diff --git a/apps/api/src/module-registry/module-access.service.spec.ts b/apps/api/src/module-registry/module-access.service.spec.ts
new file mode 100644
index 0000000..1568705
--- /dev/null
+++ b/apps/api/src/module-registry/module-access.service.spec.ts
@@ -0,0 +1,217 @@
+import { describe, expect, it, vi } from 'vitest';
+import { ModuleAccessService } from './module-access.service';
+
+/**
+ * ModuleAccessService.getAccessibleModuleIds — Single Source of Truth für
+ * Modulzugriff (D-01, PERM-04/05/06). Deckt die vollständige Behavior-
+ * Liste aus 15-01-PLAN.md, Task 2 ab.
+ *
+ * Hand-gerollter Prisma-Mock (Projektkonvention, siehe
+ * tender-matching.service.spec.ts) statt einer echten DB-Verbindung.
+ */
+
+function makeFakePrisma(opts: {
+  activations?: { moduleId: string }[];
+  directGrants?: { moduleId: string }[];
+  groupGrants?: { moduleId: string }[];
+} = {}) {
+  const activations = opts.activations ?? [];
+  const directGrants = opts.directGrants ?? [];
+  const groupGrants = opts.groupGrants ?? [];
+
+  const prisma = {
+    tenantModuleActivation: {
+      findMany: vi.fn(async ({ where }: any) => {
+        // filtert die simulierten Aktivierungen zusätzlich auf moduleId,
+        // falls die Query (D-02-Schnittmenge) einen moduleId-in-Filter trägt
+        const inFilter: string[] | undefined = where?.moduleId?.in;
+        if (!inFilter) return activations;
+        return activations.filter((a) => inFilter.includes(a.moduleId));
+      }),
+    },
+    moduleGrant: {
+      findMany: vi.fn(async ({ where }: any) => {
+        // Direkt-Grant-Query trägt `userId` direkt im where, die
+        // Gruppen-Grant-Query trägt `group: { memberships: { some: { userId } } } }`
+        if (where.group) return groupGrants;
+        return directGrants;
+      }),
+    },
+    module: {
+      findMany: vi.fn(async ({ where }: any) => {
+        const ids: string[] = where.id.in;
+        return ids.map((id) => ({ id, name: id }));
+      }),
+    },
+  };
+
+  return prisma;
+}
+
+describe('ModuleAccessService.getAccessibleModuleIds — ADMIN/SUPER_ADMIN-Kurzschluss (D-03)', () => {
+  it('ADMIN erhält alle mandantenweit aktiven moduleIds ohne jede Grant-Query', async () => {
+    const prisma = makeFakePrisma({
+      activations: [{ moduleId: 'mod-1' }, { moduleId: 'mod-2' }],
+    });
+    const service = new ModuleAccessService(prisma as any);
+
+    const result = await service.getAccessibleModuleIds('t1', 'admin-1', 'ADMIN');
+
+    expect(result).toEqual(new Set(['mod-1', 'mod-2']));
+    expect(prisma.moduleGrant.findMany).not.toHaveBeenCalled();
+  });
+
+  it('SUPER_ADMIN verhält sich identisch zu ADMIN', async () => {
+    const prisma = makeFakePrisma({
+      activations: [{ moduleId: 'mod-1' }],
+    });
+    const service = new ModuleAccessService(prisma as any);
+
+    const result = await service.getAccessibleModuleIds('t1', 'sa-1', 'SUPER_ADMIN');
+
+    expect(result).toEqual(new Set(['mod-1']));
+    expect(prisma.moduleGrant.findMany).not.toHaveBeenCalled();
+  });
+
+  it('idempotency: wiederholte Aufrufe für denselben ADMIN liefern dasselbe Ergebnis, ohne Datensätze anzulegen', async () => {
+    const prisma = makeFakePrisma({ activations: [{ moduleId: 'mod-1' }] });
+    const service = new ModuleAccessService(prisma as any);
+
