diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 9587d5b6..19465a60 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -607,7 +607,8 @@ export {
 } from "./sync-scope-protocol.js";
 export { deriveTags, fileTags, normalizeTag } from "./tags.js";
 // Test utilities (exported for consumer packages like viewer-server)
-export { initTestSchema, insertTestSession } from "./test-utils.js";
+export type { MixedScopeFixture } from "./test-utils.js";
+export { initTestSchema, insertTestSession, seedMixedScopeFixture } from "./test-utils.js";
 export type {
 	Actor,
 	Artifact,
diff --git a/packages/core/src/scope-regression.test.ts b/packages/core/src/scope-regression.test.ts
new file mode 100644
index 00000000..10ab0f5c
--- /dev/null
+++ b/packages/core/src/scope-regression.test.ts
@@ -0,0 +1,124 @@
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { connect, type Database } from "./db.js";
+import * as embeddings from "./embeddings.js";
+import { exportMemories } from "./export-import.js";
+import { buildMemoryPack } from "./pack.js";
+import { MemoryStore } from "./store.js";
+import type { MixedScopeFixture } from "./test-utils.js";
+import { initTestSchema, seedMixedScopeFixture } from "./test-utils.js";
+import { semanticSearch } from "./vectors.js";
+
+vi.mock("./embeddings.js", async () => {
+	const actual = await vi.importActual<typeof import("./embeddings.js")>("./embeddings.js");
+	return {
+		...actual,
+		embedTexts: vi.fn(),
+		getEmbeddingClient: vi.fn(),
+		resolveEmbeddingModel: vi.fn(() => "test-model"),
+	};
+});
+
+describe("mixed-domain scope regression", () => {
+	let tmpDir: string;
+	let dbPath: string;
+	let store: MemoryStore;
+	let fixture: MixedScopeFixture;
+
+	beforeEach(() => {
+		vi.clearAllMocks();
+		tmpDir = mkdtempSync(join(tmpdir(), "codemem-scope-regression-"));
+		dbPath = join(tmpDir, "test.sqlite");
+		const db = connect(dbPath);
+		initTestSchema(db);
+		db.close();
+		store = new MemoryStore(dbPath);
+		fixture = seedMixedScopeFixture(store.db, store.deviceId);
+	});
+
+	afterEach(() => {
+		store?.close();
+		rmSync(tmpDir, { recursive: true, force: true });
+	});
+
+	it("keeps unauthorized scope rows out of store, search, recent, timeline, and explain", () => {
+		const visibleIds = new Set(fixture.visibleIds);
+
+		expect(store.get(fixture.personalId)?.title).toBe(fixture.visibleTitles[0]);
+		expect(store.get(fixture.authorizedId)?.title).toBe(fixture.visibleTitles[1]);
+		expect(store.get(fixture.unauthorizedId)).toBeNull();
+
+		for (const ids of [
+			store.recent(10).map((item) => item.id),
+			store.search(fixture.query, 10).map((item) => item.id),
+			store.timeline(null, fixture.authorizedId, 5, 5).map((item) => item.id),
+			store.explain(fixture.query, fixture.allIds, 10).items.map((item) => item.id),
+		]) {
+			expect(ids.some((id) => visibleIds.has(id))).toBe(true);
+			expect(ids).not.toContain(fixture.unauthorizedId);
+		}
+		expect(store.timeline(null, fixture.unauthorizedId, 5, 5)).toEqual([]);
+
+		const explain = store.explain(null, fixture.allIds, 10);
+		expect(explain.items.map((item) => item.id).sort((a, b) => a - b)).toEqual(
+			[...fixture.visibleIds].sort((a, b) => a - b),
+		);
+		expect(explain.missing_ids).toContain(fixture.unauthorizedId);
+		expect(
+			explain.errors.find((error) => error.code === "PROJECT_MISMATCH")?.ids ?? [],
+		).not.toContain(fixture.unauthorizedId);
+		expect(
