[various] Add engineIdentifier to fake plugin registrars - #13574

flutter/packages@0478162...63881f9

2026-11-06 [email protected] [material_ui] Paint Dialog.fullscreen
background color behind the keyboard (flutter/packages#13244)
2026-11-05 [email protected] [material_ui] Add tabBar/tab
roles and expanded state semantics (flutter/packages#13176)
2026-11-05 [email protected]
[material_ui] Disable the DropdownButtonFormField decoration when the
field is disabled (flutter/packages#13473)
2026-11-05 [email protected] [material_ui] Fix Switch throwing when first
painted mid-animation (flutter/packages#13496)
2026-11-05 [email protected] [various] Add
engineIdentifier to fake plugin registrars (flutter/packages#13574)
2026-11-05 [email protected] [google_sign_in]
Allow GoogleSignIn-iOS 10 (flutter/packages#13306)
2026-11-05 [email protected] [material_ui] Hit
test the floating label of InputDecorator at its painted position
(flutter/packages#13326)
2026-11-05 [email protected] [material_ui] Fix InputDecorator
intrinsic height when isDense or isC… (flutter/packages#13522)
2026-11-05 [email protected] [material_ui] Paint Scaffold
persistent bottom sheet background color behind the keyboard
(flutter/packages#13242)
2026-11-05 [email protected] [image_picker_ios] PR 5/5 Switch
Pigeon to Swift and finish the Objective-C to Swift migration.
(flutter/packages#13493)

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…droid, iOS, and macOS (#196145)

### Issue Link:
#195876

### Impact Description:
Native plugins using JNI/FFI (such as plugins generated with Pigeon's native interop support) register directly in native memory rather than on a per-engine `BinaryMessenger`, and have no non-deprecated public API on `FlutterPluginBinding` (Android) or `FlutterPluginRegistrar` (iOS/macOS) to obtain the engine identifier during plugin attachment and detachment. In apps running multiple `FlutterEngine` instances in the same process (such as background engines alongside the main UI engine), one engine attaching or detaching can overwrite or unregister another engine's JNI/FFI host API instance (#194920). This blocks shipping multi-engine-safe FFI/JNI plugins (flutter/packages#13359) against the 3.50 stable release.

**Scope of the API break:** This supersedes #195991, which was closed as a breaking change. As [@stuartmorgan noted](#195991 (comment)), the `@required` `engineIdentifier` property on `FlutterBaseRegistrar` (iOS) and `FlutterPluginRegistrar` (macOS) only affects hand-written native unit-test fakes that conform to those protocols directly. Production plugin and app code only consumes registrars provided by the engine and is unaffected. Following that, [@zanderso commented](#195991 (comment)) that if the change is safer than the earlier signals indicated, it should be considered for a hotfix release in this cycle. Affected test fakes can add `var engineIdentifier: Int64 = 0` (Swift) or `@synthesize engineIdentifier;` (Objective-C), which compiles both before and after this change. First-party fakes were already updated in flutter/packages#13574. On Android, `FlutterPluginBinding` is a concrete class, so adding `getEngineId()` does not affect mocks.

### Changelog Description:
[flutter/195876] When running multiple `FlutterEngine`s on Android, iOS, or macOS, FFI/JNI plugins could not determine which engine a `FlutterPluginBinding` or `FlutterPluginRegistrar` belonged to.

### Workaround:
On Android, plugins can call the deprecated `FlutterPluginBinding.getFlutterEngine().getEngineId()`. On iOS and macOS, there is no public API workaround (`engineIdentifier` is only declared in internal headers, and the registrar's weak engine reference is already `nil` during `detachFromEngineForRegistrar:`).

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
1. On Android, verify `FlutterPluginBinding.getEngineId()` returns the associated `FlutterEngine.getEngineId()`.
2. On iOS, verify `registrar.engineIdentifier` on `FlutterPluginRegistrar` and `FlutterApplicationRegistrar` matches the owning `FlutterEngine.engineIdentifier`, both during registration and during `detachFromEngineForRegistrar:`.
3. On macOS, verify `registrar.engineIdentifier` on `FlutterPluginRegistrar` matches the owning `FlutterEngine.engineIdentifier`.