diff --git a/assistant/src/memory/v3/__tests__/retriever.test.ts b/assistant/src/memory/v3/__tests__/retriever.test.ts
new file mode 100644
index 00000000000..bc514be301e
--- /dev/null
+++ b/assistant/src/memory/v3/__tests__/retriever.test.ts
@@ -0,0 +1,226 @@
+/**
+ * Route-assembly tests for the v3 retriever wiring in
+ * `handleCompareRetrievers` (`assistant/src/runtime/routes/memory-v2-routes.ts`).
+ *
+ * The compare route always includes the router retriever as comparand #1 and
+ * adds the v3 retriever as comparand #2 only when `config.memory.v3.enabled`.
+ * These tests exercise that gating end-to-end through the real handler and the
+ * real `runComparisonOverHistory`, with a fixture DB seeded with one logged
+ * router turn (mirroring `assistant/src/memory/v2/__tests__/harness-compare.test.ts`).
+ *
+ * Neither the real router nor the real v3 loop runs here — both would hit a
+ * provider. `../loop.js` (the v3 loop) and `../../v2/harness/router-retriever.js`
+ * are `mock.module`-stubbed to return deterministic selections, so the tests
+ * assert *which retrievers were assembled* (by the names in the report), not
+ * their retrieval quality. `loadConfig` is stubbed so each test controls
+ * `memory.v3.enabled`; workspace/page-index helpers are stubbed to keep the
+ * handler off the filesystem.
+ */
+
+import { beforeEach, describe, expect, mock, test } from "bun:test";
+
+import type { AssistantConfig } from "../../../config/types.js";
+import { getDb } from "../../db-connection.js";
+import { initializeDb } from "../../db-init.js";
+import type { MemoryV2ConceptRowRecord } from "../../memory-v2-activation-log-store.js";
+import {
+  conversations,
+  memoryV2ActivationLogs,
+  messages,
+} from "../../schema.js";
+import type {
+  RetrievalInput,
+  RetrievalOutput,
+} from "../../v2/harness/retriever.js";
+
+initializeDb();
+
+// Silence the route's logger.
+mock.module("../../../util/logger.js", () => ({
+  getLogger: () =>
+    new Proxy({} as Record<string, unknown>, { get: () => () => {} }),
+}));
+
+// loadNowText / page-index read workspace files; a nonexistent dir yields "".
+const WORKSPACE = "/tmp/v3-retriever-nonexistent-workspace";
+
+// Controllable config: each test sets `v3Enabled` before invoking the handler.
+let v3Enabled = false;
+
+mock.module("../../../config/loader.js", () => ({
+  loadConfig: (): AssistantConfig =>
+    ({
+      memory: {
+        v2: { enabled: true, router: { historical_pairs: 1 } },
+        v3: { enabled: v3Enabled },
+      },
+    }) as unknown as AssistantConfig,
+}));
+
+mock.module("../../../util/platform.js", () => ({
+  getWorkspaceDir: (): string => WORKSPACE,
+}));
+
+// page-index is intentionally NOT mocked: it has a wide export surface
+// (`invalidatePageIndex` etc.) that transitive importers in the route's
+// dependency graph rely on, and `getPageIndex` over the nonexistent workspace
+// returns a benign index. The retriever names are what we assert, not the
+// page set, so the real (empty-ish) index is harmless here.
+
+// Stub the router retriever — the real one calls a provider.
+mock.module("../../v2/harness/router-retriever.js", () => ({
+  createRouterRetriever: () => ({
+    name: "router",
+    retrieve: async (): Promise<RetrievalOutput> => ({
+      selectedSlugs: ["p1"],
+      sourceBySlug: new Map([["p1", "router"]]),
+    }),
+  }),
+}));
+
+// Stub the v3 loop — the real one runs scout/filter/tree/edge/gate lanes that
+// hit providers, embeddings, and the filesystem.
