Limitations
The honest list. Most of these are deliberate trade-offs; the rest are edges of the current implementation.
Pinned effect version
The engine implements interfaces from effect/unstable/*, whose API can move between releases — the effect peer dependency is pinned exactly, and tracking a new effect release is a new release of this package. Plan for lockstep upgrades until Effect v4's workflow API stabilizes.
Attach polling costs history
Attaching to a foreign execution (a child id already taken) polls through the bridge activity: one activity plus one timer of history per poll, backing off from 5s to a 60s cap. Fine for quick attaches; hour-scale foreign runs still accrue history. Don't use attach as a long-wait primitive — share results through a workflow both parties execute, or a mailbox.
Effect timers are history events
Effect.sleep, Effect.timeout*, and Schedule delays inside the sandbox become durable Temporal timers — deterministic and correct, but each is a history event. A retry policy with many short delays writes many timers. Prefer activity-level retries (the activity definition's retry options) for retrying I/O, and named DurableClock.sleep for waits that matter.
Schedule fires sit outside idempotency
Fired runs get schedule-generated workflow ids and are addressed by those ids; a digest-addressed execute can run concurrently with a fired run. See Schedules.
Nexus attach refuses closed executions
A repeated Nexus operation call attaches to a running execution but fails loudly against a closed one — deliberately stricter than direct execute. See Nexus.
Mailbox offers are best-effort
Offers to closed executions are dropped by design, and on the workflow side any delivery failure is logged and swallowed — a mailbox offer is not a delivery guarantee. Use an update when the sender needs an answer.
The sandbox is still the sandbox
Temporal's determinism constraints apply to the code you write inside workflow handlers: no direct I/O, no non-deterministic module state, versioned changes to in-flight code. The authoring rules and the engine remove the accidental ways to trip — they cannot remove the model.
Polyfilled sandbox globals
The sandbox exposes no crypto, TextEncoder, or performance; this package installs deterministic polyfills for exactly the surface Effect needs (SHA-256 digests, UTF-8 encoding, performance.now). Code relying on other Node globals inside a workflow body will still fail — reach for an activity instead.