Honor Ghostty background opacity across cmux chrome

[lawrencecchen]

Summary

• Propagate Ghostty background opacity into Bonsplit chrome updates by emitting RGBA hex when opacity is below 1.0.
• Make workspace/pane/titlebar empty-state backgrounds follow the same Ghostty color+opacity path for live updates.
• Clamp Ghostty config opacity parsing and use clear window backgrounds for non-opaque cases to avoid flattening transparency through host layers.
• Add regression coverage for background-opacity parsing and Bonsplit chrome hex generation.
• Bump vendor/bonsplit to include RGBA chrome hex parsing support.

Testing

• swift test (in vendor/bonsplit) (passed)
• xcodebuild -project GhosttyTabs.xcodeproj -scheme cmux-unit -destination 'platform=macOS' -only-testing:cmuxTests/GhosttyConfigTests -only-testing:cmuxTests/WorkspaceChromeColorTests -only-testing:cmuxTests/GhosttyBackgroundThemeTests test (passed)
• xcodebuild -project GhosttyTabs.xcodeproj -scheme cmux -configuration Debug -destination 'platform=macOS' build (passed)

Related

• Task: ghostty transparency not supported #263
• Bonsplit dependency PR: Support alpha in chrome background hex bonsplit#6

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Feb 21, 2026 2:35pm

[lawrencecchen]

Superseded by #667 — clean reimplementation from main with RRGGBBAA bonsplit support, decoupled glass effect, and GhosttyBackgroundTheme helper.