feat: deliver batched CSS events to JS

[MatiPl01]

The JS half of the CSS events channel: a registry that receives batched events from native and hands each one to the subscribers listening for that view tag, plus the module plumbing that installs the handler.

Subscription is keyed by view tag rather than by object identity, since nested animated components can share a tag. An event can outlive the view it was emitted for, so an event for a tag nobody listens to is dropped.

A batch carries events for unrelated views, so a throwing subscriber is reported through ErrorUtils.reportFatalError rather than left to unwind. The error stays fatal, as an uncaught one would be, without starving the views queued behind it in the same batch.

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• New Features

  • Added support for receiving and dispatching CSS animation and transition events.
  • Added event subscription management by view, including registration, removal, and cleanup.
  • Added native event handling integration for supported runtime environments.

• Bug Fixes

  • Unknown event targets are safely ignored.
  • Errors in event callbacks are reported while allowing other callbacks to continue.

Walkthrough

The PR adds typed CSS animation and transition events, a per-view callback registry, and setCSSEventHandler plumbing through the native Reanimated module. Native initialization dispatches event batches to registered subscribers.

Changes

CSS native event handling

Layer / File(s)	Summary
Event contracts and callback registry packages/react-native-reanimated/src/css/native/events/*, packages/react-native-reanimated/src/css/native/index.ts	Defines CSS event payloads and subscriber contracts. The registry routes events by view tag, handles subscriber errors, and supports cleanup. Tests cover registration, dispatch, errors, mutation during dispatch, and clearing.
Module handler API packages/react-native-reanimated/src/ReanimatedModule/*, packages/react-native-reanimated/src/css/native/proxy.ts	Adds setCSSEventHandler to the native module, module proxy, CSS proxy, dummy proxy, and JS implementation.
Native event initialization packages/react-native-reanimated/src/initializers.native.ts	Registers the CSS event handler during native initialization and forwards event batches to cssCallbacksRegistry.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• software-mansion/react-native-reanimated#10108: Adds the native CSS event emitter that uses the handler plumbing introduced here.

Suggested labels: lib: Reanimated

Suggested reviewers: tjzel

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The description accurately explains the CSS event registry, batched event delivery, subscription behavior, error propagation, and module plumbing.
Title check	✅ Passed	The title clearly summarizes the main change: delivering batched CSS events from native code to JavaScript.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch @matipl01/css-events-js

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In
`@packages/react-native-reanimated/src/css/native/events/CSSCallbacksRegistry.ts`:
- Around line 46-48: The subscriber callback delivery in the nested event and
subscriber loops exits prematurely when handleCSSEvent throws, preventing later
subscribers and later events from receiving delivery. Wrap the
subscriber.handleCSSEvent(event) call in a try-catch block to capture errors
without exiting the loops. Store only the first caught error in a variable and
continue iterating through all subscribers and events. After both loops
complete, rethrow the captured error if one was encountered. Update the error
test to verify that a later subscriber in the same batch still receives its
event even when an earlier subscriber's handleCSSEvent throws.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 8faeb439-6ff8-4591-b3cd-940826c58af9

📥 Commits

Reviewing files that changed from the base of the PR and between cab405c and 801a7e4.

📒 Files selected for processing (10)

• packages/react-native-reanimated/src/ReanimatedModule/NativeReanimated.ts
• packages/react-native-reanimated/src/ReanimatedModule/js-reanimated/JSReanimated.ts
• packages/react-native-reanimated/src/ReanimatedModule/reanimatedModuleProxy.ts
• packages/react-native-reanimated/src/css/native/events/CSSCallbacksRegistry.ts
• packages/react-native-reanimated/src/css/native/events/__tests__/CSSCallbacksRegistry.test.ts
• packages/react-native-reanimated/src/css/native/events/index.ts
• packages/react-native-reanimated/src/css/native/events/types.ts
• packages/react-native-reanimated/src/css/native/index.ts
• packages/react-native-reanimated/src/css/native/proxy.ts
• packages/react-native-reanimated/src/initializers.native.ts