Error Handling

Overview

Cross-language error-handling reference. The recurring mistakes are not syntactic: swallowing errors, retrying non-idempotent operations, losing the cause chain when wrapping, leaking internals in API responses, and log-and-rethrow double logging. This skill leads with the decision rules an expert applies, then shows the minimum code to implement each.

Agent Delegation

• loom-senior-software-engineer (Opus) — DEFAULT. Error architecture, strategy choice, secure handling (no info leak), infra resilience (retry/circuit breaker/fallback).
• loom-software-engineer (Sonnet) — ONLY boilerplate error types / unit tests following an established pattern.

Error Taxonomy — Classify First

Every failure is exactly one of three kinds; the kind dictates handling: