Resolved: fb_send_output sends data immediately but never enables write flag for select().  Sockets thus get stuck if their output buffer overflows.

Rx
Enable write flag for socket if there is queued output remaining when writes fail.

Also:
Address unchecked calls in fb_http to provide sane behavior on server failure (generally memory allocation errors).  These generally report 500 internal server error, if possible, then close the connection.


Notes
Description suggests pianod isn’t serving complete files.
- Lots of unchecked http_queue_* things in fb_http; data will be silently lost.  Asking for messages?
- Running it under GB.  Is it ^C or trapped?