Demo pause: freeze svs.time, hold demo data consumption

svdemo_pause toggles playback pause. When paused:
- svs.time frozen so entity trajectories freeze correctly
- No demo frames consumed (SVD_PlaybackFrame returns early)
- Game frame still runs at frozen time for spectator movement
- No time jump on unpause — svs.time resumes from where it was

Spectator movement degrades during pause (200ms PmoveSingle cap)
— will be resolved by client-owned camera in a future change.

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

code/server/server.h

@@ -353,9 +353,11 @@ void		SVD_CaptureServerCommand( const char *cmd );
 void		SVD_Play_f( void );
 void		SVD_StopPlay_f( void );
 void		SVD_Stop_f( void );
+void		SVD_Pause_f( void );
 qboolean	SVD_PlaybackFrame( void );
 qboolean	SVD_IsRecording( void );
 qboolean	SVD_IsPlaying( void );
+qboolean	SVD_IsPaused( void );
 qboolean	SVD_ShouldPause( void );
 
 //============================================================

code/server/sv_ccmds.c

@@ -744,6 +744,7 @@ void SV_AddOperatorCommands( void ) {
 	Cmd_AddCommand ("svdemo_record", SVD_Record_f);
 	Cmd_AddCommand ("svdemo_stop", SVD_Stop_f);
 	Cmd_AddCommand ("svdemo_play", SVD_Play_f);
+	Cmd_AddCommand ("svdemo_pause", SVD_Pause_f);
 }
 
 /*

code/server/sv_main.c

@@ -831,6 +831,15 @@ void SV_Frame( int msec ) {
 	// run the game simulation in chunks
 	while ( sv.timeResidual >= frameMsec ) {
 		sv.timeResidual -= frameMsec;
+
+		if ( SVD_IsPaused() ) {
+			// demo paused: freeze svs.time so trajectories freeze
+			// and client doesn't see time jumps on unpause.
+			// still run game frame for spectator movement (at frozen time).
+			VM_Call( gvm, GAME_RUN_FRAME, svs.time );
+			continue;
+		}
+
 		svs.time += frameMsec;
 
 		if ( SVD_IsPlaying() ) {

code/server/sv_netdemo.c

@@ -104,6 +104,7 @@ typedef struct {
 	char			playMapName[SVDEMO_MAX_MAPNAME];
 	qboolean		endOfDemo;
 	qboolean		needConfigstrings;	// apply saved configstrings on first frame
+	qboolean		paused;
 	svdEntityState_t	playPrevEntities[MAX_GENTITIES];  // previous frame for delta read
 	svdPlayerState_t	playPrevPlayers[MAX_CLIENTS];     // previous frame player states
 } svDemo_t;
@@ -987,6 +988,15 @@ void SVD_Stop_f( void ) {
 	}
 }
 
+void SVD_Pause_f( void ) {
+	if ( !demo.playing ) {
+		Com_Printf( "Not playing a server demo.\n" );
+		return;
+	}
+	demo.paused = !demo.paused;
+	Com_Printf( "Demo playback %s.\n", demo.paused ? "paused" : "resumed" );
+}
+
 /*
 Called from SV_Frame() to advance playback by one frame.
 Returns qtrue if a frame was read, qfalse if demo ended.
@@ -996,6 +1006,11 @@ qboolean SVD_PlaybackFrame( void ) {
 		return qfalse;
 	}
 
+	// manual pause — don't consume demo data
+	if ( demo.paused ) {
+		return qfalse;
+	}
+
 	// wait for a spectator to be fully in-game before starting playback.
 	// the server keeps running frames (so the connection handshake completes)
 	// but no demo data is consumed until someone is CS_ACTIVE.
@@ -1034,6 +1049,10 @@ qboolean SVD_IsPlaying( void ) {
 	return demo.playing;
 }
 
+qboolean SVD_IsPaused( void ) {
+	return demo.playing && demo.paused;
+}
+
 /*
 Returns qtrue if demo playback should pause (no active spectators).
 Controlled by svdemo_pauseEmpty cvar.