Resolve current React context from the captured host

Summary:
`ReactDelegate` selects its host when it is constructed, but `currentReactContext` previously re-read the process-wide architecture flag to decide which host to query. If those states disagreed, a delegate containing a `ReactHost` could incorrectly access its absent legacy host and crash.

Resolve the context from the host captured by the delegate instead. Prefer `ReactHost` when present; otherwise return the context from an already initialized `ReactNativeHost`. The legacy path remains non-creating when no instance exists.

Add focused coverage for bridgeless and legacy hosts, including a contradictory architecture flag and initialized, uninitialized, and absent legacy hosts.

Changelog:
[Android][Fixed] - Prevent `ReactDelegate.currentReactContext` from querying the wrong host when architecture state changes

Differential Revision: D119096676

Author: andrewdacenko

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/ReactDelegate.kt

@@ -7,6 +7,7 @@
 
 package com.facebook.react
 
+import android.annotation.SuppressLint
 import android.app.Activity
 import android.content.Intent
 import android.content.res.Configuration
@@ -425,16 +426,20 @@ public open class ReactDelegate {
    * Do not store a reference to this, if the React instance is reloaded or destroyed, this context
    * will no longer be valid.
    */
+  @get:SuppressLint("DeprecatedClass")
   public val currentReactContext: ReactContext?
     get() {
-      return if (ReactNativeNewArchitectureFeatureFlags.enableBridgelessArchitecture()) {
-        if (reactHost != null) {
-          reactHost?.currentReactContext
+      reactHost?.let {
+        return it.currentReactContext
+      }
+
+      val reactNativeHost = reactNativeHost ?: return null
+      synchronized(reactNativeHost) {
+        return if (reactNativeHost.hasInstance()) {
+          reactNativeHost.reactInstanceManager.currentReactContext
         } else {
           null
         }
-      } else {
-        getReactInstanceManager().currentReactContext
       }
     }
 }

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/ReactDelegateTest.kt

@@ -0,0 +1,141 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react
+
+import android.annotation.SuppressLint
+import android.app.Activity
+import android.app.Application
+import com.facebook.react.bridge.ReactContext
+import com.facebook.react.internal.featureflags.ReactNativeFeatureFlags
+import com.facebook.react.internal.featureflags.ReactNativeFeatureFlagsDefaults
+import com.facebook.react.internal.featureflags.ReactNativeFeatureFlagsForTests
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.kotlin.doReturn
+import org.mockito.kotlin.mock
+import org.robolectric.Robolectric
+import org.robolectric.RobolectricTestRunner
+
+@SuppressLint(
+    "ActivityStoredInField",
+    "DeprecatedClass",
+    "DeprecatedMethod",
+    "DeprecatedSuperclass",
+)
+@RunWith(RobolectricTestRunner::class)
+class ReactDelegateTest {
+
+  private lateinit var activity: Activity
+
+  @Before
+  fun setUp() {
+    ReactNativeFeatureFlagsForTests.setUp()
+    activity = Robolectric.buildActivity(Activity::class.java).create().get()
+  }
+
+  @After
+  fun tearDown() {
+    ReactNativeFeatureFlags.dangerouslyReset()
+  }
+
+  @Test
+  fun currentReactContext_withReactHost_returnsContext() {
+    overrideBridgelessArchitecture(true)
+    val reactContext = mock<ReactContext>()
+    val reactHost = mock<ReactHost> { on { currentReactContext } doReturn reactContext }
+    val delegate = ReactDelegate(activity, reactHost, "test-app", null)
+
+    assertThat(delegate.currentReactContext).isSameAs(reactContext)
+  }
+
+  @Test
+  fun currentReactContext_withReactHost_ignoresArchitectureFlag() {
+    overrideBridgelessArchitecture(false)
+    val reactContext = mock<ReactContext>()
+    val reactHost = mock<ReactHost> { on { currentReactContext } doReturn reactContext }
+    val delegate = ReactDelegate(activity, reactHost, "test-app", null)
+
+    assertThat(delegate.currentReactContext).isSameAs(reactContext)
+  }
+
+  @Suppress("DEPRECATION")
+  @Test
+  fun currentReactContext_withoutReactNativeHost_returnsNull() {
+    overrideBridgelessArchitecture(false)
+    val delegate = ReactDelegate(activity, null as ReactNativeHost?, "test-app", null)
+
+    assertThat(delegate.currentReactContext).isNull()
+  }
+
+  @Suppress("DEPRECATION")
+  @Test
+  fun currentReactContext_withUninitializedReactNativeHost_doesNotCreateInstance() {
+    overrideBridgelessArchitecture(false)
+    val reactNativeHost =
+        object : ReactNativeHost(activity.application as Application) {
+          override fun getUseDeveloperSupport(): Boolean = false
+
+          override fun getPackages(): List<ReactPackage> = emptyList()
+        }
+    val delegate = ReactDelegate(activity, reactNativeHost, "test-app", null)
+
+    assertThat(delegate.currentReactContext).isNull()
+    assertThat(reactNativeHost.hasInstance()).isFalse()
+  }
+
+  @Suppress("DEPRECATION")
+  @Test
+  fun currentReactContext_withInitializedReactNativeHost_returnsContext() {
+    overrideBridgelessArchitecture(false)
+    val reactContext = mock<ReactContext>()
+    val instanceManager =
+        mock<ReactInstanceManager> { on { currentReactContext } doReturn reactContext }
+    val reactNativeHost = createInitializedReactNativeHost(instanceManager)
+    val delegate = ReactDelegate(activity, reactNativeHost, "test-app", null)
+
+    assertThat(delegate.currentReactContext).isSameAs(reactContext)
+  }
+
+  @Suppress("DEPRECATION")
+  @Test
+  fun currentReactContext_withReactNativeHost_ignoresArchitectureFlag() {
+    overrideBridgelessArchitecture(true)
+    val reactContext = mock<ReactContext>()
+    val instanceManager =
+        mock<ReactInstanceManager> { on { currentReactContext } doReturn reactContext }
+    val reactNativeHost = createInitializedReactNativeHost(instanceManager)
+    val delegate = ReactDelegate(activity, reactNativeHost, "test-app", null)
+
+    assertThat(delegate.currentReactContext).isSameAs(reactContext)
+  }
+
+  @Suppress("DEPRECATION")
+  private fun createInitializedReactNativeHost(
+      instanceManager: ReactInstanceManager,
+  ): ReactNativeHost =
+      object : ReactNativeHost(activity.application as Application) {
+        override val reactInstanceManager: ReactInstanceManager = instanceManager
+
+        override fun hasInstance(): Boolean = true
+
+        override fun getUseDeveloperSupport(): Boolean = false
+
+        override fun getPackages(): List<ReactPackage> = emptyList()
+      }
+
+  private fun overrideBridgelessArchitecture(enabled: Boolean) {
+    ReactNativeFeatureFlags.override(
+        object : ReactNativeFeatureFlagsDefaults() {
+          override fun enableBridgelessArchitecture(): Boolean = enabled
+        },
+    )
+  }
+}