v3.1.0

Added

• select-fds/wait-for-input: a select(2)-based file-descriptor
  readiness primitive for event loops that need to block on several raw
  descriptors at once -- several PTY masters, a unix socket, and stdin,
  say -- and be told which woke it. This is the one primitive an event
  loop could not previously build out of the rest of the library:
  process-wait/communicate each drive a single child. select-fds
  returns the three ready read/write/exceptional descriptor sub-lists;
  wait-for-input is the common read-only, single-descriptor-list case
  reduced to one argument and one return value. Both retry transparently
  on EINTR against the original deadline, so a periodic signal (
  SIGWINCH, SIGCHLD) never truncates or extends the caller's timeout.
  New public conditions fd-set-overflow (a descriptor at or above
  +maximum-fd+) and fd-wait-failed (any other failing errno) cover
  the two failure modes; every other bound documented on select-fds
  cannot be reached from SB-UNIX:UNIX-FAST-SELECT's own argument checks.
  See the File-Descriptor Readiness guide.