# Principles

- [Separate what was braided](/principles/separate-what-was-braided): Complection is two independent concerns woven together so that neither can change alone.
- [Make the interface deep](/principles/make-the-interface-deep): A deep module hides a hard problem behind a small interface.
- [Optimize for deletion](/principles/optimize-for-deletion): Build small programs you can replace when their model stops fitting reality.
- [Put authority in the right boundary](/principles/put-authority-in-the-right-boundary): A read model can report a decision, but only the aggregate that owns the invariant makes it.
- [Keep the pure core pure](/principles/keep-the-pure-core-pure): An effect system earns its place at effectful boundaries.
- [Make essential time visible](/principles/make-essential-time-visible): Use an explicit state machine when modes change which events are legal, or when work needs cancellation, retries, resumability, or child work.
- [Make the separation stick](/principles/make-the-separation-stick): Agents copy the patterns they find, so a separation must live in code, types, or checks rather than in one reviewer's head.
- [Admission control protects recovery](/principles/admission-controls-new-work): Refuse or defer work that cannot be served usefully under current load.
- [Backpressure reaches the producer](/principles/backpressure-reaches-the-producer): Bounded consumption helps only when upstream respects waiting or refusal.
- [Bulkheads isolate scarce capacity](/principles/bulkheads-isolate-capacity): Reserve independent capacity for workloads that must not starve each other.
- [Checkpoints follow the promised commit](/principles/checkpoints-follow-commits): Persist state and progress together when one store can transact both.
- [Circuit breakers have state](/principles/circuit-breakers-have-state): A breaker stops doomed calls and controls probes before restoring traffic.
- [Cleanup can be an idempotent postcondition](/principles/cleanup-can-be-an-idempotent-postcondition): Already-absent state can be success when absence is the operation’s intended result.
- [Dead letters need a return path](/principles/dead-letters-need-a-return-path): Exhausted work needs durable evidence, an owner, and deliberate redrive.
- [Durability starts with a recovery record](/principles/durability): A reading order for storage, replay, worker ownership, overload, and recovery tests.
- [Durable timers need recovery](/principles/durable-timers-need-recovery): Persist scheduled intent when losing a worker must not lose its deadlines.
- [Durable work needs storage](/principles/durable-work-needs-storage): A restarted worker cannot recover intent that existed only in memory.
- [Effect is not BEAM](/principles/effect-is-not-beam): Fibers share a runtime; scope ownership does not supply isolated heaps or OTP restart strategies.
- [Every task needs an owner](/principles/every-task-needs-an-owner): Give child work a lifetime, a failure observer, and a recovery decision.
- [Failures keep their meaning](/principles/failures-keep-their-meaning): Expected refusals, infrastructure faults, and defects need different policies.
- [Golden signals expose overload](/principles/golden-signals-expose-overload): Measure latency, traffic, errors, and saturation, including failed work.
- [Old events must still decode](/principles/old-events-must-still-decode): Retained data needs compatibility rules before recovery depends on it.
- [Pure cores reduce timeline coupling](/principles/pure-cores-reduce-timelines): Move deterministic rules out of time-dependent actions and shared mutable state.
- [Queries need result bounds](/principles/queries-need-result-bounds): Limit result cardinality before the driver materializes an oversized response.
- [Recovery needs model tests](/principles/recovery-needs-model-tests): Test sequences of failures and recoveries against explicit invariants.
- [Replay needs stable inputs](/principles/replay-needs-stable-inputs): Historical processing must not silently depend on today’s clock or external decisions.
- [Request lifetime is not durability](/principles/request-lifetime-is-not-durability): Worker waitUntil has a shared post-response allowance; required work needs a durable marker and redrive.
- [Restart must reconstruct known state](/principles/restart-from-known-state): Execution recovery and state recovery need separate contracts.
- [Retry load needs a budget](/principles/retry-load-needs-a-budget): One retry owner must control attempts, delay, and aggregate load.
- [Retry needs idempotent effects](/principles/retry-needs-idempotency): Repeating an operation must preserve its intended observable result.
- [Shared schemas need a transition period](/principles/schema-changes-need-a-transition): Keep old and new representations usable while consumers migrate.
- [Steady state recycles resources](/principles/steady-state-recycles-resources): Every accumulation needs a deliberate recycling policy.
- [Supervision chooses what restarts](/principles/supervision-is-a-recovery-policy): Restart policy follows dependency shape and bounds repeated recovery.
- [Timeouts bound waiting](/principles/timeouts-bound-waiting): A local timeout stops waiting; it does not prove the remote action never happened.