Merge branch 'backend-selection' into main

- Implement runtime backend selection (Wayland, X11, Cocoa)
- Add native X11 backend with clipboard, keyboard, mouse, and placement
- Integrate multi-backend integration tests running under Weston and Xwayland
- Retain zero-hole struct packing, branchless ALU/LUT primitives, and paced event loop

1 files changed, 13 insertions, 0 deletions

diff --git a/include/yasl/yasl.h b/include/yasl/yasl.h
index c211a0b..6fea487 100644
--- a/include/yasl/yasl.h
+++ b/include/yasl/yasl.h
@@ -259,14 +259,25 @@ struct yasl_surface_cbs {
 };
 
 /* Display Lifecycle */
+enum yasl_backend {
+    YASL_BACKEND_AUTO = 0,
+    YASL_BACKEND_WAYLAND,
+    YASL_BACKEND_X11,
+    YASL_BACKEND_COCOA,
+};
+
 struct yasl_display_spec {
     const char *app_id;
     const struct yasl_display_cbs *cbs;
     void *ud;
+    /* Zero selects the native backend. An explicit choice never falls back. */
+    enum yasl_backend backend;
 };
 
+/* Return NULL and set errno if the requested backend cannot open. */
 YASL_API struct yasl_display *yasl_display_open(struct yasl_loop *loop,
                                                const struct yasl_display_spec *spec);
+YASL_API enum yasl_backend yasl_display_backend(const struct yasl_display *d);
 YASL_API void yasl_display_close(struct yasl_display *d);
 YASL_API uint32_t yasl_display_caps(const struct yasl_display *d);
 YASL_API void yasl_display_dispatch(struct yasl_display *d);
@@ -287,6 +298,7 @@ struct yasl_surface_spec {
     struct yasl_vector2i size;
     bool fullscreen;
     bool tearing;
+    /* Optional native graphics device. NULL selects CPU pixel presentation. */
     void *graphics_device;
 };
 
@@ -347,6 +359,7 @@ YASL_API void yasl_loop_destroy(struct yasl_loop *l);
 YASL_API int yasl_loop_run(struct yasl_loop *l);
 YASL_API int yasl_loop_step(struct yasl_loop *l, int timeout_ms);
 YASL_API void yasl_loop_quit(struct yasl_loop *l);
+YASL_API bool yasl_loop_is_running(const struct yasl_loop *l);
 YASL_API void yasl_loop_kick(struct yasl_loop *l);
 YASL_API uint64_t yasl_loop_now_ns(void);
 YASL_API int yasl_loop_add_fd(struct yasl_loop *l, int fd, short events,