Add Page.captureScreenshot CDP support (#56307)

Summary:
Pull Request resolved: #56307

Implement the `Page.captureScreenshot` CDP command in the inspector backend, allowing DevTools to capture an on-demand screenshot of the current app view. This is a minimal implementation supporting only the `format` (jpeg/png/webp) and `quality` (0-100, jpeg only) parameters, returning base64-encoded image data.

The feature is gated behind a new `fuseboxCaptureScreenshotEnabled` React Native feature flag, wired through `InspectorFlags` following the same pattern as frame recording.

**Motivation**

Improve agent verification / user feedback during AI sessions. We've proven that screenshots (in performance traces) are useful for understanding how components render on screen, and exposing this as an on-demand CDP method is relatively cheap today vs the larger task of modelling the DOM (Elements panel).

**Changes**

- New `fuseboxCaptureScreenshotEnabled` feature flag + `InspectorFlags` wiring (C++, Android JNI, Kotlin)
- `HostTargetDelegate::captureScreenshot()` virtual method with async callback
- C++ CDP handler in `HostAgent` — parses `format`/`quality`, delegates to platform, sends async CDP response (gated by flag)
- iOS (`RCTHost.mm`): Captures key window via `UIGraphicsImageRenderer` + `drawViewHierarchyInRect`, encodes to PNG/JPEG
- Android (`ReactHostImpl.kt`): Captures decor view via `Bitmap` + `Canvas` + `View.draw()`, encodes to PNG/JPEG/WebP
- 4 C++ tests: success, failure, param forwarding, flag-disabled rejection

Changelog: [Internal]

Differential Revision: D99099930

Author: huntie

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

@@ -19,6 +19,8 @@ internal object InspectorFlags {
     SoLoader.loadLibrary("react_devsupportjni")
   }
 
+  @DoNotStrip @JvmStatic external fun getScreenshotCaptureEnabled(): Boolean
+
   @DoNotStrip @JvmStatic external fun getFuseboxEnabled(): Boolean
 
   @DoNotStrip @JvmStatic external fun getIsProfilingBuild(): Boolean

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<<84bfc7b7a1b239c514b6d7c38dd91283>>
+ * @generated SignedSource<<eacf6769e8598f88fe1790149e437f3f>>
  */
 
 /**
@@ -408,6 +408,12 @@ public object ReactNativeFeatureFlags {
   @JvmStatic
   public fun fuseboxNetworkInspectionEnabled(): Boolean = accessor.fuseboxNetworkInspectionEnabled()
 
+  /**
+   * Enable Page.captureScreenshot CDP method support in the React Native DevTools CDP backend. This flag is global and should not be changed across React Host lifetimes.
+   */
+  @JvmStatic
+  public fun fuseboxScreenshotCaptureEnabled(): Boolean = accessor.fuseboxScreenshotCaptureEnabled()
+
   /**
    * Hides offscreen VirtualViews on iOS by setting hidden = YES to avoid extra cost of views
    */

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<<1b59188082b9222b22b5cb0585cd166f>>
+ * @generated SignedSource<<668885665a149d50bdff92bd96a297f0>>
  */
 
 /**
@@ -83,6 +83,7 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
   private var fuseboxEnabledReleaseCache: Boolean? = null
   private var fuseboxFrameRecordingEnabledCache: Boolean? = null
   private var fuseboxNetworkInspectionEnabledCache: Boolean? = null
+  private var fuseboxScreenshotCaptureEnabledCache: Boolean? = null
   private var hideOffscreenVirtualViewsOnIOSCache: Boolean? = null
   private var overrideBySynchronousMountPropsAtMountingAndroidCache: Boolean? = null
   private var perfIssuesEnabledCache: Boolean? = null
@@ -677,6 +678,15 @@ internal class ReactNativeFeatureFlagsCxxAccessor : ReactNativeFeatureFlagsAcces
     return cached
   }
 
