diff --git a/eval/runner/multi-adapter.ts b/eval/runner/multi-adapter.ts
index 4aa4782c3..70e505746 100644
--- a/eval/runner/multi-adapter.ts
+++ b/eval/runner/multi-adapter.ts
@@ -26,7 +26,7 @@ import { RipgrepBm25Adapter } from './adapters/ripgrep-bm25.ts';
 import { VectorOnlyAdapter } from './adapters/vector-only.ts';
 import { HybridNoGraphAdapter } from './adapters/hybrid-nograph.ts';
 import type { Adapter, Page, Query, RankedDoc } from './types.ts';
-import { precisionAtK, recallAtK } from './types.ts';
+import { precisionAtK, recallAtK, sanitizePage, sanitizeQuery } from './types.ts';
 
 const TOP_K = 5;
 
@@ -331,13 +331,19 @@ async function scoreOneRun(
   pages: Page[],
   queries: Query[],
 ): Promise<RunResult> {
-  const state = await adapter.init(pages, { name: adapter.name });
+  // Day 9 sealed qrels enforcement (codex fix #1, #2, #3):
+  // Build sanitized copies with no `_facts` and no `gold` fields before
+  // handing them to the adapter. The scorer retains the full Query shape
+  // (including gold.relevant) to compute precision/recall below.
+  const publicPages = pages.map(sanitizePage);
+  const state = await adapter.init(publicPages, { name: adapter.name });
   let totalP = 0;
   let totalR = 0;
   let totalCorrect = 0;
   let totalExpected = 0;
   for (const q of queries) {
-    const results = await adapter.query(q, state);
+    const publicQ = sanitizeQuery(q);
+    const results = await adapter.query(publicQ as unknown as Query, state);
     const relevant = new Set(q.gold.relevant ?? []);
     totalP += precisionAtK(results, relevant, TOP_K);
     totalR += recallAtK(results, relevant, TOP_K);
diff --git a/eval/runner/types.ts b/eval/runner/types.ts
index 325e22e1c..94017d9fa 100644
--- a/eval/runner/types.ts
+++ b/eval/runner/types.ts
@@ -39,6 +39,30 @@ export interface Page {
   frontmatter?: Record<string, unknown>;
 }
 
+/**
+ * PublicPage — the shape adapters SEE at runtime (Day 9 sealed-qrels).
+ *
+ * Multi-adapter.ts calls `sanitizePage()` before passing the array to
+ * `adapter.init()`. The sanitized copy has NO `_facts`, NO `frontmatter`,
+ * NO arbitrary keys — only the five public fields below. Adapters that
+ * try `(page as any)._facts` get `undefined` instead of the gold object.
+ *
+ * This is soft enforcement (a misbehaving adapter could still open
+ * `eval/data/gold/*.json` from disk). Hard enforcement via process
+ * isolation ships with BrainBench v2's Docker sandbox.
+ */
+export type PublicPage = Pick<Page, 'slug' | 'type' | 'title' | 'compiled_truth' | 'timeline'>;
+
+export function sanitizePage(p: Page): PublicPage {
+  return {
+    slug: p.slug,
+    type: p.type,
+    title: p.title,
+    compiled_truth: p.compiled_truth,
+    timeline: p.timeline,
+  };
+}
+
 // ─── Query ───────────────────────────────────────────────────────────
 
 export type Tier =
@@ -89,6 +113,37 @@ export interface Query {
   tags?: string[];                  // 'identity-collision', 'contradiction', etc.
 }
 
+/**
+ * PublicQuery — the shape adapters SEE at runtime (Day 9 sealed-qrels).
+ *
+ * Multi-adapter.ts calls `sanitizeQuery()` before passing each query to
+ * `adapter.query()`. The sanitized copy strips the `gold` field entirely,
+ * so an adapter cannot read `q.gold.relevant` to cheat. Scorers keep the
+ * full Query shape and compare adapter output against gold after the call.
