diff --git a/README.md b/README.md
index 7eebea9..fdc2039 100644
--- a/README.md
+++ b/README.md
@@ -176,7 +176,7 @@ the trigger, policy decisions, tool calls, approvals, the reply, and what it cos
 pnpm typecheck            # strict TypeScript, no build step (tsx runs source)
 pnpm eval                 # 500+ deterministic checks, no API key needed
 RUN_LLM_EVALS=1 pnpm eval # plus live checks: grounded Q&A, red team, answer golden set per model
-pnpm mutate               # sabotage each of 408 guardrails; its eval must catch it
+pnpm mutate               # sabotage each of 412 guardrails; its eval must catch it
 pnpm auditlog verify      # the audit log's hash chain holds
 ```
 
diff --git a/evals/retrieval-contract.test.ts b/evals/retrieval-contract.test.ts
new file mode 100644
index 0000000..e284cfc
--- /dev/null
+++ b/evals/retrieval-contract.test.ts
@@ -0,0 +1,87 @@
+import fs from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { Vault } from "@scriptorium/core";
+import { buildIndex, withEmbeddings, type Embedder, type SearchHit, type VaultIndex } from "@scriptorium/curator";
+
+/**
+ * What every retriever behind `search_vault` promises, whichever it is: BM25 alone, or BM25
+ * fused with embeddings. A retriever swapped in later runs this same contract.
+ */
+
+const CONCEPTS: Record<string, number> = { spreadsheet: 0, csv: 0, import: 1, thousands: 1, people: 2, subscribers: 2, downtime: 3, maintenance: 3 };
+const conceptEmbedder: Embedder = {
+  name: "concepts",
+  embedDocuments: async (texts) => texts.map(embed),
+  embedQuery: async (text) => embed(text),
+};
+function embed(text: string): number[] {
+  const vector = [0, 0, 0, 0];
+  for (const word of text.toLowerCase().split(/[^a-z]+/)) {
+    const dim = CONCEPTS[word];
+    if (dim !== undefined) vector[dim] = (vector[dim] ?? 0) + 1;
+  }
+  return vector;
+}
+
+const RETRIEVERS: Array<[string, (vault: Vault) => Promise<VaultIndex>]> = [
+  ["BM25", (vault) => buildIndex(vault)],
+  ["hybrid", async (vault) => withEmbeddings(vault, await buildIndex(vault), conceptEmbedder)],
+];
+
+/** As the Q&A tool asks: the async search where there is one. */
+async function find(index: VaultIndex, query: string, limit?: number): Promise<SearchHit[]> {
+  return index.searchAsync ? index.searchAsync(query, limit) : index.search(query, limit);
+}
+
+let tmpRoot: string;
+let vault: Vault;
+
+beforeEach(async () => {
+  tmpRoot = await fs.mkdtemp(path.join(os.tmpdir(), "scriptorium-retrieval-contract-"));
+  vault = new Vault(tmpRoot);
+  await vault.ensure();
+  for (let i = 0; i < 8; i += 1) await vault.writeNote(`docs/maintenance-${i}.md`, `# Maintenance window ${i}\n\nAnnounce planned downtime for maintenance ${i}.`, {});
+  await vault.writeNote("_lessons/L-003-csv.md", "Always import subscribers from a CSV file.", { id: "L-003", status: "rejected", rejected_by: "Alex Kim" });
+  await vault.writeNote("_memory/M-1.md", "Priya keeps a spreadsheet of people to import.", { id: "M-1", status: "approved", scope: "person:slack:U1" });
+  await vault.writeNote("_gaps/G-1.md", "Someone asked how to import a spreadsheet of thousands.", {});
+  await vault.writeNote("_inbox/unreleased.md", "# Unreleased\n\nImport thousands of people from a spreadsheet, launching next quarter.", {});
+});
+
+afterEach(async () => {
+  await fs.rm(tmpRoot, { recursive: true, force: true, maxRetries: 5 });
+});
+
+for (const [name, build] of RETRIEVERS) {
+  describe(`the retrieval contract: ${name}`, () => {
+    it("returns hits a citation can name, at most as many as asked for", async () => {
+      const hits = await find(await build(vault), "maintenance downtime", 3);
+      expect(hits.length).toBeGreaterThan(0);
+      expect(hits.length).toBeLessThanOrEqual(3);
+      for (const hit of hits) {
+        expect(hit.relPath).toMatch(/^docs\/maintenance-\d\.md$/);
+        expect(typeof hit.title).toBe("string");
+        expect(typeof hit.score).toBe("number");
+        expect(hit.snippet.length).toBeLessThanOrEqual(240);
+      }
+    });
+
+    it("never returns a private note, even asked in its own words", async () => {
+      const index = await build(vault);
+      for (const query of ["Priya keeps a spreadsheet of people to import", "Someone asked how to import a spreadsheet of thousands", "Unreleased import thousands of people launching next quarter"]) {
+        for (const hit of await find(index, query, 20)) expect(hit.relPath, query).not.toMatch(/^_(memory|gaps|inbox)\//);
+      }
+    });
+
+    it("a rule a human refused carries its notice, however it was found", async () => {
+      const index = await build(vault);
+      // In its own words, and (where there are embeddings) in none of them.
