fix(cocoapods): harden prebuilt-deps header search paths and artifact handling

- rndependencies.rb: the previous "||= [] << path" only added the deps
  header search path when HEADER_SEARCH_PATHS was unset — with an existing
  value the path was silently dropped. Normalize string values and always
  append. Also point the search path at the pod-local flattened Headers/
  (single header home) instead of the artifact root.
- ReactNativeDependencies.podspec: prepare_command exited 0 when
  XCFRAMEWORK_PATH/HEADERS_PATH resolved empty, producing a silent
  no-link pod; fail closed with exit 1.
- reactNativeDependencies.js: an artifact without a version marker logged
  "we are going to use it anyway" but then fell through to rmSync +
  re-download, destroying locally staged deps builds; honor the message
  and use it as-is.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: chrfalch

packages/react-native/scripts/cocoapods/rndependencies.rb

@@ -49,8 +49,19 @@ def add_rn_third_party_dependencies(s)
 
         current_pod_target_xcconfig["HEADER_SEARCH_PATHS"] = header_search_paths
     else
+        # Prebuilt-deps mode: this pod SELF-SERVES the third-party headers from its
+        # own xcframework (incl. SocketRocket - sole supplier in this mode). See
+        # scripts/cocoapods/__docs__/prebuilt-deps.md for the full contract.
         s.dependency "ReactNativeDependencies"
-        current_pod_target_xcconfig["HEADER_SEARCH_PATHS"] ||= [] << "$(PODS_ROOT)/ReactNativeDependencies"
+
+        header_search_paths = current_pod_target_xcconfig["HEADER_SEARCH_PATHS"] || []
+        if header_search_paths.is_a?(String)
+            header_search_paths = header_search_paths.split(" ")
+        end
+        # Artifact headers are flattened into the pod-local Headers/ by the podspec
+        # prepare_command (see __docs__/prebuilt-deps.md).
+        header_search_paths << "$(PODS_ROOT)/ReactNativeDependencies/Headers"
+        current_pod_target_xcconfig["HEADER_SEARCH_PATHS"] = header_search_paths
     end
 
     s.pod_target_xcconfig = current_pod_target_xcconfig

packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js

@@ -161,6 +161,10 @@ function checkExistingVersion(
       dependencyLog(
         `React Native Dependencies found on disk at: ${artifactsPath}.\nNo version file has been found. We are going to use it anyway, but there might be some unexpected behaviors.`,
       );
+      // Honor the message above: an artifact without a version marker is a
+      // locally-staged one (e.g. a freshly composed deps build) — falling
+      // through here rmSync'd it and re-downloaded. Use it as-is.
+      return true;
     }
   } else {
     dependencyLog('React Native Dependencies not found on disk');

packages/react-native/third-party-podspecs/ReactNativeDependencies.podspec

@@ -53,13 +53,13 @@ Pod::Spec.new do |spec|
     # Check if XCFRAMEWORK_PATH is empty
     if [ -z "$XCFRAMEWORK_PATH" ]; then
       echo "ERROR: XCFRAMEWORK_PATH is empty."
-      exit 0
+      exit 1
     fi
 
     # Check if HEADERS_PATH is empty
     if [ -z "$HEADERS_PATH" ]; then
       echo "ERROR: HEADERS_PATH is empty."
-      exit 0
+      exit 1
     fi
 
     cp -R "$HEADERS_PATH/." Headers