fix(lifecycle): late signal kills Nvim mid-teardown

Problem:
A deadly signal arriving during teardown can kill Nvim while it is
preserving swapfiles. `os_exit()` ignores deadly signals via
`signal_reject_deadly()`, but `signal_teardown()` => `uv_signal_stop()`
resets them to the default behavior, so SIGHUP arriving after that
kills the process:

    [Process exited 129]      // 128 + SIGHUP

This is a race when closing a pty: kernel sends SIGHUP to foreground
process group *and* the reads return EOF, so `chanclose()` on a TUI job
prepares to exit twice. This means it is unpredictable whether Nvim
exits 1 or is terminated.

Solution:
Ignore deadly signals once the watchers are closed. Only SIGKILL
interrupts it now.

0 files changed, 0 insertions, 0 deletions