fix(mobile): thinking no longer looks like a regular message

[bradhave94]

Closes #12155.

Android paints thinking as a regular assistant message. Servers that do not hear reasoningMessages=true rewrite those traces to system; mobile only gave Thought chrome to role === "reasoning", so the remapped rows used the same markdown as the answer.

This routes system traces through the existing Thought / Thinking disclosure (isThinkingTraceMessage), including folds, grouping, row sizing, and list recycle types. One feed test covers a remapped trace next to a real answer.

vp test run apps/mobile/src/lib/threadActivity.test.ts — 108 passed.

UI Changes

Before:

After is the existing Thought / Thinking row already used for reasoning. No device capture of the patched build.

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

Summary by CodeRabbit

• Bug Fixes
  • Improved thread feed handling for thinking-trace messages, including correct grouping, sizing, and display across message types.
  • Turn-scoped system messages are now displayed as thinking traces, while unrelated system messages are excluded from the thread feed.
  • Prevented unscoped system instructions from appearing as thinking traces or message rows.
  • Preserved assistant answers and other relevant conversation content when filtering system messages.

[macroscopeapp]

Approvability

Verdict: Approved at 6037fa8

Macroscope's review found this PR approvable — This is a narrowly scoped mobile compatibility fix that routes legacy system-role thinking traces through the existing Thought-row presentation and virtualization logic. It does not alter server behavior, schemas, defaults, deployment, or static-analysis configuration, and includes regression coverage.

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📒 Files selected for processing (3)

• apps/mobile/src/features/threads/ThreadFeed.tsx
• apps/mobile/src/lib/threadActivity.test.ts
• apps/mobile/src/lib/threadActivity.ts

🚧 Files skipped from review as they are similar to previous changes (3)

• apps/mobile/src/lib/threadActivity.test.ts
• apps/mobile/src/lib/threadActivity.ts
• apps/mobile/src/features/threads/ThreadFeed.tsx

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📝 Walkthrough

Walkthrough

The mobile thread activity logic now identifies turn-scoped system messages as thinking traces. The feed renders them as reasoning rows and excludes ordinary system messages. Tests cover grouped traces and unscoped system instructions.

Changes

Thinking-trace compatibility

Layer / File(s)	Summary
Thinking-trace classification and folding apps/mobile/src/lib/threadActivity.ts	isThinkingTraceMessage recognizes reasoning messages and turn-scoped system messages. Folding, streaming checks, activity assignment, grouping, and feed construction use this classification.
Thread feed reasoning rendering apps/mobile/src/features/threads/ThreadFeed.tsx	The feed renders recognized traces as reasoning rows, applies collapsed-row sizing, uses a shared reasoning item type, and skips system-role rows.
System-role trace coverage apps/mobile/src/lib/threadActivity.test.ts	Tests verify grouped system traces render as Thought (×2) and unscoped system instructions produce no trace or message row.

Priority: ⬆️ High

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: High

Sequence Diagram(s)

sequenceDiagram
  participant ThreadActivity
  participant ThreadFeed
  participant ThreadPresentation
  ThreadActivity->>ThreadActivity: Classify turn-scoped system messages as thinking traces
  ThreadActivity->>ThreadPresentation: Build grouped trace and answer entries
  ThreadPresentation->>ThreadFeed: Provide feed entries
  ThreadFeed->>ThreadFeed: Render trace as reasoning row and skip system row

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Merge Risk: ⚪ Minimal · up to b8826

Turn-scoped system traces render as Thinking content while ordinary system messages remain excluded, with no actionable merge risk identified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 14.29% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main fix: thinking traces no longer render as regular messages on mobile.
Description check	✅ Passed	The description explains what changed, why it changed, the affected UI behavior, test coverage, and checklist status. It includes a before screenshot and explicitly notes that no patched-build after s…
Linked Issues check	✅ Passed	Issue #12155 requires mobile to distinguish remapped thinking traces from the final answer and to keep unrelated system messages out of normal message rendering. isThinkingTraceMessage recognizes tu…
Out of Scope Changes check	✅ Passed	The changes are limited to mobile thread classification and rendering, plus regression tests. They directly support issue #12155. They do not change server remapping, desktop behavior, cache handling,…

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Actionable comments posted: 1

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Inline comments:
In `@apps/mobile/src/lib/threadActivity.ts`:
- Around line 44-56: Update isThinkingTraceMessage so role === "system" is
classified as thinking only when provenance confirms it was remapped from a
reasoning trace, such as an explicit legacy projection state; never classify
ordinary persisted system messages by role alone. Propagate that provenance from
the ThreadFeed call site into the helper while preserving reasoning-role
classification.

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📒 Files selected for processing (3)

• apps/mobile/src/features/threads/ThreadFeed.tsx
• apps/mobile/src/lib/threadActivity.test.ts
• apps/mobile/src/lib/threadActivity.ts

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