mav-bp-error-handling

name	mav-bp-error-handling
description	Error handling conventions for all applications. Covers error propagation, retry strategies, circuit breakers, graceful degradation, error boundaries, and typed errors. Applied when writing or reviewing error handling code.
user-invocable	false
disable-model-invocation	true

Error Handling Standards

Maverick's hard rules for intentional, typed, resilient error handling.

Maverick's Rules

• Never swallow silently — every catch handles, logs, or re-throws. An empty catch is a bug.
• Catch at boundaries only — throw/return from low-level code, catch at service boundaries and the outermost handler. Catching at every layer duplicates logging and loses stack traces. No catch-and-re-throw without adding context.
• Typed errors — every application error carries type (machine-readable classification), message, context (structured metadata), and cause (wrapped original). Never throw new Error("failed").
• Log-level mapping: 4xx → warn, 5xx → error — client errors are expected (track volume, no alert unless it spikes); server errors require investigation and alert when persistent. Log levels and alerting per mav-bp-operability.
• Retry policy — 3 attempts max (1 initial + 2 retries) unless configured otherwise; exponential backoff (base * 2^attempt) with jitter. Retry only transient failures: timeouts, 429, 502, 503, 504. Never retry 400/401/403/404 or non-idempotent operations without idempotency keys.
• Never expose internals to clients — no stack traces, SQL/database messages, file paths, internal service names, or dependency versions in responses. Return a safe message, a machine-readable error type, and a request/correlation ID.
• Critical paths must not depend on non-critical services — degrade the feature (visibly, and log/alert on degraded mode) rather than crash. Frontend: error boundaries around major UI sections with fallback UI and error reporting.
• Fail fast on unrecoverable errors — configuration failures, corruption, programming errors: crash immediately with a clear message; do not attempt recovery.

Project Implementation Lookup

Check for docs/maverick/skills/error-handling/SKILL.md. If present, read it — it wins on specifics (library, config, conventions). If missing, proceed with these standards and note the gap in your summary.

Detecting Error Handling Issues in Code Review

Pattern	Issue	Fix
Empty catch block	Silently swallowed error	Handle, log, or re-throw
catch (err) { return null }	Lost error context	Propagate the error or handle explicitly
throw new Error("failed")	Untyped, no context	Use typed error with structured metadata
Retrying on 400/401/403	Retrying permanent failures	Only retry transient errors (429, 5xx, timeouts)
No retry on external HTTP calls	Fragile to transient failures	Add retry with exponential backoff
Stack trace in API response	Leaking internals	Return safe error with request ID only
catch at every layer in the call stack	Duplicate handling/logging	Catch at the boundary, propagate elsewhere
Feature crashes app when dependency is down	No graceful degradation	Degrade the feature, keep the app running
No error boundary around UI sections	Single component crashes page	Wrap sections in error boundaries with fallback UI
Generic error message for all failures	Poor user experience	Distinguish client vs server errors