Fleet Orphan Reaper Identity Check Relies on /proc — No macOS Fallback #2256

Problem

The fleet orphan reaper in src/autoskillit/cli/fleet/_fleet_lifecycle.py:113-114 uses read_starttime_ticks(pid) from core/runtime/_linux_proc.py to verify PID identity before killing an orphan process. On macOS, /proc does not exist, so read_starttime_ticks() returns None.

The identity guard:

current_ticks = read_starttime_ticks(pid)
if current_ticks is not None and current_ticks == dispatch.dispatched_starttime_ticks:
    # KILL path — only reached on Linux
else:
    # "reaped_pid_recycled" path — NO KILL issued

When current_ticks is None (macOS), the guard evaluates False, the reaper takes the else branch, marks the dispatch as reaped_pid_recycled, and never sends a signal to the orphan process. This is a silent behavioral gap, not an intentional design choice.

Failure Chain

1. Test writes dispatched_starttime_ticks=0 (because read_starttime_ticks returns None on macOS, collapsed via or 0)
2. Reaper reads current_ticks = read_starttime_ticks(pid) → None
3. Guard current_ticks is not None → False → kill branch skipped
4. Orphan sleep 999 process stays alive
5. test_orphan_l3_reaping assertion not psutil.pid_exists(orphan_pid) or _is_zombie(orphan_pid) fails

Related Functions

• read_starttime_ticks() — src/autoskillit/core/runtime/_linux_proc.py — reads /proc/{pid}/stat
• read_boot_id() — same module — reads /proc/sys/kernel/random/boot_id
• _reap_stale_dispatches() — src/autoskillit/cli/fleet/_fleet_lifecycle.py:86-134
• kill_process_tree() — src/autoskillit/execution/process/_process_kill.py:48-58

Potential Approach

When current_ticks is None (non-Linux), fall back to psutil.Process(pid).create_time() for cross-platform PID-reuse detection. Both dispatched_starttime_ticks and the current check would use the same cross-platform API. This is already available via psutil on all platforms.

Alternatively, on non-Linux where /proc identity is unavailable, treat the process as the original orphan (assume no PID recycling) and proceed with the kill — PID-reuse protection is already degraded without /proc.

Context

• Discovered via PR test #945 macOS-15 CI failure
• Investigation report: .autoskillit/temp/investigate/investigation_macos_ci_failures_pr945_2026-05-08_160000.md
• Note: Fleet is currently a develop-only experimental feature. See companion issue for test gating.