diff --git a/src/parameters/parameters.js b/src/parameters/parameters.js
index d6de363..016bd39 100644
--- a/src/parameters/parameters.js
+++ b/src/parameters/parameters.js
@@ -17,6 +17,10 @@ function applyBoundsAndTargets(m) {
 }
 
 function validateFlowBounds(m) {
+  // nominalFlowMin / flowMax must be declared in monster.json's `constraints`
+  // section. If they aren't, configUtils strips them as unknown keys and the
+  // bounds collapse to undefined → NaN → invalid here, which silently blocks
+  // every sampling run. (Fixed 2026-05-11.)
   const min = Number(m.nominalFlowMin);
   const max = Number(m.flowMax);
   const valid = Number.isFinite(min) && Number.isFinite(max) && min >= 0 && max > 0 && min < max;