relay: bind the host LAN IP, admit the podman bridge subnet only

169.254.1.2 is not a local address on this host (netavark runs its
bridges in aardvark-dns' netns), so the relay cannot bind it — and a
loopback bind refuses container traffic. Probe-socket proof: a host
socket on 192.168.0.143:18094 answers the container's 169.254.1.2:18094
dial while the LAN IP refuses from the container. The relay binds
192.168.0.143:18093 and the deployer installs an iptables INPUT pair
(ACCEPT 10.89.0.0/16, DROP rest) so the unauthenticated endpoint stays
off the LAN.

scripts/signal-relay.py

@@ -1,9 +1,12 @@
 #!/usr/bin/env python3
 """Alertmanager-to-Signal relay for the homelab (Dankclaw).
-Listens on 169.254.1.2:18093 — the host side of host.containers.internal,
-the only address a bridge container can use to reach a host-local process —
-receives Alertmanager's webhook payload, formats
-existing account on this host. Runs as a systemd user unit
+Listens on 192.168.0.143:18093 (the host's LAN IP) and receives
+Alertmanager's webhook payload from the container as
+host.containers.internal:18093 — netavark delivers that address to the
+host's LAN IP, which is the one bind a bridge container can reach (a
+loopback bind refuses it, and 169.254.1.2 is not a local address here).
+The group is formatted into a short message and handed to signal-cli under
+the existing account on this host. Runs as a systemd user unit
 (scripts/signal-relay.service); logs go to the journal.
 
 The phone number and account name are numbers, not credentials — the
@@ -20,13 +23,16 @@ import sys
 import time
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 
-# 169.254.1.2 is the host endpoint of host.containers.internal: a socket
-# bound to 127.0.0.1 refuses container traffic that arrives via the podman
-# bridge (measured 2026-09-17: "dial tcp 169.254.1.2:18093: connection
-# refused"). The address is link-local to the podman bridge — not on any
-# LAN interface, not on loopback, reachable only from this host's
-# containers.
-LISTEN_ADDR = ("169.254.1.2", 18093)
+# The bind address is the one detail this design gets wrong twice
+# (2026-09-17): a loopback bind refuses container traffic ("dial tcp
+# 169.254.1.2:18093: connection refused"), and 169.254.1.2 itself is not a
+# local address on this host ("Cannot assign requested address") — netavark
+# runs the bridges in aardvark-dns' netns, not the host's. Traffic that
+# arrives as 169.254.1.2 lands on the host's LAN IP, so bind THAT. The
+# deployer installs an iptables INPUT rule that admits 18093/tcp from the
+# podman bridge subnet (10.89.0.0/16) only, keeping the unauthenticated
+# endpoint off the rest of the LAN.
+LISTEN_ADDR = ("192.168.0.143", 18093)
 SIGNAL_CLI = "/usr/local/bin/signal-cli"
 SIGNAL_ACCOUNT = "318311"
 SIGNAL_TO = "+12062476336"