+      for (const query of ["import subscribers from a CSV", ...(name === "hybrid" ? ["spreadsheet of thousands"] : [])]) {
+        const refused = (await find(index, query, 10)).find((hit) => hit.relPath === "_lessons/L-003-csv.md");
+        expect(refused, query).toBeDefined();
+        expect(refused?.notice, query).toMatch(/^REJECTED — Alex Kim/);
+      }
+    });
+  });
+}
diff --git a/scripts/mutate.ts b/scripts/mutate.ts
index 342feee..31f823d 100644
--- a/scripts/mutate.ts
+++ b/scripts/mutate.ts
@@ -2710,6 +2710,34 @@ export const MUTANTS: Mutant[] = [
     replace: "  if (true) await moveTo(ctx, key, pending.to, status);",
     evals: ["evals/jira-board.test.ts"],
   },
+  {
+    control: "the embedding half never indexes a private note",
+    file: "packages/curator/src/hybrid.ts",
+    find: "    if (isPrivateNote(relPath)) continue;\n",
+    replace: "",
+    evals: ["evals/retrieval-contract.test.ts", "evals/hybrid-retrieval.test.ts"],
+  },
+  {
+    control: "a refused rule found only by meaning keeps its notice",
+    file: "packages/curator/src/hybrid.ts",
+    find: ", ...(doc.notice ? { notice: doc.notice } : {}) };",
+    replace: " };",
+    evals: ["evals/retrieval-contract.test.ts"],
+  },
+  {
+    control: "retrieval falls back to BM25 when embeddings are down",
+    file: "packages/curator/src/hybrid.ts",
+    find: "    console.warn(`[curator] embeddings unavailable, BM25 only: ${error instanceof Error ? error.message : error}`);\n    return base;",
+    replace: "    throw error;",
+    evals: ["evals/hybrid-retrieval.test.ts"],
+  },
+  {
+    control: "a hybrid search returns at most what was asked for",
+    file: "packages/curator/src/hybrid.ts",
+    find: "      const fused = reciprocalRankFusion([lexical.map((hit) => hit.relPath), semantic]).slice(0, limit);",
+    replace: "      const fused = reciprocalRankFusion([lexical.map((hit) => hit.relPath), semantic]);",
+    evals: ["evals/retrieval-contract.test.ts"],
+  },
   {
     control: "a delegation ends by itself",
     file: "apps/agents/src/teammate-bot/control.ts",
diff --git a/site/data.js b/site/data.js
index 72ebeea..6cd2adb 100644
--- a/site/data.js
+++ b/site/data.js
@@ -7,7 +7,7 @@ window.SITE = {
 
   stats: [
     { value: "730+", label: "evals, deterministic, on every commit" },
-    { value: "408", label: "guardrails proven by mutation testing" },
+    { value: "412", label: "guardrails proven by mutation testing" },
     { value: "30+", label: "tools, every write approve-tier" },
     { value: "78", label: "reviewed pull requests merged" },
   ],