Fix pane background alpha stacking with translucent themes

[EduardoBautista]

Summary

• Return .clear from paneBackground() / nsColorPaneBackground() when the resolved chrome color has alpha < 1.0
• Prevents alpha stacking where two translucent layers (Ghostty renderer + Bonsplit pane background) combine to appear nearly opaque (e.g. two layers at 0.9 → 0.99)
• Matches the existing pattern in GhosttyTerminalView.panelBackgroundFillColor()
• Fixes transparency being ignored when using more than one pane in a workspace

Context

PR #29 fixed intermediate split wrapper/container layers but SplitViewContainer still applies .background(TabBarColors.paneBackground(...)) at the root, which paints a duplicate translucent layer.

Test plan

• With background-opacity = 0.9: single pane should be visibly transparent
• Split into 2+ panes: transparency maintained in all panes
• With background-opacity = 1.0 (or unset): solid background, no regression

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Summary by cubic

Fixes pane background alpha stacking with translucent themes so transparency looks correct in split panes. If the resolved chrome background is translucent, we stop drawing a second translucent layer.

• Bug Fixes
  • TabBarColors.paneBackground(...) and nsColorPaneBackground(...) return .clear when alphaComponent < 0.999.
  • Prevents compounding translucency (e.g., 0.9 + 0.9 → ~0.99) from the renderer and pane background.
  • Keeps solid backgrounds unchanged and matches GhosttyTerminalView.panelBackgroundFillColor().

^{Written for commit ac2ea07. Summary will update on new commits.}

Summary by CodeRabbit

Bug Fixes

• Fixed background color rendering in the tab bar to prevent unintended translucency stacking when using background opacity settings.

[greptile-apps]

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[coderabbitai]

📝 Walkthrough

Walkthrough

The change modifies tab bar color computation to prevent double alpha compositing when translucent backgrounds are in use. Both SwiftUI Color and AppKit NSColor variants now check the alpha component and return clear if it's below 0.999, otherwise returning the computed color.

Changes

Cohort / File(s)	Summary
Tab Bar Color Alpha Handling Sources/Bonsplit/Internal/Styling/TabBarColors.swift	Added alpha component checks to paneBackground(for:) and nsColorPaneBackground(for:) methods to return Color.clear/.clear when alpha is less than 0.999, preventing translucent color layering.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• PR #29: Complements this change by clearing split wrapper layer backgrounds and consuming TabBarColors.paneBackground(for:) to prevent double alpha compositing in the visual hierarchy.

Poem

🐰 A layer too thick, a ghost in the glass,
Two alphas collide where one should pass.
Clear wins the day when opacity hides—
Now panes breathe softly on both sides. ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 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%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Fix pane background alpha stacking with translucent themes' accurately and clearly describes the main change: fixing alpha stacking issues in pane backgrounds when using translucent themes, which is the core focus of the PR.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

📝 Coding Plan

• Generate coding plan for human review comments

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[cubic-dev-ai]

No issues found across 1 file

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