fix: Uninitialized move duration causing NaN/INT_MIN position sync

src/game/char.cpp

@@ -2733,8 +2733,8 @@ void CHARACTER::Stop()
 
 bool CHARACTER::Goto(long x, long y)
 {
-	// TODO 거리체크 필요
-	// 같은 위치면 이동할 필요 없음 (자동 성공)
+	// TODO: Distance check required
+	// If the location is the same, no need to move (automatic success)
 	if (GetX() == x && GetY() == y)
 		return false;
 
@@ -2742,6 +2742,14 @@ bool CHARACTER::Goto(long x, long y)
 	{
 		if (!IsState(m_stateMove))
 		{
+			// Without this, StateMove() may divide by 0 (duration from ctor/init) and produce NaN/INT_MIN coords.
+			CalculateMoveDuration();
+
+			// If duration is 0, do NOT enter move state (it would snap+stop in StateMove).
+			// This indicates invalid speed or no actual movement.
+			if (m_dwMoveDuration == 0)
+				return false;
+
 			m_dwStateDuration = 4;
 			GotoState(m_stateMove);
 		}
@@ -2753,12 +2761,15 @@ bool CHARACTER::Goto(long x, long y)
 
 	CalculateMoveDuration();
 
+	// If duration is 0, do NOT enter move state.
+	if (m_dwMoveDuration == 0)
+		return false;
+
 	m_dwStateDuration = 4;
 
-	
 	if (!IsState(m_stateMove))
 	{
-		MonsterLog("[MOVE] %s", GetVictim() ? "대상추적" : "그냥이동");
+		MonsterLog("[MOVE] %s", GetVictim() ? "To victim" : "Free");
 
 		if (GetVictim())
 		{
@@ -2772,7 +2783,6 @@ bool CHARACTER::Goto(long x, long y)
 	return true;
 }
 
-
 DWORD CHARACTER::GetMotionMode() const
 {
 	DWORD dwMode = MOTION_MODE_GENERAL;
@@ -2850,11 +2860,40 @@ void CHARACTER::CalculateMoveDuration()
 	m_posStart.y = GetY();
 
 	float fDist = DISTANCE_SQRT(m_posStart.x - m_posDest.x, m_posStart.y - m_posDest.y);
-
 	float motionSpeed = GetMoveMotionSpeed();
 
-	m_dwMoveDuration = CalculateDuration(GetLimitPoint(POINT_MOV_SPEED),
-			(int) ((fDist / motionSpeed) * 1000.0f));
+	// If there is no real movement or speed is invalid, duration becomes 0.
+	// This should NOT lead to NaN in StateMove (StateMove will guard).
+	if (motionSpeed <= 0.0f || fDist <= 0.0f)
+	{
+		sys_err("MOVE_DURATION_INVALID: name=%s vid=%u map=%ld dist=%.3f speed=%.3f start=(%d,%d) dest=(%d,%d)",
+			GetName(), (DWORD)GetVID(), GetMapIndex(), fDist, motionSpeed, (int)m_posStart.x, (int)m_posStart.y, (int)m_posDest.x, (int)m_posDest.y);
+
+		m_dwMoveDuration = 0;
+		m_dwMoveStartTime = get_dword_time();
+		return;
+	}
+
+	// Base duration in ms. int truncation can produce 0 for tiny moves.
+	int baseMs = (int)((fDist / motionSpeed) * 1000.0f);
+	if (baseMs <= 0)
+	{
+		sys_err("MOVE_DURATION_BASE_ZERO: name=%s vid=%u map=%ld dist=%.3f speed=%.3f base=%d start=(%d,%d) dest=(%d,%d)",
+			GetName(), (DWORD)GetVID(), GetMapIndex(), fDist, motionSpeed, baseMs, (int)m_posStart.x, (int)m_posStart.y, (int)m_posDest.x, (int)m_posDest.y);
+
+		baseMs = 1;
+	}
+
+	m_dwMoveDuration = CalculateDuration(GetLimitPoint(POINT_MOV_SPEED), baseMs);
+
+	// Defensive clamp: some duration formulas can still return 0.
+	if (m_dwMoveDuration == 0)
+	{
+		sys_err("MOVE_DURATION_FINAL_ZERO: name=%s vid=%u map=%ld base=%d dist=%.3f speed=%.3f",
+			GetName(), (DWORD)GetVID(), GetMapIndex(), baseMs, fDist, motionSpeed);
+
+		m_dwMoveDuration = 1;
+	}
 
 	if (IsNPC())
 		sys_log(1, "%s: GOTO: distance %f, spd %u, duration %u, motion speed %f pos %d %d -> %d %d",

src/game/char_state.cpp

@@ -761,11 +761,37 @@ bool __CHARACTER_GotoNearTarget(LPCHARACTER self, LPCHARACTER victim)
 
 void CHARACTER::StateMove()
 {
+	// SAFETY NET:
+	// Never allow division by zero or NaN/INF interpolation rates.
+	// Without this, NaN can become INT_MIN when cast to int and break sectree lookup (disconnect).
+	if (m_dwMoveDuration == 0)
+	{
+		sys_err("STATE_MOVE_ZERO_DURATION: name=%s vid=%u map=%ld start=(%d,%d) dest=(%d,%d)",
+			GetName(), (DWORD)GetVID(), GetMapIndex(), (int)m_posStart.x, (int)m_posStart.y, (int)m_posDest.x, (int)m_posDest.y);
+
+		// Snap to destination and stop to keep server state consistent.
+		Move(m_posDest.x, m_posDest.y);
+		Stop();
+		return;
+	}
+
 	DWORD dwElapsedTime = get_dword_time() - m_dwMoveStartTime;
-	float fRate = (float) dwElapsedTime / (float) m_dwMoveDuration;
+	float fRate = (float)dwElapsedTime / (float)m_dwMoveDuration;
+
+	if (!std::isfinite(fRate))
+	{
+		sys_err("STATE_MOVE_NONFINITE_RATE: name=%s vid=%u map=%ld elapsed=%u duration=%u",
+			GetName(), (DWORD)GetVID(), GetMapIndex(), dwElapsedTime, m_dwMoveDuration);
+
+		Move(m_posDest.x, m_posDest.y);
+		Stop();
+		return;
+	}
 
 	if (fRate > 1.0f)
 		fRate = 1.0f;
+	else if (fRate < 0.0f)
+		fRate = 0.0f;
 
 	int x = (int) ((float) (m_posDest.x - m_posStart.x) * fRate + m_posStart.x);
 	int y = (int) ((float) (m_posDest.y - m_posStart.y) * fRate + m_posStart.y);

src/game/input_main.cpp

@@ -1696,7 +1696,7 @@ void CInputMain::Move(LPCHARACTER ch, const char * data)
 	pack.dwVID        = ch->GetVID();
 	pack.lX           = pinfo->lX;
 	pack.lY           = pinfo->lY;
-	pack.dwTime       = pinfo->dwTime;
+	pack.dwTime       = get_dword_time();
 	pack.dwDuration   = (pinfo->bFunc == FUNC_MOVE) ? ch->GetCurrentMoveDuration() : 0;
 
 	ch->PacketAround(&pack, sizeof(TPacketGCMove), ch);