fix(web): preserve scroll fades while avoiding Linux sidebar flicker

[B-EtterDigital]

Linux desktop scroll areas can flicker until their rows disappear while remaining clickable. This patch replaces the stacked edge masks with one top-to-bottom gradient on Linux desktop, using additive compositing. It keeps the vertical fade instead of removing masks entirely. Fixes #7766.

The rule applies only to viewports whose ScrollArea requests scrollFade; other scroll areas receive no new mask. macOS, Windows, and browser clients retain the existing mask behavior. Linux horizontal edge fades are not included in the single vertical gradient.

The founder tested this exact gradient and compositing rule in the running desktop app over sustained normal use and reported no further flicker, with the fade still visible. Environment: Hyprland/Wayland, NVIDIA RTX 2080 SUPER, 1.25 display scale, 0.0.43-nightly.20260925.2237. GPU compositing stays enabled. This is a reported live result on one system, not proof for every Linux GPU. Private thread and project names prevent publishing the original screenshots; the issue contains the original flicker video.

Verification on Song for c5b1560:

• vp fmt --check: pass.
• vp lint: zero errors; existing warnings remain.
• tsc --noEmit in apps/web: pass.
• vp test run --project unit src/lib/utils.test.ts --maxWorkers=2: 7 tests pass.

Original implementation: Claude Code / Claude Opus 5.5. Gradient revision: Codex harness / GPT-6-Astra.

Summary by CodeRabbit

• Bug Fixes
  • Improved scroll-area fade effects in the Linux desktop app. Fades now follow the direction of overflow—vertically or horizontally—and are limited to the content overflowing at each edge. Other platforms are unchanged.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This is a focused Linux/Electron flicker fix, but it changes the default scroll-area presentation across Linux desktop windows by removing edge fades. That product-default change warrants human review.

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• apps/web/src/index.css

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📝 Walkthrough

Walkthrough

Linux platform detection now selects a Linux Electron class. Scroll-faded viewports expose a data attribute. Linux-specific CSS applies vertical or horizontal masks, with fade lengths capped by overflow distances.

Changes

Linux Electron scroll fading

Layer / File(s)	Summary
Linux platform class selection apps/web/src/lib/utils.ts, apps/web/src/lib/windowControlsOverlay.ts, apps/web/src/lib/utils.test.ts	Adds case-insensitive Linux platform detection and uses it to select an Electron Linux class. Tests cover Linux, macOS, and Windows platform strings.
Linux scroll-fade masks apps/web/src/components/ui/scroll-area.tsx, apps/web/src/index.css	Adds a data attribute to scroll-faded viewports. For Electron on Linux, CSS applies vertical masks or horizontal masks when there is no vertical overflow. Fade distances are capped by the corresponding overflow distances.

Priority: ⬆️ High

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: juliusmarminge, bil0000

Merge Risk: ⚪ Minimal · up to fb7a6

The Linux scroll-fade change is mergeable after normal checks; no outstanding behavior issue was established.

Architecture Summary

Architecture risk: 🔵 Low · up to fb7a6

The change affects 1 system.

Changed systems: apps/web

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — apps/web (ui) was modified; 5 changed files map to changed impact.

Before / after behavior

• observed — Modified behavior in apps/web/src/components/ui/scroll-area.tsx: The viewport gains a data-scroll-fade attribute when scrollFade is true; it is omitted when false.
• observed — Modified behavior in apps/web/src/lib/utils.test.ts: The test file now imports isLinuxPlatform.
• observed — Modified behavior in apps/web/src/lib/utils.test.ts: Adds tests expecting isLinuxPlatform to return true for Linux x86_64, Linux aarch64, and lowercase linux, and false for MacIntel and Win32.
• observed — Modified behavior in apps/web/src/lib/utils.ts: Added isLinuxPlatform, which matches platform strings beginning with linux without regard to case.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 4 files. (1 skipped: 1 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the web fix, the preserved scroll fades, and the Linux sidebar flicker addressed by the changes.
Description check	✅ Passed	The description explains the problem, solution, scope, testing, and known validation limits. It does not use the template headings or include the checklist, and it does not provide before/after screen…
Linked Issues check	✅ Passed	The PR addresses the Linux desktop flicker in issue #7766. ScrollArea marks fade-enabled viewports with data-scroll-fade. Linux Electron windows receive the electron-linux class. The CSS replace…
Out of Scope Changes check	✅ Passed	The changed files support issue #7766. The platform helper and its tests identify Linux. The Electron class scopes the workaround to Linux desktop windows. The viewport attribute scopes the CSS to fad…

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 4 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 2

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
In `@apps/web/src/index.css`:
- Around line 1614-1630: Add a Linux-specific rule for
`[data-scroll-fade][data-has-overflow-x]:not([data-has-overflow-y])` that
applies a single horizontal mask gradient using the horizontal overflow
variables, preserving horizontal edge fades for horizontal-only viewports
without restoring stacked masks.
- Around line 1614-1630: Update the Linux scroll-area viewport mask in the
`.electron-linux [data-slot="scroll-area-viewport"][data-scroll-fade]` rule to
use `var(--fade-size)` instead of the fixed `1.5rem` in both gradient
calculations, preserving the existing mask behavior.

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Configuration used: Repository: pingdotgg/t3code/.coderabbit.yaml

Review profile: CHILL

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📥 Commits

Reviewing files that changed from the base of the PR and between e5a46d6 and c5b1560.

📒 Files selected for processing (5)

• apps/web/src/components/ui/scroll-area.tsx
• apps/web/src/index.css
• apps/web/src/lib/utils.test.ts
• apps/web/src/lib/utils.ts
• apps/web/src/lib/windowControlsOverlay.ts

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