v0.6.0

Breaking

• Runtime.send() / Runtime.reset(): a call made while the runtime is already processing an event (from middleware, an effect handler, a subscribe or 'transition' listener, or a child runtime's listener) is now queued and processed after the current event's last notification (run-to-completion) instead of running inside it, because the README-recommended "send from an effect" pattern delivered notifications in reverse and left subscribers holding a stale snapshot; the nested call returns the snapshot committed at that moment, and an error from a queued event propagates from the outermost call. Migration: read getSnapshot() after the outer send()/reset() returns (or subscribe) instead of using a nested call's return value or reading the snapshot right after it, and catch errors around the outermost call rather than around a nested send().
• Runtime.subscribe() / Runtime.on() / Runtime.onTransition(): a listener removed while a notification is running (by its unsubscribe function, once, its signal, or dispose()) is now skipped for the rest of that round instead of still receiving the in-flight event, per the ai*js fan-out re-entrancy rule. Migration: if a removed listener must still see the current event, remove it after the call returns (for example queueMicrotask(off)), and do not rely on the remaining listeners running after a mid-notification dispose().
• mergeContext() / action results: for an object context (not an array or binary view) a plain-object patch is now merged into a copy that keeps the context's prototype, where a class-instance context used to be replaced by the bare patch and lose its other fields and methods, and a non-nullish primitive result such as false or 0 now throws InvalidActionResultError from step()/send() instead of replacing the context. Migration: return a plain-object partial (or undefined) from actions on object contexts; to replace the context wholesale, return a new instance or array (non-plain objects still replace it).
• Runtime.send() / Runtime.reset() sub-machine lifecycle: when a transition replaces a child, the new child is now constructed before the old child is disposed, so an init failure leaves the old child live and still returned by subRuntime() (it used to be disposed first, leaving undefined). Migration: code that runs while a new child is being created must not assume the previous sibling child is already disposed, and code that expected subRuntime() to be undefined after a SubMachineError with phase: "init" should expect the previous child.
• after() / createScheduler().after(): an ms that is NaN, ±Infinity, negative or not a number now throws RangeError, and a non-function fn throws TypeError, synchronously and before any timer is set (they used to fire after about 1 ms, or throw later from inside the timer), and a finite delay above 2^31-1 ms is clamped to 2^31-1 instead of firing almost at once. Migration: pass a finite ms >= 0 and a function; callers using Infinity to mean "never" should simply not schedule.
• defineMachine() / setup().defineMachine() / createMachine() / createRuntime() / Runtime.send() / Runtime.reset() / Runtime.subscribe() / Runtime.on() / Runtime.onTransition(): argument misuse now throws InvalidDefinitionError (aifsmjs: <subject> must be <constraint>) at the call — a non-object definition, states, state or transition entry; a non-object impl or options object, or a middleware option that is not an array of functions; an event that is not an object with a string type; a non-function listener or an unknown on() event type — instead of a bare TypeError (at the call or at a later send()), a listener that threw at every notification, or a silently accepted value. Migration: pass {} as impl when a machine uses no named implementations, pass object events with a string type and function listeners, and catch InvalidDefinitionError where you caught TypeError.

