# JSON Event Stream Mode

```bash
companion --mode json "Your prompt"
```

Outputs all session events as JSON lines to stdout. Useful for integrating companion into other tools or custom UIs.

## Event Types

Events are defined in [`AgentSessionEvent`](https://github.com/badlogic/companion-mono/blob/main/packages/coding-agent/src/core/agent-session.ts#L102):

```typescript
type AgentSessionEvent =
  | AgentEvent
  | { type: "auto_compaction_start"; reason: "threshold" | "overflow" }
  | {
      type: "auto_compaction_end";
      result: CompactionResult | undefined;
      aborted: boolean;
      willRetry: boolean;
      errorMessage?: string;
    }
  | {
      type: "auto_retry_start";
      attempt: number;
      maxAttempts: number;
      delayMs: number;
      errorMessage: string;
    }
  | {
      type: "auto_retry_end";
      success: boolean;
      attempt: number;
      finalError?: string;
    };
```

Base events from [`AgentEvent`](https://github.com/badlogic/companion-mono/blob/main/packages/agent/src/types.ts#L179):

```typescript
type AgentEvent =
  // Agent lifecycle
  | { type: "agent_start" }
  | { type: "agent_end"; messages: AgentMessage[] }
  // Turn lifecycle
  | { type: "turn_start" }
  | {
      type: "turn_end";
      message: AgentMessage;
      toolResults: ToolResultMessage[];
    }
  // Message lifecycle
  | { type: "message_start"; message: AgentMessage }
  | {
      type: "message_update";
      message: AgentMessage;
      assistantMessageEvent: AssistantMessageEvent;
    }
  | { type: "message_end"; message: AgentMessage }
  // Tool execution
  | {
      type: "tool_execution_start";
      toolCallId: string;
      toolName: string;
      args: any;
    }
  | {
      type: "tool_execution_update";
      toolCallId: string;
      toolName: string;
      args: any;
      partialResult: any;
    }
  | {
      type: "tool_execution_end";
      toolCallId: string;
      toolName: string;
      result: any;
      isError: boolean;
    };
```

## Message Types

Base messages from [`packages/ai/src/types.ts`](https://github.com/badlogic/companion-mono/blob/main/packages/ai/src/types.ts#L134):

- `UserMessage` (line 134)
- `AssistantMessage` (line 140)
- `ToolResultMessage` (line 152)

Extended messages from [`packages/coding-agent/src/core/messages.ts`](https://github.com/badlogic/companion-mono/blob/main/packages/coding-agent/src/core/messages.ts#L29):

- `BashExecutionMessage` (line 29)
- `CustomMessage` (line 46)
- `BranchSummaryMessage` (line 55)
- `CompactionSummaryMessage` (line 62)

## Output Format

Each line is a JSON object. The first line is the session header:

```json
{
  "type": "session",
  "version": 3,
  "id": "uuid",
  "timestamp": "...",
  "cwd": "/path"
}
```

Followed by events as they occur:

```json
{"type":"agent_start"}
{"type":"turn_start"}
{"type":"message_start","message":{"role":"assistant","content":[],...}}
{"type":"message_update","message":{...},"assistantMessageEvent":{"type":"text_delta","delta":"Hello",...}}
{"type":"message_end","message":{...}}
{"type":"turn_end","message":{...},"toolResults":[]}
{"type":"agent_end","messages":[...]}
```

## Example

```bash
companion --mode json "List files" 2>/dev/null | jq -c 'select(.type == "message_end")'
```