A command pane's command is over when its process exits, not when its pty closes

A job left in the background (sleep 100 &) held the pty open, so the pane
stayed running and the child a zombie until the job ended; a command that
closed its terminal and ran on got its end of file at once, the host waited
100 ms for an exit, reported exit ? and hung it up. Now each command's child
is watched on a thread (waitid with WNOWAIT, so its pid stays its own until
the host reaps it), and the host tells the core the exit from that: after the
pty's end of file, so the output before the exit is in, or 50 ms after the
exit without one, a job holding the pty. The pty stays open until both, so a
command that let go of its terminal is never hung up by it. All four front
ends; a host that cannot start the watcher reads the exit at end of file as
before. Tests: host_io's for both cases, and cmdexit.snap end to end.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 26 insertions, 0 deletions

diff --git a/test/snapshots/cmdexit.snap b/test/snapshots/cmdexit.snap
new file mode 100644
index 00000000..ff60a881
--- /dev/null
+++ b/test/snapshots/cmdexit.snap
@@ -0,0 +1,26 @@
+# A command pane's command is over when its process exits, not when its pty
+# closes. A job it leaves in the background holds the pty open, and the pane
+# still says `exit 0` as soon as the command itself is done; a command that
+# lets go of its terminal and runs on is not hung up at its pty's end, and
+# says how it ended when it does.
+file cmds.txt sleep 30 & echo BG''STARTED\nexec </dev/null >/dev/null 2>&1; sleep 1; false
+config Verbose off
+start 31 120 cmds.txt
+wait 8000 cmds.txt
+stable 700 20000
+snap opened
+# line 1: `sleep 30` keeps the pty, and the pane says exit 0 regardless
+press middle 7 4
+drag middle 34 4
+release middle 34 4
+wait 10000 exit 0
+stable 700 15000
+snap background
+# line 2, in the same pane now its command is done: its end of file comes at
+# once, and its exit a second later, from `false`
+press middle 7 5
+drag middle 54 5
+release middle 54 5
+wait 10000 exit 1
+stable 700 15000
+snap letgo