Keep the Project Attributes When Fastlane Writes the Project

fastlane/Fastfile

@@ -6,6 +6,8 @@
 # SPDX-License-Identifier: MIT
 #
 
+require_relative "xcodeproj_patch"
+
 default_platform(:ios)
 
 APP_CONFIG = {

fastlane/xcodeproj_patch.rb

@@ -0,0 +1,30 @@
+#
+# This source file is part of the My Heart Counts iOS open-source project
+#
+# SPDX-FileCopyrightText: 2026 Stanford University and the project authors (see CONTRIBUTORS.md)
+#
+# SPDX-License-Identifier: MIT
+#
+
+require "xcodeproj"
+
+# Xcodeproj drops attributes it does not know when it writes a project back, and it does not know
+# the traits Xcode records for a package reference or the destination it records for a copy files
+# build phase. Fastlane opens and saves the project to set the bundle identifier and the build
+# number, so a deployment silently removed the package traits and the destination of the phases
+# that embed the watch app and the extensions. Declaring both keeps the round trip lossless.
+#
+# This can be removed once Xcodeproj knows the attributes itself.
+module Xcodeproj
+  class Project
+    module Object
+      class XCRemoteSwiftPackageReference < AbstractObject
+        attribute :traits, Array
+      end
+
+      class PBXCopyFilesBuildPhase < AbstractBuildPhase
+        attribute :dstSubfolder, String
+      end
+    end
+  end
+end