+    const first = await service.getAccessibleModuleIds('t1', 'admin-1', 'ADMIN');
+    const second = await service.getAccessibleModuleIds('t1', 'admin-1', 'ADMIN');
+
+    expect(first).toEqual(second);
+  });
+
+  it('concurrency: der Bypass gilt nur für die tenantId aus dem JWT — ein Aufruf für t2 leitet keine Module von t1 ab', async () => {
+    const activationsByTenant: Record<string, { moduleId: string }[]> = {
+      t1: [{ moduleId: 'mod-tenant-1' }],
+      t2: [{ moduleId: 'mod-tenant-2' }],
+    };
+    const prisma = {
+      tenantModuleActivation: {
+        findMany: vi.fn(async ({ where }: any) => activationsByTenant[where.tenantId] ?? []),
+      },
+      moduleGrant: { findMany: vi.fn() },
+      module: { findMany: vi.fn() },
+    };
+    const service = new ModuleAccessService(prisma as any);
+
+    const resultT2 = await service.getAccessibleModuleIds('t2', 'admin-1', 'ADMIN');
+
+    expect(resultT2).toEqual(new Set(['mod-tenant-2']));
+  });
+});
+
+describe('ModuleAccessService.getAccessibleModuleIds — USER (Grant-Auflösung, D-02)', () => {
+  it('empty: USER ohne Grants erhält ein leeres Set', async () => {
+    const prisma = makeFakePrisma({});
+    const service = new ModuleAccessService(prisma as any);
+
+    const result = await service.getAccessibleModuleIds('t1', 'user-1', 'USER');
+
+    expect(result).toEqual(new Set());
+  });
+
+  it('USER mit Direkt-Grant auf ein aktives Modul: Set enthält genau diese moduleId', async () => {
+    const prisma = makeFakePrisma({
+      activations: [{ moduleId: 'mod-1' }],
+      directGrants: [{ moduleId: 'mod-1' }],
+    });
+    const service = new ModuleAccessService(prisma as any);
+
+    const result = await service.getAccessibleModuleIds('t1', 'user-1', 'USER');
+
+    expect(result).toEqual(new Set(['mod-1']));
+  });
+
+  it('USER mit Grant über eine Gruppe, in der er Mitglied ist: Set enthält diese moduleId', async () => {
+    const prisma = makeFakePrisma({
+      activations: [{ moduleId: 'mod-1' }],
+      groupGrants: [{ moduleId: 'mod-1' }],
+    });
+    const service = new ModuleAccessService(prisma as any);
+
+    const result = await service.getAccessibleModuleIds('t1', 'user-1', 'USER');
+
+    expect(result).toEqual(new Set(['mod-1']));
+  });
+
+  it('adjacency: USER mit Direkt-Grant UND Gruppen-Grant auf dasselbe Modul — die moduleId erscheint genau einmal', async () => {
+    const prisma = makeFakePrisma({
+      activations: [{ moduleId: 'mod-1' }],
+      directGrants: [{ moduleId: 'mod-1' }],
+      groupGrants: [{ moduleId: 'mod-1' }],
+    });
+    const service = new ModuleAccessService(prisma as any);
+
+    const result = await service.getAccessibleModuleIds('t1', 'user-1', 'USER');
+
+    expect(result.size).toBe(1);
+    expect(result).toEqual(new Set(['mod-1']));
+  });
+
+  it('adjacency/D-02: ein Grant auf ein mandantenweit deaktiviertes Modul gewährt KEINEN Zugriff', async () => {
+    const prisma = makeFakePrisma({
+      activations: [], // mod-1 ist NICHT (mehr) aktiv
+      directGrants: [{ moduleId: 'mod-1' }],
+    });
+    const service = new ModuleAccessService(prisma as any);
+
+    const result = await service.getAccessibleModuleIds('t1', 'user-1', 'USER');
+
+    expect(result).toEqual(new Set());
+  });
+
