fix(mobile): show checkout branch for phone-created threads

[Adamulek123]

Summary

Threads created from mobile can persist without a branch while VCS status is still loading, leaving the branch line blank even though the environment has a checked-out branch.

Changes

• Keep the stored thread branch authoritative when present.
• For local null-branch threads, reuse the deduplicated live VCS status stream to display the current checkout branch.
• Apply the fallback to both mobile thread-list implementations; worktree threads remain excluded from the fallback.

Before:

After:

Testing

• vp test run apps/mobile/src/state/thread-display-branch.test.ts (5 passed)
• vp run --filter @t3tools/mobile typecheck
• Targeted lint on the five changed files (passes with two pre-existing memo dependency warnings outside the diff)
• Android Emulator (T3_Pixel_API_36) against a disposable local server and a thread fixture with branch = NULL and worktree_path = NULL

Built with GPT-5.6 Codex in T3 Code.

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Note

Low Risk
Display-only change with stored branch unchanged for PR/compare logic; reuses an existing VCS status subscription pattern.

Overview
Fixes thread list rows that showed a blank branch when thread.branch was never persisted (common for threads created on phone while VCS status was still loading).

Adds resolveThreadDisplayBranch and useThreadDisplayBranch: stored branch still wins; for local threads with no branch, the row shows the live checkout from the existing deduplicated vcsEnvironment.status query. Worktree threads do not use that fallback.

Both thread-list-items and thread-list-v2-items now render the derived branch in subtitles instead of thread.branch directly. Unit tests cover precedence, worktree exclusion, and trimmed empty strings.

^{Reviewed by Cursor Bugbot for commit 9f8562a. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Show live checkout branch for phone-created threads in mobile thread list

• Adds resolveThreadDisplayBranch util and useThreadDisplayBranch hook to resolve a display branch: nonblank stored branch wins, otherwise fall back to the live checkout branch for local threads with a known cwd, and return null for worktree threads or unknown checkouts
• Updates ThreadListRow and ThreadListV2Row to render the resolved branch in the subtitle instead of thread.branch
• The hook only subscribes to the environment status query when the thread is local, has no stored branch, and has a usable cwd, avoiding unnecessary queries
• Risk: threads that previously showed a blank branch label will now show the live checkout branch when available; verify useThreadDisplayBranch in use-thread-display-branch.ts does not trigger status queries for worktree threads

^{Macroscope summarized 9f8562a.}

[macroscopeapp]

Approvability

Verdict: Approved at 9f8562a

Macroscope's review found this PR approvable — This is a narrowly scoped mobile display fix that falls back to the live checkout branch only for local threads missing a stored branch, while preserving existing branch and worktree behavior. Its added VCS access reuses the existing deduplicated read-only status stream and the resolution logic has focused test coverage.

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