🚧 WIP

backend/app/configgen.py

@@ -38,10 +38,13 @@ def _listener_block(listener: ListenerConfig, warnings: list[str]) -> list[str]:
     lines: list[str] = []
     if not listener.enabled:
         return lines
-    lines.append(f"listener {listener.port} {listener.bind_address or ''}".rstrip())
-    if listener.bind_address is None:
-        # `listener <port>` without bind address binds all interfaces.
-        lines[-1] = f"listener {listener.port}"
+    # Always emit an EXPLICIT bind address. Mosquitto's reload compares
+    # listeners textually; "listener 1883" vs "listener 1883 0.0.0.0" are
+    # treated as different listeners, and reload CANNOT add/remove
+    # listeners (spec section 28). Matching the bootstrap's explicit
+    # form keeps the management listener reloadable.
+    bind = listener.bind_address or "0.0.0.0"
+    lines.append(f"listener {listener.port} {bind}")
     lines.append(f"protocol {listener.protocol}")
     if listener.allow_anonymous:
         lines.append("listener_allow_anonymous true")
@@ -104,11 +107,17 @@ def generate_config(db: Session) -> GenerationResult:
                 lines.extend(block)
                 lines.append("")
     else:
+        # Empty model is a legitimate UI state (fresh platform): generate a
+        # SAFE config instead of raising, so /config/preview works. With no
+        # listener directives Mosquitto binds loopback-only (127.0.0.1/::1)
+        # on port 1883 with anonymous access — reachable only inside the
+        # container network. The warning explains exactly what will happen.
         warnings.append(
-            "no enabled listeners; broker would fall back to loopback-only "
-            "with anonymous access — refusing to generate"
+            "No enabled listeners in the configuration model. The generated "
+            "config contains no listener directives, so Mosquitto will bind "
+            "loopback-only (127.0.0.1/::1) on port 1883 with anonymous access "
+            "— internal to the container network only. Add a listener below."
         )
-        raise ValueError("no enabled listeners in configuration model")
 
     lines.append("# --- Persistence ---")
     lines.append("persistence true")