Report the system double-click interval

wsap_term hardcodes 400 ms in three places to count clicks.

yasl_display_double_click_ms() reads the interval from the system. X11
parses Net/DoubleClickTime from the XSETTINGS owner's property. Wayland
has no protocol for it, so it asks the Settings portal for KDE's
DoubleClickInterval, which KDE sends as a string and which exists only
when the user set it, then GNOME's double-click. X11 without XSETTINGS
asks the portal too. Cocoa reads NSEvent.doubleClickInterval. Missing or
implausible values give YASL_DOUBLE_CLICK_MS_DEFAULT, 400 ms.

The X11 state test covers the XSETTINGS parser in both byte orders and
with truncation. The Xwayland test owns the settings selection. The
desktop test serves both portal keys. The Cocoa path is not built or run
here.

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

2 files changed, 9 insertions, 0 deletions

diff --git a/src/common/backend.c b/src/common/backend.c
index d35d243..b15233f 100644
--- a/src/common/backend.c
+++ b/src/common/backend.c
@@ -110,6 +110,13 @@ int yasl_display_modifiers(const struct yasl_display *d)
     return d->ops->display_modifiers(d);
 }
 
+int yasl_display_double_click_ms(const struct yasl_display *d)
+{
+    int ms = d && d->ops->display_double_click_ms ? d->ops->display_double_click_ms(d) : 0;
+    /* Reject nonsense from misconfigured settings as well as no answer. */
+    return ms > 0 && ms <= 10000 ? ms : YASL_DOUBLE_CLICK_MS_DEFAULT;
+}
+
 void yasl_display_copy(struct yasl_display *d, enum yasl_selection sel, const char *text)
 {
     if (!d || !d->ops->display_copy || !text ||
diff --git a/src/common/backend.h b/src/common/backend.h
index fd60418..96ce9e7 100644
--- a/src/common/backend.h
+++ b/src/common/backend.h
@@ -57,6 +57,8 @@ struct yasl_backend_ops {
     int (*display_dispatch_timeout)(struct yasl_display *d, int timeout_ms);
     void (*display_flush)(struct yasl_display *d);
     int (*display_modifiers)(const struct yasl_display *d);
+    /* Optional; returns zero or less when the system reports no interval. */
+    int (*display_double_click_ms)(const struct yasl_display *d);
     void (*display_copy)(struct yasl_display *d, enum yasl_selection sel, const char *text);
     void (*display_paste)(struct yasl_display *d, enum yasl_selection sel, struct yasl_surface *target);
     bool (*display_drag_start)(struct yasl_display *d, struct yasl_surface *origin, const struct yasl_drag_image *image, const struct yasl_drag_listener *l, void *ud);