SNAPFLAG_RESET_ENTITIES: no-interpolation reset without gamestate resend

Replace the gamestate resend approach for map_restart with a custom
snapshot flag (SNAPFLAG_RESET_ENTITIES, bit 4 in snapFlags byte).

Server side (sv_netdemo.c):
- On restart frame, OR the flag into svs.snapFlagServerBit (one-shot)
- Cleared at the start of the next playback frame

Client side (cg_snapshot.c):
- CG_SetNextSnap: clear currentValid for all entities when flag is set,
  making them all "new" — existing interpolation check at line 228
  sets interpolate=qfalse, CG_TransitionEntity calls CG_ResetEntity
- Also set cg.nextFrameTeleport=qtrue to prevent playerstate
  interpolation during follow mode

No loading screen, no lost frames, no gamestate resend. Entities and
playerstate both snap to correct positions on map_restart.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

code/cgame/cg_snapshot.c

@@ -203,6 +203,15 @@ static void CG_SetNextSnap( snapshot_t *snap ) {
 
 	cg.nextSnap = snap;
 
+	// SNAPFLAG_RESET_ENTITIES: invalidate all entities so they are
+	// treated as new (no interpolation from old positions).
+	// Must happen before the entity loop below.
+	if ( snap->snapFlags & SNAPFLAG_RESET_ENTITIES ) {
+		for ( num = 0 ; num < MAX_GENTITIES ; num++ ) {
+			cg_entities[ num ].currentValid = qfalse;
+		}
+	}
+
 	BG_PlayerStateToEntityState( &snap->ps, &cg_entities[ snap->ps.clientNum ].nextState, qfalse );
 	cg_entities[ cg.snap->ps.clientNum ].interpolate = qtrue;
 
@@ -241,6 +250,11 @@ static void CG_SetNextSnap( snapshot_t *snap ) {
 		cg.nextFrameTeleport = qtrue;
 	}
 
+	// entity reset also prevents playerstate interpolation
+	if ( cg.nextSnap->snapFlags & SNAPFLAG_RESET_ENTITIES ) {
+		cg.nextFrameTeleport = qtrue;
+	}
+
 	// sort out solid entities
 	CG_BuildSolidList();
 }

code/game/q_shared.h

@@ -1085,6 +1085,7 @@ typedef enum {
 #define	SNAPFLAG_RATE_DELAYED	1
 #define	SNAPFLAG_NOT_ACTIVE		2	// snapshot used during connection and for zombies
 #define SNAPFLAG_SERVERCOUNT	4	// toggled every map_restart so transitions can be detected
+#define SNAPFLAG_RESET_ENTITIES	16	// snap all entities to current position, no interpolation
 
 //
 // per-level limits

code/server/server.h

@@ -289,7 +289,6 @@ void SV_AuthorizeIpPacket( netadr_t from );
 void SV_ExecuteClientMessage( client_t *cl, msg_t *msg );
 void SV_UserinfoChanged( client_t *cl );
 
-void SV_SendClientGameState( client_t *client );
 void SV_ClientEnterWorld( client_t *client, usercmd_t *cmd );
 void SV_DropClient( client_t *drop, const char *reason );
 

code/server/sv_netdemo.c

@@ -677,22 +677,14 @@ static qboolean SVD_ReadFrame( fileHandle_t f ) {
 		byte frameFlags;
 		FS_Read( &frameFlags, 1, f );
 		if ( frameFlags & 1 ) {
-			int j;
 			// map was restarted — reset playback delta state to match
 			// the recording's reset (both now decode from zero baseline).
-			// Also toggle server bit and force non-delta snapshot so the
-			// client clears old entity state and doesn't interpolate.
 			Com_Memset( demo.playPrevEntities, 0, sizeof(demo.playPrevEntities) );
 			Com_Memset( demo.playPrevPlayers, 0, sizeof(demo.playPrevPlayers) );
-			svs.snapFlagServerBit ^= SNAPFLAG_SERVERCOUNT;
-			// send a full gamestate to all active clients — this makes
-			// CL_ParseGamestate → CL_ClearState wipe all snapshot/entity
-			// history, exactly like a real map_restart does.
-			for ( j = 0; j < sv_maxclients->integer; j++ ) {
-				if ( svs.clients[j].state >= CS_PRIMED ) {
-					SV_SendClientGameState( &svs.clients[j] );
-				}
-			}
+			// set one-shot SNAPFLAG_RESET_ENTITIES so cgame snaps all
+			// entities to current position without interpolation.
+			// OR'd into snapFlagServerBit, cleared after one frame.
+			svs.snapFlagServerBit |= SNAPFLAG_RESET_ENTITIES;
 		}
 	}
 
@@ -1020,6 +1012,9 @@ qboolean SVD_PlaybackFrame( void ) {
 		demo.needConfigstrings = qfalse;
 	}
 
+	// clear one-shot reset flag from previous frame before reading new one
+	svs.snapFlagServerBit &= ~SNAPFLAG_RESET_ENTITIES;
+
 	if ( !SVD_ReadFrame( demo.playFile ) ) {
 		Com_Printf( "Server demo playback finished.\n" );
 		SVD_CleanupPlayback();