(CODUX-125) Gate title-bar Update button on real availability

[numnx]

🧩 Task: Gate title-bar Update button on real availability

Automated task PR opened by Code UX for T02.

📋 Summary

Sprint: Sprint 199 · Fix Update Button · Task: T02

Fix the Electron title-bar Update button so it reflects real update availability: surface the update affordance only when a newer version exists (driven by the existing /api/system/update-status pipeline) instead of being hardcoded to always show, and communicate the available version.

🤖 Model & Provider

Provider	Codex CLI
Model	gpt-5.5

⏱️ Timing

Started	2026-07-09 04:04:05 UTC
Finished	2026-07-09 04:07:46 UTC
Duration	3m 41s

📊 Token Usage

Metric	Value
Input tokens	76,238
Cached input tokens	453,376
Output tokens	6,308
Total tokens	535,922
Invocations	1
Tool calls	25
Active time	3m 10s

Included usage estimate (subscription/local login): $0.80

✅ QA Review

⏳ QA review runs after this PR is opened. Check the task card in the dashboard for the outcome once it lands.

📝 Full Task Prompt

## Objective
Wire `dashboard/src/v2/components/TitleBar.tsx` to the update-status hook so the amber "Update" button renders only when an update is actually available, instead of always showing. When shown, it should communicate the available version; the click behavior (open updates) stays the same.

## Scope
- Edit `dashboard/src/v2/components/TitleBar.tsx`
- Update `dashboard/src/v2/components/__tests__/TitleBar.test.tsx`
- Consumes the `useUpdateStatus` hook contract created in T01 (`dashboard/src/v2/hooks/use-update-status.ts`), specifically `updateAvailable` and `latestVersion`

## Implementation Requirements
1. Import and call `useUpdateStatus()` in `TitleBar`. Preserve the existing early return `if (!windowApi) return null;` (the title bar is Electron-only) — call the hook before that return so hook order stays stable.
2. Render the existing Update `<button>` (the block with `aria-label="Open updates"`, `handleUpdateClick`, `Download` icon) only when `updateAvailable` is true; when false, render nothing in its place and keep the surrounding version label/layout stable (no empty gap or placeholder).
3. When shown, make the affordance version-aware: set an accessible label/title that includes the latest version when available (e.g. `aria-label={latestVersion ? \`Update available: v${latestVersion}\` : "Open updates"}`), keeping the visible "Update" text and existing Tailwind classes/styling unchanged.
4. Keep `handleUpdateClick` calling `desktop?.openUpdates?.()` exactly as today; do not change the Electron IPC or `openCodeUxUpdatesPage` target.
5. Update `TitleBar.test.tsx`: mock the `use-update-status` hook. Add a case where `updateAvailable` is true asserting the update button renders and clicking it invokes `window.codeUxDesktop.openUpdates` once; add a case where `updateAvailable` is false asserting no button with the update affordance is present while the version label (`v...`) and window controls still render.

## Constraints
- Do not remove or alter the window min/maximize/close controls, the mac traffic-light spacer, drag/double-click behavior, or `__APP_VERSION__` version label.
- Do not show the Update button when `updateAvailable` is false (this is the core bug being fixed) and do not block title-bar render on the fetch (button simply stays hidden until/unless an update is confirmed).
- Reuse the existing button markup and Tailwind classes; do not introduce new UI frameworks or restyle unrelated title-bar elements.

## Verification
- `pnpm test tests/dashboard/v2` (or the focused command `pnpm test dashboard/src/v2/components/__tests__/TitleBar.test.tsx`) passes, including the new available/unavailable cases.
- `pnpm run typecheck:dashboard` and `pnpm run build` pass.
- Manually confirm: with a mocked up-to-date status no Update button appears; with an available update the button appears, is labeled with the version, and clicking it calls `openUpdates`.

🌿 Branch Info

Base: feature/CODUX-199-fix-update-button
Head: task/feature-codux-199-fix-update-button-t02-codex-mrczfplp

---

🤖 Generated by Code UX