openclaw channels login --channel whatsapp succeeds and saves credentials, but if channels.whatsapp doesn't exist in openclaw.json, gateway returns:

Local login saved auth for whatsapp/default, but the running gateway did not restart it: invalid channels.start channel

Two problems:

1. invalid channels.start channel is opaque. The channel isn't invalid, it's unconfigured. A clearer message would be something like:

   channel not enabled in config; run `openclaw config set channels.whatsapp.enabled true` and restart.
   

2. channels login should either auto-write a minimal channels.<name> stanza, or fail loudly before saving auth.