Design notes

• Strict envelopes: Deadline and max-attempts are enforced before each attempt; sleeps are capped to remaining deadline to avoid overruns.
• Classification first: Policies are domain-agnostic; callers map exceptions to ErrorClass via classifiers (default or custom).
• Per-class backoff: Strategies are looked up by class, falling back to a default; absence of a strategy is a hard error.
• Best-effort hooks: Metric/log hooks are isolated—exceptions are swallowed so retries never break due to observability failures.
• Deterministic jitter bounds: Built-in strategies clamp to configured maxima; property-based tests assert bounds.
• Sync/async symmetry: RetryPolicy and AsyncRetryPolicy mirror semantics; @retry decorator auto-picks the right one.
• Context reuse: Context managers bind hooks/operations once for batches; avoid repeating kwargs on every call.
• Unknowns: max_unknown_attempts prevents unbounded retries on unclassified errors; deadline remains a global guardrail.