StreamEvent

StreamEvent is the union type for all events yielded by assistant.chat(). It provides a unified interface across all engines.

Type Definition

type StreamEvent =
  | { type: 'text'; content: string }
  | { type: 'tool_call'; name: string; args: string }
  | { type: 'tool_result'; content: string }
  | { type: 'warning'; message: string }
  | { type: 'error'; message: string }
  | { type: 'done'; sessionId?: string; durationMs?: number;
      costUsd?: number; numTurns?: number };

Event Types

text

Streamed text content from the agent.

{ type: 'text', content: 'Here is the analysis...' }

Multiple text events form the complete response. Concatenate content fields to build the full text.

tool_call

The agent is invoking a tool (reading a file, running a command, etc.).

{ type: 'tool_call', name: 'readFile', args: '{"path": "data.csv"}' }

Field	Description
name	Tool name (e.g., readFile, bash, writeFile)
args	JSON string of tool arguments

tool_result

The result of a tool invocation.

{ type: 'tool_result', content: 'File contents here...' }

warning

Non-fatal warning from the engine.

{ type: 'warning', message: 'Running with --dangerously-skip-permissions' }

error

An error occurred during processing.

{ type: 'error', message: 'Engine process exited with code 1' }

done

Signals the end of a conversation turn.

{
  type: 'done',
  sessionId: 'abc-123',
  durationMs: 12345,
  costUsd: 0.042,
  numTurns: 3
}

Field	Description	Availability
sessionId	Engine session ID for resume	All engines
durationMs	Wall-clock duration	All engines
costUsd	API cost in USD	Claude Code, OpenCode
numTurns	Number of agent turns	Claude Code

Consuming Events

Print text only

for await (const event of assistant.chat('Hello')) {
  if (event.type === 'text') process.stdout.write(event.content);
}

Full event handling

let fullText = '';

for await (const event of assistant.chat('Analyze the data')) {
  switch (event.type) {
    case 'text':
      fullText += event.content;
      break;
    case 'tool_call':
      console.log(`[tool] ${event.name}`);
      break;
    case 'tool_result':
      console.log(`[result] ${event.content.slice(0, 100)}...`);
      break;
    case 'error':
      console.error(`[error] ${event.message}`);
      break;
    case 'done':
      console.log(`Done in ${event.durationMs}ms`);
      break;
  }
}

Accumulate for IM reply

let reply = '';
for await (const event of assistant.chat(message)) {
  if (event.type === 'text') reply += event.content;
}
await sendToIM(reply);