Add reap_processes to CompanionManager: drains waitpid(WNOHANG), matches each
dead pid back to its companion, and records the exit via _record_exit (signal
number or exit code, exited_at, exit_count) while freeing the pid. Returns the
reaped companions; the restart decision stays with the run loop.
Add tests for exit-code, signal, and no-children cases.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Child calls _redirect_output after env setup: each configured log path is
opened append-mode and dup2'd onto fd 1/2. None/inherit keeps the inherited
fd; stderr stdout shares stdout's fd. Rotation stays external.
Add tests for inherit, append flags, file dup2, and stderr-to-stdout.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