+  it('adjacency: eine mandantenweite Aktivierung ohne Grant ergibt ebenfalls keinen Zugriff', async () => {
+    const prisma = makeFakePrisma({
+      activations: [{ moduleId: 'mod-1' }],
+      // kein Direkt- oder Gruppen-Grant
+    });
+    const service = new ModuleAccessService(prisma as any);
+
+    const result = await service.getAccessibleModuleIds('t1', 'user-1', 'USER');
+
+    expect(result).toEqual(new Set());
+  });
+
+  it('idempotency: getAccessibleModuleIds ist rein lesend — zwei identische Aufrufe schreiben keinen Datensatz und liefern dasselbe Ergebnis', async () => {
+    const prisma = makeFakePrisma({
+      activations: [{ moduleId: 'mod-1' }],
+      directGrants: [{ moduleId: 'mod-1' }],
+    });
+    const service = new ModuleAccessService(prisma as any);
+
+    const first = await service.getAccessibleModuleIds('t1', 'user-1', 'USER');
+    const second = await service.getAccessibleModuleIds('t1', 'user-1', 'USER');
+
+    expect(first).toEqual(second);
+    expect(prisma.moduleGrant.findMany).toHaveBeenCalledTimes(4); // 2x (direct+group) je Aufruf
+  });
+});
+
+describe('ModuleAccessService.findAccessibleModules — ordering (PERM-04)', () => {
+  it('sortiert die zugänglichen Module deterministisch nach Namen aufsteigend', async () => {
+    const prisma = makeFakePrisma({
+      activations: [{ moduleId: 'mod-1' }],
+      directGrants: [{ moduleId: 'mod-1' }],
+    });
+    const service = new ModuleAccessService(prisma as any);
+
+    await service.findAccessibleModules('t1', 'user-1', 'USER');
+
+    expect(prisma.module.findMany).toHaveBeenCalledWith(
+      expect.objectContaining({ orderBy: { name: 'asc' } }),
+    );
+  });
+
+  it('empty: ein Benutzer ohne Zugriff erhält eine leere Liste, keinen Fehler', async () => {
+    const prisma = makeFakePrisma({});
+    const service = new ModuleAccessService(prisma as any);
+
+    const result = await service.findAccessibleModules('t1', 'user-1', 'USER');
+
+    expect(result).toEqual([]);
+    expect(prisma.module.findMany).not.toHaveBeenCalled();
+  });
+});
diff --git a/apps/api/src/module-registry/module-access.service.ts b/apps/api/src/module-registry/module-access.service.ts
new file mode 100644
index 0000000..4e461dd
--- /dev/null
+++ b/apps/api/src/module-registry/module-access.service.ts
@@ -0,0 +1,95 @@
+import { Injectable } from '@nestjs/common';
+import { Role } from '@prisma/client';
+import { PrismaService } from '../prisma/prisma.service';
+
+/**
+ * Single Source of Truth für Modulzugriff (D-01, PERM-04/05/06).
+ *
+ * `ModuleGuard` und `GET /modules/active` rufen beide ausschließlich
+ * `getAccessibleModuleIds` auf, damit Sidebar, Modulseiten und API
+ * niemals auseinanderdriften können — genau das Sicherheitsloch, das
+ * D-01 strukturell verhindert.
+ */
+@Injectable()
+export class ModuleAccessService {
+  constructor(private readonly prisma: PrismaService) {}
+
+  /**
+   * Berechnet die Menge der moduleIds, auf die dieser Benutzer Zugriff hat.
+   *
+   * D-03: ADMIN/SUPER_ADMIN umgehen jede Grant-Prüfung — sie erhalten alle
+   * mandantenweit aktiven Module ihres eigenen Mandanten. Diese Rolle
+   * kommt ausschließlich aus dem JWT (Aufrufer), nie aus Body/Params —
+   * der Kurzschluss kann daher keine Module eines fremden Mandanten
+   * liefern, weil `tenantId` ebenfalls aus dem JWT stammt (T-15-10).
+   *
+   * Für alle anderen Rollen (USER): Vereinigungsmenge aus Direkt-Grants
+   * und Grants über Gruppenmitgliedschaften, geschnitten mit den
+   * mandantenweit aktiven Modulen (D-02 — ein Grant auf ein deaktiviertes
+   * Modul gewährt keinen Zugriff). Die Gruppen-Query ist eine einzige
+   * verschachtelte Prisma-Query (`group: { memberships: { some: { userId } } }`)
+   * statt einer Schleife über die Gruppen des Benutzers — sonst entsteht
+   * ein N+1 pro geschütztem Endpoint.
+   *
+   * Rein lesend, kein Caching über Request-Grenzen hinweg (D-09) — ein
+   * Freigabe-Entzug wirkt bei der nächsten Anfrage.
+   */
+  async getAccessibleModuleIds(
+    tenantId: string,
+    userId: string,
+    role: Role,
+  ): Promise<Set<string>> {
+    if (role === 'ADMIN' || role === 'SUPER_ADMIN') {
+      const activations = await this.prisma.tenantModuleActivation.findMany({
+        where: { tenantId, isActive: true },
+        select: { moduleId: true },
+      });
+      return new Set(activations.map((a) => a.moduleId));
+    }
+
+    const [direct, viaGroup] = await Promise.all([
+      this.prisma.moduleGrant.findMany({
+        where: { tenantId, userId },
+        select: { moduleId: true },
+      }),
+      this.prisma.moduleGrant.findMany({
+        where: { tenantId, group: { memberships: { some: { userId } } } },
+        select: { moduleId: true },
+      }),
+    ]);
+    const grantedIds = [...direct, ...viaGroup].map((g) => g.moduleId);
+
+    if (grantedIds.length === 0) {
+      return new Set();
+    }
+
+    const activations = await this.prisma.tenantModuleActivation.findMany({
+      where: {
+        tenantId,
+        isActive: true,
+        moduleId: { in: grantedIds },
+      },
+      select: { moduleId: true },
+    });
+    return new Set(activations.map((a) => a.moduleId));
+  }
+
+  /**
+   * Lädt die vollständigen Module-Datensätze, auf die dieser Benutzer
+   * Zugriff hat, sortiert nach Name. Bedient `GET /modules/active` — die
+   * explizite Sortierung hält die Sidebar-Reihenfolge über Aufrufe hinweg
+   * stabil.
+   */
+  async findAccessibleModules(tenantId: string, userId: string, role: Role) {
+    const accessibleIds = await this.getAccessibleModuleIds(tenantId, userId, role);
+
+    if (accessibleIds.size === 0) {
+      return [];
+    }
+
+    return this.prisma.module.findMany({
+      where: { id: { in: [...accessibleIds] } },
+      orderBy: { name: 'asc' },
+    });
+  }
+}
diff --git a/apps/api/src/module-registry/module-registry.controller.ts b/apps/api/src/module-registry/module-registry.controller.ts
index 87240f6..40f3cd0 100644
--- a/apps/api/src/module-registry/module-registry.controller.ts
+++ b/apps/api/src/module-registry/module-registry.controller.ts
@@ -11,13 +11,16 @@ import { Role } from '@prisma/client';
 import { Request } from 'express';
 import { Roles } from '../auth/decorators/roles.decorator';
 import { RolesGuard } from '../auth/guards/roles.guard';
+import { ModuleAccessService } from './module-access.service';
 import { ModuleRegistryService } from './module-registry.service';
 
 /**
  * REST controller for the module registry.
  *
  * - GET /modules — list all registered modules (any authenticated user)
- * - GET /modules/active — list active modules for current tenant
+ * - GET /modules/active — list modules accessible to the requesting user
+ *   (Aktivierung UND Grant/Rolle, via ModuleAccessService — D-01: dieselbe
+ *   Auflösung wie ModuleGuard)
  * - POST /modules/:moduleId/activate — activate a module (ADMIN/SUPER_ADMIN)
  * - POST /modules/:moduleId/deactivate — deactivate a module (ADMIN/SUPER_ADMIN)
  *
@@ -28,6 +31,7 @@ import { ModuleRegistryService } from './module-registry.service';
 export class ModuleRegistryController {
   constructor(
     private readonly moduleRegistryService: ModuleRegistryService,
+    private readonly moduleAccessService: ModuleAccessService,
   ) {}
 
   /**
@@ -42,15 +46,21 @@ export class ModuleRegistryController {
 
   /**
    * GET /modules/active
-   * Returns modules that are active for the requesting tenant.
+   * Returns modules accessible to the requesting user (D-01): the same
+   * ModuleAccessService.getAccessibleModuleIds resolution ModuleGuard
+   * uses, not just tenant-wide activation. findActiveForTenant on
+   * ModuleRegistryService stays unchanged for Plan 15-03's marketplace
+   * catalog (mandantenweite Sicht, kein Benutzerfilter).
    */
   @Get('active')
   async findActive(@Req() req: Request) {
     const tenantId = (req as any).tenantId ?? (req as any).user?.tenantId;
-    if (!tenantId) {
-      throw new ForbiddenException('No tenant context');
+    const userId = (req as any).user?.id;
+    const role = (req as any).user?.role;
+    if (!tenantId || !userId || !role) {
+      throw new ForbiddenException('No user context');
     }
-    return this.moduleRegistryService.findActiveForTenant(tenantId);
+    return this.moduleAccessService.findAccessibleModules(tenantId, userId, role);
   }
 
   /**
diff --git a/apps/api/src/module-registry/module-registry.module.ts b/apps/api/src/module-registry/module-registry.module.ts
index cb9a099..e2c38b7 100644
--- a/apps/api/src/module-registry/module-registry.module.ts
+++ b/apps/api/src/module-registry/module-registry.module.ts
@@ -1,4 +1,5 @@
 import { Module } from '@nestjs/common';
+import { ModuleAccessService } from './module-access.service';
 import { ModuleRegistryController } from './module-registry.controller';
 import { ModuleRegistryService } from './module-registry.service';
 import { ModuleGuard } from './module.guard';
@@ -8,15 +9,18 @@ import { ModuleGuard } from './module.guard';
  *
  * Provides:
  * - ModuleRegistryService: CRUD for module records + per-tenant activation
+ * - ModuleAccessService: Single Source of Truth for user-level module
+ *   access (D-01) — Aktivierung UND (Rolle ODER Grant)
  * - ModuleGuard: CanActivate guard for module-specific endpoints
  * - ModuleRegistryController: REST API for listing, activating, and deactivating modules
  *
- * Exports ModuleRegistryService and ModuleGuard so downstream feature modules
- * (e.g., DomaincheckModule) can inject and use them.
+ * Exports ModuleRegistryService, ModuleAccessService and ModuleGuard so
+ * downstream feature modules (e.g., DomaincheckModule, DashboardModule
+ * Plan 15-05, Grant-Services Plan 15-03) can inject and use them.
