packages/agent/src/types.ts). Types: start (partial AssistantMessage), text_start/delta/end, thinking_start/delta/end, toolcall_start/delta/end, done (AssistantMessage with stopReason), error (stopReason “error”/“aborted” + errorMessage). Stream functions (streamSimple, provider-specific stream<Provider>()) must return AssistantMessageEventStream and encode errors in events, not throw.
Related: Agent message, Streaming chat