+ *
+ * Adapters that need as_of_date for temporal queries still get it —
+ * PublicQuery keeps every field EXCEPT gold.
+ */
+export type PublicQuery = Omit<Query, 'gold'>;
+
+export function sanitizeQuery(q: Query): PublicQuery {
+  // Build a new object to sever the reference chain. Using spread + delete
+  // would leave the `gold` key on the prototype-shape in some engines;
+  // explicit enumeration is the safest pattern.
+  const out: PublicQuery = {
+    id: q.id,
+    tier: q.tier,
+    text: q.text,
+    expected_output_type: q.expected_output_type,
+  };
+  if (q.as_of_date !== undefined) out.as_of_date = q.as_of_date;
+  if (q.acceptable_variants !== undefined) out.acceptable_variants = q.acceptable_variants;
+  if (q.known_failure_modes !== undefined) out.known_failure_modes = q.known_failure_modes;
+  if (q.author !== undefined) out.author = q.author;
+  if (q.tags !== undefined) out.tags = q.tags;
+  return out;
+}
+
 // ─── RankedDoc ──────────────────────────────────────────────────────
 
 /**
diff --git a/test/eval/sealed-qrels.test.ts b/test/eval/sealed-qrels.test.ts
new file mode 100644
index 000000000..a9969a628
--- /dev/null
+++ b/test/eval/sealed-qrels.test.ts
@@ -0,0 +1,257 @@
+/**
+ * sealed-qrels regression test — Day 9 of BrainBench v1 Complete.
+ *
+ * Enforces the sealed-qrels contract added in Day 9:
+ *   - sanitizePage() produces a new object with NO `_facts` field
+ *   - sanitizeQuery() produces a new object with NO `gold` field
+ *   - Accessing `._facts` / `.gold` on sanitized output returns `undefined`
+ *   - Scorer retains the full Query/RichPage shape (gold.relevant still usable)
+ *
+ * This is a SOFT enforcement — an adapter that runs `readFileSync(
+ * 'eval/data/gold/*.json')` could still cheat. Hard enforcement via
+ * process isolation ships with BrainBench v2's Docker sandbox.
+ *
+ * Documented as such so the adversarial reviewer doesn't get a false sense
+ * of airtight enforcement here.
+ */
+
+import { describe, test, expect } from 'bun:test';
+import {
+  sanitizePage,
+  sanitizeQuery,
+  type Page,
+  type PublicPage,
+  type Query,
+  type PublicQuery,
+} from '../../eval/runner/types.ts';
+
+// ─── RichPage helper (mirrors multi-adapter.ts internal shape) ────────
+
+interface RichPage extends Page {
+  _facts: {
+    type: string;
+    attendees?: string[];
+    employees?: string[];
+    founders?: string[];
+    investors?: string[];
+  };
+}
+
+function makeRichPage(overrides: Partial<RichPage> = {}): RichPage {
+  return {
+    slug: 'people/amara',
+    type: 'person',
+    title: 'Amara Okafor',
+    compiled_truth: 'Amara is a Partner.',
+    timeline: '',
+    _facts: { type: 'person' },
+    ...overrides,
+  } as RichPage;
+}
+
+function makeQuery(overrides: Partial<Query> = {}): Query {
+  return {
+    id: 'q-0001',
+    tier: 'easy',
+    text: 'Who is Amara?',
+    expected_output_type: 'cited-source-pages',
+    gold: { relevant: ['people/amara'] },
+    ...overrides,
+  };
+}
+
+// ─── sanitizePage ─────────────────────────────────────────────────────
+
+describe('sanitizePage — strips _facts and frontmatter', () => {
+  test('output has the 5 public fields', () => {
+    const rp = makeRichPage();
+    const sanitized = sanitizePage(rp);
+    expect(sanitized.slug).toBe(rp.slug);
+    expect(sanitized.type).toBe(rp.type);
+    expect(sanitized.title).toBe(rp.title);
+    expect(sanitized.compiled_truth).toBe(rp.compiled_truth);
+    expect(sanitized.timeline).toBe(rp.timeline);
+  });
+
+  test('output does NOT have _facts (the gold canonical leak)', () => {
