Widescreen HUD size: proportional option shrinks the auto-UI HUD beyond 16:9

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

runtime/include/gpu.h

@@ -212,6 +212,9 @@ void gpu_ws_set_auto_ui_squash(int on);
 /* [widescreen] auto_ui_anchor = "in_place": each UI run squashes about its own
  * centre rather than an edge/centre third (default "edges"). */
 void gpu_ws_set_auto_ui_in_place(int on);
+/* [widescreen] auto_ui_size: 1 = proportional (the auto-UI HUD shrinks by
+ * sqrt((16:9) / aspect) beyond 16:9), 0 = original. */
+void gpu_ws_set_auto_ui_proportional(int on);
 /* [widescreen.bg2d] Capcom 2D background tile-loop widen — hooked at the renderer's
  * column-count / start-tile-col / start-screen-x instructions. Identity at 4:3
  * and in the engine's 512 hi-res mode. */

runtime/include/mod_plugins.h

@@ -393,6 +393,15 @@ int psx_mod_set_fixed_display_aspect(uint32_t numerator,
  */
 int psx_mod_set_adaptive_display_aspect(uint32_t max_numerator,
                                         uint32_t max_denominator);
+/*
+ * HUD size for the auto-UI widescreen HUD ([widescreen] auto_ui_squash):
+ * 0 keeps it at the display height's scale ("original"), 1 makes it
+ * proportional (unchanged up to 16:9, shrinking by sqrt((16:9) / aspect)
+ * beyond, about each widget's anchors). Overrides game.toml
+ * [widescreen] auto_ui_size for the session; every session start restores the
+ * title's setting before activation.
+ */
+int psx_mod_set_widescreen_hud_size(int proportional);
 /*
  * Set the wall-clock cadence of simulated guest VBlanks. A value of zero
  * removes frontend pacing; 60 and higher request that many native guest