Add single host inspector state assertion over CDP (#54407)

Summary:

Introduces a new `InspectorSystemState` object and `ReactNativeApplication.systemStateChanged` CDP event, used to assert whether more than one React Native Host has been registered for the current app lifetime.

This will be used to disable the Performance and Network features in React Native DevTools when the debugger backend is in this currently unsupported state. We intend to implement host lifecycle correctness across all features soon.

Changelog: [Internal]

Differential Revision: D86201689

Author: huntie

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<<9646ebeba75ec903be5ade7e2333f0c8>>
+ * @generated SignedSource<<248d4e5e599c3af43dc352c8bb1a2c13>>
  */
 
 /**
@@ -360,6 +360,12 @@ public object ReactNativeFeatureFlags {
   @JvmStatic
   public fun fixMappingOfEventPrioritiesBetweenFabricAndReact(): Boolean = accessor.fixMappingOfEventPrioritiesBetweenFabricAndReact()
 
+  /**
+   * Enable system assertion validating that Fusebox is configured with a single host. When set, the CDP backend will dynamically disable features (Perf and Network) in the event that multiple hosts are registered (undefined behaviour), and broadcast this over `ReactNativeApplication.systemStateChanged`.
+   */
+  @JvmStatic
+  public fun fuseboxAssertSingleHostState(): Boolean = accessor.fuseboxAssertSingleHostState()
+
   /**
    * Flag determining if the React Native DevTools (Fusebox) CDP backend should be enabled in release builds. This flag is global and should not be changed across React Host lifetimes.
    */

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<<9d6ccbe6d02608901fc18ad88baab176>>
+ * @generated SignedSource<<fe1d9a861817477da12de7f29d01f3d6>>
  */
 
 /**
@@ -75,6 +75,7 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
   private var enableVirtualViewWindowFocusDetectionCache: Boolean? = null
   private var enableWebPerformanceAPIsByDefaultCache: Boolean? = null
   private var fixMappingOfEventPrioritiesBetweenFabricAndReactCache: Boolean? = null
+  private var fuseboxAssertSingleHostStateCache: Boolean? = null
   private var fuseboxEnabledReleaseCache: Boolean? = null
   private var fuseboxNetworkInspectionEnabledCache: Boolean? = null
   private var hideOffscreenVirtualViewsOnIOSCache: Boolean? = null
@@ -598,6 +599,15 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
     return cached
   }
 
+  override fun fuseboxAssertSingleHostState(): Boolean {
+    var cached = fuseboxAssertSingleHostStateCache
+    if (cached == null) {
+      cached = ReactNativeFeatureFlagsCxxInterop.fuseboxAssertSingleHostState()
+      fuseboxAssertSingleHostStateCache = cached
+    }
+    return cached
+  }
+
   override fun fuseboxEnabledRelease(): Boolean {
     var cached = fuseboxEnabledReleaseCache
     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<<fbc551ca005a7d8abcd2cf2e5d29a3a6>>
+ * @generated SignedSource<<be15f5dd5f62198214c956d133de4671>>
  */
 
 /**
@@ -138,6 +138,8 @@ public object ReactNativeFeatureFlagsCxxInterop {
 
   @DoNotStrip @JvmStatic public external fun fixMappingOfEventPrioritiesBetweenFabricAndReact(): Boolean
 
+  @DoNotStrip @JvmStatic public external fun fuseboxAssertSingleHostState(): Boolean
+
   @DoNotStrip @JvmStatic public external fun fuseboxEnabledRelease(): Boolean
 
   @DoNotStrip @JvmStatic public external fun fuseboxNetworkInspectionEnabled(): 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<<7b8a5ad9a3353ea32a39bd139e9174f7>>
+ * @generated SignedSource<<30041179508b76146b4a6ff70f7d2090>>
  */
 
 /**
@@ -133,6 +133,8 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun fixMappingOfEventPrioritiesBetweenFabricAndReact(): Boolean = false
 
