Description

One Line Summary

Apply the same click-listener registration safeguards added to the Android bridge in #881 to the iOS bridge, so both platforms share the identical pattern.

Details

Motivation

#881 hardened the Android Clicked event accessor based on review feedback. The iOS bridge (iOSNotificationsManager) already used lazy native registration (which is why iOS never had the cold-start click drop), but had none of the safeguards:

1. The add/remove accessors were unsynchronized, so two threads subscribing concurrently could both pass the _clickNativeListenerSet check and register the native callback twice.
2. _clickNativeListenerSet = true was set before the native call, so a transient native-call failure left the flag stuck true with no listener registered — clicks silently lost for the app's lifetime with no retry.
3. A failed native call left the managed handler subscribed, so a caller retrying the subscription would add the same handler twice.

This PR applies the identical fixes: a private lock around both accessors, the flag set only after the native call returns, and a rollback (_clicked -= value) before rethrowing on failure.

It also adds the null-handler guard in _onClicked that the Android bridge already has — without it, a click arriving after all handlers are removed (the native listener is never unregistered) would throw a NullReferenceException on the Unity main thread.

Scope

iOS only, notification click events only. No public API changes and no behavior change on any success path — the lazy registration timing is exactly as before. Android is untouched (already done in #881).

Testing

Unit testing

None added — the repo has no unit test infrastructure; this mirrors the reviewed and manually verified Android change from #881.

Manual testing

Verified with the demo app built from this branch (Unity 6000.3.6f1, IL2CPP) on an iPhone 16 Pro simulator (iOS 18.1), using xcrun simctl push with a OneSignal-format payload containing additional data:

• App initializes normally; the first Clicked += subscription registers the native callback through the new locked accessor without issues.
• Foreground receive path unchanged: C# ForegroundWillDisplay fired for each pushed notification and the notification displayed.
• Click path verified: tapping a pushed notification (app backgrounded) fired the C# Clicked handler, and the native SDK recorded the notification as a DIRECT influence.

The failure-path changes (concurrent first subscription, native call throwing) are not reachable in a normal run; correctness argued by symmetry with the reviewed Android implementation from #881.

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
• I have reviewed this PR myself, ensuring it meets each checklist item