Serialize display recovery checks

tests/quickshell/displays-contract.sh

@@ -225,8 +225,24 @@ KINDS
 now="$(status)"
 [[ "$(jq -r .scale <<<"$now")" == "$original_scale" ]] || fail 'a refused change still altered the scale'
 
-# ── An unconfirmed change reverts on its own and stores nothing ──────────────
+# An immediate Revert may race both the apply process and its first readback.
+# It must queue until both are clear, then verify the original generation.
 target_scale=$(awk -v s="$original_scale" 'BEGIN { print (s == 1.25) ? 1.5 : 1.25 }')
+[[ "$(run ipc call displays-test applyScale "$target_scale")" == "true" ]] \
+    || fail 'the immediate-revert fixture could not apply'
+run ipc call displays-test revertChange >/dev/null
+immediate_reverted=false
+for _ in $(seq 1 60); do
+    if display_is_restored && [[ "$(status | jq -r .awaiting)" == "false" ]]; then
+        immediate_reverted=true
+        break
+    fi
+    sleep 0.2
+done
+[[ "$immediate_reverted" == true ]] \
+    || fail 'an immediate Revert raced the apply/readback and did not restore the display'
+
+# ── An unconfirmed change reverts on its own and stores nothing ──────────────
 [[ "$(run ipc call displays-test applyScale "$target_scale")" == "true" ]] \
     || fail 'a valid scale change was refused'