Remove enableMainQueueCoordinatorOnIOS, make coordinator always-on

Summary:
The `enableMainQueueCoordinatorOnIOS` flag has finished rollout. Drop it from the feature-flag config, regenerate the per-language accessors, and inline the previously-gated paths:

- `RCTUtils.mm`: `RCTUnsafeExecuteOnMainQueueSync` and the `RCTUnsafeExecuteOnMainQueueOnceSync` helper always use `unsafeExecuteOnMainThreadSync` on iOS (the TV fallback to `dispatch_sync(main, ...)` stays).
- `RuntimeExecutorSyncUIThreadUtils.mm`: `executeSynchronouslyOnSameThread_CAN_DEADLOCK` switches between two paths based on the calling thread instead of the feature flag. Main-thread callers (production) take the coordinator path that pumps UI tasks while waiting for JS; off-main callers (e.g. RuntimeScheduler unit tests) take a simpler path that just waits for the runtime and runs `runtimeWork` synchronously on the calling thread. Trimmed the `runtimeCaptureBlockDone` plumbing that an old TODO already flagged as unnecessary.

Also drops the iOS override in the Wilde plugin, the now-dead `rn_fling.enable_main_queue_coordinator_on_ios` MobileConfig param, and the `flagOff` variant of the characterization test (the on-path test still pins the contract).

Changelog:
[iOS][Changed] - `RCTUnsafeExecuteOnMainQueueSync` and bridgeless sync runtime-thread calls now always use the coordinator implementation that pumps UI tasks while waiting for JS, eliminating a class of deadlocks. The previous opt-in flag has been removed.

Differential Revision: D105984547

Author: javache

packages/react-native/React/Base/RCTUtils.mm

@@ -11,7 +11,6 @@
 #import <mach/mach_time.h>
 #import <objc/message.h>
 #import <objc/runtime.h>
-#import <react/featureflags/ReactNativeFeatureFlags.h>
 #import <zlib.h>
 
 #import <UIKit/UIKit.h>
@@ -312,15 +311,12 @@ void RCTUnsafeExecuteOnMainQueueSync(dispatch_block_t block)
   }
 
 #if !TARGET_OS_TV
-  if (ReactNativeFeatureFlags::enableMainQueueCoordinatorOnIOS()) {
-    unsafeExecuteOnMainThreadSync(block);
-    return;
-  }
-#endif
-
+  unsafeExecuteOnMainThreadSync(block);
+#else
   dispatch_sync(dispatch_get_main_queue(), ^{
     block();
   });
+#endif
 }
 
 static void RCTUnsafeExecuteOnMainQueueOnceSync(dispatch_once_t *onceToken, dispatch_block_t block)
@@ -342,13 +338,10 @@ static void RCTUnsafeExecuteOnMainQueueOnceSync(dispatch_once_t *onceToken, disp
   }
 
 #if !TARGET_OS_TV
-  if (ReactNativeFeatureFlags::enableMainQueueCoordinatorOnIOS()) {
-    unsafeExecuteOnMainThreadSync(block);
-    return;
-  }
-#endif
-
+  unsafeExecuteOnMainThreadSync(block);
+#else
   dispatch_sync(dispatch_get_main_queue(), executeOnce);
+#endif
 }
 
 CGFloat RCTScreenScale(void)

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlags.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<de3444d0862944a45bfb112e649dd395>>
+ * @generated SignedSource<<1daf42834a0bcc06caae571c6541fecd>>
  */
 
 /**
@@ -234,12 +234,6 @@ public object ReactNativeFeatureFlags {
   @JvmStatic
   public fun enableLayoutAnimationsOnIOS(): Boolean = accessor.enableLayoutAnimationsOnIOS()
 
-  /**
-   * Make RCTUnsafeExecuteOnMainQueueSync less likely to deadlock, when used in conjuction with sync rendering/events.
-   */
-  @JvmStatic
-  public fun enableMainQueueCoordinatorOnIOS(): Boolean = accessor.enableMainQueueCoordinatorOnIOS()
-
   /**
    * Enable NSNull conversion when handling module arguments on iOS
    */

