[davidkpiano]

Why

Analytics attached to a root actor miss child emissions. Systems can now observe actor emissions with source identity without forwarding them into machine event handlers.

What changed

• Add createSystem({ onEmitted }) and removable system.onEmitted(listener) subscriptions.
• Release canceled pending listeners while preserving cancellation across initialization and actor-local delivery.
• Add usage docs, README guidance, and an XState Changeset.

Scope

Observes actor emission requests before runtime delivery across all actors sharing a system. Direct low-level runtime delivery calls remain delivery-only.

Blast Radius

Changes emission execution and lazy system initialization. Regression tests cover constructor and startup emissions, snapshot views, listener failures, unsubscribe, multiple roots, and runtime overrides.

Verification

• pnpm test:core --maxWorkers=3 passed. 165 files, 2,764 tests.
• pnpm typecheck, pnpm lint, pnpm format:check, pnpm check:exports, and pnpm build passed.
• A native built-package GC probe reproduced retained callbacks before the cleanup and confirmed collection after cancellation. Independent review found no blocking findings.

---

[changeset-bot]

🦋 Changeset detected

Latest commit: 1f62a03

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
xstate	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: aad9253f-d6cc-4466-b82d-275ddfad025a

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[devin-ai-integration]

Devin Review found 1 potential issue.