feat: add type-safe native platform headers and portable drag support

- Add include/yasl/native/{wayland,cocoa,x11}.h with type-safe handle accessors.
- Unify drag-and-drop and window carry support across Wayland, X11, and Cocoa.
- Preserve full ABI compatibility for capability flags.
- Install native headers conditionally based on enabled backend.
- Include missing tablet example and backend test suites.

2 files changed, 71 insertions, 0 deletions

diff --git a/tests/common/test_backends.c b/tests/common/test_backends.c
index 605dac0..4c99646 100644
--- a/tests/common/test_backends.c
+++ b/tests/common/test_backends.c
@@ -1,5 +1,11 @@
 #define _POSIX_C_SOURCE 200809L
 #include "yasl/native.h"
+#if YASL_HAS_WAYLAND
+#include "yasl/native/wayland.h"
+#endif
+#if YASL_HAS_X11
+#include "yasl/native/x11.h"
+#endif
 #include "yasl/loop.h"
 #include "yasl/yasl.h"
 
@@ -145,6 +151,8 @@ static void x11_behavior(struct yasl_loop *loop, struct yasl_display *d, struct
     Display *native = yasl_display_get_native_handle(d);
     Window window = (Window)(uintptr_t)yasl_surface_get_native_handle(w->surface);
     assert(native && window);
+    assert(yasl_x11_display_get_display(d) == native);
+    assert(yasl_x11_surface_get_window(w->surface) == (uintptr_t)window);
     XSync(native, False);
     XImage *image = XGetImage(native, window, 0, 0, 1, 1, AllPlanes, ZPixmap);
     assert(image && (XGetPixel(image, 0, 0) & 0xffffff) == 0x4080c0);
@@ -282,6 +290,16 @@ int main(int argc, char **argv)
         struct yasl_display *b = yasl_display_open(loop, &spec);
         assert(a && b);
         struct window wa = create(a), wb = create(b);
+#if YASL_HAS_WAYLAND
+        assert(yasl_wayland_display_get_wl_display(a) != NULL);
+        assert(yasl_wayland_surface_get_wl_surface(wa.surface) != NULL);
+        assert(!yasl_x11_display_get_display(a));
+#endif
+#if YASL_HAS_X11
+        assert(yasl_x11_display_get_display(b) != NULL);
+        assert(yasl_x11_surface_get_window(wb.surface) != 0);
+        assert(!yasl_wayland_display_get_wl_display(b));
+#endif
         attach(&wa);
         attach(&wb);
         pump(loop, a, b);
diff --git a/tests/common/test_tablet_example.c b/tests/common/test_tablet_example.c
new file mode 100644
index 0000000..1658174
--- /dev/null
+++ b/tests/common/test_tablet_example.c
@@ -0,0 +1,53 @@
+#define main tablet_example_main
+#include "../../examples/tablet.c"
+#undef main
+#include <assert.h>
+
+static void pointer(struct app *app, enum yasl_pointer_kind kind,
+                    enum yasl_pointer_device device, int button, int x, int y, uint16_t pressure)
+{
+    struct yasl_input_event event = {.kind = YASL_INPUT_MOUSE, .mouse = {
+        .kind = kind, .device = device, .button = button, .pos = {x, y}, .pen.pressure = pressure}};
+    input(app, &event);
+}
+
+static uint32_t pixel(const struct app *app, int x, int y)
+{
+    return app->canvas[(size_t)y * app->geometry.size.x + x];
+}
+
+int main(void)
+{
+    struct app app = {0};
+    assert(resize_canvas(&app, (struct yasl_geometry){{400, 300}, 120}));
+    pointer(&app, YASL_PTR_MOTION, YASL_PTR_DEV_PEN, 3, 80, 160, 65535);
+    assert(pixel(&app, 80, 160) == PAPER); /* Hover never paints. */
+    pointer(&app, YASL_PTR_PRESS, YASL_PTR_DEV_PEN, 2, 80, 160, 65535);
+    assert(!app.down && pixel(&app, 80, 160) == PAPER); /* Side button isn't the tip. */
+    pointer(&app, YASL_PTR_PRESS, YASL_PTR_DEV_PEN, 0, 80, 160, 0);
+    assert(app.down && pixel(&app, 80, 160) == INK && pixel(&app, 90, 160) == PAPER);
+    pointer(&app, YASL_PTR_MOTION, YASL_PTR_DEV_PEN, 0, 80, 160, 65535);
+    assert(pixel(&app, 100, 160) == INK); /* Stationary pressure widens brush. */
+    pointer(&app, YASL_PTR_MOTION, YASL_PTR_DEV_PEN, 0, 180, 160, 20000);
+    assert(pixel(&app, 130, 160) == INK); /* Segments are continuous. */
+    pointer(&app, YASL_PTR_RELEASE, YASL_PTR_DEV_PEN, 0, 180, 160, 0);
+    pointer(&app, YASL_PTR_MOTION, YASL_PTR_DEV_PEN, 3, 250, 160, 65535);
+    assert(!app.down && pixel(&app, 250, 160) == PAPER);
+    pointer(&app, YASL_PTR_PRESS, YASL_PTR_DEV_ERASER, 0, 80, 160, 65535);
+    assert(pixel(&app, 80, 160) == PAPER && pixel(&app, 130, 160) == INK);
+    struct yasl_input_event reset = {.kind = YASL_INPUT_RESET};
+    input(&app, &reset);
+    pointer(&app, YASL_PTR_MOTION, YASL_PTR_DEV_ERASER, 0, 130, 160, 65535);
+    assert(!app.down && pixel(&app, 130, 160) == INK);
+    pointer(&app, YASL_PTR_PRESS, YASL_PTR_DEV_MOUSE, 0, 300, 200, 0);
+    assert(pixel(&app, 300, 200) == INK);
+    struct yasl_input_event blur = {.kind = YASL_INPUT_FOCUS, .focus.focused = false};
+    input(&app, &blur);
+    assert(!app.down);
+    assert(resize_canvas(&app, (struct yasl_geometry){{800, 600}, 240}));
+    assert(pixel(&app, 600, 400) == INK && !app.previous); /* DPI preserves logical drawing. */
+    clear_canvas(&app);
+    assert(pixel(&app, 600, 400) == PAPER);
+    free(app.canvas);
+    return 0;
+}