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<76c912049c6cbfac8bd0e27418dab700>>
+ * @generated SignedSource<<6b189752d6dedc9d814179ddd6d605f4>>
  */
 
 /**
@@ -54,7 +54,6 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
   private var enableKeyEventsCache: Boolean? = null
   private var enableLayoutAnimationsOnAndroidCache: Boolean? = null
   private var enableLayoutAnimationsOnIOSCache: Boolean? = null
-  private var enableMainQueueCoordinatorOnIOSCache: Boolean? = null
   private var enableModuleArgumentNSNullConversionIOSCache: Boolean? = null
   private var enableMutationObserverByDefaultCache: Boolean? = null
   private var enableNativeCSSParsingCache: Boolean? = null
@@ -415,15 +414,6 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
     return cached
   }
 
-  override fun enableMainQueueCoordinatorOnIOS(): Boolean {
-    var cached = enableMainQueueCoordinatorOnIOSCache
-    if (cached == null) {
-      cached = ReactNativeFeatureFlagsCxxInterop.enableMainQueueCoordinatorOnIOS()
-      enableMainQueueCoordinatorOnIOSCache = cached
-    }
-    return cached
-  }
-
   override fun enableModuleArgumentNSNullConversionIOS(): Boolean {
     var cached = enableModuleArgumentNSNullConversionIOSCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsCxxInterop.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<425c8a86705214aa021e413211468e97>>
+ * @generated SignedSource<<34dc75d00f7dad4922361c5661a5c527>>
  */
 
 /**
@@ -96,8 +96,6 @@ public object ReactNativeFeatureFlagsCxxInterop {
 
   @DoNotStrip @JvmStatic public external fun enableLayoutAnimationsOnIOS(): Boolean
 
-  @DoNotStrip @JvmStatic public external fun enableMainQueueCoordinatorOnIOS(): Boolean
-
   @DoNotStrip @JvmStatic public external fun enableModuleArgumentNSNullConversionIOS(): Boolean
 
   @DoNotStrip @JvmStatic public external fun enableMutationObserverByDefault(): Boolean

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsDefaults.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<30bd20f9479756c3dce574c05b80a1f4>>
+ * @generated SignedSource<<e57e4a1d8593cc3574430e4ab4845894>>
  */
 
 /**
@@ -91,8 +91,6 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun enableLayoutAnimationsOnIOS(): Boolean = true
 
-  override fun enableMainQueueCoordinatorOnIOS(): Boolean = false
-
   override fun enableModuleArgumentNSNullConversionIOS(): Boolean = false
 
   override fun enableMutationObserverByDefault(): Boolean = false

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsLocalAccessor.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<e08b9d00abd67c312a50a5c893a91e1b>>
+ * @generated SignedSource<<c01926414a73e2f1249486080ef81d9b>>
  */
 
 /**
@@ -58,7 +58,6 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
   private var enableKeyEventsCache: Boolean? = null
   private var enableLayoutAnimationsOnAndroidCache: Boolean? = null
   private var enableLayoutAnimationsOnIOSCache: Boolean? = null
-  private var enableMainQueueCoordinatorOnIOSCache: Boolean? = null
   private var enableModuleArgumentNSNullConversionIOSCache: Boolean? = null
   private var enableMutationObserverByDefaultCache: Boolean? = null
   private var enableNativeCSSParsingCache: Boolean? = null
@@ -453,16 +452,6 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
     return cached
   }
 
-  override fun enableMainQueueCoordinatorOnIOS(): Boolean {
-    var cached = enableMainQueueCoordinatorOnIOSCache
-    if (cached == null) {
-      cached = currentProvider.enableMainQueueCoordinatorOnIOS()
-      accessedFeatureFlags.add("enableMainQueueCoordinatorOnIOS")
-      enableMainQueueCoordinatorOnIOSCache = cached
-    }
-    return cached
-  }
-
   override fun enableModuleArgumentNSNullConversionIOS(): Boolean {
     var cached = enableModuleArgumentNSNullConversionIOSCache
     if (cached == null) {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/featureflags/ReactNativeFeatureFlagsProvider.kt

