## What
Splits the giant
`packages/dashboard/app/components/__tests__/ChatView.test.tsx` (**231
tests, ~24s, one sequential worker**) into 3 parallelizable sibling
files sharing a harness — the same pattern already used for
`SettingsModal` — and fixes a latent test-isolation bug it exposed.
### Split (sum unchanged = 231)
| File | tests |
|------|------|
| `ChatView.core.test.tsx` | 140 |
| `ChatView.sessions-rooms.test.tsx` | 40 |
| `ChatView.mobile.test.tsx` | 51 |
`ChatView.test-harness.tsx` exports fixtures, helpers (`renderWithAct`,
`setupMockChat`, `setupMockRooms`, `mockViewportMode`,
`renderRoomCreation`, …), the `vi.mocked` handles, and
`installChatViewEnv()` (the former file-level `beforeEach`/`afterEach`).
The `vi.mock(...)` factories stay **inline & self-contained** in each
test file — delegating them to a harness export triggers a TDZ
`ReferenceError` because the harness imports `ChatView`/`../../api`.
### FN-4327 isolation bug (root cause + fix)
`Direct/Rooms scope toggle > "FN-4327: switching scope from Rooms to
Direct re-anchors direct thread"` failed standalone/split with `expected
500 to be 1200`.
**Root cause:** the Direct↔Rooms toggle swaps subtrees in ChatView's
render (`chatScope` ternary), so the `.chat-messages` container
**unmounts** on entering Rooms and a **fresh node mounts** on returning
to Direct. The re-anchor effect (`anchorToBottom` on scope change)
correctly targets that remounted node — whose jsdom `scrollHeight` is
`0`. The pre-split file mocked geometry on the *pre-toggle* node and
only passed via a timing race against the remount (confirmed:
`sameNode=false`, `afterScrollHeight=0`).
**Fix (no assertion weakening):** install scroll geometry at the
prototype level (restored in `finally`, per-node `scrollTop` backing) so
whichever `.chat-messages` node is live — including the remounted one —
reports `scrollHeight 1200`, making the re-anchor deterministic.
### vitest.config.ts
- Repoint `dashboard-app-quality-chat` (`qualityAppChatOnlyTests`) to
the 3 new files.
- Drop bare `"ChatView"` from `qualityAppComponentTests` and
`isolatedQualityAppComponentTests`.
- Spread `qualityAppChatOnlyTests` into `backfillAppExclude` (mirroring
the settings split) so the files aren't double-collected by the app
backfill lane.
## Verification
- 3 new files together: **231 passed / 0 failed**, stable across 2 runs.
- FN-4327 passes **standalone** (`-t "FN-4327"`) **and** in the full
split run.
- `vitest list --filesOnly` → each new file collected by exactly **one**
project (`dashboard-app-quality-chat`); harness not collected; no
backfill double-collection.
- ESLint on all 4 new files: exit 0.
- Combined Duration ~**17s** (vs original ~24s); in CI the 3 files
parallelize across workers within the chat project.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **Bug Fixes**
* Improved chat experience reliability across mobile and desktop,
including session switching, room navigation, keyboard behavior,
scrolling, and sidebar interactions.
* Strengthened coverage for room creation, scope switching, and message
refresh behavior to help prevent regressions.
* **Chores**
* Reorganized automated checks to run chat-related scenarios more
consistently and avoid duplicate test collection.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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