rohitg00/ai-engineering-from-scratch · error · EventStreamError

agent.message content must be a list

Error message

agent.message content must be a list

What it means

Error "agent.message content must be a list" thrown in rohitg00/ai-engineering-from-scratch.

Source

Thrown at certifications/claude/lessons/12-claude-agent-sdk-and-hooks/code/main.py:80

            if event_type == "event_delta" and isinstance(event.get("text"), str):
                preview_parts.append(event["text"])
            continue

        event_id = event.get("id")
        if not isinstance(event_id, str) or not event_id:
            raise EventStreamError("persisted events need a non-empty id")
        if event_id in seen:
            continue
        seen.add(event_id)
        last_event_id = event_id

        if event_type == "session.status_running":
            status = "running"
            stop_reason = None
        elif event_type == "agent.message":
            content = event.get("content", [])
            if not isinstance(content, list):
                raise EventStreamError("agent.message content must be a list")
            messages.append(
                "".join(
                    str(block.get("text", ""))
                    for block in content
                    if isinstance(block, dict) and block.get("type") == "text"
                )
            )
        elif event_type in {"agent.custom_tool_use", "agent.tool_use", "agent.mcp_tool_use"}:
            actionable.add(event_id)
        elif event_type in {"user.custom_tool_result", "user.tool_confirmation"}:
            reference = event.get("custom_tool_use_id") or event.get("tool_use_id")
            if not isinstance(reference, str) or reference not in actionable:
                raise EventStreamError("tool result or confirmation must reference a known action")
            pending.discard(reference)
        elif event_type == "session.status_idle":
            status = "idle"
            reason = event.get("stop_reason")
            if not isinstance(reason, dict) or reason.get("type") not in {"requires_action", "end_turn"}:

View on GitHub (pinned to 39ea8a1c6d)

When it happens

Trigger: Thrown at certifications/claude/lessons/12-claude-agent-sdk-and-hooks/code/main.py:80 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of rohitg00/ai-engineering-from-scratch@39ea8a1c6d (2026-08-26). Data as JSON: /api/errors/d301b479ba8cdece. Report an issue: GitHub.