+			explain.errors.find((error) => error.code === "FILTER_MISMATCH")?.ids ?? [],
+		).not.toContain(fixture.unauthorizedId);
+	});
+
+	it("keeps unauthorized scope rows out of semantic search", async () => {
+		insertTestVector(store.db, fixture.personalId, 0.3, "personal-vector");
+		insertTestVector(store.db, fixture.unauthorizedId, 0, "hidden-vector");
+		insertTestVector(store.db, fixture.authorizedId, 0.2, "authorized-vector");
+		vi.mocked(embeddings.embedTexts).mockResolvedValue([new Float32Array(384)]);
+
+		const results = await semanticSearch(store.db, fixture.query, 10, null, {
+			actorId: `local:${store.deviceId}`,
+			deviceId: store.deviceId,
+		});
+
+		const resultIds = results.map((item) => item.id);
+		expect(resultIds).toEqual(expect.arrayContaining(fixture.visibleIds));
+		expect(resultIds).not.toContain(fixture.unauthorizedId);
+	});
+
+	it("keeps unauthorized scope rows out of pack text and exports", () => {
+		const pack = buildMemoryPack(store, fixture.query, 10);
+		expect(pack.item_ids.some((id) => fixture.visibleIds.includes(id))).toBe(true);
+		expect(pack.item_ids).not.toContain(fixture.unauthorizedId);
+		expect(pack.pack_text).toContain(fixture.visibleTitles[1]);
+		expect(pack.pack_text).not.toContain(fixture.unauthorizedTitle);
+
+		const payload = exportMemories({ dbPath, allProjects: true });
+		const exportedTitles = payload.memory_items.map((memory) => String(memory.title));
+		expect(exportedTitles).toEqual(expect.arrayContaining(fixture.visibleTitles));
+		expect(exportedTitles).not.toContain(fixture.unauthorizedTitle);
+		expect(payload.memory_items.map((memory) => memory.scope_id)).not.toContain(
+			fixture.unauthorizedScopeId,
+		);
+	});
+});
+
+function insertTestVector(
+	db: Database,
+	memoryId: number,
+	value: number,
+	contentHash: string,
+): void {
+	const vector = new Float32Array(384).fill(value);
+	const vectorJson = JSON.stringify(Array.from(vector));
+	const escapedVectorJson = vectorJson.replaceAll("'", "''");
+	const escapedHash = contentHash.replaceAll("'", "''");
+	db.exec(`
+		INSERT INTO memory_vectors(embedding, memory_id, chunk_index, content_hash, model)
+		VALUES (vec_f32('${escapedVectorJson}'), ${memoryId}, 0, '${escapedHash}', 'test-model')
+	`);
+}
diff --git a/packages/core/src/test-utils.ts b/packages/core/src/test-utils.ts
index 4318721a..f94f6a02 100644
--- a/packages/core/src/test-utils.ts
+++ b/packages/core/src/test-utils.ts
@@ -4,6 +4,7 @@
 
 import type { Database } from "./db.js";
 import { bootstrapSchema } from "./schema-bootstrap.js";
+import { LOCAL_DEFAULT_SCOPE_ID } from "./scope-resolution.js";
 
 /**
  * Create the full schema for test databases.
@@ -25,5 +26,131 @@ export function insertTestSession(db: Database): number {
 	return Number(info.lastInsertRowid);
 }
 
+export interface MixedScopeFixture {
+	sessionId: number;
+	deviceId: string;
+	authorizedScopeId: string;
+	unauthorizedScopeId: string;
+	personalId: number;
+	authorizedId: number;
+	unauthorizedId: number;
+	visibleIds: number[];
+	allIds: number[];
+	visibleTitles: string[];
+	unauthorizedTitle: string;
+	query: string;
+}
+
+/**
+ * Seed one mixed-domain dataset for scope-leak regression tests.
+ *
+ * The local-default "personal" row and the authorized work row must be visible;
+ * the OSS row is in an active coordinator scope without local membership and
+ * must never appear through read/export surfaces.
