diff --git a/packages/mosaic/framework/tools/wake/detector.sh b/packages/mosaic/framework/tools/wake/detector.sh
index 7bd8abce..36d6fe90 100755
--- a/packages/mosaic/framework/tools/wake/detector.sh
+++ b/packages/mosaic/framework/tools/wake/detector.sh
@@ -529,6 +529,10 @@ cmd_run() {
         echo "detector.sh: WARN — off-host liveness beacon emit failed (see beacon.sh); the off-host absence check remains the authoritative dead-man." >&2
     fi
     [ "$once" -eq 1 ] && break
+    # Close the detector lock fd in the sleep child; otherwise an orphaned sleep
+    # keeps the single-instance flock (fd 9, taken at exec 9> above) alive after
+    # the detector parent dies, and no replacement instance can ever acquire it.
+    # `9>&-` closes ONLY the child's copy — the parent's lock is unaffected.
     sleep "$interval" 9>&-
   done
 }