Changes

• Added: InvalidActionResultError (root export, name === "InvalidActionResultError", with the offending actionName) for an action that returns a non-nullish primitive for an object context.
• Added: mergeContext(current, patch, actionName?) takes an optional action name for that error (default "<inline>").
• Changed: InvalidDefinitionError is also the argument-validation error of the definition/runtime boundary; its non-object states message now reads aifsmjs: definition states must be an object.
• Changed: an async effect rejection with no 'error' listener (none registered, or cleared by dispose()) is still discarded, but is now reported via console.warn when NODE_ENV !== "production"; production behaviour is unchanged and it never becomes an unhandled rejection.
• Changed: aifsmjs/pbt's properties is a frozen object carrying the same eight functions instead of a module namespace object, which drops tsup's shared __export helper chunk (about 210 B gzip) from every subpath entry.
• Changed: step() returns a shared frozen empty effects array when nothing fires.
• Changed: size budgets in scripts/check-size.mjs (maintainer-approved for 0.6.0): dist/index.js 6,500 -> 6,700 B and dist/pbt/index.js 8,500 -> 8,800 B, other budgets unchanged; measured gzip closures 0.5.9 -> 0.6.0: index 6,359 -> 6,654, guards 1,375 -> 1,161, effects 1,574 -> 1,365, inspect 552 -> 329, replay 3,115 -> 3,139, pbt 8,471 -> 8,718, timer 1,071 -> 1,018 B.
• Fixed: transition/implementation lookups (state.on[event.type], guard/action/effect refs) now resolve by own key only, so an undeclared event type or ref named after an Object.prototype member (toString, constructor, __proto__, ...) is no longer treated as a declared transition.
• Fixed: deepFreeze no longer throws on binary data (ArrayBuffer views, e.g. Uint8Array) reached through context or event payloads, in dev snapshots or via middleware in production.
• Fixed: deepFreeze recurses through an object that is already shallow-frozen (e.g. an effect descriptor), instead of stopping there — middleware can no longer mutate an effect payload before dispatch, and an already shallow-frozen dev context is still deep-frozen.
• Fixed: runtime event listeners are isolated per-listener — a throwing 'dispose' or 'error' listener no longer prevents later listeners for the same event from running.
• Fixed: assignDoesNotMutate detects mutation by a structural fingerprint instead of structuredClone, so it no longer false-fails for a pure machine whose context holds a class instance or a callback.
• Fixed: setup().defineMachine() infers States from keyof states only, so a terminal state written as {} or { final: true } no longer collapses the inferred state union.
• Fixed: an explicit context: undefined passed to defineMachine / setup().defineMachine now defaults to {}, the same as an absent context key.
• Fixed: dev-mode detection reads process.env.NODE_ENV directly, so Vite / webpack 5 define-replacement enables dev-only deep-freezing in browser builds that have no process global.
• Fixed: the PBT snapshotAlwaysFrozen and reachableStatesSubsetDeclared properties no longer dispatch real effects while driving generated commands through a runtime.
• Fixed: createScheduler().after() merges signal/setTimeout/clearTimeout field-by-field with ?? instead of an object spread, so an explicitly-undefined per-call option no longer silently overrides the scheduler's default.
• Fixed: MachineConfig, the parameter type of defineMachine, is re-exported from the package root.
• Fixed: reset() now notifies subscribers, middleware (changed: true) and 'transition' listeners when the context reference (or status) differs from the initial snapshot; it used to compare the state value alone and stay silent.
• Fixed: middleware no longer deep-freezes the caller's event object (and its payload graph) in any NODE_ENV; MiddlewareContext.event is the caller's object, passed unfrozen.
• Fixed: a parent send()/reset() issued from a child's 'dispose' listener during a transition is queued until the transition commits, so a live child can no longer be left in a state that has no sub.
• Fixed: a parent disposed by a child's 'dispose' listener during a transition no longer adopts the replacement child; the replacement is disposed and subRuntime() returns undefined.
• Fixed: send() decides whether a same-value transition is external from the guard pass that produced the snapshot, so each guard runs once per event and a non-idempotent guard can no longer desync the sub-machine lifecycle from the committed state.
• Fixed: defineMachine() rejects a sub-machine cycle through initial states with InvalidDefinitionError instead of letting createRuntime() recurse until the stack overflows; self-references through non-initial states stay legal.
• Fixed: snapshotAlwaysFrozen, reachableStatesSubsetDeclared and replayEqualsFold dispose the runtime they create for each generated run, so its AbortSignal fires and no run leaks a live runtime.
• Fixed: package.json exports nests types under import and require (require.types points at the .d.cts files) for every subpath, so node16 / nodenext CommonJS consumers no longer hit TS1479 / TS1471; verify-exports walks nested conditions.
• Docs: corrected the aifsmjs/effects Public Surface row (README/README_ZHTW) to name the real export, createEnqueuer(), instead of enqueue.effect().
• Docs: STABILITY.md's Behavioral Contract states the run-to-completion and fan-out clauses, the reset, merge, argument-validation and timer rules, and the new sub-machine order; README and README_ZHTW Lifecycle Rules and Sharp Edges mirror them, and the Runtime / MiddlewareContext JSDoc says the same.