diff --git a/fixtures/negative/rule-required-subcomponent-unknown-ref.dspack.json b/fixtures/negative/rule-required-subcomponent-unknown-ref.dspack.json
new file mode 100644
index 0000000..c22d760
--- /dev/null
+++ b/fixtures/negative/rule-required-subcomponent-unknown-ref.dspack.json
@@ -0,0 +1,62 @@
+{
+  "dspack": "0.3",
+  "name": "negative-fixture",
+  "components": {
+    "button": {
+      "name": "Button",
+      "description": "A button.",
+      "props": {
+        "variant": {
+          "type": "enum",
+          "values": [
+            "default",
+            "destructive"
+          ]
+        }
+      }
+    },
+    "alert-dialog": {
+      "name": "AlertDialog",
+      "description": "A confirmation dialog.",
+      "composition": {
+        "subComponents": [
+          {
+            "id": "alert-dialog-title",
+            "name": "AlertDialogTitle"
+          },
+          {
+            "id": "alert-dialog-cancel",
+            "name": "AlertDialogCancel"
+          }
+        ]
+      }
+    }
+  },
+  "intents": [
+    {
+      "id": "destructive-action",
+      "description": "Irreversible operations."
+    }
+  ],
+  "_comment": "CONSISTENCY: requiredSubComponents references 'ghost-panel', which is declared neither as a top-level component nor as a composition sub-component. (Ids declared as EITHER kind resolve — descendants match by node component id; see rule.review-offers-alternatives in examples/astryx.dspack.json for the top-level-component case and rule.alertdialog-requires-cancel in examples/shadcn-ui.dspack.json for the sub-component case.)",
+  "rules": [
+    {
+      "id": "rule.fixture",
+      "severity": "must",
+      "rationale": "Fixture rationale.",
+      "type": "required-composition",
+      "appliesTo": {
+        "intents": [
+          "destructive-action"
+        ]
+      },
+      "component": "alert-dialog",
+      "requiredSubComponents": [
+        {
+          "id": "ghost-panel",
+          "min": 1
+        }
+      ]
+    }
+  ]
+}
diff --git a/scripts/validate.mjs b/scripts/validate.mjs
index e4ae91b..7e56e79 100644
--- a/scripts/validate.mjs
+++ b/scripts/validate.mjs
@@ -243,12 +243,18 @@ function checkGovernance(doc, validateSurface) {
     for (const { kind, id } of ruleComponentRefs(rule)) {
       const resolvesToComponent = vocab.components.has(id);
       const resolvesToSub = vocab.subComponents.has(id);
+      // `requiredSubComponents` entries match descendant NODES by component id
+      // at lint time (spec §5), so the id may be declared as a top-level
+      // component or as a composition sub-component. Resolution here only
+      // guards the vocabulary; satisfaction (matching descendants beneath each
+      // governed node) is the S3 gate's concern, not this harness's.
+      // `on` remains sub-component-only (spec §5: "the sub-component id `on`").
       const ok =
-        kind === "requiredSubComponents" || kind === "on"
+        kind === "on"
           ? resolvesToSub
           : kind === "component"
             ? resolvesToComponent
-            : resolvesToComponent || resolvesToSub; // componentOrSub, require, forbid, forbiddenDescendants
+            : resolvesToComponent || resolvesToSub; // requiredSubComponents, componentOrSub, require, forbid, forbiddenDescendants
       if (!ok) errors.push(`${rule.id}: ${kind} reference '${id}' does not resolve in the contract`);
     }
     for (const ex of rule.examples ?? []) {
diff --git a/spec/dspack-v0.3.md b/spec/dspack-v0.3.md
index 3b4daf4..ce6d17b 100644
--- a/spec/dspack-v0.3.md
+++ b/spec/dspack-v0.3.md
@@ -175,6 +175,11 @@ present and equal to a member of `oneOf`; when `on` is given, **every** descenda
 the sub-component id `on` MUST satisfy the prop constraint, and at least one such descendant
 MUST exist.
 
+A `requiredSubComponents` entry's `id` MUST be declared in the contract — either as a
+top-level component or as a composition sub-component; descendants match by node component
+id in both cases. Declaration alone never satisfies the entry: satisfaction requires the
+matching descendants described above, beneath each governed node.
+
 **`forbidden-composition`** — structure and values no instance of a component may contain.
 Fields: `component: string`, `forbiddenDescendants?: string[]`,
 `forbiddenProps?: {on?, prop, values}[]` (at least one of the two present).