dune forwarding rpc occasionally gets EINVAL backtrace #12660
Description
dune 3.20.1, with it forwarding to another running watch instance:
Warning: Your build request is being forwarded to a running Dune instance
(pid: 66833). Note that certain command line arguments may be ignored.
Send job 1 (OCAMLRUNPARAM=b dune build @runsite -w --no-buffer) to foreground
Uncaught RPC Error
Unix.Unix_error(Unix.EINVAL, "setsockopt", "")
backtrace:
Raised by primitive operation at Csexp_rpc.Socket.maybe_set_nosigpipe in file
"csexp_rpc.ml", line 77, characters 49-69
Called from Csexp_rpc.Server.Transport.accept in file "csexp_rpc.ml", line
360, characters 11-40
Called from Fiber__Scheduler.exec in file "fiber__Scheduler.ml", line 77,
characters 8-11
There was a lot of background forwarding going on in this build, but the traceback seems like it should be caught and handled, hence this bug report.