gpuq worker: STOP sentinel for graceful drain (never kill mid-job again)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/gpuq_worker.sh

@@ -23,6 +23,10 @@
 # node loses at most one sync interval. Globs allowed in the basename.
 # Repeat the comment lines to declare more paths. No declaration = no sync
 # (old jobs keep working; they can still rclone by hand).
+#
+# GRACEFUL RESTART: touch $HOME/gpuq/<worker-id>/STOP — the worker exits
+# between jobs, never mid-job. NEVER kill the tmux session while a job
+# runs (that killed a 3.5h scan once).
 
 set -u
 ID=$1
@@ -51,6 +55,11 @@ sync_paths() {  # $1 = direction (in|out), $2 = job file
 
 echo "[gpuq $ID] worker up on GPU $GPU, polling $Q/pending (repo $REPO)"
 while true; do
+  if [ -e "$LOCAL/STOP" ]; then
+    rm -f "$LOCAL/STOP"
+    echo "[gpuq $ID] $(date +%F_%H:%M:%S) STOP sentinel — draining (no job running)"
+    break
+  fi
   rclone move "$Q/pending" "$LOCAL/pending" --include "*.sh" -q 2>/dev/null
   job=$(ls "$LOCAL"/pending/*.sh 2>/dev/null | sort | head -1)
   if [ -z "$job" ]; then