+ */
+export function seedMixedScopeFixture(db: Database, deviceId = "local"): MixedScopeFixture {
+	const now = "2026-04-01T00:00:00.000Z";
+	const authorizedScopeId = "fixture-work-authorized";
+	const unauthorizedScopeId = "fixture-oss-hidden";
+	const query = "mixedscopeleak";
+	db.prepare(
+		"INSERT OR IGNORE INTO sync_device(device_id, public_key, fingerprint, created_at) VALUES (?, ?, ?, ?)",
+	).run(deviceId, "fixture-public-key", "fixture-fingerprint", now);
+	db.prepare(
+		`INSERT OR REPLACE INTO replication_scopes(
+			scope_id, label, kind, authority_type, coordinator_id, group_id,
+			membership_epoch, status, created_at, updated_at
+		 ) VALUES (?, ?, 'team', 'coordinator', 'fixture-coordinator', 'fixture-group', 0, 'active', ?, ?)`,
+	).run(authorizedScopeId, "Authorized work fixture", now, now);
+	db.prepare(
+		`INSERT OR REPLACE INTO replication_scopes(
+			scope_id, label, kind, authority_type, coordinator_id, group_id,
+			membership_epoch, status, created_at, updated_at
+		 ) VALUES (?, ?, 'team', 'coordinator', 'fixture-coordinator', 'fixture-group', 0, 'active', ?, ?)`,
+	).run(unauthorizedScopeId, "Hidden OSS fixture", now, now);
+	db.prepare(
+		`INSERT OR REPLACE INTO scope_memberships(
+			scope_id, device_id, role, status, membership_epoch,
+			coordinator_id, group_id, updated_at
+		 ) VALUES (?, ?, 'member', 'active', 0, 'fixture-coordinator', 'fixture-group', ?)`,
+	).run(authorizedScopeId, deviceId, now);
+
+	const session = db
+		.prepare(
+			`INSERT INTO sessions(started_at, cwd, project, user, tool_version, metadata_json, import_key)
+			 VALUES (?, '/tmp/mixed-domain-fixture', 'mixed-domain-fixture', 'test-user', 'test', '{}', 'fixture-session')`,
+		)
+		.run(now);
+	const sessionId = Number(session.lastInsertRowid);
+	const insertMemory = (input: {
+		title: string;
+		body: string;
+		kind: string;
+		createdAt: string;
+		scopeId: string;
+		importKey: string;
+	}) => {
+		const info = db
+			.prepare(
+				`INSERT INTO memory_items(
+					session_id, kind, title, body_text, confidence, tags_text, active,
+					created_at, updated_at, metadata_json, rev, visibility, scope_id, import_key
+				 ) VALUES (?, ?, ?, ?, 0.9, '', 1, ?, ?, '{}', 1, 'shared', ?, ?)`,
+			)
+			.run(
+				sessionId,
+				input.kind,
+				input.title,
+				input.body,
+				input.createdAt,
+				input.createdAt,
+				input.scopeId,
+				input.importKey,
+			);
+		return Number(info.lastInsertRowid);
+	};
+	const personalTitle = "Personal mixed-domain fixture memory";
+	const authorizedTitle = "Authorized work mixed-domain fixture memory";
+	const unauthorizedTitle = "Hidden OSS mixed-domain fixture memory";
+	const personalId = insertMemory({
+		title: personalTitle,
+		body: `${query} personal visible context`,
+		kind: "discovery",
+		createdAt: "2026-04-01T00:00:01.000Z",
+		scopeId: LOCAL_DEFAULT_SCOPE_ID,
+		importKey: "fixture-memory-personal",
+	});
+	const unauthorizedId = insertMemory({
+		title: unauthorizedTitle,
+		body: `${query} hidden oss context`,
+		kind: "feature",
+		createdAt: "2026-04-01T00:00:02.000Z",
+		scopeId: unauthorizedScopeId,
+		importKey: "fixture-memory-hidden-oss",
+	});
+	const authorizedId = insertMemory({
+		title: authorizedTitle,
+		body: `${query} authorized work context`,
+		kind: "decision",
+		createdAt: "2026-04-01T00:00:03.000Z",
+		scopeId: authorizedScopeId,
+		importKey: "fixture-memory-authorized-work",
+	});
+	return {
+		sessionId,
+		deviceId,
+		authorizedScopeId,
+		unauthorizedScopeId,
+		personalId,
+		authorizedId,
+		unauthorizedId,
+		visibleIds: [personalId, authorizedId],
+		allIds: [personalId, unauthorizedId, authorizedId],
+		visibleTitles: [personalTitle, authorizedTitle],
+		unauthorizedTitle,
+		query,
+	};
+}
+
 // Re-export for test convenience
 export { MemoryStore } from "./store.js";
