Roo-Code/apps/cli/docs/AGENT_LOOP.md

CLI Agent Loop

This document explains how the Roo Code CLI detects and tracks the agent loop state.

Overview

The CLI needs to know when the agent is:

• Running (actively processing)
• Streaming (receiving content from the API)
• Waiting for input (needs user approval or answer)
• Idle (task completed or failed)

This is accomplished by analyzing the messages the extension sends to the client.

The Message Model

All agent activity is communicated through ClineMessages - a stream of timestamped messages that represent everything the agent does.

Message Structure

interface ClineMessage {
	ts: number // Unique timestamp identifier
	type: "ask" | "say" // Message category
	ask?: ClineAsk // Specific ask type (when type="ask")
	say?: ClineSay // Specific say type (when type="say")
	text?: string // Message content
	partial?: boolean // Is this message still streaming?
}

Two Types of Messages

Type	Purpose	Blocks Agent?
say	Informational - agent is telling you something	No
ask	Interactive - agent needs something from you	Usually yes

The Key Insight

The agent loop stops whenever the last message is an ask type (with partial: false).

The specific ask value tells you exactly what the agent needs.

Ask Categories

The CLI categorizes asks into four groups:

1. Interactive Asks → WAITING_FOR_INPUT state

These require user action to continue:

Ask Type	What It Means	Required Response
tool	Wants to edit/create/delete files	Approve or Reject
command	Wants to run a terminal command	Approve or Reject
followup	Asking a question	Text answer
browser_action_launch	Wants to use the browser	Approve or Reject
use_mcp_server	Wants to use an MCP server	Approve or Reject

2. Idle Asks → IDLE state

These indicate the task has stopped:

Ask Type	What It Means	Response Options
completion_result	Task completed successfully	New task or feedback
api_req_failed	API request failed	Retry or new task
mistake_limit_reached	Too many errors	Continue anyway or new task
auto_approval_max_req_reached	Auto-approval limit hit	Continue manually or stop
resume_completed_task	Viewing completed task	New task

3. Resumable Asks → RESUMABLE state

Ask Type	What It Means	Response Options
resume_task	Task paused mid-execution	Resume or abandon

4. Non-Blocking Asks → RUNNING state

Ask Type	What It Means	Response Options
command_output	Command is running	Continue or abort

Streaming Detection

The agent is streaming when:

1. partial: true on the last message, OR

2. An api_req_started message exists with cost: undefined in its text field

   // Streaming detection pseudocode
   function isStreaming(messages) {
   	const lastMessage = messages.at(-1)
   
   	// Check partial flag (primary indicator)
   	if (lastMessage?.partial === true) {
   		return true
   	}
   
   	// Check for in-progress API request
   	const apiReq = messages.findLast((m) => m.say === "api_req_started")
   	if (apiReq?.text) {
   		const data = JSON.parse(apiReq.text)
   		if (data.cost === undefined) {
   			return true // API request not yet complete
   		}
   	}
   
   	return false
   }
   

State Machine

                    ┌─────────────────┐
                    │    NO_TASK      │  (no messages)
                    └────────┬────────┘
                             │ newTask
                             ▼
              ┌─────────────────────────────┐
         ┌───▶│         RUNNING             │◀───┐
         │    └──────────┬──────────────────┘    │
         │               │                       │
         │    ┌──────────┼──────────────┐        │
         │    │          │              │        │
         │    ▼          ▼              ▼        │
         │ ┌──────┐  ┌─────────┐  ┌──────────┐   │
         │ │STREAM│  │WAITING_ │  │   IDLE   │   │
         │ │ ING  │  │FOR_INPUT│  │          │   │
         │ └──┬───┘  └────┬────┘  └────┬─────┘   │
         │    │           │            │         │
         │    │ done      │ approved   │ newTask │
         └────┴───────────┴────────────┘         │
                                                 │
         ┌──────────────┐                        │
         │  RESUMABLE   │────────────────────────┘
         └──────────────┘  resumed

Architecture

┌─────────────────────────────────────────────────────────────────┐
│                        ExtensionHost                            │
│                                                                 │
│  ┌──────────────────┐                                           │
│  │   Extension      │──── extensionWebviewMessage ─────┐        │
│  │   (Task.ts)      │                                  │        │
│  └──────────────────┘                                  │        │
│                                                        ▼        │
│  ┌───────────────────────────────────────────────────────────┐  │
│  │                    ExtensionClient                        │  │
│  │                (Single Source of Truth)                   │  │
│  │                                                           │  │
│  │  ┌─────────────────┐    ┌────────────────────┐            │  │
│  │  │ MessageProcessor │───▶│    StateStore     │            │  │
│  │  │                 │    │  (clineMessages)   │            │  │
│  │  └─────────────────┘    └────────┬───────────┘            │  │
│  │                                  │                        │  │
│  │                                  ▼                        │  │
│  │                         detectAgentState()                │  │
│  │                                  │                        │  │
│  │                                  ▼                        │  │
│  │  Events: stateChange, message, waitingForInput, etc.      │  │
│  └───────────────────────────────────────────────────────────┘  │
│                           │                                     │
│                           ▼                                     │
│  ┌────────────────┐  ┌────────────────┐  ┌────────────────┐     │
│  │ OutputManager  │  │  AskDispatcher │  │ PromptManager  │     │
│  │  (stdout)      │  │  (ask routing) │  │  (user input)  │     │
│  └────────────────┘  └────────────────┘  └────────────────┘     │
└─────────────────────────────────────────────────────────────────┘

