Introduce platform services interface

docs/modernization/roadmap.md

@@ -1,7 +1,7 @@
 # PanoPainter Modernization Roadmap
 
 Status: live
-Last updated: 2026-06-02
+Last updated: 2026-06-03
 
 This is the living roadmap for modernizing PanoPainter into independently
 testable C++23 components while retaining all existing functionality. Keep this
@@ -87,6 +87,8 @@ Intended responsibilities:
 - `pp_ui_core`: `Node`, layout, generic controls, text/image primitives.
 - `pp_panopainter_ui`: panels, dialogs, `NodeCanvas`, and app-specific
   workflows.
+- `pp_platform_api`: SDK-free service interfaces for clipboard, cursor,
+  virtual keyboard, file pickers, sharing, and future platform automation.
 - `pp_platform_*`: Windows, macOS/iOS, Android, Linux, and WebGL shells.
 - `panopainter_app`: composition root only.
 
@@ -466,6 +468,11 @@ cursor bridges continue.
 `pano_cli plan-clipboard-read` and `pano_cli plan-clipboard-write` expose the
 app-core clipboard text decisions used by live clipboard get/set requests
 before retained platform clipboard bridges continue.
+`pp_platform_api` now owns a headless `PlatformServices` interface for
+clipboard text, cursor visibility, and virtual-keyboard visibility. Live app
+clipboard/cursor/keyboard execution routes through a debt-tracked legacy
+adapter in `app_events.cpp`, so behavior is preserved while later platform
+shell implementations can replace direct bridge calls.
 `pano_cli plan-cloud-upload` exposes the app-core cloud upload decision used by
 the live cloud upload command for missing-canvas, new-document warning, publish
 prompt, and dirty-document save-before-upload states before legacy UI, canvas,
@@ -494,8 +501,9 @@ Implementation tasks:
   7. `pp_paint_renderer`
   8. `pp_ui_core`
   9. `pp_panopainter_ui`
-  10. `pp_platform_*`
-  11. `panopainter_app`
+  10. `pp_platform_api`
+  11. `pp_platform_*`
+  12. `panopainter_app`
 - Remove renderer/platform dependencies from pure headers first, especially:
   - `Brush`
   - document/layer model
@@ -975,6 +983,11 @@ Results:
   `pano_cli_plan_clipboard_write_smoke`, and
   `pano_cli_plan_clipboard_write_empty_smoke` passed and expose app-core
   clipboard decisions as JSON, including empty write text.
+- `pp_platform_api_tests` passed, covering the SDK-free `PlatformServices`
+  interface for clipboard read/write, empty clipboard writes, cursor
+  visibility dispatch, and virtual-keyboard visibility dispatch. The live app
+  now consumes this interface through the legacy platform adapter for
+  clipboard/cursor/keyboard execution.
 - `panopainter_validate_shaders` passed, validating 25 shader programs and 7
   shader includes for stage markers and include graph integrity.
 - `pp_renderer_gl_capabilities_tests` passed on default MSVC, vcpkg-headless,