emrg: read-only lock probe + stop-chain caller logging (rants 13:08:41 + 13:11:34)

[argszero]

Fixes two P0 host rants about the Windows stop/installer chain:

1. Windows data-deletion bug (rant 2026-08-19T13:08:41)
_win_exclusive_open opened files with FILE_FLAG_DELETE_ON_CLOSE and cleared the disposition afterwards via the file-disposition-info API. That clear only works on Windows 10 1903+ — on older systems (or any failed/best-effort clear) the disposition stays set and CloseHandle DELETES the probed file. The probe is meant to be read-only ("would DeleteFile succeed?"), so it must never set a delete disposition.

• Probe now opens with DELETE access + FILE_SHARE_NONE + plain FILE_ATTRIBUTE_NORMAL — identical sharing semantics, zero deletion risk.
• Removed the disposition-clear API wiring entirely.

2. P0 stop-chain logging (rant 2026-08-19T13:11:34)
Every emrg stop / stop_all run must be attributable so "谁杀 daemon / 谁删文件" can be traced post-mortem:

• New _caller_context(): parent pid + parent command line (ps / Get-CimInstance) + argv — printed in the stop_all header alongside a wall-clock start timestamp.
• Daemon-side: the shutdown message now logs the requesting peer address in emrgd.log.

Tests: updated the lock-probe wiring test to assert the dangerous delete-on-close tokens are gone; +3 tests for _caller_context (POSIX/Windows/failure degradation). Test suite 974 collected, all green; import + CLI checks pass. Agent.md test count synced.

[argszero]

✅ LGTM — cycle. Verified the read-only lock probe (delete-on-close disposition removed; GENERIC_DELETE + FILE_SHARE_NONE + FILE_ATTRIBUTE_NORMAL preserves DeleteFile sharing semantics with zero deletion risk — the 64-bit handle-truncation fix is kept), the stop-chain caller logging (pure-stdlib _caller_context with POSIX/Windows probes and graceful degrade, started timestamp in stop_all header, daemon shutdown peer log), and the test updates (dangerous tokens asserted absent, +3 _caller_context tests, Agent.md count synced 971→974). CI test + test-windows both PASS; local suite 974 collected all green.

[argszero]

✅ LGTM — cycle (2/3). Re-verified: head unchanged (5ddeba4), mergeable, CI test + test-windows still green. The read-only probe (GENERIC_DELETE + FILE_SHARE_NONE + FILE_ATTRIBUTE_NORMAL, no delete-on-close disposition) and stop-chain caller logging are correct and complete.

[argszero]

✅ LGTM — cycle (3/3). Head unchanged (5ddeba4), CI test + test-windows green, mergeable. Three consecutive LGTMs from different cycles (900/901/902) — merging.