van-router-mqtt: subscribe and publish discovery in on_connect

Clean sessions lose subscriptions on reconnect and a refused first connect
loses the retained discovery, so both now happen on every successful connect.
Adds reason codes 132-136 and behavioural tests.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KqhjP7nud5gdBg25zCiRk9

router-status/van-router-mqtt

@@ -561,7 +561,8 @@ def on_message(mqc, userdata, msg):
 REFUSAL_REASONS = {
     1: "unacceptable protocol version", 2: "client identifier rejected",
     3: "server unavailable", 4: "bad username or password", 5: "not authorised",
-    134: "bad username or password", 135: "not authorised",
+    132: "unsupported protocol version", 133: "client identifier rejected",
+    134: "bad username or password", 135: "not authorised", 136: "server unavailable",
 }
 _mqtt_state = None  # None | "connected" | "refused" | "down": log changes only
 
@@ -597,6 +598,16 @@ def note_disconnect(rc):
 
 def on_connect(mqc, userdata, flags, reason_code, properties=None):
     note_connect(reason_code)
+    if getattr(reason_code, "value", reason_code) != 0:
+        return
+    # (Re)subscribe and republish discovery on EVERY successful connect: a clean
+    # session drops subscriptions on reconnect and a refused first connect loses them.
+    try:
+        for topic in COMMANDS:
+            mqc.subscribe(topic)
+        publish_discovery(mqc)
+    except Exception as e:
+        log(f"MQTT on_connect setup failed: {type(e).__name__}: {e}")
 
 
 def on_disconnect(mqc, userdata, disconnect_flags, reason_code, properties=None):
@@ -611,10 +622,7 @@ def main():
     mqc.on_connect = on_connect
     mqc.on_disconnect = on_disconnect
     mqc.connect(broker, mqtt_port, keepalive=60)
-    for topic in COMMANDS:
-        mqc.subscribe(topic)
     mqc.loop_start()
-    publish_discovery(mqc)
     log(f"van-router-mqtt started: broker={broker}:{mqtt_port} poll={poll_interval_s}s")
     while True:
         publish_state(mqc)