U4 step3: external oomd-resilient requeue guard

systemd-oomd kills the fit's whole pueue task-scope (task 554 died with bash
+ python together, no retry line), defeating the in-cgroup retry wrapper. This
guard runs detached in its own session/cgroup (~0 RAM, so oomd ignores it) and
keeps the resumable fit queued until u4_loopclose.txt appears. Grinds through
the user's active-hours GPU bursts, finishes clean overnight. Layered with the
retry wrapper (in-cgroup CUDA-OOM retry) for both kill modes.

Co-Authored-By: Claudypoo <288921227+claudypoo@users.noreply.github.com>

scripts/u4_step3_guard.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# Claude: external requeue guard for the U4 4B Jacobian fit.
+#
+# WHY not just the in-task retry wrapper: systemd-oomd is active on this box and
+# kills the fit's ENTIRE pueue task-scope (bash + python together) under memory
+# pressure from the user's live VS Code GPU kernel -- so the in-cgroup retry in
+# u4_step3_retry.sh dies with it (observed: task 554 Killed whole, no retry line).
+#
+# This guard runs DETACHED in its own session/cgroup, uses ~0 RAM (so oomd never
+# targets it), and keeps the resumable fit queued until it completes. jlens
+# checkpoints every prompt (n_done monotonic: 36->45->64->69 across kills), so
+# each oomd kill only costs a model reload. It grinds slowly during the user's
+# active hours and finishes clean overnight once their kernel idles.
+#
+# Stops itself the instant artifacts/u4_loopclose.txt exists (success). To stop
+# early:  pkill -f u4_step3_guard.sh
+set -u
+cd /media/wassname/SGIronWolf/projects5/2026/jspace/jsteer
+LABEL='U4 step3 guard-requeue'
+while [ ! -f artifacts/u4_loopclose.txt ]; do
+  active=$(pueue status --json | jq -r --arg l "$LABEL" \
+    '.tasks[] | select((.label // "") | contains($l)) | .status | if type=="object" then keys[0] else . end' \
+    | grep -Ec 'Running|Queued|Stashed|Paused')
+  if [ "$active" -eq 0 ]; then
+    pueue add \
+      -l "why: $LABEL -- oomd-resilient external requeue of the 4B fit; resolve: resume checkpoint to n_done=400, writes u4_loopclose.txt on success" \
+      -w "$PWD" -o 0 -- bash scripts/u4_step3_retry.sh
+    echo "$(date '+%F %H:%M:%S') requeued fit (was not active)"
+  fi
+  sleep 300
+done
+echo "$(date '+%F %H:%M:%S') u4_loopclose.txt exists -- fit complete, guard exiting"