fix: prevent LKObjCHelpers from leaking into swiftinterface

Use @_implementationOnly import under LK_XCFRAMEWORK flag so the
ObjC helpers module is available at compile time but excluded from
the public .swiftinterface, which consumers cannot resolve.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pblazej

Sources/LiveKit/Broadcast/LKSampleHandler.swift

@@ -23,7 +23,9 @@ import ReplayKit
 import Combine
 import OSLog
 
-#if !COCOAPODS
+#if LK_XCFRAMEWORK
+@_implementationOnly import LKObjCHelpers
+#elseif !COCOAPODS
 import LKObjCHelpers
 #endif
 

scripts/xcframework.swift

@@ -261,7 +261,9 @@ func generateFrameworkProject(at projectPath: Path, repoRoot: Path) throws {
         "MACH_O_TYPE": "mh_dylib",
         "CLANG_ENABLE_MODULES": "YES",
         "HEADER_SEARCH_PATHS": "$(inherited) " + (repoRoot + "Sources/LKObjCHelpers/include").string,
-        // LKObjCHelpers needs its own modulemap so `import LKObjCHelpers` works in Swift
+        // LK_XCFRAMEWORK flag replaces `import LKObjCHelpers` with `@_implementationOnly`
+        // to prevent leaking into .swiftinterface
+        "SWIFT_ACTIVE_COMPILATION_CONDITIONS": "LK_XCFRAMEWORK",
         "SWIFT_INCLUDE_PATHS": "$(inherited) " + (repoRoot + "Sources/LKObjCHelpers").string,
     ])
     pbxProj.add(object: targetConfig)
@@ -316,7 +318,7 @@ func generateFrameworkProject(at projectPath: Path, repoRoot: Path) throws {
         }
     }
 
-    // --- Create LKObjCHelpers modulemap if it doesn't exist ---
+    // --- Create LKObjCHelpers modulemap if needed ---
     let modulemapPath = repoRoot + "Sources" + "LKObjCHelpers" + "module.modulemap"
     if !modulemapPath.exists {
         try modulemapPath.write("module LKObjCHelpers {\n    header \"include/LKObjCHelpers.h\"\n    export *\n}\n")