+  override fun fuseboxAssertSingleHostState(): Boolean = true
+
   override fun fuseboxEnabledRelease(): Boolean = false
 
   override fun fuseboxNetworkInspectionEnabled(): 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<<9bb9a7cf89c92f5a397b2328fa983dc6>>
+ * @generated SignedSource<<78f60952fc7a5cd0efbf8ba8478251a7>>
  */
 
 /**
@@ -79,6 +79,7 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
   private var enableVirtualViewWindowFocusDetectionCache: Boolean? = null
   private var enableWebPerformanceAPIsByDefaultCache: Boolean? = null
   private var fixMappingOfEventPrioritiesBetweenFabricAndReactCache: Boolean? = null
+  private var fuseboxAssertSingleHostStateCache: Boolean? = null
   private var fuseboxEnabledReleaseCache: Boolean? = null
   private var fuseboxNetworkInspectionEnabledCache: Boolean? = null
   private var hideOffscreenVirtualViewsOnIOSCache: Boolean? = null
@@ -657,6 +658,16 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
     return cached
   }
 
+  override fun fuseboxAssertSingleHostState(): Boolean {
+    var cached = fuseboxAssertSingleHostStateCache
+    if (cached == null) {
+      cached = currentProvider.fuseboxAssertSingleHostState()
+      accessedFeatureFlags.add("fuseboxAssertSingleHostState")
+      fuseboxAssertSingleHostStateCache = cached
+    }
+    return cached
+  }
+
   override fun fuseboxEnabledRelease(): Boolean {
     var cached = fuseboxEnabledReleaseCache
     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<<eeb5d70e45eecdef0d9307cbe8ff17c2>>
+ * @generated SignedSource<<865a11fa77d36e33d3bb6548cce01e66>>
  */
 
 /**
@@ -133,6 +133,8 @@ public interface ReactNativeFeatureFlagsProvider {
 
   @DoNotStrip public fun fixMappingOfEventPrioritiesBetweenFabricAndReact(): Boolean
 
+  @DoNotStrip public fun fuseboxAssertSingleHostState(): Boolean
+
   @DoNotStrip public fun fuseboxEnabledRelease(): Boolean
 
   @DoNotStrip public fun fuseboxNetworkInspectionEnabled(): 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<<0527dbb4a838be34b80d76b11d18cea0>>
+ * @generated SignedSource<<975dfce969af2eda791cd6dc37d6ccc2>>
  */
 
 /**
@@ -369,6 +369,12 @@ class ReactNativeFeatureFlagsJavaProvider
     return method(javaProvider_);
   }
 
+  bool fuseboxAssertSingleHostState() override {
+    static const auto method =
+        getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("fuseboxAssertSingleHostState");
+    return method(javaProvider_);
+  }
+
   bool fuseboxEnabledRelease() override {
     static const auto method =
         getReactNativeFeatureFlagsProviderJavaClass()->getMethod<jboolean()>("fuseboxEnabledRelease");
@@ -810,6 +816,11 @@ bool JReactNativeFeatureFlagsCxxInterop::fixMappingOfEventPrioritiesBetweenFabri
   return ReactNativeFeatureFlags::fixMappingOfEventPrioritiesBetweenFabricAndReact();
 }
 
+bool JReactNativeFeatureFlagsCxxInterop::fuseboxAssertSingleHostState(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
+  return ReactNativeFeatureFlags::fuseboxAssertSingleHostState();
+}
+
 bool JReactNativeFeatureFlagsCxxInterop::fuseboxEnabledRelease(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop> /*unused*/) {
   return ReactNativeFeatureFlags::fuseboxEnabledRelease();
@@ -1141,6 +1152,9 @@ void JReactNativeFeatureFlagsCxxInterop::registerNatives() {
       makeNativeMethod(
         "fixMappingOfEventPrioritiesBetweenFabricAndReact",
         JReactNativeFeatureFlagsCxxInterop::fixMappingOfEventPrioritiesBetweenFabricAndReact),
+      makeNativeMethod(
+        "fuseboxAssertSingleHostState",
+        JReactNativeFeatureFlagsCxxInterop::fuseboxAssertSingleHostState),
       makeNativeMethod(
         "fuseboxEnabledRelease",
         JReactNativeFeatureFlagsCxxInterop::fuseboxEnabledRelease),

