frame_fingerprint reset_on_load for A/B runs from one savestate

frame_fingerprint reset_on_load=1 restarts the rolling hashes and the ring
when the next savestate load completes, so two runs that load the same state
(for example with and without a presentation mod) compare frame by frame
from the same guest point. Debug tooling only.

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

runtime/include/debug_server.h

@@ -255,6 +255,9 @@ void debug_server_freeze_dump_dirty_block_json(FILE *f, uint32_t max_count);
 void debug_server_freeze_dump_dirty_insn_json(FILE *f, uint32_t max_count);
 void debug_server_freeze_dump_evcb_json(FILE *f, uint32_t max_count);
 
+/* frame_fingerprint reset_on_load: called when a savestate load completes. */
+void debug_server_note_savestate_loaded(void);
+
 #ifdef __cplusplus
 }
 #endif

runtime/src/debug_server.c

@@ -5028,8 +5028,29 @@ static void handle_frame(int id, const char *json)
  * of two runs (native vs interp/oracle): the first frame whose wr or pc differs
  * is the first-divergence frame. Small integer fields only — no large/ragged
  * payload, so it never trips the trace-dump JSON/eviction problems. */
+/* frame_fingerprint reset_on_load=1: restart the rolling hashes and the ring
+ * when the next savestate load completes, so two runs that load the same state
+ * (for example with and without a presentation mod) compare frame by frame
+ * from that guest point on, independent of what happened before the load. */
+static int s_fp_reset_on_load = 0;
+void debug_server_note_savestate_loaded(void)
+{
+    if (!s_fp_reset_on_load) return;
+    s_fp_reset_on_load = 0;
+    g_fp_wr_hash = g_fp_pc_hash = 1469598103934665603ULL;
+    g_fp_mmio_hash = g_fp_sp_hash = 1469598103934665603ULL;
+    g_fp_write_count = g_fp_mmio_count = g_fp_sp_count = 0;
+    s_fp_head = 0;
+    s_fp_total = 0;
+}
+
 static void handle_frame_fingerprint(int id, const char *json)
 {
+    if (json_get_int(json, "reset_on_load", 0)) {
+        s_fp_reset_on_load = 1;
+        send_fmt("{\"id\":%d,\"ok\":true,\"armed\":1}", id);
+        return;
+    }
     int count = json_get_int(json, "count", 1024);
     if (count < 1) count = 1;
     if (count > FP_RING_CAP) count = FP_RING_CAP;

runtime/src/main.cpp

@@ -1018,6 +1018,9 @@ extern "C" void psx_frontend_on_savestate_notify(int is_load, int slot, int ok)
 
 extern "C" void psx_frontend_on_savestate_loaded(void) {
     mod_runtime_on_savestate_loaded();
+#ifndef PSX_NO_DEBUG_TOOLS
+    debug_server_note_savestate_loaded();
+#endif
     s_disabled_frame_presented = false;
     s_force_present_after_load = true;
     smooth_60_reset();