diff --git a/packages/mcp-server/src/memory-access.test.ts b/packages/mcp-server/src/memory-access.test.ts
index ddae376a..3d6fb47e 100644
--- a/packages/mcp-server/src/memory-access.test.ts
+++ b/packages/mcp-server/src/memory-access.test.ts
@@ -4,7 +4,7 @@ import { join } from "node:path";
 import { MemoryStore } from "@codemem/core";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import { connect } from "../../core/src/db.js";
-import { initTestSchema } from "../../core/src/test-utils.js";
+import { initTestSchema, seedMixedScopeFixture } from "../../core/src/test-utils.js";
 import {
 	forgetMemoryForMcp,
 	getManyForMcp,
@@ -62,6 +62,19 @@ describe("MCP memory access scope guards", () => {
 		expect(getMemoryForMcp(store, authorizedId, { scope_id: "scope-b" })).toBe(null);
 	});
 
+	it("keeps mixed-domain unauthorized scope rows out of MCP direct reads", () => {
+		const fixture = seedMixedScopeFixture(store.db, store.deviceId);
+
+		expect(getMemoryForMcp(store, fixture.personalId)?.title).toBe(fixture.visibleTitles[0]);
+		expect(getMemoryForMcp(store, fixture.authorizedId)?.title).toBe(fixture.visibleTitles[1]);
+		expect(getMemoryForMcp(store, fixture.unauthorizedId)).toBe(null);
+		expect(
+			getManyForMcp(store, fixture.allIds)
+				.map((item) => item.id)
+				.sort((a, b) => a - b),
+		).toEqual([...fixture.visibleIds].sort((a, b) => a - b));
+	});
+
 	it("refuses to forget unauthorized or explicitly filtered-out memories", () => {
 		const authorizedId = insertScopedMemory(store, {
 			sessionId,
diff --git a/packages/viewer-server/src/index.test.ts b/packages/viewer-server/src/index.test.ts
index 5ac5d077..81b485d7 100644
--- a/packages/viewer-server/src/index.test.ts
+++ b/packages/viewer-server/src/index.test.ts
@@ -17,6 +17,7 @@ import {
 	insertTestSession,
 	loadPublicKey,
 	MemoryStore,
+	seedMixedScopeFixture,
 	startMaintenanceJob,
 	updateMaintenanceJob,
 	VERSION,
@@ -629,6 +630,47 @@ describe("viewer-server", () => {
 			}
 		});
 
+		it("keeps mixed-domain unauthorized scope rows out of viewer direct surfaces", async () => {
+			const { app, getStore, cleanup } = createTestApp();
+			try {
+				await app.request("/api/stats");
+				const store = getStore();
+				if (!store) throw new Error("store not initialized");
+				const fixture = seedMixedScopeFixture(store.db, store.deviceId);
+
+				const memoryRes = await app.request("/api/memory?limit=10");
+				expect(memoryRes.status).toBe(200);
+				const memory = (await memoryRes.json()) as {
+					items: Array<{ id: number; title: string }>;
+				};
+				expect(memory.items.map((item) => item.id)).toEqual(
+					expect.arrayContaining(fixture.visibleIds),
+				);
+				expect(memory.items.map((item) => item.id)).not.toContain(fixture.unauthorizedId);
+
+				const observationsRes = await app.request("/api/observations?limit=10");
+				expect(observationsRes.status).toBe(200);
+				const observations = (await observationsRes.json()) as {
+					items: Array<{ id: number; title: string }>;
+				};
+				expect(observations.items.map((item) => item.id)).toEqual(
+					expect.arrayContaining(fixture.visibleIds),
+				);
+				expect(observations.items.map((item) => item.title)).not.toContain(
+					fixture.unauthorizedTitle,
+				);
+
+				const packRes = await app.request(`/api/pack?context=${fixture.query}&limit=10`);
+				expect(packRes.status).toBe(200);
+				const pack = (await packRes.json()) as { item_ids: number[]; pack_text: string };
+				expect(pack.item_ids.some((id) => fixture.visibleIds.includes(id))).toBe(true);
+				expect(pack.item_ids).not.toContain(fixture.unauthorizedId);
+				expect(pack.pack_text).not.toContain(fixture.unauthorizedTitle);
+			} finally {
+				cleanup();
+			}
+		});
+
 		it("applies mine/theirs scope filters to observations", async () => {
 			const { app, getStore, cleanup } = createTestApp();
 			try {