Close memory holes, adjust tests

main.go

@@ -546,6 +546,10 @@ func ensureSlotConnected(s *UserMasterSession, slotIdx int, background bool, cli
 		IsBound:       isBound,
 		MaxBufferSize: maxBuf,
 	}
+	if GlobalConfig != nil {
+		slot.AutoHoldDiscardLimit = GlobalConfig.Server.AutoHoldDiscardLimit
+		slot.AutoHoldBurstLimit = GlobalConfig.Server.AutoHoldBurstLimit
+	}
 	s.Slots[slotIdx] = slot
 	go upstreamReader(s, slot, slotIdx)
 	return slot
@@ -575,8 +579,7 @@ func connectOrResumeSlot(s *UserMasterSession, slotIdx int, clientConn net.Conn)
 	}()
 
 	slot.Mu.Lock()
-	slot.ScreenChanged = false
-	slot.IsHeld = false
+	slot.resetHoldAndLoopCountersLocked()
 	if len(slot.LastScreen) > 0 {
 		_, _ = clientConn.Write(slot.LastScreen)
 	}
@@ -781,6 +784,21 @@ func upstreamReader(s *UserMasterSession, slot *SessionSlot, slotIdx int) {
 		// Cap buffer at 64KB to avoid unbounded memory use from constant ticks
 		if len(recBuf) > 65536 {
 			recBuf = recBuf[len(recBuf)-16384:]
+			if !isActive {
+				slot.Mu.Lock()
+				slot.DiscardCount++
+				discardLimit := slot.AutoHoldDiscardLimit
+				if discardLimit == 0 {
+					discardLimit = defaultAutoHoldDiscardLimit
+				}
+				if discardLimit > 0 && slot.DiscardCount >= discardLimit {
+					slot.IsHeld = true
+					slot.ScreenChanged = false
+					slot.DiscardCount = 0
+					log.Printf("[%s] '%s' System [%d] %s placed on automatic HOLD (raw receive buffer discard loop detected)", displayTag, username, slotIdx+1, slot.System.Name)
+				}
+				slot.Mu.Unlock()
+			}
 		}
 		recBuf = append(recBuf, data...)
 		for {
@@ -870,8 +888,41 @@ func upstreamReader(s *UserMasterSession, slot *SessionSlot, slotIdx int) {
 					continue
 				}
 
+				now := time.Now()
+
+				// Auto-hold loop detection for background sessions:
+				// 1. High frequency write updates (excessive update rate loop)
+				if !isActive {
+					burstLimit := slot.AutoHoldBurstLimit
+					if burstLimit == 0 {
+						burstLimit = defaultAutoHoldBurstLimit
+					}
+					if burstLimit > 0 {
+						if slot.WriteBurstWindow.IsZero() || now.Sub(slot.WriteBurstWindow) > autoHoldBurstWindow {
+							slot.WriteBurstCount = 1
+							slot.WriteBurstWindow = now
+						} else {
+							slot.WriteBurstCount++
+						}
+
+						if slot.WriteBurstCount >= burstLimit {
+							slot.IsHeld = true
+							slot.ScreenChanged = false
+							slot.WriteBurstCount = 0
+							slot.DiscardCount = 0
+							log.Printf("[%s] '%s' System [%d] %s placed on automatic HOLD (excessive update rate detected)", displayTag, username, slotIdx+1, slot.System.Name)
+							if isEraseWrite || len(slot.LastScreen) == 0 {
+								slot.LastScreen = bytes.Clone(screenData)
+							}
+							slot.Mu.Unlock()
+							continue
+						}
+					}
+				}
+
 				if isEraseWrite || len(slot.LastScreen) == 0 {
 					slot.LastScreen = bytes.Clone(screenData)
+					slot.DiscardCount = 0
 				} else if len(slot.LastScreen)+len(screenData) <= maxBuf {
 					slot.LastScreen = append(slot.LastScreen, screenData...)
 				} else {
@@ -886,6 +937,33 @@ func upstreamReader(s *UserMasterSession, slot *SessionSlot, slotIdx int) {
 					newBuf = append(newBuf, slot.LastScreen[:baseLen]...)
 					newBuf = append(newBuf, screenData...)
 					slot.LastScreen = newBuf
+
+					// Auto-hold loop detection for background sessions:
+					// 2. Buffer overflow discard loop (repeated discards of older intermediate writes)
+					if !isActive {
+						discardLimit := slot.AutoHoldDiscardLimit
+						if discardLimit == 0 {
+							discardLimit = defaultAutoHoldDiscardLimit
+						}
+						if discardLimit > 0 {
+							if slot.DiscardWindow.IsZero() || now.Sub(slot.DiscardWindow) > autoHoldDiscardWindow {
+								slot.DiscardCount = 1
+								slot.DiscardWindow = now
+							} else {
+								slot.DiscardCount++
+							}
+
+							if slot.DiscardCount >= discardLimit {
+								slot.IsHeld = true
+								slot.ScreenChanged = false
+								slot.DiscardCount = 0
+								slot.WriteBurstCount = 0
+								log.Printf("[%s] '%s' System [%d] %s placed on automatic HOLD (discard loop detected)", displayTag, username, slotIdx+1, slot.System.Name)
+								slot.Mu.Unlock()
+								continue
+							}
+						}
+					}
 				}
 				if !isActive {
 					slot.ScreenChanged = true