SessionEnd hook intermittently not fired for headless (-p) sessions (~50% observed)

Summary

When running claude -p headless sessions programmatically (spawned by an external daemon, permission-mode acceptEdits, --allowedTools set, --session-id given), the SessionEnd hook fires for only about half of the sessions. The other half terminate normally (transcript complete, exit) but never execute the SessionEnd hook — no hook process launch, no manifest, nothing.

Environment

• Windows 11, claude CLI via cmd.exe shim
• -p mode, --session-id provided
• SessionEnd hook registered in project settings — works reliably in interactive sessions and fires in some headless runs

Reproduction (A/B pair from the same daemon, same code path, minutes apart)

• Session A (1110c2e7…): headless -p run → SessionEnd fired → our hook created its expected on-disk artifact (session-end-jobs/<sid>.json).
• Session B (fd32ff8f…): headless -p run, same shape → no SessionEnd at all: transcript exists and is complete, but the hook never launched (no artifact, no log entry from the hook itself).
• Across 6 headless sessions in one day: 3 fired, 3 didn't. Presence/absence of specific transcript ending shapes did not correlate with firing.

Impact

Anything that relies on SessionEnd for cleanup or downstream triggering in headless/automation contexts (CI agents, daemon-driven agent fleets) silently loses the signal ~50% of the time.

Workaround

None found; we currently poll for artifacts instead of trusting the hook (undesirable).