cmux sidebar builder

Use this skill when the task is to create or modify a cmux custom sidebar view. These are user/agent-authored .swift files in ~/.config/cmux/sidebars/ rendered by cmux's runtime SwiftUI-style interpreter, not compiled app code. The primary dogfood surface is a normal Bonsplit pane tab opened with cmux sidebar open <name>; the left sidebar picker remains useful for previews.

Orientation

• The original work is PR https://github.com/manaflow-ai/cmux/pull/5254 by Aziz Albahar.
• The feature is opt-in behind the UserDefaults-backed key customSidebars.beta.enabled.
• Custom sidebars live under ~/.config/cmux/sidebars/. They can be opened as normal Bonsplit pane tabs with cmux sidebar open <name> and appear in the left sidebar picker when the beta is enabled.
• Start from the cmux app checkout docs: repo/docs/custom-sidebars.md.

Important cmux source entrypoints: