diff --git a/apps/gateway/src/mcp/mcp.controller.ts b/apps/gateway/src/mcp/mcp.controller.ts
index 55ad75e..cfdbb3e 100644
--- a/apps/gateway/src/mcp/mcp.controller.ts
+++ b/apps/gateway/src/mcp/mcp.controller.ts
@@ -3,7 +3,11 @@ import { Logger } from '@nestjs/common';
 import { fromNodeHeaders } from 'better-auth/node';
 import type { Auth } from '@mosaicstack/auth';
 import type { NestFastifyApplication } from '@nestjs/platform-fastify';
-import type { McpService } from './mcp.service.js';
+import {
+  createMcpActorContext,
+  deriveMcpToolScopesForUser,
+  type McpService,
+} from './mcp.service.js';
 import { AUTH } from '../auth/auth.tokens.js';
 
 /**
@@ -67,14 +71,25 @@ async function handleMcpRequest(
     return;
   }
 
-  const userId = result.user.id;
+  const authUser = result.user as {
+    id: string;
+    role?: string | null;
+    tenantId?: string | null;
+    organizationId?: string | null;
+  };
+  const actor = createMcpActorContext({
+    userId: authUser.id,
+    role: authUser.role,
+    tenantId: authUser.tenantId ?? authUser.organizationId ?? undefined,
+    scopes: deriveMcpToolScopesForUser({ role: authUser.role }),
+  });
 
   // ─── Session routing ─────────────────────────────────────────────────────
   const sessionId = req.raw.headers['mcp-session-id'];
 
   if (typeof sessionId === 'string' && sessionId.length > 0) {
     // Existing session request
-    const transport = mcpService.getSession(sessionId);
+    const transport = mcpService.getSession(sessionId, actor);
     if (!transport) {
       logger.warn(`MCP session not found: ${sessionId}`);
       reply.raw.writeHead(404, { 'Content-Type': 'application/json' });
@@ -112,8 +127,10 @@ async function handleMcpRequest(
   }
 
   // Create new session and handle this initializing request
-  const { transport } = mcpService.createSession(userId);
-  logger.log(`New MCP session created for user ${userId}`);
+  const { transport } = mcpService.createSession(actor);
+  logger.log(
+    `New MCP session created for actor=${actor.userId} tenant=${actor.tenantId} correlation=${actor.correlationId}`,
+  );
 
   await transport.handleRequest(req.raw, reply.raw, body);
 }
diff --git a/apps/gateway/src/mcp/mcp.service.spec.ts b/apps/gateway/src/mcp/mcp.service.spec.ts
new file mode 100644
index 0000000..9842fee
--- /dev/null
+++ b/apps/gateway/src/mcp/mcp.service.spec.ts
@@ -0,0 +1,461 @@
+import { describe, expect, it, vi } from 'vitest';
+import type { z } from 'zod';
+import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import type { Brain } from '@mosaicstack/brain';
+import type { Memory } from '@mosaicstack/memory';
+import type { EmbeddingService } from '../memory/embedding.service.js';
+import type { CoordService } from '../coord/coord.service.js';
+import {
+  assertMcpToolAuthorized,
+  createMcpActorContext,
+  deriveMcpToolScopesForUser,
+  MCP_TOOL_SCOPES,
+  McpService,
+  type McpToolName,
+} from './mcp.service.js';
+
+type ToolResult = { content: Array<{ type: 'text'; text: string }> };
+type ToolHandler = (params: Record<string, unknown>) => Promise<ToolResult>;
+
+interface CapturedTool {
+  inputSchema: z.ZodType;
+  handler: ToolHandler;
+}
+
+function makeCapturingServer(): { server: McpServer; tools: Map<string, CapturedTool> } {
+  const tools = new Map<string, CapturedTool>();
+  const server = {
+    registerTool(name: string, config: { inputSchema: z.ZodType }, handler: ToolHandler): void {
+      tools.set(name, { inputSchema: config.inputSchema, handler });
+    },
+  };
+  return { server: server as unknown as McpServer, tools };
+}
+
+function makeService(opts?: {
+  projects?: Array<Record<string, unknown> & { id: string; ownerId?: string | null }>;
+  missions?: Array<
+    Record<string, unknown> & { id: string; projectId?: string | null; userId?: string | null }
+  >;
+  tasks?: Array<
+    Record<string, unknown> & {
+      id: string;
+      projectId?: string | null;
+      missionId?: string | null;
+      status?: string;
+    }
+  >;
+}) {
+  const projects = opts?.projects ?? [];
+  const missions = opts?.missions ?? [];
+  const tasks = opts?.tasks ?? [];
+  const brain = {
+    projects: {
+      findAll: vi.fn(async () => projects),
+      findById: vi.fn(async (id: string) => projects.find((project) => project.id === id) ?? null),
+    },
+    tasks: {
+      findAll: vi.fn(async () => tasks),
+      findById: vi.fn(async (id: string) => tasks.find((task) => task.id === id) ?? null),
+      findByProject: vi.fn(async (projectId: string) =>
+        tasks.filter((task) => task.projectId === projectId),
+      ),
+      findByMission: vi.fn(async (missionId: string) =>
+        tasks.filter((task) => task.missionId === missionId),
+      ),
+      findByStatus: vi.fn(async (status: string) => tasks.filter((task) => task.status === status)),
+      create: vi.fn(async (task: Record<string, unknown>) => ({ id: 'task-1', ...task })),
+      update: vi.fn(async (id: string, updates: Record<string, unknown>) => ({ id, ...updates })),
+    },
+    missions: {
+      findAll: vi.fn(async () => missions),
+      findById: vi.fn(async (id: string) => missions.find((mission) => mission.id === id) ?? null),
+      findByProject: vi.fn(async (projectId: string) =>
+        missions.filter((mission) => mission.projectId === projectId),
+      ),
+    },
+    conversations: {
+      findAll: vi.fn(async (userId: string) => [{ id: 'conversation-1', userId }]),
+    },
+  } as unknown as Brain;
+
+  const memory = {
+    insights: {
+      searchByEmbedding: vi.fn(async (userId: string) => [{ id: 'insight-1', userId }]),
+      create: vi.fn(async (insight: Record<string, unknown>) => ({ id: 'insight-2', ...insight })),
+    },
+    preferences: {
+      findByUser: vi.fn(async (userId: string) => [{ key: 'theme', userId }]),
+      findByUserAndCategory: vi.fn(async (userId: string, category: string) => [
+        { key: 'theme', userId, category },
+      ]),
+      upsert: vi.fn(async (preference: Record<string, unknown>) => ({
+        id: 'pref-1',
+        ...preference,
+      })),
+    },
+  } as unknown as Memory;
+
+  const embeddings = {
+    available: true,
+    embed: vi.fn(async () => [0.1, 0.2, 0.3]),
+  } as unknown as EmbeddingService;
+
+  const coord = {
+    getMissionStatus: vi.fn(async () => null),
+    listTasks: vi.fn(async () => []),
+    getTaskStatus: vi.fn(async () => null),
+  } as unknown as CoordService;
+
+  return {
+    service: new McpService(brain, memory, embeddings, coord),
+    brain: brain as unknown as {
+      conversations: { findAll: ReturnType<typeof vi.fn> };
+      tasks: {
+        create: ReturnType<typeof vi.fn>;
+        update: ReturnType<typeof vi.fn>;
+      };
+    },
+    memory: memory as unknown as {
+      insights: { searchByEmbedding: ReturnType<typeof vi.fn> };
+    },
+    coord: coord as unknown as {
+      listTasks: ReturnType<typeof vi.fn>;
+    },
+  };
+}
+
+function getTool(tools: Map<string, CapturedTool>, name: McpToolName): CapturedTool {
+  const tool = tools.get(name);
+  if (!tool) throw new Error(`Missing captured tool ${name}`);
+  return tool;
+}
+
+function makeMemberActor(userId = 'authenticated-user') {
+  return createMcpActorContext({
+    userId,
+    role: 'member',
+    scopes: deriveMcpToolScopesForUser({ role: 'member' }),
+  });
+}
+
+function makeAdminActor(userId = 'admin-user', tenantId?: string) {
+  return createMcpActorContext({
+    userId,
+    tenantId,
+    role: 'admin',
+    scopes: deriveMcpToolScopesForUser({ role: 'admin' }),
+  });
+}
+
+function makePlatformAdminActor(userId = 'platform-admin-user') {
+  return createMcpActorContext({
+    userId,
+    role: 'platform-admin',
+    scopes: deriveMcpToolScopesForUser({ role: 'platform-admin' }),
+  });
+}
+
+describe('MCP actor identity and tool scope enforcement', () => {
+  it('derives immutable actor, tenant, channel, correlation, and explicit tool scopes server-side', () => {
+    const actor = createMcpActorContext({
+      userId: ' user-authenticated ',
+      role: 'member',
+      scopes: deriveMcpToolScopesForUser({ role: 'member' }),
+    });
+
+    expect(actor.userId).toBe('user-authenticated');
+    expect(actor.tenantId).toBe('user:user-authenticated');
+    expect(actor.role).toBe('member');
+    expect(actor.channel).toBe('mcp');
+    expect(actor.correlationId).toMatch(/[0-9a-f-]{36}/i);
+    expect(actor.scopes.has(MCP_TOOL_SCOPES.memory_search)).toBe(true);
+    expect(actor.scopes.has(MCP_TOOL_SCOPES.coord_list_tasks)).toBe(false);
+    expect(
+      deriveMcpToolScopesForUser({ role: 'admin' }).has(MCP_TOOL_SCOPES.coord_list_tasks),
+    ).toBe(false);
+    expect(
+      deriveMcpToolScopesForUser({ role: 'platform-admin' }).has(MCP_TOOL_SCOPES.coord_list_tasks),
+    ).toBe(true);
+  });
+
+  it('fails closed when scopes are not supplied by the authenticated context policy', () => {
+    const actor = createMcpActorContext({ userId: 'user-authenticated' });
+
+    expect(actor.scopes.size).toBe(0);
+    expect(() => assertMcpToolAuthorized(actor, 'memory_search', { query: 'notes' })).toThrow(
+      'MCP tool scope denied: memory:insight:read',
+    );
+  });
+
+  it('fails closed when a tool caller supplies actor or tenant identity fields', () => {
+    const actor = createMcpActorContext({ userId: 'user-authenticated' });
+
+    expect(() =>
+      assertMcpToolAuthorized(actor, 'memory_search', {
+        userId: 'victim-user',
+        query: 'private data',
+      }),
+    ).toThrow('MCP caller-controlled identity field is forbidden: userId');
+
+    expect(() =>
+      assertMcpToolAuthorized(actor, 'coord_list_tasks', {
+        tenantId: 'victim-tenant',
+        projectPath: '/tmp/project',
+      }),
+    ).toThrow('MCP caller-controlled identity field is forbidden: tenantId');
+
+    expect(() =>
+      assertMcpToolAuthorized(actor, 'brain_create_task', {
+        title: 'forged org',
+        organizationId: 'victim-org',
+      }),
+    ).toThrow('MCP caller-controlled identity field is forbidden: organizationId');
+
+    expect(() =>
+      assertMcpToolAuthorized(actor, 'brain_update_task', {
+        title: 'forged team',
+        teamId: 'victim-team',
+      }),
+    ).toThrow('MCP caller-controlled identity field is forbidden: teamId');
+  });
+
+  it('fails closed when the server-derived actor lacks the required per-tool scope', () => {
+    const actor = createMcpActorContext({ userId: 'user-authenticated', scopes: [] });
+
+    expect(() => assertMcpToolAuthorized(actor, 'memory_search', { query: 'notes' })).toThrow(
+      'MCP tool scope denied: memory:insight:read',
+    );
+  });
+
+  it('removes caller-controlled userId from memory schemas and never queries victim memory', async () => {
+    const { service, memory } = makeService();
+    const { server, tools } = makeCapturingServer();
+    const actor = makeMemberActor('authenticated-user');
+
+    service.registerTools(server, actor);
+    const tool = getTool(tools, 'memory_search');
+
+    expect(tool.inputSchema.safeParse({ userId: 'victim-user', query: 'anything' }).success).toBe(
+      false,
+    );
+    await expect(tool.handler({ userId: 'victim-user', query: 'anything' })).rejects.toThrow(
+      'MCP caller-controlled identity field is forbidden: userId',
+    );
+    expect(memory.insights.searchByEmbedding).not.toHaveBeenCalled();
+
+    await tool.handler({ query: 'only my notes' });
+    expect(memory.insights.searchByEmbedding).toHaveBeenCalledWith(
+      'authenticated-user',
+      [0.1, 0.2, 0.3],
+      5,
+    );
+  });
+
+  it('binds conversation listing to the authenticated actor instead of a caller-supplied userId', async () => {
+    const { service, brain } = makeService();
+    const { server, tools } = makeCapturingServer();
+    const actor = makeMemberActor('authenticated-user');
+
+    service.registerTools(server, actor);
+    const tool = getTool(tools, 'brain_list_conversations');
+
+    expect(tool.inputSchema.safeParse({ userId: 'victim-user' }).success).toBe(false);
+    await expect(tool.handler({ userId: 'victim-user' })).rejects.toThrow(
+      'MCP caller-controlled identity field is forbidden: userId',
+    );
+    expect(brain.conversations.findAll).not.toHaveBeenCalled();
+
+    await tool.handler({});
+    expect(brain.conversations.findAll).toHaveBeenCalledWith('authenticated-user');
+  });
+
+  it('scopes brain project, mission, and task reads to the authenticated actor', async () => {
+    const { service } = makeService({
+      projects: [
+        { id: 'project-owned', ownerId: 'authenticated-user', name: 'owned' },
+        { id: 'project-victim', ownerId: 'victim-user', name: 'victim' },
+      ],
+      missions: [
+        { id: 'mission-owned', projectId: 'project-owned' },
+        { id: 'mission-victim', userId: 'victim-user', projectId: 'project-victim' },
+      ],
+      tasks: [
+        { id: 'task-owned-project', projectId: 'project-owned', status: 'not-started' },
+        { id: 'task-owned-mission', missionId: 'mission-owned', status: 'not-started' },
+        { id: 'task-victim-project', projectId: 'project-victim', status: 'not-started' },
+        { id: 'task-unowned', status: 'not-started' },
+      ],
+    });
+    const { server, tools } = makeCapturingServer();
+    const actor = makeMemberActor('authenticated-user');
+
+    service.registerTools(server, actor);
+
+    const projects = JSON.parse(
+      (await getTool(tools, 'brain_list_projects').handler({})).content[0]!.text,
+    );
+    expect(projects.map((project: { id: string }) => project.id)).toEqual(['project-owned']);
+
+    const missions = JSON.parse(
+      (await getTool(tools, 'brain_list_missions').handler({})).content[0]!.text,
+    );
+    expect(missions.map((mission: { id: string }) => mission.id)).toEqual(['mission-owned']);
+
+    const tasks = JSON.parse(
+      (await getTool(tools, 'brain_list_tasks').handler({})).content[0]!.text,
+    );
+    expect(tasks.map((task: { id: string }) => task.id)).toEqual([
+      'task-owned-project',
+      'task-owned-mission',
+    ]);
+  });
+
+  it('enforces tenant boundaries for tenant-admin brain project, mission, and task reads', async () => {
+    const { service } = makeService({
+      projects: [
+        {
+          id: 'project-tenant-a',
+          ownerId: 'other-user-a',
+          teamId: 'tenant-a',
+          name: 'same tenant',
+        },
+        {
+          id: 'project-tenant-b',
+          ownerId: 'other-user-b',
+          teamId: 'tenant-b',
+          name: 'other tenant',
+        },
+      ],
+      missions: [
+        { id: 'mission-tenant-a', tenantId: 'tenant-a', projectId: 'project-tenant-a' },
+        { id: 'mission-tenant-b', tenantId: 'tenant-b', projectId: 'project-tenant-b' },
+      ],
+      tasks: [
+        { id: 'task-tenant-a', projectId: 'project-tenant-a', status: 'not-started' },
+        { id: 'task-tenant-b', projectId: 'project-tenant-b', status: 'not-started' },
+      ],
+    });
+    const { server, tools } = makeCapturingServer();
+    const actor = makeAdminActor('tenant-admin-user', 'tenant-a');
+
+    service.registerTools(server, actor);
+
+    const projects = JSON.parse(
+      (await getTool(tools, 'brain_list_projects').handler({})).content[0]!.text,
+    );
+    expect(projects.map((project: { id: string }) => project.id)).toEqual(['project-tenant-a']);
+
+    const missions = JSON.parse(
+      (await getTool(tools, 'brain_list_missions').handler({})).content[0]!.text,
+    );
+    expect(missions.map((mission: { id: string }) => mission.id)).toEqual(['mission-tenant-a']);
+
+    const tasks = JSON.parse(
+      (await getTool(tools, 'brain_list_tasks').handler({})).content[0]!.text,
+    );
+    expect(tasks.map((task: { id: string }) => task.id)).toEqual(['task-tenant-a']);
+  });
+
+  it('denies tenant-admin task writes outside the authenticated tenant', async () => {
+    const { service, brain } = makeService({
+      projects: [
+        { id: 'project-tenant-a', ownerId: 'other-user-a', teamId: 'tenant-a' },
+        { id: 'project-tenant-b', ownerId: 'other-user-b', teamId: 'tenant-b' },
+      ],
+      missions: [
+        { id: 'mission-tenant-a', tenantId: 'tenant-a', projectId: 'project-tenant-a' },
+        { id: 'mission-tenant-b', tenantId: 'tenant-b', projectId: 'project-tenant-b' },
+      ],
+      tasks: [
+        { id: 'task-tenant-a', projectId: 'project-tenant-a', status: 'not-started' },
+        { id: 'task-tenant-b', projectId: 'project-tenant-b', status: 'not-started' },
+      ],
+    });
+    const { server, tools } = makeCapturingServer();
+    const actor = makeAdminActor('tenant-admin-user', 'tenant-a');
+
+    service.registerTools(server, actor);
+
+    await expect(
+      getTool(tools, 'brain_create_task').handler({
+        title: 'unscoped tenant write',
+      }),
+    ).rejects.toThrow('MCP task scope denied');
+    expect(brain.tasks.create).not.toHaveBeenCalled();
+
+    await expect(
+      getTool(tools, 'brain_create_task').handler({
+        title: 'cross-tenant write',
+        projectId: 'project-tenant-b',
+      }),
+    ).rejects.toThrow('MCP task project scope denied');
+    expect(brain.tasks.create).not.toHaveBeenCalled();
+
+    await expect(
+      getTool(tools, 'brain_update_task').handler({
+        id: 'task-tenant-a',
+        projectId: 'project-tenant-b',
+      }),
+    ).rejects.toThrow('MCP task project scope denied');
+    expect(brain.tasks.update).not.toHaveBeenCalled();
+
+    const updateResult = await getTool(tools, 'brain_update_task').handler({
+      id: 'task-tenant-b',
+      title: 'cross-tenant update',
+    });
+    expect(updateResult.content[0]!.text).toBe('Task not found: task-tenant-b');
+    expect(brain.tasks.update).not.toHaveBeenCalled();
+
+    await getTool(tools, 'brain_create_task').handler({
+      title: 'same-tenant write',
+      projectId: 'project-tenant-a',
+    });
+    expect(brain.tasks.create).toHaveBeenCalledWith(
+      expect.objectContaining({ projectId: 'project-tenant-a', title: 'same-tenant write' }),
+    );
+  });
+
+  it('keeps admin-only coordination tools on server-derived paths', async () => {
+    const { service, coord } = makeService();
+    const { server, tools } = makeCapturingServer();
+    const member = makeMemberActor('authenticated-user');
+    const tenantAdmin = makeAdminActor('admin-user');
+    const platformAdmin = makePlatformAdminActor('platform-admin-user');
+
+    service.registerTools(server, member);
+    const memberTool = getTool(tools, 'coord_list_tasks');
+    expect(memberTool.inputSchema.safeParse({ projectPath: '/tmp/victim' }).success).toBe(false);
+    await expect(memberTool.handler({})).rejects.toThrow('MCP tool scope denied: coord:read');
+
+    tools.clear();
+    service.registerTools(server, tenantAdmin);
+    const tenantAdminTool = getTool(tools, 'coord_list_tasks');
+    await expect(tenantAdminTool.handler({})).rejects.toThrow('MCP tool scope denied: coord:read');
+
+    tools.clear();
+    service.registerTools(server, platformAdmin);
+    const platformAdminTool = getTool(tools, 'coord_list_tasks');
+    await platformAdminTool.handler({ projectPath: '/tmp/victim' });
+    expect(coord.listTasks).toHaveBeenCalledWith(process.cwd());
+  });
+
+  it('does not attach a guessed or stale-scope MCP session to another authenticated context', async () => {
+    const { service } = makeService();
+    const owner = makeMemberActor('owner-user');
+    const attacker = makeMemberActor('attacker-user');
+    const admin = makeAdminActor('admin-user');
+    const downgradedAdmin = makeMemberActor('admin-user');
+
+    const { sessionId, transport } = service.createSession(owner);
+    const staleSession = service.createSession(admin);
+
+    expect(service.getSession(sessionId, owner)).toBe(transport);
+    expect(service.getSession(sessionId, attacker)).toBeNull();
+    expect(service.getSession(sessionId, owner)).toBe(transport);
+    expect(service.getSession(staleSession.sessionId, downgradedAdmin)).toBeNull();
+    expect(service.getSession(staleSession.sessionId, admin)).toBe(staleSession.transport);
+
+    await service.onModuleDestroy();
+  });
+});
diff --git a/apps/gateway/src/mcp/mcp.service.ts b/apps/gateway/src/mcp/mcp.service.ts
index c32dfc0..e5fb6b9 100644
--- a/apps/gateway/src/mcp/mcp.service.ts
+++ b/apps/gateway/src/mcp/mcp.service.ts
@@ -10,11 +10,216 @@ import { MEMORY } from '../memory/memory.tokens.js';
 import { EmbeddingService } from '../memory/embedding.service.js';
 import { CoordService } from '../coord/coord.service.js';
 
+export const MCP_CALLER_IDENTITY_FIELDS = [
+  'actorId',
+  'actor',
+  'authenticatedUserId',
+  'channel',
+  'organizationId',
+  'ownerId',
+  'sessionUserId',
+  'teamId',
+  'tenant',
+  'tenantId',
+  'user',
+  'userId',
+] as const;
+
+type McpCallerIdentityField = (typeof MCP_CALLER_IDENTITY_FIELDS)[number];
+
+export const MCP_TOOL_SCOPES = {
+  brain_list_projects: 'brain:project:read',
+  brain_get_project: 'brain:project:read',
+  brain_list_tasks: 'brain:task:read',
+  brain_create_task: 'brain:task:write',
+  brain_update_task: 'brain:task:write',
+  brain_list_missions: 'brain:mission:read',
+  brain_list_conversations: 'brain:conversation:read',
+  memory_search: 'memory:insight:read',
+  memory_get_preferences: 'memory:preference:read',
+  memory_save_preference: 'memory:preference:write',
+  memory_save_insight: 'memory:insight:write',
+  coord_mission_status: 'coord:read',
+  coord_list_tasks: 'coord:read',
+  coord_task_detail: 'coord:read',
+} as const;
+
+export type McpToolName = keyof typeof MCP_TOOL_SCOPES;
+export type McpToolScope = (typeof MCP_TOOL_SCOPES)[McpToolName];
+
+export interface McpActorContext {
+  userId: string;
+  tenantId: string;
+  role: string;
+  channel: 'mcp';
+  correlationId: string;
+  scopes: ReadonlySet<McpToolScope>;
+}
+
 interface SessionEntry {
   server: McpServer;
   transport: StreamableHTTPServerTransport;
   createdAt: Date;
+  actor: McpActorContext;
+}
+
+const GLOBAL_ADMIN_MCP_SCOPES = new Set<McpToolScope>(Object.values(MCP_TOOL_SCOPES));
+const TENANT_ADMIN_MCP_SCOPES = new Set<McpToolScope>([
+  MCP_TOOL_SCOPES.brain_list_projects,
+  MCP_TOOL_SCOPES.brain_get_project,
+  MCP_TOOL_SCOPES.brain_list_tasks,
+  MCP_TOOL_SCOPES.brain_create_task,
+  MCP_TOOL_SCOPES.brain_update_task,
+  MCP_TOOL_SCOPES.brain_list_missions,
+  MCP_TOOL_SCOPES.brain_list_conversations,
+  MCP_TOOL_SCOPES.memory_search,
+  MCP_TOOL_SCOPES.memory_get_preferences,
+  MCP_TOOL_SCOPES.memory_save_preference,
+  MCP_TOOL_SCOPES.memory_save_insight,
+]);
+const MEMBER_MCP_SCOPES = new Set<McpToolScope>([
+  MCP_TOOL_SCOPES.brain_list_projects,
+  MCP_TOOL_SCOPES.brain_get_project,
+  MCP_TOOL_SCOPES.brain_list_tasks,
+  MCP_TOOL_SCOPES.brain_list_missions,
+  MCP_TOOL_SCOPES.brain_list_conversations,
+  MCP_TOOL_SCOPES.memory_search,
+  MCP_TOOL_SCOPES.memory_get_preferences,
+  MCP_TOOL_SCOPES.memory_save_preference,
+  MCP_TOOL_SCOPES.memory_save_insight,
+]);
+
+export function deriveMcpToolScopesForUser(input: {
+  role?: string | null;
+}): ReadonlySet<McpToolScope> {
+  if (input.role === 'platform-admin' || input.role === 'super-admin') {
+    return new Set(GLOBAL_ADMIN_MCP_SCOPES);
+  }
+  if (input.role === 'admin') {
+    return new Set(TENANT_ADMIN_MCP_SCOPES);
+  }
+  return new Set(MEMBER_MCP_SCOPES);
+}
+
+export function createMcpActorContext(input: {
   userId: string;
+  tenantId?: string;
+  role?: string | null;
+  scopes?: Iterable<McpToolScope>;
+  correlationId?: string;
+}): McpActorContext {
+  const userId = input.userId.trim();
+  if (userId.length === 0) {
+    throw new Error('MCP authenticated user is required');
+  }
+
+  return {
+    userId,
+    tenantId: input.tenantId?.trim() || `user:${userId}`,
+    role: input.role ?? 'member',
+    channel: 'mcp',
+    correlationId: input.correlationId ?? randomUUID(),
+    scopes: new Set(input.scopes ?? []),
+  };
+}
+
+export function assertNoCallerControlledIdentity(params: unknown): void {
+  if (params === null || typeof params !== 'object') return;
+
+  const keys = new Set(Object.keys(params));
+  const forbidden = MCP_CALLER_IDENTITY_FIELDS.find((field: McpCallerIdentityField) =>
+    keys.has(field),
+  );
+  if (forbidden) {
+    throw new Error(`MCP caller-controlled identity field is forbidden: ${forbidden}`);
+  }
+}
+
+export function assertMcpToolAuthorized(
+  actor: McpActorContext,
+  toolName: McpToolName,
+  params: unknown,
+): void {
+  assertNoCallerControlledIdentity(params);
+  const requiredScope = MCP_TOOL_SCOPES[toolName];
+  if (!actor.scopes.has(requiredScope)) {
+    throw new Error(`MCP tool scope denied: ${requiredScope}`);
+  }
+}
+
+function strictObject<T extends z.ZodRawShape>(shape: T): z.ZodObject<T> {
+  return z.object(shape).strict();
+}
+
+type TenantScopedLike = {
+  tenantId?: string | null;
+  organizationId?: string | null;
+  teamId?: string | null;
+};
+type ProjectLike = TenantScopedLike & { id: string; ownerId?: string | null };
+type MissionLike = TenantScopedLike & {
+  id: string;
+  projectId?: string | null;
+  userId?: string | null;
+};
+type TaskLike = TenantScopedLike & {
+  projectId?: string | null;
+  missionId?: string | null;
+  userId?: string | null;
+};
+
+function isGlobalAdminActor(actor: McpActorContext): boolean {
+  return actor.role === 'platform-admin' || actor.role === 'super-admin';
+}
+
+function isTenantAdminActor(actor: McpActorContext): boolean {
+  return actor.role === 'admin';
+}
+
+function matchesTenant(actor: McpActorContext, record: TenantScopedLike): boolean {
+  return (
+    record.tenantId === actor.tenantId ||
+    record.organizationId === actor.tenantId ||
+    record.teamId === actor.tenantId
+  );
+}
+
+function filterProjectsForActor<T extends ProjectLike>(actor: McpActorContext, projects: T[]): T[] {
+  if (isGlobalAdminActor(actor)) return projects;
+  return projects.filter(
+    (project) =>
+      project.ownerId === actor.userId ||
+      (isTenantAdminActor(actor) && matchesTenant(actor, project)),
+  );
+}
+
+function filterMissionsByDirectActorScope<T extends MissionLike>(
+  actor: McpActorContext,
+  missions: T[],
+): T[] {
+  if (isGlobalAdminActor(actor)) return missions;
+  return missions.filter(
+    (mission) =>
+      mission.userId === actor.userId ||
+      (isTenantAdminActor(actor) && matchesTenant(actor, mission)),
+  );
+}
+
+function scopesEqual(left: ReadonlySet<McpToolScope>, right: ReadonlySet<McpToolScope>): boolean {
+  if (left.size !== right.size) return false;
+  for (const scope of left) {
+    if (!right.has(scope)) return false;
+  }
+  return true;
+}
+
+function sameActorAuthorization(stored: McpActorContext, current: McpActorContext): boolean {
+  return (
+    stored.userId === current.userId &&
+    stored.tenantId === current.tenantId &&
+    stored.role === current.role &&
+    scopesEqual(stored.scopes, current.scopes)
+  );
 }
 
 @Injectable()
@@ -33,13 +238,18 @@ export class McpService implements OnModuleDestroy {
    * Creates a new MCP session with its own server + transport pair.
    * Returns the transport for use by the controller.
    */
-  createSession(userId: string): { sessionId: string; transport: StreamableHTTPServerTransport } {
+  createSession(actor: McpActorContext): {
+    sessionId: string;
+    transport: StreamableHTTPServerTransport;
+  } {
     const sessionId = randomUUID();
 
     const transport = new StreamableHTTPServerTransport({
       sessionIdGenerator: () => sessionId,
       onsessioninitialized: (id) => {
-        this.logger.log(`MCP session initialized: ${id} for user ${userId}`);
+        this.logger.log(
+          `MCP session initialized: ${id} for actor=${actor.userId} tenant=${actor.tenantId} correlation=${actor.correlationId}`,
+        );
       },
     });
 
@@ -48,7 +258,7 @@ export class McpService implements OnModuleDestroy {
       { capabilities: { tools: {} } },
     );
 
-    this.registerTools(server, userId);
+    this.registerTools(server, actor);
 
     transport.onclose = () => {
       this.logger.log(`MCP session closed: ${sessionId}`);
@@ -61,31 +271,126 @@ export class McpService implements OnModuleDestroy {
       );
     });
 
-    this.sessions.set(sessionId, { server, transport, createdAt: new Date(), userId });
+    this.sessions.set(sessionId, { server, transport, createdAt: new Date(), actor });
     return { sessionId, transport };
   }
 
   /**
-   * Returns the transport for an existing session, or null if not found.
+   * Returns the transport for an existing session only when it belongs to the
+   * currently authenticated MCP actor. Guessed or cross-tenant session IDs grant
+   * no authority.
    */
-  getSession(sessionId: string): StreamableHTTPServerTransport | null {
-    return this.sessions.get(sessionId)?.transport ?? null;
+  getSession(sessionId: string, actor: McpActorContext): StreamableHTTPServerTransport | null {
+    const entry = this.sessions.get(sessionId);
+    if (!entry) return null;
+    if (!sameActorAuthorization(entry.actor, actor)) {
+      this.logger.warn(
+        `MCP session actor or scope mismatch: session=${sessionId} actor=${actor.userId} tenant=${actor.tenantId} role=${actor.role}`,
+      );
+      return null;
+    }
+    return entry.transport;
+  }
+
+  private async isProjectAuthorized(actor: McpActorContext, projectId: string): Promise<boolean> {
+    if (isGlobalAdminActor(actor)) return true;
+    const project = (await this.brain.projects.findById(projectId)) as ProjectLike | undefined;
+    return project ? filterProjectsForActor(actor, [project]).length === 1 : false;
+  }
+
+  private async filterMissionsForActor<T extends MissionLike>(
+    actor: McpActorContext,
+    missions: T[],
+  ): Promise<T[]> {
+    if (isGlobalAdminActor(actor)) return missions;
+
+    const projects = (await this.brain.projects.findAll()) as ProjectLike[];
+    const projectIds = new Set(
+      filterProjectsForActor(actor, projects).map((project) => project.id),
+    );
+
+    return missions.filter(
+      (mission) =>
+        filterMissionsByDirectActorScope(actor, [mission]).length === 1 ||
+        (typeof mission.projectId === 'string' && projectIds.has(mission.projectId)),
+    );
+  }
+
+  private async isMissionAuthorized(actor: McpActorContext, missionId: string): Promise<boolean> {
+    if (isGlobalAdminActor(actor)) return true;
+    const mission = (await this.brain.missions.findById(missionId)) as MissionLike | undefined;
+    if (!mission) return false;
+    return (await this.filterMissionsForActor(actor, [mission])).length === 1;
+  }
+
+  private async assertTaskReferencesAuthorized(
+    actor: McpActorContext,
+    refs: { projectId?: string | null; missionId?: string | null },
+  ): Promise<void> {
+    if (refs.projectId && !(await this.isProjectAuthorized(actor, refs.projectId))) {
+      throw new Error('MCP task project scope denied');
+    }
+    if (refs.missionId && !(await this.isMissionAuthorized(actor, refs.missionId))) {
+      throw new Error('MCP task mission scope denied');
+    }
+  }
+
+  private async assertTaskCreateScopeAuthorized(
+    actor: McpActorContext,
+    refs: { projectId?: string | null; missionId?: string | null },
+  ): Promise<void> {
+    if (!isGlobalAdminActor(actor) && !refs.projectId && !refs.missionId) {
+      throw new Error('MCP task scope denied');
+    }
+    await this.assertTaskReferencesAuthorized(actor, refs);
+  }
+
+  private async filterTasksForActor<T extends TaskLike>(
+    actor: McpActorContext,
+    tasks: T[],
+  ): Promise<T[]> {
+    if (isGlobalAdminActor(actor)) return tasks;
+
+    const [projects, missions] = await Promise.all([
+      this.brain.projects.findAll(),
+      this.brain.missions.findAll(),
+    ]);
+    const projectIds = new Set(
+      filterProjectsForActor(actor, projects as ProjectLike[]).map((project) => project.id),
+    );
+    const missionIds = new Set(
+      (await this.filterMissionsForActor(actor, missions as MissionLike[])).map(
+        (mission) => mission.id,
+      ),
+    );
+
+    return tasks.filter(
+      (task) =>
+        task.userId === actor.userId ||
+        (isTenantAdminActor(actor) && matchesTenant(actor, task)) ||
+        (typeof task.projectId === 'string' && projectIds.has(task.projectId)) ||
+        (typeof task.missionId === 'string' && missionIds.has(task.missionId)),
+    );
   }
 
   /**
    * Registers all platform tools on the given McpServer instance.
    */
-  private registerTools(server: McpServer, _userId: string): void {
+  registerTools(server: McpServer, actor: McpActorContext): void {
     // ─── Brain: Project tools ────────────────────────────────────────────
 
     server.registerTool(
       'brain_list_projects',
       {
         description: 'List all projects in the brain.',
-        inputSchema: z.object({}),
+        inputSchema: strictObject({}),
       },
-      async () => {
-        const projects = await this.brain.projects.findAll();
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'brain_list_projects', params);
+        const projects = filterProjectsForActor(
+          actor,
+          (await this.brain.projects.findAll()) as ProjectLike[],
+        );
         return {
           content: [{ type: 'text' as const, text: JSON.stringify(projects, null, 2) }],
         };
@@ -96,17 +401,21 @@ export class McpService implements OnModuleDestroy {
       'brain_get_project',
       {
         description: 'Get a project by ID.',
-        inputSchema: z.object({
+        inputSchema: strictObject({
           id: z.string().describe('Project ID (UUID)'),
         }),
       },
-      async ({ id }) => {
-        const project = await this.brain.projects.findById(id);
+      async ({ id, ...params }) => {
+        assertMcpToolAuthorized(actor, 'brain_get_project', params);
+        const project = (await this.brain.projects.findById(id)) as ProjectLike | undefined;
+        const authorizedProject = project ? filterProjectsForActor(actor, [project])[0] : undefined;
         return {
           content: [
             {
               type: 'text' as const,
-              text: project ? JSON.stringify(project, null, 2) : `Project not found: ${id}`,
+              text: authorizedProject
+                ? JSON.stringify(authorizedProject, null, 2)
+                : `Project not found: ${id}`,
             },
           ],
         };
@@ -119,20 +428,23 @@ export class McpService implements OnModuleDestroy {
       'brain_list_tasks',
       {
         description: 'List tasks, optionally filtered by project, mission, or status.',
-        inputSchema: z.object({
+        inputSchema: strictObject({
           projectId: z.string().optional().describe('Filter by project ID'),
           missionId: z.string().optional().describe('Filter by mission ID'),
           status: z.string().optional().describe('Filter by status'),
         }),
       },
-      async ({ projectId, missionId, status }) => {
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'brain_list_tasks', params);
+        const { projectId, missionId, status } = params;
         type TaskStatus = 'not-started' | 'in-progress' | 'blocked' | 'done' | 'cancelled';
         let tasks;
         if (projectId) tasks = await this.brain.tasks.findByProject(projectId);
         else if (missionId) tasks = await this.brain.tasks.findByMission(missionId);
         else if (status) tasks = await this.brain.tasks.findByStatus(status as TaskStatus);
         else tasks = await this.brain.tasks.findAll();
-        return { content: [{ type: 'text' as const, text: JSON.stringify(tasks, null, 2) }] };
+        const scopedTasks = await this.filterTasksForActor(actor, tasks as TaskLike[]);
+        return { content: [{ type: 'text' as const, text: JSON.stringify(scopedTasks, null, 2) }] };
       },
     );
 
