Pace frame requests by the frame presented after them

A frame request now only records intent. Each loop step resolves it after
the callbacks that present, so a request made before the present waits for
that frame. An animation that asked first got two REFRESH events per frame
on X11 and with GL.

With no frame in flight, the REFRESH comes one refresh interval after the
last present or answer, so a request without a present cannot spin.

Queued events now go before an owed REFRESH. Input reaches the application
before it draws, and a queued REFRESH pays an owed one for the same surface.

The loop prepare only peeks at a lost event, so deliver can report it as a
final loss. A failed push from another thread wakes the loop.

Signals and posts run at the end of a step, after descriptors and timers.
A signal handler now sees the output that came with it.

A render-thread GL swap counts as in flight on Wayland.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/common/types.h b/src/common/types.h
index 8d00d0b..67aaaa3 100644
--- a/src/common/types.h
+++ b/src/common/types.h
@@ -874,9 +874,9 @@ bool yasl_private_frame_present(struct yasl_private_frame *frame,
                                 const struct yasl_private_rect2i *rects, size_t count);
 /** Coalesce a redraw request; use on the display thread. NULL is ignored. */
 void yasl_private_surface_request_frame(struct yasl_surface *s);
-/** Owe s a REFRESH once the system shows its frame in flight, or at once when
- * none is. False with errno when the fallback timer cannot start. */
-bool yasl_private_surface_request_shown_frame(struct yasl_surface *s);
+/** Owe s a REFRESH after the next frame shown. The next loop step decides
+ * which frame that is, so a present after the request counts. */
+void yasl_private_surface_request_shown_frame(struct yasl_surface *s);
 /** Set drawing policy for either loop style. Returns false with errno on failure. */
 bool yasl_private_surface_set_pacing(struct yasl_surface *s, yasl_private_pacing_mode mode);