fix(preview): restore v2 sizing and project access

[juliusmarminge]

The v2 branch lifted preview sizing into ChatView without the row measurement or per-thread storage key. A saved 800px panel in a 1024px workspace left only 224px for chat, and resizing one thread changed the width used by others. The preview list/close tools rejected a project's browser-access opt-in when the global setting was off.

This follow-up to #2829 reuses ChatView's existing row measurement and restores the scoped thread width key. The list/close handlers now use the project-aware preview capability issued with the credential, matching the other preview tools. A credential without that capability still cannot list or close tabs.

Validation

• 16 focused tests passed across preview controls, toolkit registration, panel clamping, and credential issuance. The new opt-in test fails against the parent implementation with capability_denied and passes with this fix; opt-out remains denied and leaves the tab open.
• Scoped web and server typechecks passed. Changed-file formatting/lint passed with existing ChatView warnings; React Doctor found no errors and one existing ChatView complexity warning.
• Real client pass in isolated state: thread switch/resize, sidebar resize, window resize, sheet mode, maximize/restore, and close/reopen. Resizing B from 480px to 500px preserves A's saved 800px width. No new ResizeObserver is added.

Review status

CI passed on 71ee9a3b8b53. Macroscope correctness, Effect conventions, and UI consistency checks passed with no actionable findings. Its approvability check is neutral and requests human review of the project-aware browser access change. CodeRabbit skipped review because this base branch is disabled in its configuration. No review threads are unresolved.

Evidence

Matching 1280×900 captures from parent fd8ea2fb2dd6 and this change, with a 1024px workspace and the same saved 800px panel width. The Files surface exercises the shared preview panel shell in the web client; Electron browser automation itself was not re-tested by this pass. The backend tests cover the actual list/close handlers and preview manager.

Before: 224px chat, 800px panel	After: 360px chat, 664px panel

Thread width restoration and sidebar resize recording

Model: GPT-6. Harness: Codex.

[macroscopeapp]

All clear

^{Posted via Macroscope — UI Consistency}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	4.9 KiB	—	6.8 KiB	✅
Codex	Thread snapshot wire	—	3.7 KiB	—	4.9 KiB	✅
Codex	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Codex	Live turn WebSocket decoded	—	20.4 KiB	—	29.3 KiB	✅
Codex	Live turn messages	—	2	—	8	✅
Claude	Total thread wire	—	4.9 KiB	—	6.8 KiB	✅
Claude	Thread snapshot wire	—	3.7 KiB	—	4.9 KiB	✅
Claude	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Claude	Live turn WebSocket decoded	—	20.7 KiB	—	29.3 KiB	✅
Claude	Live turn messages	—	1	—	8	✅

Baseline: unavailable · PR result: 71ee9a3 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 106.1 KiB
• Claude decoded thread snapshot: 106.4 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — The UI portion restores workspace-aware, per-thread preview sizing with focused coverage. The server portion changes the authorization boundary for preview-tab controls by relying on project-aware credential capabilities, so the resulting access behavior warrants human review.

^{You can add or adjust custom eligibility rules. Learn more.}