+    const rp = makeRichPage({
+      _facts: { type: 'person', employees: ['people/amara'] },
+    });
+    const sanitized = sanitizePage(rp);
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    expect((sanitized as any)._facts).toBeUndefined();
+    expect('_facts' in sanitized).toBe(false);
+  });
+
+  test('output does NOT have frontmatter (potential hiding spot)', () => {
+    const rp = makeRichPage();
+    // Caller could have dumped _facts into frontmatter as a workaround
+    rp.frontmatter = { _facts_leak: 'gold data' };
+    const sanitized = sanitizePage(rp);
+    expect('frontmatter' in sanitized).toBe(false);
+  });
+
+  test('output is a NEW object (not a reference to the original)', () => {
+    const rp = makeRichPage();
+    const sanitized = sanitizePage(rp);
+    expect(sanitized).not.toBe(rp as unknown as PublicPage);
+  });
+
+  test('output has exactly the 5 expected keys (no hidden properties)', () => {
+    const rp = makeRichPage();
+    rp._facts = { type: 'person', employees: ['x'] };
+    rp.frontmatter = { anything: 'goes' };
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    (rp as any).leak = 'secret';
+    const sanitized = sanitizePage(rp);
+    const keys = Object.keys(sanitized).sort();
+    expect(keys).toEqual(['compiled_truth', 'slug', 'timeline', 'title', 'type']);
+  });
+
+  test('sanitized page when cast to any cannot reach original _facts', () => {
+    const rp = makeRichPage({
+      _facts: { type: 'company', investors: ['people/alice'] },
+    });
+    const sanitized = sanitizePage(rp);
+    // A cheating adapter does: const x = (page as any)._facts;
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const facts = (sanitized as any)._facts;
+    expect(facts).toBeUndefined();
+    // And cannot reach the original by prototype chain either
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const proto = Object.getPrototypeOf(sanitized);
+    expect(proto).toBe(Object.prototype);
+  });
+});
+
+// ─── sanitizeQuery ────────────────────────────────────────────────────
+
+describe('sanitizeQuery — strips gold', () => {
+  test('output has public fields only', () => {
+    const q = makeQuery();
+    const sanitized = sanitizeQuery(q);
+    expect(sanitized.id).toBe(q.id);
+    expect(sanitized.tier).toBe(q.tier);
+    expect(sanitized.text).toBe(q.text);
+    expect(sanitized.expected_output_type).toBe(q.expected_output_type);
+  });
+
+  test('output does NOT have gold', () => {
+    const q = makeQuery({ gold: { relevant: ['people/amara'], grades: { 'people/amara': 3 } } });
+    const sanitized = sanitizeQuery(q);
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    expect((sanitized as any).gold).toBeUndefined();
+    expect('gold' in sanitized).toBe(false);
+  });
+
+  test('retains optional fields (as_of_date, tags, author)', () => {
+    const q = makeQuery({
+      as_of_date: '2026-04-20',
+      tags: ['temporal'],
+      author: 'internal',
+      acceptable_variants: ['who works at Halfway'],
+      known_failure_modes: ['bare-name-collision'],
+    });
+    const sanitized = sanitizeQuery(q);
+    expect(sanitized.as_of_date).toBe('2026-04-20');
+    expect(sanitized.tags).toEqual(['temporal']);
+    expect(sanitized.author).toBe('internal');
+    expect(sanitized.acceptable_variants).toEqual(['who works at Halfway']);
+    expect(sanitized.known_failure_modes).toEqual(['bare-name-collision']);
+  });
+
+  test('omits undefined optional fields from the sanitized shape', () => {
+    const q = makeQuery(); // no as_of_date, no tags, etc.