  */
 @Module({
   controllers: [ModuleRegistryController],
-  providers: [ModuleRegistryService, ModuleGuard],
-  exports: [ModuleRegistryService, ModuleGuard],
+  providers: [ModuleRegistryService, ModuleAccessService, ModuleGuard],
+  exports: [ModuleRegistryService, ModuleAccessService, ModuleGuard],
 })
 export class ModuleRegistryModule {}
diff --git a/apps/api/src/module-registry/module.guard.spec.ts b/apps/api/src/module-registry/module.guard.spec.ts
new file mode 100644
index 0000000..84d836a
--- /dev/null
+++ b/apps/api/src/module-registry/module.guard.spec.ts
@@ -0,0 +1,119 @@
+import { ForbiddenException } from '@nestjs/common';
+import { describe, expect, it, vi } from 'vitest';
+import { ModuleGuard } from './module.guard';
+
+/**
+ * ModuleGuard.canActivate — deckt die vollständige Behavior-Liste aus
+ * 15-01-PLAN.md, Task 2 ab. ModuleAccessService und ModuleRegistryService
+ * sind gemockt (Guard-Unit-Test, kein DB-Zugriff).
+ */
+
+function makeContext(request: any) {
+  return {
+    getHandler: () => ({}),
+    getClass: () => ({}),
+    switchToHttp: () => ({
+      getRequest: () => request,
+    }),
+  } as any;
+}
+
+function makeReflector(slug: string | undefined) {
+  return { getAllAndOverride: vi.fn(() => slug) } as any;
+}
+
+describe('ModuleGuard.canActivate', () => {
+  it('gibt true zurück und ruft keinen Service auf, wenn kein @UseModule-Slug in den Metadaten steht', async () => {
+    const moduleRegistryService = { findBySlug: vi.fn() } as any;
+    const moduleAccessService = { getAccessibleModuleIds: vi.fn() } as any;
+    const guard = new ModuleGuard(makeReflector(undefined), moduleRegistryService, moduleAccessService);
+
+    const result = await guard.canActivate(makeContext({}));
+
+    expect(result).toBe(true);
+    expect(moduleRegistryService.findBySlug).not.toHaveBeenCalled();
+    expect(moduleAccessService.getAccessibleModuleIds).not.toHaveBeenCalled();
+  });
+
+  it('wirft ForbiddenException("No tenant context"), wenn weder request.tenantId noch request.user.tenantId gesetzt sind', async () => {
+    const moduleRegistryService = { findBySlug: vi.fn() } as any;
+    const moduleAccessService = { getAccessibleModuleIds: vi.fn() } as any;
+    const guard = new ModuleGuard(makeReflector('domaincheck'), moduleRegistryService, moduleAccessService);
+
+    await expect(guard.canActivate(makeContext({ user: {} }))).rejects.toThrow(
+      new ForbiddenException('No tenant context'),
+    );
+  });
+
+  it('wirft ForbiddenException("No user context"), wenn tenantId gesetzt ist, aber userId/role fehlen', async () => {
+    const moduleRegistryService = { findBySlug: vi.fn() } as any;
+    const moduleAccessService = { getAccessibleModuleIds: vi.fn() } as any;
+    const guard = new ModuleGuard(makeReflector('domaincheck'), moduleRegistryService, moduleAccessService);
+
+    await expect(
+      guard.canActivate(makeContext({ tenantId: 't1', user: {} })),
+    ).rejects.toThrow(new ForbiddenException('No user context'));
+  });
+
+  it('wirft ForbiddenException bei unbekanntem Slug (findBySlug liefert null)', async () => {
+    const moduleRegistryService = { findBySlug: vi.fn().mockResolvedValue(null) } as any;
+    const moduleAccessService = { getAccessibleModuleIds: vi.fn() } as any;
+    const guard = new ModuleGuard(makeReflector('unknown-slug'), moduleRegistryService, moduleAccessService);
+
+    await expect(
+      guard.canActivate(
+        makeContext({ tenantId: 't1', user: { id: 'user-1', role: 'USER' } }),
+      ),
+    ).rejects.toThrow(ForbiddenException);
