Extract the generic process lifecycle layer (src/process_lifecycle.py)
shared by runtime-owned subprocesses: process identity (pid + boot-bound
start token), identity-bound observation, group and pidfd probes, the
TERM -> verify -> KILL -> verify escalation with re-gating before
escalation, identity-scoped sweeps, and the termination receipt.
Containment, the PTY shell, the Cookbook survivor sweep, the browser
lifecycle, web_tools browser cleanup, kill_process_tree and the startup
reaper consume it while keeping their own ownership semantics.
Safety corrections:
- browser membership and identity are bound in one snapshot; no identity
is recaptured after membership is decided
- web_tools legacy pid-file and profile-match kills signal only verified
identities; browser CLI groups only while their spawn identity verifies
- Cookbook and legacy-tmux descendant capture bind membership to identity
- PTY teardown never signals the server's own process group
- unverifiable processes are reported, never signalled
