Shell Integration

Shell Integration

Sidecar's interactive shell allows users to type directly into tmux sessions from within the TUI. Tmux remains the PTY backend. Sidecar renders ordered control-mode bytes through the shared tty.Model, whose VT behavior is behind the screenmodel adapter rather than implemented in plugin code.

Package Structure

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internal/tty/                    # Shared tmux terminal abstraction
  tty.go                         # Core Model and State types
  keymap.go                      # Bubble Tea -> tmux key translation
  messages.go                    # Owner/target/generation-scoped messages
  session.go                     # tmux operations (send-keys, capture-pane, resize)
  scheduler.go                   # Keyed fallback-poll generation ownership
  control_*.go                   # Session-keyed tmux -C transport and manager
  capture_range.go               # Atomic bounded history capture
  cursor.go                      # Cursor positioning helpers
  paste.go                       # Paste handling (clipboard, bracketed paste)
  terminal_mode.go               # Capture-fallback mode recovery
  output_buffer.go               # Absolute, bounded live/history buffer
  editor_session.go              # Shared inline-editor tmux lifecycle

internal/plugins/workspace/
  interactive.go                 # Workspace-specific interactive mode logic
  interactive_selection.go       # Text selection in interactive mode
  terminal_viewport.go           # Pure shared terminal viewport renderer
  terminal_control.go            # Workspace target/layout policy for tty.Model
  terminal_history.go            # Lazy absolute scrollback loading
  terminal_search.go             # Loaded-history search
  terminal_links.go              # Safe URL/path detection and activation
  native_terminal.go             # Native cursor and contextual mouse mode
  view_preview.go                # Agent/shell preview composition
  mouse.go                       # Scroll handling
  types.go                       # InteractiveState type

internal/plugins/filebrowser/
  inline_edit.go                 # Inline editor mode using tty.Model
  handlers.go                    # Message handling for inline edit

Data Flow

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User Keypress -> handleInteractiveKeys() -> tty.MapKeyToTmux() -> tmux send-keys

Pane output -> tmux -C ordered %output bytes
            -> session-pooled control actor
            -> seeded screenmodel adapter
            -> adaptive per-feed presentation publication
            -> owner/target/generation-scoped Tea message
            -> OutputBuffer + cursor/modes/history
            -> pure terminal viewport + native Bubble Tea cursor

Open/resync/history -> bounded capture seed/range
Control unavailable/dead -> one scoped capture-poll fallback + clean reseed

Core Abstractions

tty.Model

Embeddable component for interactive tmux functionality:

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type Model struct {
    Config   Config        // Exit key, copy/paste keys, scrollback lines
    State    *State        // Current interactive state
    Width    int
    Height   int
    OnExit   func() tea.Cmd
    OnAttach func() tea.Cmd
}

// Usage:
p.inlineEditor = tty.New(&tty.Config{
    ExitKey: "ctrl+\\",
    ScrollbackLines: 600,
})
cmd := p.inlineEditor.Enter(sessionName, paneID)

tty.State

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type State struct {
    Active        bool
    TargetPane    string      // tmux pane ID (e.g., "%12")
    TargetSession string
    LastKeyTime   time.Time   // Input timing and fallback polling decay
    CursorRow, CursorCol int
    CursorVisible        bool
    PaneHeight, PaneWidth int
    BracketedPasteEnabled bool
    MouseReportingEnabled bool
    OutputBuf      *OutputBuffer
    PollGeneration int          // For invalidating stale fallback polls
}

tty.OutputBuffer

Thread-safe bounded buffer with hash-based change detection:

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func (b *OutputBuffer) Update(content string) bool {
    rawHash := maphash.String(seed, content)
    if rawHash == b.lastRawHash { return false }  // Skip ALL processing
    content = mouseEscapeRegex.ReplaceAllString(content, "")
    b.lines = strings.Split(content, "\n")
    return true
}
func (b *OutputBuffer) LinesRange(start, end int) []string

Key Mapping (keymap.go)

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func MapKeyToTmux(msg tea.KeyPressMsg) (key string, useLiteral bool) {
    if msg.Mod.Contains(tea.ModCtrl) && msg.Code >= 'a' && msg.Code <= 'z' {
        return "C-" + string(msg.Code), false
    }
    switch msg.Code {
    case tea.KeyEnter:     return "Enter", false
    case tea.KeyBackspace: return "BSpace", false
    case tea.KeyTab:       return "Tab", false
    case tea.KeyUp:        return "Up", false
    }
    if msg.Text != "" {
        return msg.Text, true // Literal mode
    }
    return "", true
}

Modified keys use CSI sequences:

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case "shift+up":   return "\x1b[1;2A", true
case "ctrl+up":    return "\x1b[1;5A", true
case "alt+up":     return "\x1b[1;3A", true
case "shift+tab":  return "\x1b[Z", true

For printable characters, tmux send-keys -l prevents interpretation.

