refactor(ChatView): consolidate button state into useReducer

[hannesrudolph]

Summary

Replace 5 independent useState calls (clineAsk, enableButtons, sendingDisabled, primaryButtonText, secondaryButtonText) with a single useReducer to eliminate partial-update race windows.

Problem

When an api_req_started message arrives, button state is cleared via 5 separate setState calls. React can render between updates, creating a window where clineAsk is undefined but primaryButtonText still shows "Start New Task". Button clicks during this window are silently swallowed.

A secondary issue: after api_req_failed, the isStreaming heuristic can remain stale-true (because the last api_req_started has no cost), causing "Start New Task" clicks to route to cancelTask instead of clearTask.

Solution

• useReducer with 4 action types replaces the 5 useState calls:
  • SET_ASK_STATE: atomic update of all 5 fields
  • SET_SENDING_DISABLED: partial update for retry delay / condensing
  • SET_BUTTON_TEXT: partial update for subtask resume
  • RESET_WITHOUT_BUTTON_TEXT: resets without clearing button text (handleChatReset)
• Secondary button fix: api_req_failed / mistake_limit_reached / resume_task checks moved above the isStreaming guard in handleSecondaryButtonClick, so authoritative clineAsk state always wins over the heuristic
• 2 new tests covering both edge cases

What was removed

• The default fallback bandaid in handlePrimaryButtonClick that checked primaryButtonText as a string proxy — no longer needed since atomic updates prevent the desync

Verification

• ✅ TypeScript: clean
• ✅ Lint: clean (0 warnings)
• ✅ Tests: 26/26 ChatView tests pass, 5496/5496 full suite pass

[roomote]

Rooviewer   See task

Clean refactor. The useReducer approach eliminates the partial-update race window correctly and the secondary button fix is sound. One minor comment left on a stale test comment.

• Stale test comment references a removed default case fallback in handlePrimaryButtonClick (ChatView.spec.tsx:1366-1370)

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[roomote]

This comment references a default case fallback in handlePrimaryButtonClick that was removed in this PR. The only reason this test passes is the completion_result case, not any default fallback. Leaving this comment in could mislead someone into thinking there is a safety net for undefined clineAsk when there isn't.

Suggested change

	// Click the primary button. With clineAsk = "completion_result", the
	// handler's case "completion_result" calls startNewTask(). The default
	// case fallback also checks primaryButtonText against
	// t("chat:startNewTask.title") for safety when clineAsk becomes undefined
	// due to race conditions.
	// Click the primary button. With clineAsk = "completion_result", the
	// handler's case "completion_result" calls startNewTask().

_{Fix it with Roo Code or mention @roomote and request a fix.}