diff --git a/package.json b/package.json
index 8315f74..382e27a 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@aestheticfunction/dspack-gen",
-  "version": "0.2.2",
+  "version": "0.3.0",
   "description": "Generation + governance pipeline for dspack contracts: prompt/context compiler, surface gates S1\u2013S3, bounded repair, protocol emission, audit reports.",
   "type": "module",
   "license": "Apache-2.0",
diff --git a/src/core/lint/containment.test.ts b/src/core/lint/containment.test.ts
new file mode 100644
index 0000000..6f4ee92
--- /dev/null
+++ b/src/core/lint/containment.test.ts
@@ -0,0 +1,204 @@
+/**
+ * S2 sub-component containment (spec v0.4 §5.1, the 2026-08-07 amendment).
+ *
+ * The ratified invariant, verbatim:
+ *
+ *   A component declared as a sub-component of a compound may appear only
+ *   within the subtree of a valid owning compound, unless the contract
+ *   explicitly declares that component as independently usable.
+ *
+ * Fail-first (captured before implementation): the four production shapes
+ * below — root-level `form-label`, `select-trigger` beside its `select`,
+ * bare `alert-dialog-content` duplicated next to a nested one, and the
+ * field-trio exemplar corruption (dspack#40) — all PASSED S2 as membership,
+ * were inexpressible in every S3 rule type, and died terminally at the
+ * emitter after the repair loop had already run (post-T3 Build matrix:
+ * 2/6 scenarios; probe: 19% of generated nodes).
+ *
+ * Ownership comes ONLY from composition.subComponents — never names,
+ * prefixes, adjacency, or examples.
+ */
+import { describe, expect, it } from "vitest";
+import { lintSurface } from "./index.js";
+import { renderRepairMessage } from "../../repair/render.js";
+import type { Contract } from "../contract.js";
+import type { Surface } from "../surface-schema.js";
+
+/** Hermetic contract mirroring the four measured production shapes. */
+const contract: Contract = {
+  dspack: "0.4",
+  name: "containment-fixture",
+  description: "S2 containment pins",
+  version: "0.0.1",
+  components: {
+    card: {
+      name: "Card", description: "A container.", props: {},
+      composition: { subComponents: [{ id: "card-header", description: "Header region." }] },
+    },
+    form: {
+      name: "Form", description: "A form.", props: {},
+      composition: { subComponents: [{ id: "form-item", description: "One field.", slot: "body" }, { id: "form-label", description: "The field label.", acceptsChildren: "text" }] },
+    },
+    select: {
+      name: "Select", description: "Choose one.", props: {},
+      composition: { subComponents: [{ id: "select-trigger", description: "Opens the listbox." }, { id: "select-item", description: "One option." }] },
+    },
+    "alert-dialog": {
+      name: "AlertDialog", description: "Confirm dialog.", props: {},
+      composition: { subComponents: [{ id: "alert-dialog-content", description: "The dialog body." }] },
+    },
+    // The dspack#40 shape as currently (mis)declared: the wrapper trio as subs of field.
+    field: {
+      name: "Field", description: "One labelled field.", props: {},
+      composition: {
+        subComponents: [
+          { id: "field-set", description: "Groups controls answering one question." },
+          { id: "field-legend", description: "Names a FieldSet." },
+          { id: "field-group", description: "Stacks Fields." },
+          { id: "field-label", description: "The label." },
+        ],
+      },
+    },
+    input: { name: "Input", description: "Text entry.", props: {} },
+  },
+  intents: [{ id: "data-entry", name: "Data entry", description: "Collect input." }],
+} as unknown as Contract;
+
+/** The corrected dspack#40 model: the trio promoted per the real shadcn API. */
+const corrected: Contract = (() => {
+  const c = structuredClone(contract) as unknown as {
+    components: Record<string, { composition?: { subComponents: Array<{ id: string; description: string }> } }>;
+  };
+  c.components.field.composition = { subComponents: [{ id: "field-label", description: "The label." }] };
+  c.components["field-set"] = {
+    composition: { subComponents: [{ id: "field-legend", description: "Names the set." }] },
+    ...( { name: "FieldSet", description: "Groups fields answering one question.", props: {} } as object),
+  } as never;
+  c.components["field-group"] = { ...( { name: "FieldGroup", description: "Stacks fields.", props: {} } as object) } as never;
+  return c as unknown as Contract;
+})();
+
+const surface = (root: unknown): Surface =>
+  ({ dspackSurface: "0.1", system: "containment-fixture", intent: "data-entry", root }) as Surface;
+
+const s2 = (root: unknown, c: Contract = contract) => {
+  const report = lintSurface(surface(root), c);
+  const gate = report.gates.find((g) => g.gate === "S2")!;
+  return { status: gate.status, errors: gate.errors ?? [] };
+};
+
+describe("S2 containment — the four measured production shapes refuse", () => {
+  it("1. root-level form-label (no owner anywhere) fails with a pathed finding naming sub and owner", () => {
+    const { status, errors } = s2({ component: "form-label", text: "Merchant" });
+    expect(status).toBe("FAIL");
+    const finding = errors.find((e) => e.includes("form-label"))!;
+    expect(finding).toContain("$.root");
+    expect(finding).toContain("'form'");
+  });
+
+  it("2. select-trigger beside rather than beneath its select fails; properly nested passes", () => {
+    const sibling = s2({
+      component: "card",
+      children: [
+        { component: "select" },
+        { component: "select-trigger", text: "Role" },
+      ],
+    });
+    expect(sibling.status).toBe("FAIL");
+    expect(sibling.errors.some((e) => e.includes("select-trigger") && e.includes("'select'"))).toBe(true);
+
+    const nested = s2({
+      component: "card",
+      children: [{ component: "select", children: [{ component: "select-trigger", text: "Role" }] }],
+    });
+    expect(nested.status).toBe("PASS");
+  });
+
+  it("3. a bare alert-dialog-content duplicated beside a correctly nested one flags ONLY the bare path", () => {
+    const { status, errors } = s2({
+      component: "form",
+      children: [
+        { component: "alert-dialog", children: [{ component: "alert-dialog-content", text: "Are you sure?" }] },
+        { component: "alert-dialog-content", text: "Are you sure?" },
+      ],
+    });
+    expect(status).toBe("FAIL");
+    const hits = errors.filter((e) => e.includes("alert-dialog-content"));
+    expect(hits).toHaveLength(1);
+    expect(hits[0]).toContain("$.root.children[1]");
+  });
+
+  it("4. the dspack#40 exemplar shape fails under the inverted declaration and passes under the corrected one", () => {
+    const exemplar = {
+      component: "card",
+      children: [
+        {
+          component: "field-set",
+          children: [
+            { component: "field-legend", text: "Digest" },
+            { component: "field-group", children: [{ component: "field", children: [{ component: "field-label", text: "Cadence" }, { component: "input" }] }] },
+          ],
+        },
+      ],
+    };
+    const inverted = s2(exemplar);
+    expect(inverted.status).toBe("FAIL");
+    expect(inverted.errors.some((e) => e.includes("field-set") && e.includes("'field'"))).toBe(true);
+
+    // The containment amendment and the field correction converge: the SAME
+    // surface is green once ownership is declared the way the family is used.
+    expect(s2(exemplar, corrected).status).toBe("PASS");
+  });
+});
+
+describe("S2 containment — semantics", () => {
+  it("valid nested use with arbitrary intermediate structure stays green (owner is an ancestor, not the parent)", () => {
+    const { status } = s2({
+      component: "form",
+      children: [
+        {
+          component: "card", // intermediate structural node between owner and sub
+          children: [{ component: "form-item", children: [{ component: "form-label", text: "A" }, { component: "input" }] }],
+        },
+      ],
+    });
+    expect(status).toBe("PASS");
+  });
+
+  it("a sub reached through an ancestor's slots is contained (walk parity with S3)", () => {
+    const { status } = s2({
+      component: "form",
+      slots: { body: [{ component: "form-label", text: "A" }] },
+    });
+    expect(status).toBe("PASS");
+  });
+
+  it("an id declared BOTH top-level and as a sub is a component everywhere — containment does not apply", () => {
+    const both = structuredClone(contract) as unknown as { components: Record<string, unknown> };
+    both.components["form-label"] = { name: "FormLabel", description: "Also independently usable.", props: {} };
+    const { status } = s2({ component: "form-label", text: "standalone" }, both as unknown as Contract);
+    expect(status).toBe("PASS");
+  });
+
+  it("ownership is never inferred: a name-alike inside a name-alike compound still refuses", () => {
+    // select-item inside CARD (prefix-similar sibling family present elsewhere):
+    // only the declared owner counts.
+    const { status, errors } = s2({
+      component: "card",
+      children: [{ component: "select-item", text: "Admins" }],
+    });
+    expect(status).toBe("FAIL");
+    expect(errors.some((e) => e.includes("select-item") && e.includes("'select'"))).toBe(true);
+  });
+});
+
+describe("the repair loop receives containment findings", () => {
+  it("renderRepairMessage carries S2 vocabulary errors so a repair round can relocate the sub", () => {
+    const report = lintSurface(surface({ component: "form-label", text: "Merchant" }), contract);
+    const gate = report.gates.find((g) => g.gate === "S2")!;
+    const message = renderRepairMessage(report.findings, contract, "standard", gate.errors ?? []);
+    expect(message).toContain("form-label");
+    expect(message).toContain("'form'");
+    expect(message).toContain("$.root");
+  });
+});
diff --git a/src/core/lint/vocabulary.ts b/src/core/lint/vocabulary.ts
index d22fc0c..2b971a5 100644
--- a/src/core/lint/vocabulary.ts
+++ b/src/core/lint/vocabulary.ts
@@ -4,12 +4,18 @@
  * constrained: the S0 spike caught Ollama's mlx engine silently ignoring
  * `format`, which is why S2 is never assumed from generation.