Capture fallback and semantic observation

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const (
    PollingDecayFast   = 50ms    // During active typing
    PollingDecayMedium = 200ms   // After 2s inactivity
    PollingDecaySlow   = 250ms   // After 10s inactivity
    KeystrokeDebounce  = 20ms    // Delay after keystroke
)

Control-mode bytes are the ordinary presentation source for every visible terminal surface. Adaptive capture polling exists only until the first seeded frame and after control/model failure. Workspace agent and shell observation continues independently for provider activity evidence; those captures never overwrite a model-owned presentation buffer.

The control actor writes every ordered byte into screenmodel immediately. Presentation alone is adaptive: the first changed frame after idle publishes inline, sustained changed frames publish at no more than 30 fps per pane-model feed, and one tokenized timer guarantees the newest trailing frame. Seed, reseed, and generation changes bypass the cap; input never enters this cadence. Ordinary Frame() snapshots omit diagnostic cells, while screen comparison explicitly requests the canonical grid.

For isolated performance diagnostics, run with both SIDECAR_PPROF=<port> and SIDECAR_TERMINAL_PERF=1, then read GET /debug/terminalperf. The endpoint is localhost-only and returns fixed numeric counts plus output-to-frame samples, p95, and maximum in microseconds. Its fixed vocabulary covers model publication, terminal views, row hits/misses/bypasses, link resolution, global Sessions list/preview work, application/Workspace/sidebar views, project preview composes/cache hits, and document frame builds/cache hits/scans/resolution. A pulse-only interval should reuse the project preview and perform no terminal, document, or row work. Keep counters off during CPU profiles, use a separate diagnostic process, and never interpret process-wide model-frame counts as per-feed fps when more than one pane-model feed may be live.

Set SIDECAR_TERMINAL_TRACE=1 only in an isolated proof run to log privacy-safe capture metadata (surface, role, reason, and generation). It never logs session or pane identity, terminal text, commands, paths, titles, or provider payloads. This distinguishes intentional semantic observation from presentation fallback.

Visibility and focus

Keyed generation ownership

tty.KeyedScheduler owns a generation per logical source (agent:<name>, shell:<tmuxName>, terminal-panel). Every schedule allocates a fresh token, and the token travels through capture, result, retry, and continuation messages. Reset invalidates pending timers and in-flight results.

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token, cmd := scheduler.Schedule(key, delay, makeMessage)
if scheduler.IsCurrent(key, token) { /* apply result */ }

Control subscriptions are pooled by tmux session because a control client cannot observe panes in another session. Subscription close and manager stop invalidate and drain queued callbacks before returning.

Cursor Positioning (cursor.go)

Query

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func QueryCursorPositionSync(target string) (row, col, paneHeight, paneWidth int, visible, ok bool) {
    cmd := exec.Command("tmux", "display-message", "-t", target,
        "-p", "#{cursor_x},#{cursor_y},#{cursor_flag},#{pane_height},#{pane_width}")
}

Rendering

Focused live terminal surfaces expose a tea.Cursor through the plugin CursorProvider capability. Workspace, filebrowser, and notes compute exact application coordinates and suppress the cursor under modals, while scrolled back, outside the visible slice, or when another surface owns focus. A painted cursor is not added to native-cursor content.

Height Mismatch Adjustment

When display height differs from tmux pane height:

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if paneHeight > displayHeight {
    relativeRow = cursorRow - (paneHeight - displayHeight)
} else if paneHeight > 0 && paneHeight < displayHeight {
    relativeRow = cursorRow + (displayHeight - paneHeight)
}

Scrolling

Scrolling operates on the captured buffer. No tmux copy-mode involved.