+mock.module("../loop.js", () => ({
+  runRetrievalLoop: async (
+    _input: RetrievalInput,
+  ): Promise<RetrievalOutput> => ({
+    selectedSlugs: ["p2"],
+    sourceBySlug: new Map([["p2", "dense"]]),
+  }),
+}));
+
+// Import the handler only after the mocks are installed.
+const { handleCompareRetrievers } =
+  await import("../../../runtime/routes/memory-v2-routes.js");
+
+const ZERO_CONFIG = {
+  d: 0,
+  c_user: 0,
+  c_assistant: 0,
+  c_now: 0,
+  k: 0,
+  hops: 0,
+  top_k: 0,
+  epsilon: 0,
+};
+
+let seq = 0;
+
+function ensureConversation(id: string): void {
+  getDb()
+    .insert(conversations)
+    .values({ id, createdAt: 0, updatedAt: 0 })
+    .onConflictDoNothing()
+    .run();
+}
+
+function insertMessage(
+  id: string,
+  conversationId: string,
+  role: string,
+  text: string,
+  createdAt: number,
+): void {
+  ensureConversation(conversationId);
+  getDb()
+    .insert(messages)
+    .values({
+      id,
+      conversationId,
+      role,
+      content: JSON.stringify([{ type: "text", text }]),
+      createdAt,
+    })
+    .run();
+}
+
+function makeConcept(
+  slug: string,
+  status: MemoryV2ConceptRowRecord["status"],
+): MemoryV2ConceptRowRecord {
+  return {
+    slug,
+    finalActivation: 0,
+    ownActivation: 0,
+    priorActivation: 0,
+    simUser: 0,
+    simAssistant: 0,
+    simNow: 0,
+    simUserRerankBoost: 0,
+    simAssistantRerankBoost: 0,
+    inRerankPool: false,
+    spreadContribution: 0,
+    source: "router",
+    status,
+  };
+}
+
+function insertRouterLog(
+  conversationId: string,
+  messageId: string,
+  turn: number,
+  concepts: MemoryV2ConceptRowRecord[],
+  createdAt: number,
+): void {
+  ensureConversation(conversationId);
+  getDb()
+    .insert(memoryV2ActivationLogs)
+    .values({
+      id: `log-${seq++}`,
+      conversationId,
+      messageId,
+      turn,
+      mode: "router",
+      conceptsJson: JSON.stringify(concepts),
+      skillsJson: "[]",
+      configJson: JSON.stringify(ZERO_CONFIG),
+      createdAt,
+    })
+    .run();
+}
+
+/** Seed one router turn: user msg, assistant anchor, and the logged picks. */
+function seedTurn(groundTruth: string[]): void {
+  insertMessage("u1", "c1", "user", "hello", 10);
+  insertMessage("a1", "c1", "assistant", "hi", 20); // anchor for turn 1
+  insertRouterLog(
+    "c1",
+    "a1",
+    1,
+    groundTruth.map((slug) => makeConcept(slug, "injected")),
+    20,
+  );
+}
+
+function reset(): void {
+  const db = getDb();
+  db.delete(memoryV2ActivationLogs).run();
+  db.delete(messages).run();
+  v3Enabled = false;
+}
+
+describe("handleCompareRetrievers v3 wiring", () => {
+  beforeEach(reset);
+
+  test("includes only router when memory.v3.enabled is false", async () => {
+    seedTurn(["p1", "p2"]);
+
+    const report = await handleCompareRetrievers({ body: {} });
+
+    const names = report.retrievers.map((r) => r.name);
+    expect(names).toEqual(["router"]);
+  });
+
+  test("includes router and v3 when memory.v3.enabled is true", async () => {
+    v3Enabled = true;
+    seedTurn(["p1", "p2"]);
+
+    const report = await handleCompareRetrievers({ body: {} });
+
+    const names = report.retrievers.map((r) => r.name);
+    expect(names).toEqual(["router", "v3"]);
+    // Router is always comparand #1; v3 joins as comparand #2.