+    const sanitized = sanitizeQuery(q);
+    expect('as_of_date' in sanitized).toBe(false);
+    expect('tags' in sanitized).toBe(false);
+  });
+
+  test('output is a NEW object', () => {
+    const q = makeQuery();
+    expect(sanitizeQuery(q)).not.toBe(q as unknown as PublicQuery);
+  });
+});
+
+// ─── Proxy-based adversarial adapter simulation ───────────────────────
+
+describe('adversarial adapter access — Proxy tripwire', () => {
+  test('Proxy-wrapped PublicPage throws on `_facts` access (tripwire)', () => {
+    const sanitized = sanitizePage(makeRichPage({ _facts: { type: 'person' } }));
+    const tripwire = new Proxy(sanitized, {
+      get(target, prop) {
+        if (prop === '_facts' || prop === 'gold') {
+          throw new Error(`sealed-qrels violation: adapter read forbidden field "${String(prop)}"`);
+        }
+        return target[prop as keyof PublicPage];
+      },
+    });
+    // Normal reads work
+    expect(tripwire.slug).toBe('people/amara');
+    // Adversarial read throws
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    expect(() => (tripwire as any)._facts).toThrow(/sealed-qrels violation/);
+  });
+
+  test('Proxy-wrapped PublicQuery throws on `gold` access', () => {
+    const sanitized = sanitizeQuery(makeQuery());
+    const tripwire = new Proxy(sanitized, {
+      get(target, prop) {
+        if (prop === 'gold') {
+          throw new Error('sealed-qrels violation: adapter read q.gold');
+        }
+        return target[prop as keyof PublicQuery];
+      },
+    });
+    expect(tripwire.id).toBe('q-0001');
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    expect(() => (tripwire as any).gold).toThrow(/sealed-qrels violation/);
+  });
+});
+
+// ─── Honest documentation of the seal's limits ────────────────────────
+
+describe('soft-seal documentation', () => {
+  test('sanitize cannot protect against filesystem access', () => {
+    // This test is intentionally EDUCATIONAL — it documents that the seal
+    // is only at the object level. A malicious adapter that does
+    // readFileSync('eval/data/gold/qrels.json') bypasses the seal entirely.
+    // BrainBench v2's Docker sandbox is the real enforcement.
+    const pseudocode =
+      "const gold = JSON.parse(readFileSync('eval/data/gold/qrels.json'))";
+    expect(pseudocode.length).toBeGreaterThan(0);
+    // The defense is deliberate and documented in types.ts.
+  });
+
+  test('sanitize cannot prevent a malicious Proxy setup from the adapter', () => {
+    // Similarly: a malicious adapter could set up its own Proxy to probe
+    // values. The seal is "can a well-behaved adapter accidentally cheat?",
+    // not "can a malicious adapter never cheat?"
+    const sanitized = sanitizePage(makeRichPage());
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const asAny = sanitized as any;
+    expect(asAny._facts).toBeUndefined();
+    // A malicious adapter with network access could still exfiltrate the
+    // page list and correlate externally. Hard enforcement requires
+    // process isolation.
+  });
+});
+
+// ─── Integration: scorer still sees full Query ────────────────────────
+
+describe('scorer retains gold', () => {
+  test('original Query object still has gold after sanitization (immutable copy)', () => {
+    const q = makeQuery({ gold: { relevant: ['people/amara', 'companies/halfway'] } });
+    const sanitized = sanitizeQuery(q);
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    expect((sanitized as any).gold).toBeUndefined();
+    // Scorer still has access to q.gold.relevant
+    expect(q.gold.relevant).toEqual(['people/amara', 'companies/halfway']);
+  });
+
+  test('original RichPage still has _facts after sanitization', () => {
+    const rp = makeRichPage({ _facts: { type: 'meeting', attendees: ['people/amara'] } });
+    sanitizePage(rp);
+    expect(rp._facts.attendees).toEqual(['people/amara']);
+  });
+});