Fix multiplayer standalone crash: client stats race + host accept code

code/network/multimsgs.cpp

@@ -4046,9 +4046,17 @@ void process_endgame_packet(ubyte * /*data*/, header *hinfo)
 		// do any special processing for being in a state other than the gameplay state
 		multi_handle_state_special();
 
+		// If end-mission fired via SEXP, enter debrief immediately (skipping warp-out).
+		// Stats have already been received via multi_broadcast_stats() which send_endgame_packet()
+		// calls before sending this packet, so scoring_level_close() will see correct kill data.
+		if (Multi_sexp_end_mission_pending) {
+			Multi_sexp_end_mission_pending = false;
+			send_debrief_event();
+		}
+
 		// make sure we're not already in the debrief state
 		if((gameseq_get_state() != GS_STATE_DEBRIEF) && (gameseq_get_state() != GS_STATE_MULTI_DOGFIGHT_DEBRIEF)){
-			multi_warpout_all_players();			
+			multi_warpout_all_players();
 		}
 	}	
 }

code/network/multiui.cpp

@@ -8836,6 +8836,7 @@ void multi_debrief_esc_hit()
 						multi_sw_report(stats_saved);
 					}
 				}
+
 			}
 
 			multi_quit_game(PROMPT_HOST);

code/network/multiutil.cpp

@@ -1231,6 +1231,12 @@ void multi_apply_ship_status(net_player *p,button_info *bi,int locally)
 // send 10x a second MAX
 #define MULTI_SHIP_STATUS_TIME			350
 int Multi_ship_status_stamp = -1;
+
+// Set by multi_sexp_end_mission() so that process_endgame_packet() knows to call
+// send_debrief_event() immediately upon receiving MISSION_END, skipping warp-out.
+// Must be checked after stats have been broadcast by the server (which happens
+// in send_endgame_packet() before the MISSION_END packet is sent).
+bool Multi_sexp_end_mission_pending = false;
 button_info Multi_ship_status_bi;
 
 void multi_maybe_send_ship_status()

code/network/multiutil.h

@@ -232,6 +232,10 @@ short multi_get_new_id();
 // Karajorma - sends the player to the correct debrief for this game type
 void send_debrief_event();
 
+// Set by multi_sexp_end_mission() to signal that process_endgame_packet() should
+// enter debrief immediately (skipping warp-out) once stats have been received.
+extern bool Multi_sexp_end_mission_pending;
+
 // Karajorma - Performs any cleanup needed by missions which don't end with a warpout.
 void multi_handle_sudden_mission_end();
 

code/parse/sexp.cpp

@@ -17216,10 +17216,18 @@ void sexp_end_mission(int n)
 
 void multi_sexp_end_mission()
 {
-	// This is a bit of hack, but when in a debrief state clients will skip the
-	// warp out sequence when the endgame packet is processed.
-	send_debrief_event();
-	// Standard way to end mission (equivalent to Alt-J)
+	// Signal process_endgame_packet() to skip the warp-out sequence by entering
+	// debrief immediately when the MISSION_END packet arrives.  We cannot call
+	// send_debrief_event() here directly: on standalone servers the client has not
+	// yet received mission stats (m_okKills etc.) at this point, so
+	// scoring_level_close() would run with zeroed kill counts and
+	// Pilot.update_stats() would create no kill entries.  debrief_close() would
+	// then try to back out entries that were never created and hit an UNREACHABLE.
+	//
+	// send_endgame_packet() broadcasts stats to clients *before* sending MISSION_END,
+	// so by the time process_endgame_packet() fires, the stats are already present
+	// and it is safe to enter debrief there.
+	Multi_sexp_end_mission_pending = true;
 	multi_handle_end_mission_request();
 }