@@ -140,7 +452,7 @@ export class McpService implements OnModuleDestroy {
       'brain_create_task',
       {
         description: 'Create a new task in the brain.',
-        inputSchema: z.object({
+        inputSchema: strictObject({
           title: z.string().describe('Task title'),
           description: z.string().optional().describe('Task description'),
           projectId: z.string().optional().describe('Project ID'),
@@ -149,6 +461,8 @@ export class McpService implements OnModuleDestroy {
         }),
       },
       async (params) => {
+        assertMcpToolAuthorized(actor, 'brain_create_task', params);
+        await this.assertTaskCreateScopeAuthorized(actor, params);
         type Priority = 'low' | 'medium' | 'high' | 'critical';
         const task = await this.brain.tasks.create({
           ...params,
@@ -162,7 +476,7 @@ export class McpService implements OnModuleDestroy {
       'brain_update_task',
       {
         description: 'Update an existing task.',
-        inputSchema: z.object({
+        inputSchema: strictObject({
           id: z.string().describe('Task ID'),
           title: z.string().optional(),
           description: z.string().optional(),
@@ -171,9 +485,17 @@ export class McpService implements OnModuleDestroy {
             .optional()
             .describe('not-started, in-progress, blocked, done, cancelled'),
           priority: z.string().optional(),
+          projectId: z.string().optional().describe('Project ID'),
+          missionId: z.string().optional().describe('Mission ID'),
         }),
       },
       async ({ id, ...updates }) => {
+        assertMcpToolAuthorized(actor, 'brain_update_task', updates);
+        const existing = (await this.brain.tasks.findById(id)) as TaskLike | undefined;
+        if (!existing || (await this.filterTasksForActor(actor, [existing])).length === 0) {
+          return { content: [{ type: 'text' as const, text: `Task not found: ${id}` }] };
+        }
+        await this.assertTaskReferencesAuthorized(actor, updates);
         type TaskStatus = 'not-started' | 'in-progress' | 'blocked' | 'done' | 'cancelled';
         type Priority = 'low' | 'medium' | 'high' | 'critical';
         const task = await this.brain.tasks.update(id, {
@@ -198,14 +520,19 @@ export class McpService implements OnModuleDestroy {
       'brain_list_missions',
       {
         description: 'List all missions, optionally filtered by project.',
-        inputSchema: z.object({
+        inputSchema: strictObject({
           projectId: z.string().optional().describe('Filter by project ID'),
         }),
       },
-      async ({ projectId }) => {
-        const missions = projectId
-          ? await this.brain.missions.findByProject(projectId)
-          : await this.brain.missions.findAll();
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'brain_list_missions', params);
+        const { projectId } = params;
+        const missions = await this.filterMissionsForActor(
+          actor,
+          (projectId
+            ? await this.brain.missions.findByProject(projectId)
+            : await this.brain.missions.findAll()) as MissionLike[],
+        );
         return { content: [{ type: 'text' as const, text: JSON.stringify(missions, null, 2) }] };
       },
     );
@@ -213,13 +540,12 @@ export class McpService implements OnModuleDestroy {
     server.registerTool(
       'brain_list_conversations',
       {
-        description: 'List conversations for a user.',
-        inputSchema: z.object({
-          userId: z.string().describe('User ID'),
-        }),
+        description: 'List conversations for the authenticated MCP actor.',
+        inputSchema: strictObject({}),
       },
-      async ({ userId }) => {
-        const conversations = await this.brain.conversations.findAll(userId);
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'brain_list_conversations', params);
+        const conversations = await this.brain.conversations.findAll(actor.userId);
         return {
           content: [{ type: 'text' as const, text: JSON.stringify(conversations, null, 2) }],
         };
@@ -232,14 +558,15 @@ export class McpService implements OnModuleDestroy {
       'memory_search',
       {
         description:
-          'Search across stored insights and knowledge using natural language. Returns semantically similar results.',
-        inputSchema: z.object({
-          userId: z.string().describe('User ID to search memory for'),
+          'Search stored insights and knowledge for the authenticated MCP actor using natural language.',
+        inputSchema: strictObject({
           query: z.string().describe('Natural language search query'),
           limit: z.number().optional().describe('Max results (default 5)'),
         }),
       },
-      async ({ userId, query, limit }) => {
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'memory_search', params);
+        const { query, limit } = params;
         if (!this.embeddings.available) {
           return {
             content: [
@@ -251,7 +578,11 @@ export class McpService implements OnModuleDestroy {
           };
         }
         const embedding = await this.embeddings.embed(query);
-        const results = await this.memory.insights.searchByEmbedding(userId, embedding, limit ?? 5);
+        const results = await this.memory.insights.searchByEmbedding(
+          actor.userId,
+          embedding,
+          limit ?? 5,
+        );
         return { content: [{ type: 'text' as const, text: JSON.stringify(results, null, 2) }] };
       },
     );
@@ -259,20 +590,21 @@ export class McpService implements OnModuleDestroy {
     server.registerTool(
       'memory_get_preferences',
       {
-        description: 'Retrieve stored preferences for a user.',
-        inputSchema: z.object({
-          userId: z.string().describe('User ID'),
+        description: 'Retrieve stored preferences for the authenticated MCP actor.',
+        inputSchema: strictObject({
           category: z
             .string()
             .optional()
             .describe('Filter by category: communication, coding, workflow, appearance, general'),
         }),
       },
-      async ({ userId, category }) => {
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'memory_get_preferences', params);
+        const { category } = params;
         type Cat = 'communication' | 'coding' | 'workflow' | 'appearance' | 'general';
         const prefs = category
-          ? await this.memory.preferences.findByUserAndCategory(userId, category as Cat)
-          : await this.memory.preferences.findByUser(userId);
+          ? await this.memory.preferences.findByUserAndCategory(actor.userId, category as Cat)
+          : await this.memory.preferences.findByUser(actor.userId);
         return { content: [{ type: 'text' as const, text: JSON.stringify(prefs, null, 2) }] };
       },
     );
@@ -281,9 +613,8 @@ export class McpService implements OnModuleDestroy {
       'memory_save_preference',
       {
         description:
-          'Store a learned user preference (e.g., "prefers tables over paragraphs", "timezone: America/Chicago").',
-        inputSchema: z.object({
-          userId: z.string().describe('User ID'),
+          'Store a learned preference for the authenticated MCP actor (e.g., "prefers tables over paragraphs").',
+        inputSchema: strictObject({
           key: z.string().describe('Preference key'),
           value: z.string().describe('Preference value (JSON string)'),
           category: z
@@ -292,7 +623,9 @@ export class McpService implements OnModuleDestroy {
             .describe('Category: communication, coding, workflow, appearance, general'),
         }),
       },
-      async ({ userId, key, value, category }) => {
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'memory_save_preference', params);
+        const { key, value, category } = params;
         type Cat = 'communication' | 'coding' | 'workflow' | 'appearance' | 'general';
         let parsedValue: unknown;
         try {
@@ -301,7 +634,7 @@ export class McpService implements OnModuleDestroy {
           parsedValue = value;
         }
         const pref = await this.memory.preferences.upsert({
-          userId,
+          userId: actor.userId,
           key,
           value: parsedValue,
           category: (category as Cat) ?? 'general',
@@ -315,9 +648,8 @@ export class McpService implements OnModuleDestroy {
       'memory_save_insight',
       {
         description:
-          'Store a learned insight, decision, or knowledge extracted from the current interaction.',
-        inputSchema: z.object({
-          userId: z.string().describe('User ID'),
+          'Store a learned insight, decision, or knowledge for the authenticated MCP actor.',
+        inputSchema: strictObject({
           content: z.string().describe('The insight or knowledge to store'),
           category: z
             .string()
@@ -325,11 +657,13 @@ export class McpService implements OnModuleDestroy {
             .describe('Category: decision, learning, preference, fact, pattern, general'),
         }),
       },
-      async ({ userId, content, category }) => {
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'memory_save_insight', params);
+        const { content, category } = params;
         type Cat = 'decision' | 'learning' | 'preference' | 'fact' | 'pattern' | 'general';
         const embedding = this.embeddings.available ? await this.embeddings.embed(content) : null;
         const insight = await this.memory.insights.create({
-          userId,
+          userId: actor.userId,
           content,
           embedding,
           source: 'agent',
@@ -346,16 +680,11 @@ export class McpService implements OnModuleDestroy {
       {
         description:
           'Get the current orchestration mission status including milestones, tasks, and active session.',
-        inputSchema: z.object({
-          projectPath: z
-            .string()
-            .optional()
-            .describe('Project path. Defaults to gateway working directory.'),
-        }),
+        inputSchema: strictObject({}),
       },
-      async ({ projectPath }) => {
-        const resolvedPath = projectPath ?? process.cwd();
-        const status = await this.coordService.getMissionStatus(resolvedPath);
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'coord_mission_status', params);
+        const status = await this.coordService.getMissionStatus(process.cwd());
         return {
           content: [
             {
@@ -371,16 +700,11 @@ export class McpService implements OnModuleDestroy {
       'coord_list_tasks',
       {
         description: 'List all tasks from the orchestration TASKS.md file.',
-        inputSchema: z.object({
-          projectPath: z
-            .string()
-            .optional()
-            .describe('Project path. Defaults to gateway working directory.'),
-        }),
+        inputSchema: strictObject({}),
       },
-      async ({ projectPath }) => {
-        const resolvedPath = projectPath ?? process.cwd();
-        const tasks = await this.coordService.listTasks(resolvedPath);
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'coord_list_tasks', params);
+        const tasks = await this.coordService.listTasks(process.cwd());
         return { content: [{ type: 'text' as const, text: JSON.stringify(tasks, null, 2) }] };
       },
     );
@@ -389,17 +713,14 @@ export class McpService implements OnModuleDestroy {
       'coord_task_detail',
       {
         description: 'Get detailed status for a specific orchestration task.',
-        inputSchema: z.object({
+        inputSchema: strictObject({
           taskId: z.string().describe('Task ID (e.g. P2-005)'),
-          projectPath: z
-            .string()
-            .optional()
-            .describe('Project path. Defaults to gateway working directory.'),
         }),
       },
-      async ({ taskId, projectPath }) => {
-        const resolvedPath = projectPath ?? process.cwd();
-        const detail = await this.coordService.getTaskStatus(resolvedPath, taskId);
+      async (params) => {
+        assertMcpToolAuthorized(actor, 'coord_task_detail', params);
+        const { taskId } = params;
+        const detail = await this.coordService.getTaskStatus(process.cwd(), taskId);
         return {
           content: [
             {