fix(web): restore composer expansion after tool calls

[t3dotgg]

Opening tool calls could collapse the composer and leave it small after scrolling back to the bottom. The bottom handler cleared scroll collapse but left blur collapse active.

Restore the expanded desktop composer without taking keyboard focus. Closing tool output also restores it when the resized timeline is at the bottom. Reading history and the phone composer keep their current behavior.

Verification

• 199 focused tests pass, including both failure cases.
• Web typecheck and formatting checks pass.
• Browser verification skipped at maintainer request.

Created with GPT-6 Astra (preview) in Codex.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.6 KiB	+52 B (+0.4%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	+2 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.6 KiB	+50 B (+0.7%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	57.1 KiB	+88 B (+0.2%)	66.4 KiB	✅
Codex	Live turn messages	8	10	+2 (+25.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.6 KiB	+6 B (+0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	−11 B (−0.2%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.5 KiB	+17 B (+0.3%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.8 KiB	57.8 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: 935917f · PR result: 387caec · 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: 113.8 KiB
• Claude decoded thread snapshot: 114.5 KiB

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

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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[macroscopeapp]

Approvability

Verdict: Approved at 387caec

Macroscope's review found this PR approvable — This is a narrowly scoped UI bug fix that restores desktop composer expansion after tool output is collapsed at the timeline end, while preserving mobile behavior and DOM focus. Focused tests cover the relevant timeline and composer states, with no schema, security, infrastructure, or static-analysis changes.

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