Marcus Sidecar Worktree Switching

Worktree Switching

Sidecar supports seamless switching between git worktrees. When switching:

1. All plugins are stopped, reinitialized with the new WorkDir, and restarted
2. Per-worktree state (active plugin, sidebar selections) is saved/restored
3. Project-specific themes are applied
4. If a worktree is deleted externally, sidecar gracefully falls back to main

Core Mechanism

Project Switching

Worktree switching uses Model.switchProject() in internal/app/model.go:

m.switchProject(worktreePath)

This triggers in order:

1. Save active plugin for old WorkDir
2. Update m.ui.WorkDir to new path
3. Apply resolved theme for new path
4. Call registry.Reinit(newWorkDir) -- stops all plugins, updates context, reinits all
5. Send WindowSizeMsg to all plugins for layout recalculation
6. Restore saved active plugin for new WorkDir
7. Show toast notification

Registry Reinitialization

Registry.Reinit() in internal/plugin/registry.go:

func (r *Registry) Reinit(newWorkDir string) []tea.Cmd {
    // Stop all plugins (reverse order)
    for i := len(r.plugins) - 1; i >= 0; i-- {
        r.safeStop(r.plugins[i])
    }
    // Update context
    r.ctx.WorkDir = newWorkDir
    // Reinit all plugins
    for _, p := range r.plugins {
        r.safeInit(p)
    }
    // Collect and return start commands
    return startCmds
}

Plugin Responsibilities on Worktree Switch

Handle Reinitialization Cleanly

Your plugin will be stopped and reinitialized on worktree switch. Ensure:

1. Stop() releases all resources (watchers, goroutines, channels)
2. Init(ctx) resets state and reads from new ctx.WorkDir
3. Start() kicks off fresh async work for the new context

func (p *Plugin) Stop() {
    p.stopOnce.Do(func() {
        if p.watcher != nil {
            p.watcher.Close()
        }
        close(p.done)
    })
}

func (p *Plugin) Init(ctx *plugin.Context) error {
    p.ctx = ctx
    p.items = nil            // Reset state
    p.stopOnce = sync.Once{} // Reset stop guard
    p.done = make(chan struct{})
    return nil
}

Handle WindowSizeMsg After Switch

After reinitialization, the app sends tea.WindowSizeMsg. Handle it in Update:

case tea.WindowSizeMsg:
    p.width = msg.Width
    p.height = msg.Height
    return p, nil

Persist Per-Worktree State

Use internal/state to save/restore preferences keyed by WorkDir:

// Restore state in Init or Start
saved := state.GetMyPluginState(p.ctx.WorkDir)
if saved.Selection != "" {
    p.selection = saved.Selection
}

// Save state on user action
state.SetMyPluginState(p.ctx.WorkDir, MyPluginState{
    Selection: p.selection,
})

Add state struct and accessors following internal/state/state.go:

type MyPluginState struct {
    Selection string `json:"selection,omitempty"`
}

func GetMyPluginState(workdir string) MyPluginState {
    mu.RLock()
    defer mu.RUnlock()
    if current == nil || current.MyPlugin == nil {
        return MyPluginState{}
    }
    return current.MyPlugin[workdir]
}

State is saved to ~/.config/sidecar/state.json keyed by absolute WorkDir path. State is automatically per-worktree when you pass p.ctx.WorkDir.

Deleted Worktree Detection

When a worktree is deleted externally, plugins should detect this and request fallback to main.

App-Level Commands

Defined in internal/app/commands.go:

• SwitchWorktreeMsg{WorktreePath} -- requests switching to a specific worktree
• SwitchWorktree(path) tea.Cmd -- helper to create the above
• SwitchToMainWorktreeMsg{MainWorktreePath} -- requests fallback to main worktree
• SwitchToMainWorktree(mainPath) tea.Cmd -- helper to create the above

Detection Pattern (from workspace plugin)

1. Define plugin-local message (internal/plugins/workspace/worktree.go):

type WorkDirDeletedMsg struct {
    MainWorktreePath string
}

2. Detect deletion in refresh command:

func (p *Plugin) refreshWorktrees() tea.Cmd {
    workDir := p.ctx.WorkDir
    return func() tea.Msg {
        if _, err := os.Stat(workDir); os.IsNotExist(err) {
            mainPath := findMainWorktreeFromDeleted(workDir)
            if mainPath != "" {
                return WorkDirDeletedMsg{MainWorktreePath: mainPath}
            }
        }
        return RefreshDoneMsg{Worktrees: worktrees, Err: err}
    }
}

3. Handle message, return app command:

case WorkDirDeletedMsg:
    p.refreshing = false
    if msg.MainWorktreePath != "" {
        return p, app.SwitchToMainWorktree(msg.MainWorktreePath)
    }
    return p, nil

Git Helpers

internal/app/git.go provides:

Per-WorkDir State Keys

Best Practices

1. Reset all state in Init() -- do not carry over stale data from previous worktree
2. Use sync.Once for Stop() -- prevents double-close panics during rapid switching
3. Validate WorkDir exists before expensive operations
4. Store WorkDir at command creation time -- closures may execute after switch
5. Keep Start() non-blocking -- return commands that do async work

Testing Worktree Switching

1. Create a worktree: git worktree add ../my-feature feature-branch
2. Switch to it via project switcher or workspace plugin
3. Verify your plugin reinitializes with correct data
4. Delete the worktree externally and trigger a refresh
5. Verify graceful fallback to main repo

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