fix(web): preserve multiline composer drafts during timeline scrolling

[Yash-Singh1]

What Changed

• Keep multiline composer prompts expanded while scrolling the message timeline.
• Handle keyboard and pointer-based timeline navigation consistently, including when focus is outside the timeline.
• Add composer focus, selection, scroll-gesture, and multiline-prompt coverage.
• Tighten provider-session recovery and temporary-branch handling to avoid resuming stale runtime state.

Why

Scrolling the timeline could collapse the composer and make multiline drafts difficult to review or continue editing. The updated focus and scroll handling preserves the draft’s usable layout while still allowing the composer to collapse in appropriate states. Related server-side checks ensure recovery only continues when persisted session records agree.

UI Changes

Before/after screenshots are not included.

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: Would Approve

Macroscope's review found this PR approvable — This is a contained web UI bug fix that keeps multiline drafts readable while scrolling and extends existing keyboard timeline handling with targeted guards. The changes are localized to composer/timeline behavior and include focused tests for scroll-collapse and multiline measurement logic.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

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[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	13.6 KiB	13.6 KiB	−32 B (−0.2%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	−4 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.6 KiB	6.5 KiB	−28 B (−0.4%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.1 KiB	57.1 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.5 KiB	13.6 KiB	+34 B (+0.2%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	+4 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.5 KiB	+30 B (+0.5%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.8 KiB	57.8 KiB	+44 B (+0.1%)	66.4 KiB	✅
Claude	Live turn messages	8	9	+1 (+12.5%)	21	✅

Baseline: 1e740e4 · PR result: 33acd9b · 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: 113.9 KiB
• Claude decoded thread snapshot: 114.6 KiB

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

[cursor]

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