The code execution tool runs commands inside TTY-backed shells (local PTY and
remote SSH). Commands like `git diff`/`git log` detect the TTY and pipe output
through a pager (more/less). These shells never receive interactive input, so
the pager blocks forever and spins at 100% CPU per process — on a 16-core host
5 pager processes pegged 5 cores for 8+ hours (#1697).
Disable pagers in both session types:
- LocalInteractiveSession: inject PAGER=cat / GIT_PAGER=cat into the TTY env
- SSHInteractiveSession: export the same in the initial shell command
`cat` streams the output through instead of blocking, and also covers other
pager-using tools (man, systemctl, journalctl). Adds regression tests.
Fixes#1697
Store and close POSIX PTY master descriptors when terminal sessions are closed or killed, and make local terminal session shutdown await the full TTY cleanup path. This prevents leaked /dev/ptmx descriptors from exhausting the process file descriptor limit.