+    expect(names[0]).toBe("router");
+    expect(names[1]).toBe("v3");
+  });
+});
diff --git a/assistant/src/memory/v3/retriever.ts b/assistant/src/memory/v3/retriever.ts
new file mode 100644
index 00000000000..eee8aed369d
--- /dev/null
+++ b/assistant/src/memory/v3/retriever.ts
@@ -0,0 +1,33 @@
+/**
+ * v3 retriever — the multi-lane bounded-descent retrieval loop
+ * ({@link runRetrievalLoop}) adapted to the harness {@link Retriever}
+ * interface.
+ *
+ * This is the offline, zero-production-risk shadow path: the comparison harness
+ * replays historical oracle turns and scores v3's selection against the v2
+ * router's logged picks (recall@k). Nothing here runs on a live injection turn
+ * — the loop reads the DB handle for its hot lane but never mutates production
+ * state, matching the {@link Retriever} contract.
+ */
+
+import type { DrizzleDb } from "../db-connection.js";
+import type {
+  RetrievalInput,
+  RetrievalOutput,
+  Retriever,
+} from "../v2/harness/retriever.js";
+import { runRetrievalLoop } from "./loop.js";
+
+/**
+ * Wrap the v3 retrieval loop as a named harness {@link Retriever}.
+ *
+ * @param db handle threaded to {@link runRetrievalLoop} for the scout hot lane.
+ */
+export function createV3Retriever(db: DrizzleDb): Retriever {
+  return {
+    name: "v3",
+    retrieve(input: RetrievalInput): Promise<RetrievalOutput> {
+      return runRetrievalLoop(input, { db });
+    },
+  };
+}
diff --git a/assistant/src/runtime/routes/memory-v2-routes.ts b/assistant/src/runtime/routes/memory-v2-routes.ts
index 124cfa480fa..5f987c82fb3 100644
--- a/assistant/src/runtime/routes/memory-v2-routes.ts
+++ b/assistant/src/runtime/routes/memory-v2-routes.ts
@@ -24,6 +24,7 @@ import {
   validateEdgeTargets,
 } from "../../memory/v2/edge-index.js";
 import { runComparisonOverHistory } from "../../memory/v2/harness/compare.js";
+import type { Retriever } from "../../memory/v2/harness/retriever.js";
 import { createRouterRetriever } from "../../memory/v2/harness/router-retriever.js";
 import type { ComparisonReport } from "../../memory/v2/harness/runner.js";
 import { computeInjectionScores } from "../../memory/v2/injection-events.js";
@@ -38,6 +39,7 @@ import {
 import { ROUTER_PROMPT } from "../../memory/v2/prompts/router.js";
 import { type RouterSource, runRouter } from "../../memory/v2/router.js";
 import { seedV2SkillEntries } from "../../memory/v2/skill-store.js";
+import { createV3Retriever } from "../../memory/v3/retriever.js";
 import { getLogger } from "../../util/logger.js";
 import { getWorkspaceDir } from "../../util/platform.js";
 import { RouteError } from "./errors.js";
@@ -637,11 +639,20 @@ export async function handleCompareRetrievers({
   const pageIndex = await getPageIndex(workspaceDir);
   const db = getDb();
 
+  // The router is always comparand #1 (the harness self-test against its own
+  // logged ground truth). v3 joins as comparand #2 only when explicitly
+  // enabled, so the default compare surface is unchanged until v3 is switched
+  // on. v3 is offline-only here — the loop reads `db` but mutates nothing.
+  const retrievers: Retriever[] = [createRouterRetriever(db)];
+  if (config.memory.v3.enabled) {
+    retrievers.push(createV3Retriever(db));
+  }
+
   return runComparisonOverHistory({
     db,
     workspaceDir,
     config,
-    retrievers: [createRouterRetriever(db)],
+    retrievers,
     ks: ks ?? DEFAULT_COMPARE_KS,
     limit: limit ?? DEFAULT_COMPARE_LIMIT,
     pageExists: (slug) => pageIndex.bySlug.has(slug),