Sorry, this one escaped onto the network, was meant to be local only (and this is a broken example). Reviewing https://github.com/nostr-protocol/nips/pull/635 to see what we should do for escaping control characters other than /n and ", such as the bell character (\b or 0x07).
Fixed! Minor difference in how Damus sends a Host header (for default ports, damus sends hostname:port, even for default ports) compared to other clients. My HAProxy rules were doing an exact match for the hostname, changed it to a prefix match, and all works!