fix(web): scroll sidebar after external thread navigation

[tarik02]

What Changed

Backports pingdotgg/t3code#8065.

• Reveal the active thread instantly when the sidebar becomes visible.
• Smooth-scroll to thread selections made outside the sidebar.
• Keep direct sidebar navigation and settings round-trips from moving the list.
• Keep the active thread rendered when project scope or a collapsed preview would otherwise hide it.

The fork already had the upstream visible-thread helper, so this backport applies the remaining changes to both sidebar implementations.

Why

Thread changes from the command palette, deletion fallback, and other external navigation can select a row outside the visible sidebar area. Direct sidebar clicks already start from a visible row and should not move the list.

UI Changes

Opening the sidebar reveals the active thread without animation. External thread changes use smooth scrolling. Direct sidebar navigation and returning from settings do not scroll.

Screenshots and video were not captured because browser verification was not requested.

Verification

• vp i, including the lockfile supply-chain check
• Formatting check for all 3 changed files
• Targeted lint for all 3 changed files
• Web typecheck
• Changed lines match upstream PR #8065; the identical shared helper was already on org/main

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for the UI changes
• I included a video for the interaction change

Made with GPT-5.6 Sol using the Codex harness in T3 Code.

[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	12.1 KiB	12.1 KiB	−79 B (−0.6%)	15.1 KiB	✅
Codex	Thread snapshot wire	5.8 KiB	5.8 KiB	+3 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.3 KiB	−82 B (−1.3%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	55.5 KiB	54.7 KiB	−822 B (−1.4%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	12.2 KiB	12.2 KiB	−39 B (−0.3%)	15.1 KiB	✅
Claude	Thread snapshot wire	5.8 KiB	5.8 KiB	+7 B (+0.1%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	−46 B (−0.7%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	56.4 KiB	56.4 KiB	−44 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	10	9	−1 (−10.0%)	21	✅

Baseline: 04932a5 · PR result: 80b6686 · 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: 84.1 KiB
• Claude decoded thread snapshot: 84.5 KiB

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