fix(web): scope PR title collapse to tab scrollers

[Adamulek123]

Replaces #14302 with corrected After recording and the rebased branch.

What Changed

The PR title now collapses and reopens only when the active tab's main vertical scroller moves. Summary, Timeline, and Code register their own scroller; Code also registers its loading, error, empty, and raw diff views. The scroll adjustment made when the title collapses is tied to the same tab and element that triggered it. A focused panel test covers nested scrolls, tab switches, and that adjustment.

Why

While viewing a PR with a long, unwrapped code block in its description, scrolling the block sideways could reopen a collapsed title even though the Summary tab had not moved vertically. The panel's onScrollCapture treated every descendant scroll target as the tab scroller and later applied its scroll adjustment to whichever descendant had most recently scrolled. The nested "Conversations not on the current diff" list in Code could therefore change the title and receive that adjustment too.

The Code diff's horizontal scroller lives inside the viewer's shadow DOM; its sideways scroll does not reach the panel. The Code tab's main vertical scroller does, so scrolling back to the top can already reopen the title. This change makes that ownership explicit without changing horizontal diff scrolling.

Scope and approval

This is a small, focused fix for an obvious bug: scrolling nested content must not change the PR title when the active tab's main vertical scroller has not moved. It keeps the existing collapse and reopen behavior and qualifies for the focused bug-fix exception in CONTRIBUTING.md. It applies to the shared web panel used by web and desktop; mobile has a separate UI. It changes no provider behavior or wire contracts.

UI Changes

Before:

T3_Code_.Nightly._elxplgRCW0.mp4

After:

brave_Xutwhtk2DP.mp4

After video recorded on head 3d48f423e707d290a9e8a4a6edbed12988b819ea, rebased onto main base a97a4a9d189f145afe79c3a6f8533bbf9a6b40b1, using the isolated web dev server.

Validation

• vp test run apps/web/src/components/pullRequest/PullRequestDetailPanel.test.tsx apps/web/src/components/pullRequest/PullRequestSummaryTab.test.tsx: 32 tests passed. The new test checks that nested scrolls do not change the title, the active tab's scroller does, and scroll adjustment stays on that scroller.
• Before/After videos captured in a real vp run dev session against isolated dev state.
• Targeted lint: completed with warnings in these files, no errors.
• Targeted format check: passed for all six changed files.
• Web typecheck: no errors in the six changed files; full apps/web tsc --noEmit still reports pre-existing errors elsewhere (e.g. useBrowserViewportResize.ts, threadSort.test.ts, ProviderSettingsPanel.logic.test.ts).

Checklist

• This PR is small and focused
• I explained what changed and why
• I included a video for animation/interaction changes

GPT-6-Sol via the Codex harness in T3 Code.

[macroscopeapp]

Approvability

Verdict: Approved at 6886f45

Macroscope's review found this PR approvable — This is a localized web bug fix that scopes existing PR-header collapse and scroll compensation to the active tab’s actual scroller, with focused regression coverage for nested and cross-tab behavior. It introduces no schema, deployment, security, billing, default, or static-analysis changes.

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

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📥 Commits

Reviewing files that changed from the base of the PR and between 6ea01f8 and 3d48f42.

📒 Files selected for processing (6)

• apps/web/src/components/pullRequest/PullRequestCodeTab.tsx
• apps/web/src/components/pullRequest/PullRequestDetailPanel.test.tsx
• apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx
• apps/web/src/components/pullRequest/PullRequestSummaryTab.test.tsx
• apps/web/src/components/pullRequest/PullRequestSummaryTab.tsx
• apps/web/src/components/pullRequest/PullRequestTimelineTab.tsx

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📝 Walkthrough

Walkthrough

The pull-request detail panel now tracks separate scroll containers for the summary, timeline, and code tabs. Title folding and scroll compensation use the active tab’s registered scroller. Tests cover nested scrolling, inactive tabs, and tab switching.

Changes

Pull-request tab scrolling

Layer / File(s)	Summary
Register tab scroll containers apps/web/src/components/pullRequest/PullRequestCodeTab.tsx, apps/web/src/components/pullRequest/PullRequestSummaryTab.tsx, apps/web/src/components/pullRequest/PullRequestTimelineTab.tsx, apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx, apps/web/src/components/pullRequest/PullRequestSummaryTab.test.tsx	The summary, timeline, and code tabs accept callbacks for their scroll containers. The detail panel stores and passes separate refs for each tab.
Use the active tab scroller apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx, apps/web/src/components/pullRequest/PullRequestDetailPanel.test.tsx	Scroll handling ignores targets other than the active tab’s scroller. Scroll compensation records the originating tab and container. Tests cover nested and inactive-tab scroll events, the position cap, and tab switching.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Bug fix

Suggested reviewers: bil0000

Merge Risk: ⚪ Minimal · up to 3d48f

No actionable merge-blocking issue is established. Title folding and scroll adjustment are scoped to the active tab’s main scroller, with focused regression coverage. Mergeable subject to normal checks.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 6 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main fix: scoping PR title collapse to the active tab's scroller.
Description check	✅ Passed	The description explains the problem, change, scope, approval exception, UI evidence, and focused validation results. It uses different headings from the template, but all required information is pres…

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Dismissing prior approval to re-evaluate 3d48f42

Dismissing prior approval to re-evaluate 6886f45

[maria-rcks]

Note

Written by claude-opus-5-5 on behalf of Maria

Hi! We are cleaning up open PRs, and this one appears to have been created with an older model (gpt-6-sol). If this change is really important, we recommend rebuilding the PR with a newer model if possible.

[maria-rcks]

Note

Written by claude-opus-5-5 on behalf of Maria

Reopening, this was closed by mistake. Sorry for the noise!