fix: suppress connection noise, MOTD, CTCP, and DCC from clients

Filter out messages that are useless to bouncer clients:
- Server notices (prefix without !, NOTICE to */AUTH)
- MOTD numerics (375, 372, 376, 422)
- Welcome/stats numerics (001-005, 042, 250-255, 265-266)
- User mode changes (MODE to non-channel targets)
- CTCP queries and DCC requests (PRIVMSG with \x01, except ACTION)
- CTCP replies in NOTICE

Filter applies to both live dispatch and backlog replay. Purged
existing noise from the backlog database.

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

src/bouncer/router.py

@@ -25,6 +25,59 @@ _TARGET0_COMMANDS = {
     "PRIVMSG", "NOTICE", "JOIN", "PART", "MODE", "TOPIC", "NAMES", "WHO", "WHOIS",
 }
 
+# Numerics suppressed from client delivery (connection noise, MOTD, server stats)
+_SUPPRESS_NUMERICS = {
+    # Welcome block (we synthesize our own)
+    "001", "002", "003", "004", "005",
+    # Unique ID
+    "042",
+    # LUSERS / server stats
+    "250", "251", "252", "253", "254", "255",
+    # Local/global user counts
+    "265", "266",
+    # MOTD
+    "375", "372", "376", "422",
+    # Visible host (handled internally by network)
+    "396",
+    # Nick in use (handled internally by network)
+    "433",
+}
+
+_CTCP_MARKER = "\x01"
+
+
+def _suppress(msg: IRCMessage) -> bool:
+    """Return True if this message should not reach the client."""
+    # Noisy numerics
+    if msg.command in _SUPPRESS_NUMERICS:
+        return True
+
+    # Server notices: prefix without '!' is a server, not a user
+    if msg.command == "NOTICE" and msg.prefix and "!" not in msg.prefix:
+        return True
+
+    # Connection notices (NOTICE to * or AUTH, regardless of prefix)
+    if msg.command == "NOTICE" and msg.params and msg.params[0] in ("*", "AUTH"):
+        return True
+
+    # CTCP replies in NOTICE
+    if msg.command == "NOTICE" and len(msg.params) >= 2:
+        if msg.params[1].startswith(_CTCP_MARKER):
+            return True
+
+    # CTCP/DCC inside PRIVMSG (keep ACTION)
+    if msg.command == "PRIVMSG" and len(msg.params) >= 2:
+        text = msg.params[1]
+        if text.startswith(_CTCP_MARKER) and not text.startswith("\x01ACTION"):
+            return True
+
+    # User mode changes (MODE for non-channel targets)
+    if msg.command == "MODE" and msg.params:
+        if not msg.params[0].startswith(("#", "&", "+", "!")):
+            return True
+
+    return False
+
 
 class Router:
     """Central message hub linking clients to networks."""
@@ -165,6 +218,9 @@ class Router:
 
     async def _dispatch(self, network_name: str, msg: IRCMessage) -> None:
         """Dispatch a network message to attached clients and backlog."""
+        if _suppress(msg):
+            return
+
         # Store in backlog (raw, un-namespaced)
         if msg.command in BACKLOG_COMMANDS and msg.params:
             target = msg.params[0]
@@ -204,6 +260,8 @@ class Router:
                 params=[entry.target, entry.content],
                 prefix=entry.sender,
             )
+            if _suppress(msg):
+                continue
             namespaced = encode_message(
                 msg, network_name, own_nicks, client_nick=client.nick,
             )