network_backend: fix crash on lost/refused connection

getpeername() raised ENOTCONN when a connect failed or the peer
closed the socket, crashing the event loop thread. Identify sockets
via the selector key's data (set at register time) instead, and
catch OSError on recv/send to cleanly close and unregister a dead
socket rather than crashing.

Also fix select(timeout=100) which waited 100 seconds instead of
100ms, causing stop() to hang after a dead socket was unregistered.

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

backend/network_backend.py

@@ -20,7 +20,7 @@ class NetworkBackend(ABackend):
 		sock = self.find_by_name(xcvr.name)
 		sock['queue'].put(data)
 		if sock is not None:
-			self.sel.modify(sock['sock'], selectors.EVENT_READ + selectors.EVENT_WRITE, None)
+			self.sel.modify(sock['sock'], selectors.EVENT_READ + selectors.EVENT_WRITE, sock)
 
 	def start(self):
 		self.thread.start()
@@ -42,12 +42,6 @@ class NetworkBackend(ABackend):
 		if not found:
 			raise Exception(f"No socket found for \"{xcvr.name}\"")
 
-	def find_by_addr(self, addr):
-		for sock in self.sock_list:
-			if sock['addr'] == addr:
-				return sock
-		return None
-
 	def find_by_name(self, name: str):
 		for sock in self.sock_list:
 			if sock['name'] == name:
@@ -66,35 +60,35 @@ class NetworkBackend(ABackend):
 		events = selectors.EVENT_READ
 		for sock in self.sock_list:
 			print(f"Starting connection {sock['name']} to {sock['addr']}")
-			self.sel.register(sock['sock'], events, data=None)
+			self.sel.register(sock['sock'], events, data=sock)
 			sock['sock'].connect_ex(sock['addr'])
 
 	def disconnect(self):
 		for sock in self.sock_list:
 			sock['sock'].close()
 
-	def on_send(self, name: str, data: bytes):
-		sock = self.find_by_name(name)
-		if sock is not None:
-			self.sel.modify(sock['sock'], selectors.EVENT_READ + selectors.EVENT_WRITE, data)
-
 	def event_loop(self):
 		try:
 			while self.loop_enable:
-				events = self.sel.select(timeout=100)
+				events = self.sel.select(timeout=0.1)
 				for key, mask in events:
-					descr = self.find_by_addr(key.fileobj.getpeername())
-					name = descr['name']
-					sock = self.find_by_name(name)
-					if mask & selectors.EVENT_READ:
-						data = key.fileobj.recv(64)
-						sock['xcvr'].on_recv(MsgContainer(data, sock['xcvr']))
-					if mask & selectors.EVENT_WRITE:
-						data = sock['queue'].get()
-						key.fileobj.send(data)
-						print(f"Send: {sock['name']}: {data}")
-						if sock['queue'].empty():
-							self.sel.modify(sock['sock'], selectors.EVENT_READ, None)
+					sock = key.data
+					try:
+						if mask & selectors.EVENT_READ:
+							data = key.fileobj.recv(64)
+							if not data:
+								raise OSError("connection closed by peer")
+							sock['xcvr'].on_recv(MsgContainer(data, sock['xcvr']))
+						if mask & selectors.EVENT_WRITE:
+							data = sock['queue'].get()
+							key.fileobj.send(data)
+							print(f"Send: {sock['name']}: {data}")
+							if sock['queue'].empty():
+								self.sel.modify(sock['sock'], selectors.EVENT_READ, sock)
+					except OSError as exc:
+						print(f"Connection {sock['name']} to {sock['addr']} lost: {exc}")
+						self.sel.unregister(key.fileobj)
+						key.fileobj.close()
 
 		except KeyboardInterrupt:
 			print("Caught keyboard interrupt, exiting")