs:events). The generic
  preload bridge needs no changes.
- main: sessions:* handlers as thin pass-throughs to the DI'd sessions
  service; startSessionsWatcher forwards the session bus to all windows;
  startup awaits the session-index scan before the renderer can list.
- renderer architecture per review guidance — all logic in framework-
  agnostic, dependency-injected modules; hooks are thin
  useSyncExternalStore subscriptions; components will consume pre-digested
  view models:
  - client.ts: narrow SessionsClient over window.ipc (fakeable).
  - feed.ts: one shared sessions:events consumer with fan-out (factory
    for tests).
  - turn-view.ts: pure derivations — live overlay (deltas accumulate,
    canonical events clear), TurnState -> ConversationItem[], and the
    session chat state (permission/ask-human maps re-manufactured in the
    runs-era shapes so existing components render unchanged;
    isProcessing/isThinking contract preserved).
  - store.ts: SessionChatStore (seed via getSession/getTurn, shared
    reduceTurn over live events, prior-turn freezing, unknown-turn
    reconciliation, stale-load guard, action routing) + SessionListStore.
  - hooks/useSessionChat + useSessions: thin wrappers, deps injectable.
- renderer test infra added from scratch (vitest + jsdom +
  testing-library); 29 tests across stores, pure views, feed, and hooks.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/x/apps/renderer/package.json

@@ -6,7 +6,9 @@
     "dev": "vite",
     "build": "tsc -b && vite build",
     "lint": "eslint .",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "dependencies": {
     "@codemirror/language": "^6.12.3",
@@ -83,6 +85,9 @@
   },
   "devDependencies": {
     "@eslint/js": "^9.39.1",
+    "@testing-library/dom": "^10.4.1",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
     "@types/node": "^24.10.1",
     "@types/react": "^19.2.5",
     "@types/react-dom": "^19.2.3",
@@ -91,9 +96,11 @@
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.4.24",
     "globals": "^16.5.0",
+    "jsdom": "^29.1.1",
     "tw-animate-css": "^1.4.0",
     "typescript": "~5.9.3",
     "typescript-eslint": "^8.46.4",
-    "vite": "^7.2.4"
+    "vite": "^7.2.4",
+    "vitest": "catalog:"
   }
 }