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<<a1deb0145d8c51d608903e1704e96b8d>>
+ * @generated SignedSource<<97c126a1763860d25ee216150156e200>>
  */
 
 /**
@@ -195,6 +195,9 @@ class JReactNativeFeatureFlagsCxxInterop
   static bool fixMappingOfEventPrioritiesBetweenFabricAndReact(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 
+  static bool fuseboxAssertSingleHostState(
+    facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
+
   static bool fuseboxEnabledRelease(
     facebook::jni::alias_ref<JReactNativeFeatureFlagsCxxInterop>);
 

packages/react-native/ReactCommon/jsinspector-modern/HostAgent.cpp

@@ -10,6 +10,7 @@
 
 #ifdef REACT_NATIVE_DEBUGGER_ENABLED
 #include "InspectorFlags.h"
+#include "InspectorInterfaces.h"
 #include "NetworkIOAgent.h"
 #include "SessionState.h"
 #include "TracingAgent.h"
@@ -216,6 +217,11 @@ class HostAgent::Impl final {
           cdp::jsonNotification(
               "ReactNativeApplication.metadataUpdated",
               createHostMetadataPayload(hostMetadata_)));
+      auto& inspector = getInspectorInstance();
+      bool isSingleHost = inspector.getSystemState().registeredPagesCount <= 1;
+      if (!isSingleHost) {
+        emitSystemStateChanged(isSingleHost);
+      }
 
       auto stashedTraceRecording =
           targetController_.getDelegate()
@@ -374,6 +380,17 @@ class HostAgent::Impl final {
     tracingAgent_.emitExternalTraceRecording(std::move(traceRecording));
   }
 
+  void emitSystemStateChanged(bool isSingleHost) {
+    frontendChannel_(
+        cdp::jsonNotification(
+            "ReactNativeApplication.systemStateChanged",
+            folly::dynamic::object("isSingleHost", isSingleHost)));
+
+    if (!isSingleHost) {
+      frontendChannel_(cdp::jsonNotification("Network.disable"));
+    }
+  }
+
  private:
   enum class FuseboxClientType { Unknown, Fusebox, NonFusebox };
 
@@ -480,6 +497,7 @@ class HostAgent::Impl final {
   }
   void emitExternalTraceRecording(tracing::TraceRecordingState traceRecording) {
   }
+  void emitSystemStateChanged(bool isSingleHost) {}
 };
 
 #endif // REACT_NATIVE_DEBUGGER_ENABLED
@@ -519,6 +537,10 @@ void HostAgent::emitExternalTraceRecording(
   impl_->emitExternalTraceRecording(std::move(traceRecording));
 }
 
+void HostAgent::emitSystemStateChanged(bool isSingleHost) const {
+  impl_->emitSystemStateChanged(isSingleHost);
+}
+
 #pragma mark - Tracing
 
 HostTracingAgent::HostTracingAgent(tracing::TraceRecordingState& state)

packages/react-native/ReactCommon/jsinspector-modern/HostAgent.h

@@ -79,6 +79,12 @@ class HostAgent final {
    */
   void emitExternalTraceRecording(tracing::TraceRecordingState traceRecording) const;
 
+  /**
+   * Emits a system state changed event when the number of ReactHost instances
+   * changes.
+   */
+  void emitSystemStateChanged(bool isSingleHost) const;
+
  private:
   // We use the private implementation idiom to ensure this class has the same
   // layout regardless of whether REACT_NATIVE_DEBUGGER_ENABLED is defined. The