fix(mobile): running threads open at the latest message

[AKolenda]

What Changed

ThreadFeed's list mount key no longer counts the synthetic thinking row as content, so a running thread's list mounts empty and remounts once its messages arrive.

Why

Opening a thread whose agent is still working showed the start of the thread for a moment, then a blank list, then jumped to the latest message. The feed already remounts the list when messages first arrive, so the fresh list positions itself at the end during attach. A running thread shows the thinking row before its messages load, which made the feed count as filled, so that remount never happened and the first page landed in the already-mounted list at the top.

Measured on a Pixel 9 with a list-state log (first open of a running thread, no cache, since running threads are not cached):

• Before: the list mounted as filled with 1 entry (the thinking row). 1.3 s later 25 entries arrived into it at scroll offset 0, and the end-follow jumped it down afterwards.

• After: the list mounts empty with the thinking row, remounts as filled with 25 entries, and its first frame is already at the end (offset 2,849 of 3,643, last rows visible).

Idle threads were not affected: their messages load before anything else is shown. Unchanged by this PR: the fresh list is still blank for about 0.4 s while it measures, as for every thread today.

UI Changes

Opening a running thread, before on the left, after on the right, half speed (two different running threads; MP4). Before shows the start of the thread, goes blank, then jumps to the latest message; after goes straight to the latest message.

Checklist

• This PR is small and focused

• I explained what changed and why

• I included before/after screenshots for any UI changes

• I included a video for animation/interaction changes

[macroscopeapp]

Approvability

Verdict: Approved at 2398a0b

Macroscope's review found this PR approvable — This small mobile bug fix changes only the list’s empty-versus-filled mount classification, excluding the synthetic thinking row so real messages trigger a fresh list mount at the latest position. It is isolated to thread-feed scroll initialization and does not affect schemas, defaults, infrastructure, or static-analysis settings.

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📝 Walkthrough

Walkthrough

ThreadFeed now treats a feed containing only thinking entries as empty when choosing listMountKey. The list uses the filled key when presentedFeed contains a non-thinking entry.

Changes

Feed mount state

Layer / File(s)	Summary
Determine feed mount key apps/mobile/src/features/threads/ThreadFeed.tsx	listMountKey is "empty" unless presentedFeed contains a non-thinking entry. Comments clarify that thinking rows do not count as content for list mounting.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~5 minutes

Change: Bug fix

Suggested reviewers: juliusmarminge

Merge Risk: 🔵 Low · up to 2398a

A thread in this limited state may initially open at the top instead of the latest message. The issue is localized, so the PR is otherwise mergeable with follow-up.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main change: running threads now open at the latest message.
Description check	✅ Passed	The description covers what changed, why it changed, the UI impact, evidence, and all checklist items. It is focused and complete.

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[coderabbitai]

Actionable comments posted: 1

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🤖 Prompt to fix review comments

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Inline comments:
In `@apps/mobile/src/features/threads/ThreadFeed.tsx`:
- Around line 2480-2483: Update the `listMountKey` content check in `ThreadFeed`
so a live `work-toggle` with summary `"Thinking"` counts as empty, just like a
`"thinking"` entry. Use that check to keep the list key `"empty"` until user or
assistant content appears, then switch it to `"filled"`.

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 72447f2 and 2398a0b.

📒 Files selected for processing (1)

• apps/mobile/src/features/threads/ThreadFeed.tsx

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