Terminal UI (TUI)

Tau's terminal UI is a reactive, inline-rendering chat interface built on the pkg/taui framework. It renders directly into the terminal scrollback (no alternate screen) and communicates with the coordinator through the event bus.

Architecture

internal/tui/
├── inline_chat.go       # Root component - event loop, rendering, tool display
├── run.go               # Run() entry point, delegates to RunInline
├── run_taui.go          # RunInline - taui bootstrap, event subscription, cleanup
├── api.go               # TUIConfig struct, ModelRefresher type
├── inline_commands.go   # Slash command table
├── inline_completions.go # Tab-completion engine
└── notify/
    └── notify.go        # Queue-based notification system

Lifecycle

1. app.RunChat() creates the coordinator and TUIConfig, then calls tui.Run().
2. Run() delegates to RunInline(), which:
   • Creates the taui.TUI engine
   • Subscribes to ChatEvent on the event bus (client name "tui")
   • Creates an inlineChat instance
   • Enters the taui render loop
3. inlineChat starts three goroutines:
   • eventLoop() - receives ChatEvent from the bus, dispatches to onRuntimeEvent()
   • spinnerLoop() - animates the working indicator while the model is generating
   • statusLoop() - rotates through queued notifications

inlineChat State

The inlineChat struct holds all UI state:

Field	Purpose
provider	Current provider name
modelName	Current model ID
sessionID	Session identifier
showReasoning	Whether reasoning content is displayed
availableModels	Model list for /model completions
availableProviders	Provider list for provider switching
registryCommands	Command registry entries
extensionCommands	Plugin command entries
sessionSummaries	Session list for /sessions
turnText	Accumulated assistant text for current turn
turnReasoning	Accumulated reasoning text for current turn
activeTools	Map of in-progress tool calls
working	Whether a request is in flight
running	Whether the TUI is running
webURL	Web UI URL to display in status bar

Event Handling

onRuntimeEvent() routes each ChatEvent type to state updates:

Event	State Update
ChatSessionSnapshotEvent	Sync full session state, update message history
ChatResponseStartedEvent	Set working = true, clear turnText/turnReasoning
ChatResponseDeltaEvent	Append to turnText
ChatReasoningDeltaEvent	Append to turnReasoning
ChatToolCallDeltaEvent	Update tool name/args in activeTools
ChatToolExecutionStartedEvent	Add tool to activeTools with "running" status
ChatToolOutputEvent	Append live tool output
ChatToolExecutionCompletedEvent	Set tool status to "ok" or "error"
ChatResponseCompletedEvent	Set working = false, finalize message
ChatRuntimeErrorEvent	Show error notification
ChatNotificationEvent	Queue notification
InteractivePromptRequestedEvent	Show inline confirm/input prompt
SessionsListedEvent	Update sessionSummaries
CommandsChangedEvent	Update registryCommands

Rendering

The inline render uses taui widgets:

• taui.Box - Layout container (vertical/horizontal stacking)
• taui.Text - Styled text spans with color, bold, italic
• taui.Paragraph - Word-wrapped text blocks
• taui.LineInput - Single-line text input with history
• taui.Completions - Drop-down autocomplete menu
• taui.ToolRow - Tool call status display with icons
• taui.Loader - Animated spinner

Each turn is rendered as:

1. User message (prefixed with >)
2. Reasoning content (if showReasoning is enabled, dimmed color)
3. Tool calls (each as a ToolRow with status icons and truncated arguments)
4. Assistant response text
5. Completion indicator (model name, token count, timing)

Slash Commands

All slash commands are defined in internal/tui/inline_commands.go as a slashCommand slice. Each entry has:

type slashCommand struct {
    name        string
    aliases     []string
    usage       string
    description string
    run         func(args string) error
    complete    func(token string) []string
}

Built-in Commands

Command	Aliases	Description
/model		Switch the active model
/system		View or edit the system prompt
/temperature		Set sampling temperature
/max-tokens		Set max completion tokens
/reset		Reset the session
/reasoning	/think	Toggle reasoning visibility or set effort
/refresh		Refresh the models.dev catalog
/sessions	/history	List saved sessions
/export		Export session as JSONL
/help	/?	Show command help
/debug		Toggle debug mode
/provider		Toggle a provider on/off, or /provider login <name> for OAuth
/quit	/exit	Exit tau

Extension Commands

Plugin slash commands are dynamically added to the table when plugins are loaded. They appear as /plugin:<name>:<command>.

Tab Completions

internal/tui/inline_completions.go provides dynamic tab completions:

1. If input starts with /, complete command names from the registry.
2. For /model, complete model IDs from availableModels.
3. For /sessions, complete session IDs.
4. For boolean toggles, complete on/off.
5. For model names without / prefix, complete from available models.

The completions use taui.CompletionSet and fuzzy-match against the current token under the cursor.

Notifications

internal/tui/notify/notify.go implements a queue-based notification system:

• Notifications are queued with a Level (info, warn, error) and expiry time.
• The statusLoop() goroutine rotates through queued notifications at ~3-second intervals.
• Notifications are rendered in the status bar area.
• Expired notifications are automatically removed.

Model Refresher

The ModelRefresher type (internal/tui/api.go) is a function that the TUI can call to re-discover available models:

type ModelRefresher func(ctx context.Context) ([]chat.ChatModelRef, error)

It's called by /refresh and on demand when the model list needs updating.

TUIConfig

type TUIConfig struct {
    SessionID          string
    ModelName          string
    Provider           string
    AvailableModels    []chat.ChatModelRef
    AvailableProviders []string
    InitialCommands    []chat.CommandRef
    Bus                *eventbus.Bus
    RefreshModels      ModelRefresher
    ShowReasoning      bool
    ReasoningEffort    string
    Debug              bool
    WebURL             string           // Web UI URL to display
}