docs: close the EMULATOR GONE item - it was the Stop hook, and note the one-turn rule

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMRJjbxLqZtsb5Vb7KunPE

docs/re/BACKLOG.md

@@ -343,6 +343,13 @@ is what the autopilot needs in order to CHOOSE a target. One run in:
   write to the dead FIFO and `ctrl_probe.py`/`target_probe.py` still use
   `pad.f`; all flagged in place, none repaired.
   See [`pilot-never-fires.md`](pilot-never-fires.md).
+* ✅ **`EMULATOR GONE` is SOLVED — it was this project's own `Stop` hook**
+  (2026-08-24), which `kill -9`s `xenia_canary` at the end of every agent turn.
+  Every "mysterious" death was a turn boundary. **Operational rule:** an emulator
+  experiment must complete **inside one turn** — nothing can be left running for
+  a later tick, and a watcher armed for 1 500 s only watches the rest of *this*
+  turn. Memory pressure was raised and refuted along the way; that measurement
+  stands, it just was not pointing at anything.
 * 🔴 **An in-mission freeze — the item in front of everything else.** Reproduced
   with the Kernel channel on. 🔴 The resume-spin lead is **refuted by its own
   control**: a still-flying run has *more* refused resumes (2 738) than a frozen