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type Plugin struct {
    previewOffset    int   // Lines from bottom (0 = at bottom/live)
    autoScrollOutput bool  // Auto-follow new output?
}

• Scroll UP: pause auto-scroll, increment previewOffset
• Scroll DOWN: decrement previewOffset, re-enable auto-scroll at 0
• Live capture stays bounded at 600 lines; older 600-line ranges load lazily
• Absolute buffer coordinates keep selections and search matches stable
• Scrollback is bounded by the shared 10,000-line tmux history policy
• Instant response (pure state manipulation, no subprocess calls)

Copy/Paste

• Copy: alt+c (configurable via interactiveCopyKey), or super+c (Cmd+C) as a built-in that a configured key does not replace. Cmd+C only arrives when the emulator passes it through — terminals that keep it for themselves (iTerm2) never deliver it, so alt+c stays the portable chord.
• Paste: alt+v (configurable via interactivePasteKey)

Paste wraps text with bracketed paste sequences (\x1b[200~...\x1b[201~) when the application has enabled bracketed paste mode.

Fallback Terminal Mode Recovery (terminal_mode.go)

When capture fallback owns presentation, detects bracketed paste and mouse reporting modes by scanning the fallback snapshot. Healthy model-backed presentation receives these modes from the shared screen model.

Width Synchronization

Tmux panes are resized in background at all times (not just interactive mode):

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func ResizeTmuxPane(paneID string, width, height int) {
    // resize-window, fallback to resize-pane for older tmux
}

Resize triggers: window resize, sidebar toggle/drag, selection change, agent/shell creation, interactive mode entry.

Inline Edit Mode (Filebrowser)

Uses tty.Model plus tty.EditorSession for vim/nano/emacs editing in the file preview pane. Session creation is history-safe and asynchronous:

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func (p *Plugin) enterInlineEditMode(path string) tea.Cmd {
    return func() tea.Msg {
        session, err := tty.StartEditorSession(tty.EditorSessionOptions{Path: path})
        return InlineEditStartedMsg{Session: session, Err: err}
    }
}

Entry and Exit

Workspace Plugin:

• Enter: enter / E when preview pane focused with output tab
• Exit: Ctrl+\ (instant) or double-Escape (150ms delay)
• Attach: Ctrl+] / t only when tmux_full_attach is on (default off)

Filebrowser Plugin:

• Enter: e or Enter on a file (if inline edit enabled)
• Exit: Ctrl+\ or double-Escape
• Attach: Ctrl+] only when tmux_full_attach is on (default off)

Feature Flags

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{
  "features": {
    "tmux_interactive_input": true,
    "tmux_inline_edit": true,
    "tmux_full_attach": false,
    "workspace_terminal_panel": true
  }
}

Configuration

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{
  "plugins": {
    "workspace": {
      "interactiveExitKey": "ctrl+\\",
      "interactiveAttachKey": "ctrl+]",
      "interactiveCopyKey": "alt+c",
      "interactivePasteKey": "alt+v",
      "tmuxCaptureMaxBytes": 2097152,
      "copyOnSelect": false
    }
  }
}

Critical Rules

1. Scope every async result by owner, target/role, activation, and keyed generation.
2. Carry the generation end to end through capture, result, retry, and continuation.
3. Never call subprocesses from Init() or View(); use Start()/tea.Cmd.
4. Do not mutate model state in tea.Cmd callbacks; return a scoped message.
5. Hash raw capture before cleaning/splitting, but mode changes must still clear coordinate state.
6. Preserve newer live overlap when delayed history ranges prepend.
7. Control clients are per tmux session and close/stop must invalidate and drain deliveries.
8. Keep keyed capture fallback working until the first accepted model frame and after control failure; never run it as the healthy renderer.
9. Consume all model bytes immediately and cadence only presentation snapshots; preserve immediate idle-leading output, a newest trailing frame, and unconditional seed/generation publication.
10. Use native cursor only for the focused live viewport; hide it offscreen, under modals, and in scrollback.
11. Treat source OSC as untrusted; the sanitizer and independent fuzz oracle must cover nested 7-bit/C1 forms and removal-boundary synthesis.
12. Width sync matters; resize panes/control clients when terminal geometry changes.

References

• Tmux integration notes -- detailed tmux CLI techniques, cursor tracking, resize sync, bracketed paste, mouse forwarding, modified keys, adaptive polling, debugging
• Original spec: docs/plans/implemented/spec-tmux-interactive-input.md