fix(web): prevent seams in the topbar scroll fade

[caezium]

What Changed

Overlap the gradient and solid layers of the topbar scroll mask by 1px, in both mask-size and -webkit-mask-size.

Why

Text scrolling under the workspace title bar can acquire a thin dark line where the mask layers meet. At a 17px interface font, the 1.5rem fade is 25.5px high; rasterization can leave a partially transparent row at that fractional boundary. The overlap closes that gap.

The shared utility covers the message timeline, Settings, and pull-request views on web and desktop.

This uses the same approach as the still-open #7787. The screenshots below independently reproduce the issue and verify the fix.

UI Changes

Captured from the actual T3 Code Electron app with an isolated profile and invented workspace, chat, and browser content. Iris dark theme, 17px interface font, 100% zoom, 1440 × 960 window. Each pair changes only this PR's fix.

Before	After

Full app captures

Before:

After:

Validation

• bun fmt
• bun lint
• bun typecheck (full workspace)
• From apps/web: bun run test src/components/chat/MessagesTimeline.test.tsx — 46 tests passed.
• Reproduced the line through real chat text in the desktop test instance and verified that the overlap removes it.

Checklist

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

No animation or interaction behavior changes; a video is not applicable.

Summary by CodeRabbit

• Bug Fixes
  • Adjusted the title bar fade mask to provide smoother scrolling transitions at the top and bottom edges.

[macroscopeapp]

Approvability

Verdict: Approved at 326bfdb

Macroscope's review found this PR approvable — This CSS-only change adjusts the existing topbar fade mask by one pixel in both browser-specific declarations, affecting only a localized visual detail. It is small, self-contained, and does not alter product defaults, interfaces, workflows, or static-analysis configuration.

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

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ℹ️ Recent review info

⚙️ Run configuration

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Plan: Advanced

Run ID: 424d29ca-16e6-4ff3-94c4-7877f5af1747

📥 Commits

Reviewing files that changed from the base of the PR and between 6c58362 and 326bfdb.

📒 Files selected for processing (1)

• apps/web/src/index.css

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📝 Walkthrough

Walkthrough

The titlebar scroll-fade masks now extend their configured fade height by 1px for WebKit and standard mask implementations.

Changes

Titlebar fade

Layer / File(s)	Summary
Extend both mask dimensions apps/web/src/index.css	The WebKit and standard mask declarations add 1px to the configured titlebar fade height.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to 326bf

The shared topbar scroll fade now overlaps its layers by 1px to eliminate visible seams. No current merge-blocking risk remains.

Suggested reviewers: juliusmarminge, maria-rcks, t3dotgg

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the web fix and the specific topbar scroll fade issue. It is concise and directly matches the main change.
Description check	✅ Passed	The description includes the required What Changed, Why, UI Changes, and Checklist sections. It explains the rasterization issue, documents the focused fix, provides before-and-after screenshots, and …
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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