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<babb0304c7232e14d8dd807032bcbc53>>
+ * @generated SignedSource<<3bdd4f869245c79c42fbd09646d753ba>>
  */
 
 /**
@@ -91,8 +91,6 @@ public interface ReactNativeFeatureFlagsProvider {
 
   @DoNotStrip public fun enableLayoutAnimationsOnIOS(): Boolean
 
-  @DoNotStrip public fun enableMainQueueCoordinatorOnIOS(): Boolean
-
   @DoNotStrip public fun enableModuleArgumentNSNullConversionIOS(): Boolean
 
   @DoNotStrip public fun enableMutationObserverByDefault(): Boolean

packages/react-native/ReactAndroid/src/main/jni/react/featureflags/JReactNativeFeatureFlagsCxxInterop.cpp

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<c939675c97b36966d0cc852389c23450>>
+ * @generated SignedSource<<641a3191c119df804bdf975fd4841072>>
  */
 
 /**
@@ -243,12 +243,6 @@ class ReactNativeFeatureFlagsJavaProvider
     return method(javaProvider_);
   }
 
-  bool enableMainQueueCoordinatorOnIOS() override {
-    static const auto method =
-        getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("enableMainQueueCoordinatorOnIOS");
-    return method(javaProvider_);
-  }
-
   bool enableModuleArgumentNSNullConversionIOS() override {
     static const auto method =
         getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("enableModuleArgumentNSNullConversionIOS");
@@ -741,11 +735,6 @@ bool JReactNativeFeatureFlagsCxxInterop::enableLayoutAnimationsOnIOS(
   return ReactNativeFeatureFlags::enableLayoutAnimationsOnIOS();
 }
 
-bool JReactNativeFeatureFlagsCxxInterop::enableMainQueueCoordinatorOnIOS(
-    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
-  return ReactNativeFeatureFlags::enableMainQueueCoordinatorOnIOS();
-}
-
 bool JReactNativeFeatureFlagsCxxInterop::enableModuleArgumentNSNullConversionIOS(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
   return ReactNativeFeatureFlags::enableModuleArgumentNSNullConversionIOS();
@@ -1144,9 +1133,6 @@ void JReactNativeFeatureFlagsCxxInterop::registerNatives() {
       makeNativeMethod(
         "enableLayoutAnimationsOnIOS",
         JReactNativeFeatureFlagsCxxInterop::enableLayoutAnimationsOnIOS),
-      makeNativeMethod(
-        "enableMainQueueCoordinatorOnIOS",
-        JReactNativeFeatureFlagsCxxInterop::enableMainQueueCoordinatorOnIOS),
       makeNativeMethod(
         "enableModuleArgumentNSNullConversionIOS",
         JReactNativeFeatureFlagsCxxInterop::enableModuleArgumentNSNullConversionIOS),

packages/react-native/ReactAndroid/src/main/jni/react/featureflags/JReactNativeFeatureFlagsCxxInterop.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<5501bc377ccafc4dab778978ee3f33b2>>
+ * @generated SignedSource<<8ae9d1ef2789deae877f273dc47a5cad>>
  */
 
 /**
@@ -132,9 +132,6 @@ class JReactNativeFeatureFlagsCxxInterop
   static bool enableLayoutAnimationsOnIOS(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 
-  static bool enableMainQueueCoordinatorOnIOS(
-    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
-
   static bool enableModuleArgumentNSNullConversionIOS(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlags.cpp

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<f1b8c3c7118c94617233847bf2d31428>>
+ * @generated SignedSource<<28287e973a90e07fb8cfc2c0c2e8396f>>
  */
 
 /**
@@ -162,10 +162,6 @@ bool ReactNativeFeatureFlags::enableLayoutAnimationsOnIOS() {
   return getAccessor().enableLayoutAnimationsOnIOS();
 }
 
-bool ReactNativeFeatureFlags::enableMainQueueCoordinatorOnIOS() {
-  return getAccessor().enableMainQueueCoordinatorOnIOS();
-}
-
 bool ReactNativeFeatureFlags::enableModuleArgumentNSNullConversionIOS() {
   return getAccessor().enableModuleArgumentNSNullConversionIOS();
 }