Risky behavior now covered

Recent desktop fixes in #349 left these fail-closed paths without direct tests:

• The update-ready notification is held until click, action, or a non-timeout close. A timed-out Windows toast stays referenced so Action Center can still deliver Restart. Closing an older toast does not drop the toast that replaced it.
• Restored maximize runs once, on the first live reveal. A window that was not maximized is left alone, and a destroyed window does not consume the one shot.
• Opening a previewed file externally, opening a truncated code preview, or popping a canvas out reports a foreground error instead of swallowing it. Error messages and non-Error rejections are both shown. A successful open stays quiet, and a blank code-preview path does not call openPath.
• getWorkspaceServerStatus, hydrateTranscript, and unwatchWorkspaceDirectory name themselves when preload input validation fails, and they do not invoke IPC.

Test files added/updated

• Added apps/desktop/test/update-ready-notification.test.ts and apps/desktop/electron/services/updateReadyNotification.ts
• Added apps/desktop/test/deferred-maximize.test.ts and apps/desktop/electron/services/deferredMaximize.ts
• Updated apps/desktop/test/file-preview-modal.test.tsx and apps/desktop/src/ui/CodeFilePreview.tsx (openCodePreviewExternally)
• Updated apps/desktop/test/canvas-window-lifecycle.test.tsx
• Updated apps/desktop/test/preload-boundary.test.ts
• apps/desktop/electron/main.ts calls the extracted hold and deferred-maximize helpers. Click, Restart Now, and focus behavior are unchanged.

Why this reduces regression risk

These were bug fixes that previously lived only in main.ts or as empty .catch handlers. A garbage-collected update toast drops Restart, maximizing at construction flashes an unpainted window, and a failed open or pop-out used to look like a no-op. The new tests lock the policies that prevent those regressions without snapshotting UI chrome.

Validation

• bun test on the five touched desktop test files: 53 pass
• bunx biome check on touched files: clean
• bun run typecheck: clean
• bun run docs:check: clean
• Full suite not re-run; this environment's historical full runs truncate, and the change is covered by the targeted files.