Chapter 10: Error Handling in Multi-agent Systems

10.1 Error Categories

Category	Examples	Retryable	Agent action
Transient	Timeout, 503, network failure	Yes	Retry with exponential backoff
Validation	Invalid input format, missing required field	No (fix input)	Modify request and retry
Business	Policy violation, threshold exceeded	No	Explain to the user; propose an alternative
Permission	Access denied	No	Escalate

10.2 Error-handling Anti-patterns

Anti-pattern	Problem	Correct approach
Generic status "search unavailable"	The coordinator can't decide how to recover	Return error type, query, partial results, alternatives
Silent suppression (empty result = success)	Coordinator thinks there were no matches, but it was a failure	Distinguish "no results" from "search failure"
Aborting the whole workflow on one failure	You lose all partial results	Continue with partial results; annotate gaps
Infinite retries inside a subagent	Latency and wasted resources	Local recovery (1–2 retries), then propagate to coordinator

10.3 A Structured Subagent Error

{
  "status": "partial_failure",
  "failure_type": "timeout",
  "attempted_query": "AI impact on music industry 2024",
  "partial_results": [
    {"title": "AI Music Generation Report", "url": "...", "relevance": 0.8}
  ],
  "alternative_approaches": [
    "Try a narrower query: 'AI music composition tools'",
    "Use an alternative data source"
  ],
  "coverage_impact": "Not covered: AI impact on music production"
}

This provides the coordinator with the information needed to decide:

Retry with a modified query?
Use partial results?
Delegate to a different subagent?
Continue without this section and annotate the gap?

10.4 Coverage Annotations in the Final Synthesis

## Report: AI Impact on Creative Industries

### Visual Art (FULL COVERAGE)
[research results]

### Music (PARTIAL COVERAGE — search agent timeout)
[partial results]
⚠️ Note: coverage for this section is limited due to a timeout in the search agent.

### Literature (FULL COVERAGE)
[research results]