  *
- * Scope per spec §8: component/sub-component ids, prop names on components,
- * enum prop values, declared slot names, plus surface-level consistency
- * (registered intent, matching system name). Deliberately NOT checked:
- * acceptsChildren semantics, non-enum prop types, ordering.
+ * Scope per spec v0.3 §8 + the v0.4 §5.1 amendment: component/sub-component
+ * ids, prop names on components, enum prop values, declared slot names,
+ * surface-level consistency (registered intent, matching system name), and
+ * sub-component CONTAINMENT — a sub-declared id may appear only within the
+ * subtree of an instance of a declaring compound, unless the contract also
+ * declares the id as a top-level component (independently usable).
+ * Ownership comes only from composition.subComponents; it is never inferred
+ * from names, prefixes, adjacency, or examples. Deliberately NOT checked:
+ * acceptsChildren semantics, non-enum prop types, ordering (containment is
+ * ownership, not order).
  */
-import { type Contract, type Surface, duplicateSubComponentIds, enumValues, subComponentIndex } from "../contract.js";
+import { type Contract, type Surface, type SurfaceNode, duplicateSubComponentIds, enumValues, subComponentIndex } from "../contract.js";
 import { walkSurface } from "./walk.js";
 
 export function checkVocabulary(surface: Surface, contract: Contract): string[] {
@@ -76,5 +82,39 @@ export function checkVocabulary(surface: Surface, contract: Contract): string[]
       }
     }
   }
+
+  // Containment (spec v0.4 §5.1): every sub-declared id needs a declaring
+  // compound among its ANCESTORS (any depth — intermediate structure is
+  // fine; parent-only would be a different, stricter rule). Owners are the
+  // full declaration set (exactly one today, since duplicate sub ids refuse
+  // above; the set form is the spec's, not a behavior). An id that is also
+  // a top-level component is a component everywhere and exempt. The
+  // ancestor-carrying walk mirrors walkSurface exactly (children + slots).
+  const owners = new Map<string, string[]>();
+  for (const [id, component] of Object.entries(components)) {
+    for (const sub of component.composition?.subComponents ?? []) {
+      owners.set(sub.id, [...(owners.get(sub.id) ?? []), id]);
+    }
+  }
+  const containment = (node: SurfaceNode, path: string, ancestors: ReadonlySet<string>): void => {
+    const id = node.component;
+    const declaredBy = owners.get(id);
+    if (declaredBy && !(id in components) && !declaredBy.some((owner) => ancestors.has(owner))) {
+      const ownerList = declaredBy.map((o) => `'${o}'`).join(" or ");
+      errors.push(
+        `${path}: sub-component '${id}' of ${ownerList} appears outside any ${ownerList} subtree — ` +
+          `a declared sub-component is only valid within its declaring compound (declare '${id}' as a top-level ` +
+          `component if it is independently usable)`,
+      );
+    }
+    const next = new Set(ancestors);
+    next.add(id);
+    (node.children ?? []).forEach((child, i) => containment(child, `${path}.children[${i}]`, next));
+    for (const slot of Object.keys(node.slots ?? {}).sort()) {
+      node.slots![slot].forEach((child, i) => containment(child, `${path}.slots.${slot}[${i}]`, next));
+    }
+  };
+  containment(surface.root, "$.root", new Set());
+
   return errors;
 }
diff --git a/src/repair/render.ts b/src/repair/render.ts
index e30ac40..f64359f 100644
--- a/src/repair/render.ts
+++ b/src/repair/render.ts
@@ -29,12 +29,37 @@ export function renderRepairMessage(
   findings: Finding[],
   contract: Contract,
   template: RepairTemplate = "standard",
+  /**
+   * S2 vocabulary errors (pathed strings from the gate report), rendered in
+   * their own section BEFORE governance findings: spec v0.4 §5.1 requires
+   * containment defects to reach the repair loop, and vocabulary errors are
+   * more fundamental than rule findings (a rule cannot be judged on
+   * vocabulary the contract does not have). Empty/omitted keeps the message
+   * byte-identical to the pre-amendment rendering.
