Guard best-effort Electron window-state persistence so an unwritable data directory cannot crash the main process. Validate portable data directories before app-mode persistence and surface failures back to settings so restart is not attempted after rollback.
Tested: cd desktop && bun test electron/services/windows.test.ts electron/services/appMode.test.ts
Tested: cd desktop && bun run test src/stores/settingsStore.test.ts -t "settingsStore app mode" --run
Tested: cd desktop && bun run check:electron
Tested: bun run check:desktop
Not-tested: bun run check:native; bun run verify; coverage gates not run for scoped local handoff.
Confidence: high
Scope-risk: narrow
718e80f8c5