diff --git a/packages/core/src/loop/acceptance/acceptance-spec.ts b/packages/core/src/loop/acceptance/acceptance-spec.ts
index a6be9c9c..7768cc2f 100644
--- a/packages/core/src/loop/acceptance/acceptance-spec.ts
+++ b/packages/core/src/loop/acceptance/acceptance-spec.ts
@@ -225,22 +225,29 @@ function buildEntityAcceptance(
   };
 }
 
+function escapeRegExp(s: string): string {
+  return s.replace(/[.*+?^${}()|[\]\\]/gu, "\\$&");
+}
+
 /**
  * Check if a field is mentioned (by exact name or humanized form) in a constraint.
+ * Matches on WORD BOUNDARIES, not raw substring: a short field name like `id`/`age` must not
+ * match a longer word that merely contains it (`valid`, `manage`), which would wrongly
+ * associate the field with an unrelated constraint and fabricate a spurious negative test.
  */
-function fieldIsMentioned(
+export function fieldIsMentioned(
   field: IAcceptField,
   constraintLower: string
 ): boolean {
-  const exactMatch = constraintLower.includes(field.name.toLowerCase());
+  const mentions = (needle: string): boolean =>
+    needle.length > 0 &&
+    new RegExp(`\\b${escapeRegExp(needle)}\\b`, "u").test(constraintLower);
   const humanized = field.name
     .replace(/([A-Z])/g, " $1")
     .toLowerCase()
     .trim();
-  const humanizedMatch =
-    humanized.length > 0 && constraintLower.includes(humanized);
 
-  return exactMatch || humanizedMatch;
+  return mentions(field.name.toLowerCase()) || mentions(humanized);
 }
 
 /**
diff --git a/packages/core/tests/acceptance-spec.test.ts b/packages/core/tests/acceptance-spec.test.ts
index b8bdfad4..91505f6a 100644
--- a/packages/core/tests/acceptance-spec.test.ts
+++ b/packages/core/tests/acceptance-spec.test.ts
@@ -3,7 +3,9 @@ import type { IProductPlan } from "../src/loop/planning/plan-types";
 import {
   planToAcceptanceSpec,
   testIdsFor,
+  fieldIsMentioned,
 } from "../src/loop/acceptance/acceptance-spec";
+import type { IAcceptField } from "../src/loop/acceptance/acceptance.types";
 
 const plan: IProductPlan = {
   product: "CRM",
@@ -452,3 +454,32 @@ test("FIX 7: mustNotHappen does not duplicate negatives when field already has o
   // Should NOT have duplicates — only ONE negative for name=""
   expect(nameEmptyNegatives.length).toBe(1);
 });
+
+function acceptField(name: string): IAcceptField {
+  return { name, type: "string", optional: false, valid: "x", invalid: [] };
+}
+
+test("fieldIsMentioned matches on WORD BOUNDARIES, not raw substring", () => {
+  // Positive: the field name (or its humanized form) appears as a whole word.
+  expect(
+    fieldIsMentioned(acceptField("email"), "a valid email is required")
+  ).toBe(true);
+  expect(fieldIsMentioned(acceptField("name"), "name must be unique")).toBe(
+    true
+  );
+  // Humanized: camelCase field, spaced constraint.
+  expect(
+    fieldIsMentioned(acceptField("firstName"), "the first name is required")
+  ).toBe(true);
+
+  // Negative (the bug): a short field name must NOT match a longer word that contains it —
+  // `id` inside `valid`, `age` inside `manage` — which would fabricate a spurious negative.
+  expect(fieldIsMentioned(acceptField("id"), "must be a valid email")).toBe(
+    false
+  );
+  expect(fieldIsMentioned(acceptField("age"), "manage the records")).toBe(
+    false
+  );
+  // And it isn't tripped by an unrelated word either.
+  expect(fieldIsMentioned(acceptField("name"), "the total amount")).toBe(false);
+});