Success case:
    >>> outcome = AgentRunOutcome(status="success", output="Task completed")
    >>> assert outcome.is_success()
    
    Validation failure:
    >>> outcome = AgentRunOutcome(
    ...     status="invalid_output", 
    ...     error="Output format is invalid",
    ...     error_category="validation"
    ... )
    >>> assert outcome.is_retryable()
    
    Timeout with context:
    >>> outcome = AgentRunOutcome(
    ...     status="timeout",
    ...     error="Agent timed out after 30s",
    ...     elapsed_s=30.0,
    ...     agent_name="researcher"
    ... )