whatsapp.reply_prefix from config.yaml was written into the bridge env and then
popped again by the WHATSAPP_* passthrough loop (the key was in
_BRIDGE_PASSTHROUGH_ENV and the scoped env lookup came back empty), so bridge.js
always fell back to its built-in header and the documented reply_prefix: ""
could not disable it. Resolve the prefix once (scoped env first, then the
adapter value) and keep it out of the passthrough loop.
Fixes#116059
3cbd3cce0a