+  override fun fuseboxScreenshotCaptureEnabled(): Boolean {
+    var cached = fuseboxScreenshotCaptureEnabledCache
+    if (cached == null) {
+      cached = ReactNativeFeatureFlagsCxxInterop.fuseboxScreenshotCaptureEnabled()
+      fuseboxScreenshotCaptureEnabledCache = cached
+    }
+    return cached
+  }
+
   override fun hideOffscreenVirtualViewsOnIOS(): Boolean {
     var cached = hideOffscreenVirtualViewsOnIOSCache
     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<<2fd657c62d07ed766a9241cb1c14d98d>>
+ * @generated SignedSource<<aa4a2ab7af66d857da4318ac2e75899b>>
  */
 
 /**
@@ -154,6 +154,8 @@ public object ReactNativeFeatureFlagsCxxInterop {
 
   @DoNotStrip @JvmStatic public external fun fuseboxNetworkInspectionEnabled(): Boolean
 
+  @DoNotStrip @JvmStatic public external fun fuseboxScreenshotCaptureEnabled(): Boolean
+
   @DoNotStrip @JvmStatic public external fun hideOffscreenVirtualViewsOnIOS(): Boolean
 
   @DoNotStrip @JvmStatic public external fun overrideBySynchronousMountPropsAtMountingAndroid(): 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<<f3204842cd731d7eff8c4c4eeeead515>>
+ * @generated SignedSource<<6348c0cc9285f2bac6df9986155b584f>>
  */
 
 /**
@@ -149,6 +149,8 @@ public open class ReactNativeFeatureFlagsDefaults : ReactNativeFeatureFlagsProvi
 
   override fun fuseboxNetworkInspectionEnabled(): Boolean = true
 
+  override fun fuseboxScreenshotCaptureEnabled(): Boolean = false
+
   override fun hideOffscreenVirtualViewsOnIOS(): Boolean = false
 
   override fun overrideBySynchronousMountPropsAtMountingAndroid(): 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<<251381892c7d15310d61b35913c5cba6>>
+ * @generated SignedSource<<f545945b19339923fcafab4eeb1da134>>
  */
 
 /**
@@ -87,6 +87,7 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
   private var fuseboxEnabledReleaseCache: Boolean? = null
   private var fuseboxFrameRecordingEnabledCache: Boolean? = null
   private var fuseboxNetworkInspectionEnabledCache: Boolean? = null
+  private var fuseboxScreenshotCaptureEnabledCache: Boolean? = null
   private var hideOffscreenVirtualViewsOnIOSCache: Boolean? = null
   private var overrideBySynchronousMountPropsAtMountingAndroidCache: Boolean? = null
   private var perfIssuesEnabledCache: Boolean? = null
@@ -744,6 +745,16 @@ internal class ReactNativeFeatureFlagsLocalAccessor : ReactNativeFeatureFlagsAcc
     return cached
   }
 
+  override fun fuseboxScreenshotCaptureEnabled(): Boolean {
+    var cached = fuseboxScreenshotCaptureEnabledCache
+    if (cached == null) {
+      cached = currentProvider.fuseboxScreenshotCaptureEnabled()
+      accessedFeatureFlags.add("fuseboxScreenshotCaptureEnabled")
+      fuseboxScreenshotCaptureEnabledCache = cached
+    }
+    return cached
+  }
+
   override fun hideOffscreenVirtualViewsOnIOS(): Boolean {
     var cached = hideOffscreenVirtualViewsOnIOSCache
     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<<7e47ac680222281a813e65484e7f8e39>>
+ * @generated SignedSource<<e340fe9805381dcf818f51e333f7c120>>
  */
 
 /**
@@ -149,6 +149,8 @@ public interface ReactNativeFeatureFlagsProvider {
 
   @DoNotStrip public fun fuseboxNetworkInspectionEnabled(): Boolean
 
+  @DoNotStrip public fun fuseboxScreenshotCaptureEnabled(): Boolean
+
   @DoNotStrip public fun hideOffscreenVirtualViewsOnIOS(): Boolean
 
   @DoNotStrip public fun overrideBySynchronousMountPropsAtMountingAndroid(): Boolean

