Persistent RCON connections — fixes server crash from connection spam

Root cause: self-play opened/closed a new TCP socket for every RCON command
(hundreds/minute). Paper's RCON listener creates a thread per connection,
overwhelming the server until it stopped.

Fix: PersistentRCON class maintains a single connection per server with
auto-reconnect. Thread-safe via lock. Connection pool keyed by host:port.

Applied to:
- mc_aigod_paper.py (prod paper-ai + dev)
- mc_aigod.py (shrink-world)
- self_play.py (training data generation)
- persistent_rcon.py (shared module)

Before: ~100+ RCON connections/minute → server crash
After: 3 persistent connections total → stable

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

training/scripts/self_play.py

@@ -42,33 +42,16 @@ sys.path.insert(0, str(ROOT))
 
 OUTPUT = ROOT / "data" / "processed" / "self_play.jsonl"
 
-# --- RCON ---
+# --- RCON (persistent connection) ---
+
+from agent.tools.persistent_rcon import get_rcon
 
 def rcon_command(cmd, host, port, password):
-    """Execute via RCON, return (success, result_text)."""
-    import socket, struct
+    """Execute via persistent RCON, return (success, result_text)."""
     try:
-        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-        s.settimeout(5)
-        s.connect((host, port))
-        def send(rid, ptype, payload):
-            data = struct.pack("<ii", rid, ptype) + payload.encode("utf-8") + b"\x00\x00"
-            s.sendall(struct.pack("<i", len(data)) + data)
-        def recv():
-            raw = s.recv(4)
-            if len(raw) < 4: return None
-            length = struct.unpack("<i", raw)[0]
-            data = s.recv(length)
-            return data[8:-2].decode("utf-8", errors="replace")
-        send(1, 3, password)
-        time.sleep(0.1)
-        recv()
-        send(2, 2, cmd)
-        time.sleep(0.2)
-        result = recv() or ""
-        s.close()
+        conn = get_rcon(host, port, password)
+        result = conn.command(cmd)
 
-        # Detect errors
         error_patterns = [
             "Unknown or incomplete command",
             "Incorrect argument",
@@ -76,8 +59,12 @@ def rcon_command(cmd, host, port, password):
             "Unknown item",
             "Invalid or unknown",
             "Expected",
+            "<--[HERE]",
         ]
         is_error = any(p.lower() in result.lower() for p in error_patterns)
+        # Benign non-errors
+        if "no player was found" in result.lower():
+            is_error = False
         return (not is_error, result.strip())
     except Exception as e:
         return (False, f"RCON error: {e}")