Component Responsibilities

ExtensionClient

The single source of truth for agent state, including the current mode. It:

• Receives all messages from the extension
• Stores them in the StateStore
• Tracks the current mode from state messages
• Computes the current state via detectAgentState()

• Emits events when state changes (including mode changes)

  const client = new ExtensionClient({
  	sendMessage: (msg) => extensionHost.sendToExtension(msg),
  	debug: true, // Writes to ~/.roo/cli-debug.log
  })
  
  // Query state at any time
  const state = client.getAgentState()
  if (state.isWaitingForInput) {
  	console.log(`Agent needs: ${state.currentAsk}`)
  }
  
  // Query current mode
  const mode = client.getCurrentMode()
  console.log(`Current mode: ${mode}`) // e.g., "code", "architect", "ask"
  
  // Subscribe to events
  client.on("waitingForInput", (event) => {
  	console.log(`Waiting for: ${event.ask}`)
  })
  
  // Subscribe to mode changes
  client.on("modeChanged", (event) => {
  	console.log(`Mode changed: ${event.previousMode} -> ${event.currentMode}`)
  })
  

StateStore

Holds the clineMessages array, computed state, and current mode:

interface StoreState {
	messages: ClineMessage[] // The raw message array
	agentState: AgentStateInfo // Computed state
	isInitialized: boolean // Have we received any state?
	currentMode: string | undefined // Current mode (e.g., "code", "architect")
}

MessageProcessor

Handles incoming messages from the extension:

• "state" messages → Update clineMessages array and track mode
• "messageUpdated" messages → Update single message in array
• Emits events for state transitions and mode changes

AskDispatcher

Routes asks to appropriate handlers:

• Uses type guards: isIdleAsk(), isInteractiveAsk(), etc.
• Coordinates between OutputManager and PromptManager
• In non-interactive mode (-y flag), auto-approves everything

OutputManager

Handles all CLI output:

• Streams partial content with delta computation
• Tracks what's been displayed to avoid duplicates
• Writes directly to process.stdout (bypasses quiet mode)

PromptManager

Handles user input:

• Yes/no prompts
• Text input prompts
• Timed prompts with auto-defaults

Response Messages

When the agent is waiting, send these responses:

// Approve an action (tool, command, browser, MCP)
client.sendMessage({
	type: "askResponse",
	askResponse: "yesButtonClicked",
})

// Reject an action
client.sendMessage({
	type: "askResponse",
	askResponse: "noButtonClicked",
})

// Answer a question
client.sendMessage({
	type: "askResponse",
	askResponse: "messageResponse",
	text: "My answer here",
})

// Start a new task
client.sendMessage({
	type: "newTask",
	text: "Build a web app",
})

// Cancel current task
client.sendMessage({
	type: "cancelTask",
})

Type Guards

The CLI uses type guards from @roo-code/types for categorization:

import { isIdleAsk, isInteractiveAsk, isResumableAsk, isNonBlockingAsk } from "@roo-code/types"

const ask = message.ask
if (isInteractiveAsk(ask)) {
	// Needs approval: tool, command, followup, etc.
} else if (isIdleAsk(ask)) {
	// Task stopped: completion_result, api_req_failed, etc.
} else if (isResumableAsk(ask)) {
	// Task paused: resume_task
} else if (isNonBlockingAsk(ask)) {
	// Command running: command_output
}

Debug Logging

Enable with -d flag. Logs go to ~/.roo/cli-debug.log:

roo -d -y -P "Build something" --no-tui

View logs:

tail -f ~/.roo/cli-debug.log

Example output:

[MessageProcessor] State update: {
  "messageCount": 5,
  "lastMessage": {
    "msgType": "ask:completion_result"
  },
  "stateTransition": "running → idle",
  "currentAsk": "completion_result",
  "isWaitingForInput": true
}
[MessageProcessor] EMIT waitingForInput: { "ask": "completion_result" }
[MessageProcessor] EMIT taskCompleted: { "success": true }

Summary

1. Agent communicates via ClineMessage stream
2. Last message determines state
3. ask messages (non-partial) block the agent
4. Ask category determines required action
5. partial: true or api_req_started without cost = streaming
6. ExtensionClient is the single source of truth