Add Trace DASP preference to print protocol transactions to terminal

New checkbox in Preferences (default off). When enabled, every DASP
send (>>>) and receive (<<<) prints message type, seq/ack numbers,
payload size, and remote address to stdout.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dasp.py

@@ -78,6 +78,24 @@ ERR_TIMEOUT              = 0xE5
 
 DEFAULT_PORT = 1876
 
+_MSG_TYPE_NAMES = {
+    DISCOVER: "DISCOVER", HELLO: "HELLO", CHALLENGE: "CHALLENGE",
+    AUTHENTICATE: "AUTHENTICATE", WELCOME: "WELCOME", KEEPALIVE: "KEEPALIVE",
+    DATAGRAM: "DATAGRAM", CLOSE: "CLOSE",
+}
+
+
+def _trace(direction, msg, addr=None):
+    import app_state
+    if not app_state.TRACE_DASP:
+        return
+    name = _MSG_TYPE_NAMES.get(msg.msg_type, f"?{msg.msg_type}")
+    seq = f" seq={msg.seq_num}" if msg.seq_num >= 0 else ""
+    ack = f" ack={msg.ack}" if msg.ack >= 0 else ""
+    plen = len(msg.payload) if msg.payload else 0
+    dest = f" {addr[0]}:{addr[1]}" if addr else ""
+    print(f"[DASP] {direction}{dest} {name}{seq}{ack} payload={plen}")
+
 
 class DaspException(Exception):
     def __init__(self, msg, error_code=-1):
@@ -898,6 +916,7 @@ class DaspSocket:
     # ── Network I/O ─────────────────────────────────────────────
 
     def _send_msg(self, session, msg):
+        _trace(">>>", msg, (session.host, session.port))
         data = msg.encode()
         with self._send_lock:
             try:
@@ -922,6 +941,7 @@ class DaspSocket:
                 break
 
     def _dispatch(self, msg, addr):
+        _trace("<<<", msg, addr)
         session_id = msg.session_id
         with self._sessions_lock:
             session = self._sessions.get(session_id)