+   */
+  vocabularyErrors: readonly string[] = [],
 ): string {
   const errors = findings.filter((f) => f.level === "error");
-  const lines: string[] = [
-    `Your surface violates ${errors.length} governance rule finding(s) of the "${contract.name}" design system:`,
-    "",
-  ];
+  const lines: string[] = [];
+  if (vocabularyErrors.length > 0) {
+    lines.push(
+      `Your surface uses the "${contract.name}" vocabulary incorrectly in ${vocabularyErrors.length} place(s):`,
+      "",
+    );
+    vocabularyErrors.forEach((error, index) => {
+      lines.push(`Vocabulary error ${index + 1}: ${error}`);
+    });
+    lines.push("");
+  }
+  // The governance header is unconditional when there are no vocabulary
+  // errors (byte-compatible with the pre-§5.1 rendering); with vocabulary
+  // errors present, a zero-findings governance section would be noise.
+  if (errors.length > 0 || vocabularyErrors.length === 0) {
+    lines.push(
+      `Your surface violates ${errors.length} governance rule finding(s) of the "${contract.name}" design system:`,
+      "",
+    );
+  }
 
   errors.forEach((finding, index) => {
     const where = finding.location.nodeId
diff --git a/src/run/orchestrator.ts b/src/run/orchestrator.ts
index 10dfa3e..0e17373 100644
--- a/src/run/orchestrator.ts
+++ b/src/run/orchestrator.ts
@@ -276,7 +276,10 @@ export async function runPipeline(options: RunOptions): Promise<RunResult> {
     }
 
     if (index < maxRepairs) {
-      const repair = renderRepairMessage(lint.findings, contract, repairTemplate);
+      // S2 errors ride the repair message alongside governance findings
+      // (spec v0.4 §5.1: containment defects must be repairable in-loop).
+      const s2Errors = lint.gates.find((g) => g.gate === "S2")?.errors ?? [];
+      const repair = renderRepairMessage(lint.findings, contract, repairTemplate, s2Errors);
       repairMessages.push(repair);
       conversation.push({ role: "assistant", content: generated.raw }, { role: "user", content: repair });
       emit({ type: "repair", index, message: repair });
diff --git a/src/run/pipeline.test.ts b/src/run/pipeline.test.ts
index 904e559..4ef2874 100644
--- a/src/run/pipeline.test.ts
+++ b/src/run/pipeline.test.ts
@@ -146,16 +146,21 @@ describe("failure paths are first-class artifacts", () => {
 
   it("emitter REFUSAL: lint-clean surface the emitter cannot project at all → failed-gate, exit 3, refusal recorded", async () => {
     // The live-eval discovery (2026-07-03, qwen): a sub-component outside its
-    // compound parent is in-vocabulary (S2), ungoverned (S3), but the a2ui
+    // compound parent was in-vocabulary (S2), ungoverned (S3), but the a2ui
     // profile cannot emit it standalone — EmitSurfaceError. That is the
     // target-equivalent emitter-gate failure, never a crash.
     //
-    // Fixture note (2026-08-06): the stray sub is table-footer, not
-    // card-header. card-header INSIDE a card stopped being a refusal the day
-    // the card plan learned to dissolve its own sub-family (emit 0.3.2's
-    // subFlatten) — this test only stayed green because the lockfile froze
-    // emit 0.3.1. A table sub inside a CARD is outside its compound under
-    // every emitter version, which is what the discovery actually was.
+    // Fixture note (2026-08-06): the stray sub became table-footer, not
+    // card-header, after emit 0.3.2's subFlatten dissolved card's family.
+    //
+    // Fixture note (2026-08-07, spec v0.4 §5.1): the stray-sub shape is no
+    // longer lint-clean — S2 containment now catches it in-loop, which is
+    // the amendment's whole point (see containment.test.ts). The
+    // lint-clean-but-refused class this test pins is exercised through its
+    // other member: a declared CASUALTY component ('dropdown-menu' in the
+    // shipped profile; 'dialog' is intent-forbidden by S3 here) —
+    // in-vocabulary, ungoverned in this surface, and refused by the emitter
+    // with the casualty reason.
     const refusalBreaker: Surface = {
       dspackSurface: "0.1",
       system: "shadcn/ui",
@@ -164,7 +169,7 @@ describe("failure paths are first-class artifacts", () => {
         component: "card",
         children: [
           (workedExample.root.children![0] as Surface["root"]),
-          { component: "table-footer", text: "stray sub-component" },
+          { component: "dropdown-menu", text: "stray casualty" },
         ],
       },
     };
@@ -172,7 +177,7 @@ describe("failure paths are first-class artifacts", () => {
     const result = await runPipeline({ ...baseOptions, adapter });
     expect(result.report.outcome).toBe("failed-gate");
     expect(result.exitCode).toBe(3);
-    expect(result.report.emitted!.refusal).toContain("table-footer");
+    expect(result.report.emitted!.refusal).toContain("dropdown-menu");
     expect(result.report.emitted!.validations).toEqual([]);
     expect(result.surfaceMessages).toBeUndefined();
     expect(validateReport(JSON.parse(JSON.stringify(result.report)))).toBe(true);