Isolate platform SDK includes from app header

docs/modernization/build-inventory.md

@@ -583,6 +583,12 @@ Known local toolchain state:
   while non-Windows platforms still reach retained platform bridges through
   the debt-tracked adapter isolated in
   `src/platform_legacy/legacy_platform_services.*`.
+- `src/app.h` now forward-declares retained platform handles instead of
+  including Objective-C, Android, or GLFW SDK headers. The full platform SDK
+  headers needed by retained non-Windows bridges are included in
+  `src/platform_legacy/legacy_platform_services.cpp`, keeping central app
+  header consumers lighter while `DEBT-0055` tracks removal of those handles
+  from `App`.
 - `pp_platform_api` also owns `plan_asset_file_load`, the SDK-free file-load
   policy consumed by `LayoutManager` for XML layout reload decisions. The
   helper preserves desktop mtime-based reload behavior and non-desktop

docs/modernization/debt.md

@@ -72,6 +72,7 @@ agent or engineer to remove them without reconstructing context from chat.
 | DEBT-0052 | Open | Modernization | Native UI/window state saving now dispatches through `PlatformServices`, but macOS execution still lives in `src/platform_legacy/legacy_platform_services.*` and forwards to the retained Objective-C app bridge | Preserve current Windows/macOS UI persistence while platform shells are extracted incrementally | `pp_platform_api_tests`; `ctest --preset desktop-fast --build-config Debug`; Windows app build; Apple package smoke once root Apple builds exist | UI/window state persistence is owned by injected platform services with no legacy adapter branch |
 | DEBT-0053 | Open | Modernization | Prepared-file writable target selection and prepared-file export-dialog policy now dispatch through `PlatformServices`, but iOS/Web target selection still lives in `src/platform_legacy/legacy_platform_services.*` | Preserve mobile/Web export handoff behavior while platform shells are extracted incrementally | `pp_platform_api_tests`; `ctest --preset desktop-fast --build-config Debug`; Windows app build; Apple/Web package smoke once root package builds exist | Prepared-file target selection, export-dialog policy, and save/download handoff are owned by injected platform services with no legacy adapter branch |
 | DEBT-0054 | Open | Modernization | Layout XML file read/reload decisions now consume `pp_platform_api::plan_asset_file_load`, but that helper still encodes the retained compile-time platform policy: Windows/macOS use `stat` mtime reload checks, while other platforms treat already-loaded layouts as successful no-op loads | Preserve current layout hot-reload and mobile/Web single-load behavior while removing platform guards from the shared `LayoutManager` parser | `pp_platform_api_tests`; `ctest --preset desktop-fast --build-config Debug -R pp_platform_api_tests`; Windows app build | Layout reload decisions are owned by injected platform storage/file-watch services or an asset manager boundary with platform-specific file watching removed from compile-time helpers |
+| DEBT-0055 | Open | Modernization | `src/app.h` now forward-declares retained iOS/macOS/Android/Linux/Web platform handles instead of including platform SDK headers, and full SDK includes are isolated in `src/platform_legacy/legacy_platform_services.cpp`, but the `App` singleton still stores those platform handles directly | Reduce central header platform coupling incrementally without rewriting non-Windows platform entrypoints before Phase 6 | Windows app build; Apple/Android/Linux/Web package smoke once platform root builds are active | Platform handles are owned by injected `pp_platform_*` shell state or services, and `App` has no platform SDK handle fields or platform conditional members |
 
 ## Closed Debt
 

docs/modernization/roadmap.md

@@ -658,6 +658,10 @@ Windows installs an injected `WindowsPlatformServices` implementation from
 other platforms still route through the debt-tracked legacy fallback adapter
 now isolated in `src/platform_legacy/legacy_platform_services.*`, so behavior
 is preserved while their platform shell implementations are extracted.
+The central `App` header now forward-declares retained platform handles instead
+of including Objective-C, Android, or GLFW SDK headers; the full platform
+headers live in the legacy platform adapter until those handles move out of
+`App` during Phase 6.
 Prepared-file save/download handoff is now also part of the service contract,
 so iOS/Web export completion routes through `PlatformServices` after the app
 writes the temporary/exported payload.

src/app.h

@@ -32,23 +32,23 @@ struct PlatformStoragePaths;
 }
 
 #if defined(__OBJC__) && defined(__IOS__)
-#import <Foundation/Foundation.h>
-#import "GameViewController.h"
-#import "AppDelegate.h"
+@class GameViewController;
+@class AppDelegate;
 #endif
 
 #if defined(__OBJC__) && defined(__OSX__)
-#import "main.h"
+@class View;
+@class AppOSX;
 #endif
 
 #ifdef __ANDROID__
-#include "main.h"
+struct android_app;
+struct engine;
 #endif
 
-#ifdef __LINUX__
-#include <GLFW/glfw3.h>
+#if __LINUX__ || __WEB__
+struct GLFWwindow;
 #endif
-
 struct VRController
 {
     enum class kButton : uint8_t

src/platform_legacy/legacy_platform_services.cpp

@@ -7,6 +7,7 @@
 #include "renderer_gl/opengl_capabilities.h"
 
 #ifdef __ANDROID__
+#include "main.h"
 void displayKeyboard(bool pShow);
 void android_async_lock();
 void android_async_swap();
@@ -18,16 +19,26 @@ void android_pick_file_save(std::function<void(std::string)> callback);
 std::string android_get_clipboard();
 bool android_set_clipboard(const std::string& s);
 #elif __APPLE__
+#include <Foundation/Foundation.h>
+#include "objc_utils.h"
+#ifdef __IOS__
+#include "AppDelegate.h"
+#include "GameViewController.h"
+#elif defined(__OSX__)
+#include "main.h"
+#endif
 void delete_all_files_in_path(const std::string& source_path);
 #ifdef __IOS__
 void save_image_library(const std::string& path);
 #endif
 #elif __LINUX__
+#include <GLFW/glfw3.h>
 #include <tinyfiledialogs.h>
 std::string linux_home_path();
 int mkpath(const std::string& dir, mode_t mode = DEFFILEMODE);
 void linux_update_fps(int frames);
 #elif __WEB__
+#include <GLFW/glfw3.h>
 void webgl_pick_file(std::function<void(std::string)> callback);
 void webgl_pick_file_save(
     const std::string& path,