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

@@ -12,6 +12,7 @@ import android.content.Context
 import android.content.Intent
 import android.nfc.NfcAdapter
 import android.os.Bundle
+import androidx.core.graphics.createBitmap
 import com.facebook.common.logging.FLog
 import com.facebook.infer.annotation.Assertions
 import com.facebook.infer.annotation.ThreadConfined
@@ -447,6 +448,43 @@ public class ReactHostImpl(
     InspectorNetworkHelper.loadNetworkResource(url, listener)
   }
 
+  @DoNotStrip
+  private fun captureScreenshot(format: String, quality: Int): String? {
+    val activity = currentActivity ?: return null
+    val window = activity.window ?: return null
+    val decorView = window.decorView.rootView
+
+    val width = decorView.width
+    val height = decorView.height
+    if (width <= 0 || height <= 0) {
+      return null
+    }
+
+    val bitmap = createBitmap(width, height)
+    val canvas = android.graphics.Canvas(bitmap)
+    decorView.draw(canvas)
+
+    val outputStream = java.io.ByteArrayOutputStream()
+    val compressFormat =
+        when (format) {
+          "jpeg" -> android.graphics.Bitmap.CompressFormat.JPEG
+          "webp" ->
+              if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.R) {
+                android.graphics.Bitmap.CompressFormat.WEBP_LOSSY
+              } else {
+                @Suppress("DEPRECATION") android.graphics.Bitmap.CompressFormat.WEBP
+              }
+          else -> android.graphics.Bitmap.CompressFormat.PNG
+        }
+    val compressQuality = if (quality in 0..100) quality else 80
+
+    bitmap.compress(compressFormat, compressQuality, outputStream)
+    bitmap.recycle()
+
+    val bytes = outputStream.toByteArray()
+    return android.util.Base64.encodeToString(bytes, android.util.Base64.NO_WRAP)
+  }
+
   /**
    * Entrypoint to destroy the ReactInstance. If the ReactInstance is reloading, will wait until
    * reload is finished, before destroying.

packages/react-native/ReactAndroid/src/main/jni/react/devsupport/JInspectorFlags.cpp

@@ -11,6 +11,12 @@
 
 namespace facebook::react::jsinspector_modern {
 
+bool JInspectorFlags::getScreenshotCaptureEnabled(
+    jni::alias_ref<jclass> /*unused*/) {
+  auto& inspectorFlags = InspectorFlags::getInstance();
+  return inspectorFlags.getScreenshotCaptureEnabled();
+}
+
 bool JInspectorFlags::getFuseboxEnabled(jni::alias_ref<jclass> /*unused*/) {
   auto& inspectorFlags = InspectorFlags::getInstance();
   return inspectorFlags.getFuseboxEnabled();
@@ -28,6 +34,11 @@ bool JInspectorFlags::getFrameRecordingEnabled(
 }
 
 void JInspectorFlags::registerNatives() {
+  javaClassLocal()->registerNatives({
+      makeNativeMethod(
+          "getScreenshotCaptureEnabled",
+          JInspectorFlags::getScreenshotCaptureEnabled),
+  });
   javaClassLocal()->registerNatives({
       makeNativeMethod("getFuseboxEnabled", JInspectorFlags::getFuseboxEnabled),
   });

packages/react-native/ReactAndroid/src/main/jni/react/devsupport/JInspectorFlags.h

@@ -18,6 +18,7 @@ class JInspectorFlags : public jni::JavaClass<JInspectorFlags> {
  public:
   static constexpr auto kJavaDescriptor = "Lcom/facebook/react/devsupport/InspectorFlags;";
 
+  static bool getScreenshotCaptureEnabled(jni::alias_ref<jclass> /*unused*/);
   static bool getFuseboxEnabled(jni::alias_ref<jclass> /*unused*/);
   static bool getIsProfilingBuild(jni::alias_ref<jclass> /*unused*/);
   static bool getFrameRecordingEnabled(jni::alias_ref<jclass> /*unused*/);