+    expect(moduleAccessService.getAccessibleModuleIds).not.toHaveBeenCalled();
+  });
+
+  it('USER ohne Grant auf ein aktives Modul: wirft ForbiddenException', async () => {
+    const moduleRegistryService = {
+      findBySlug: vi.fn().mockResolvedValue({ id: 'mod-1', slug: 'domaincheck' }),
+    } as any;
+    const moduleAccessService = {
+      getAccessibleModuleIds: vi.fn().mockResolvedValue(new Set()),
+    } as any;
+    const guard = new ModuleGuard(makeReflector('domaincheck'), moduleRegistryService, moduleAccessService);
+
+    await expect(
+      guard.canActivate(
+        makeContext({ tenantId: 't1', user: { id: 'user-1', role: 'USER' } }),
+      ),
+    ).rejects.toThrow(ForbiddenException);
+  });
+
+  it('ADMIN ohne Grant auf ein aktives Modul: gibt true zurück (D-03-Kurzschluss lebt in ModuleAccessService)', async () => {
+    const moduleRegistryService = {
+      findBySlug: vi.fn().mockResolvedValue({ id: 'mod-1', slug: 'domaincheck' }),
+    } as any;
+    const moduleAccessService = {
+      getAccessibleModuleIds: vi.fn().mockResolvedValue(new Set(['mod-1'])),
+    } as any;
+    const guard = new ModuleGuard(makeReflector('domaincheck'), moduleRegistryService, moduleAccessService);
+    const request = { tenantId: 't1', user: { id: 'admin-1', role: 'ADMIN' } };
+
+    const result = await guard.canActivate(makeContext(request));
+
+    expect(result).toBe(true);
+    expect(moduleAccessService.getAccessibleModuleIds).toHaveBeenCalledWith('t1', 'admin-1', 'ADMIN');
+  });
+
+  it('USER mit Zugriff: gibt true zurück und legt das Ergebnis auf request.moduleAccessIds ab (Per-Request-Memoisierung, D-09)', async () => {
+    const moduleRegistryService = {
+      findBySlug: vi.fn().mockResolvedValue({ id: 'mod-1', slug: 'domaincheck' }),
+    } as any;
+    const accessibleIds = new Set(['mod-1']);
+    const moduleAccessService = {
+      getAccessibleModuleIds: vi.fn().mockResolvedValue(accessibleIds),
+    } as any;
+    const guard = new ModuleGuard(makeReflector('domaincheck'), moduleRegistryService, moduleAccessService);
+    const request = { tenantId: 't1', user: { id: 'user-1', role: 'USER' } };
+
+    const result = await guard.canActivate(makeContext(request));
+
+    expect(result).toBe(true);
+    expect((request as any).moduleAccessIds).toBe(accessibleIds);
+  });
+});
diff --git a/apps/api/src/module-registry/module.guard.ts b/apps/api/src/module-registry/module.guard.ts
index a080ca3..947dc1a 100644
--- a/apps/api/src/module-registry/module.guard.ts
+++ b/apps/api/src/module-registry/module.guard.ts
@@ -8,6 +8,7 @@ import {
   UseGuards,
 } from '@nestjs/common';
 import { Reflector } from '@nestjs/core';
+import { ModuleAccessService } from './module-access.service';
 import { ModuleRegistryService } from './module-registry.service';
 
 /**
@@ -16,17 +17,24 @@ import { ModuleRegistryService } from './module-registry.service';
 export const MODULE_SLUG_KEY = 'moduleSlug';
 
 /**
- * Guard that checks whether the requesting tenant has an active
- * module activation for the module identified by its slug.
+ * Guard that checks whether the requesting user has access to the module
+ * identified by its slug — Aktivierung UND (Rolle ODER Direkt-Grant ODER
+ * Gruppen-Grant), D-01.
  *
- * Per T-03-04: tenantId is sourced from JWT (via TenantMiddleware),
- * not from user-supplied input, preventing elevation of privilege.
+ * Per T-03-04/T-15-10: tenantId, userId und role stammen ausschließlich
+ * aus dem validierten JWT (via TenantMiddleware/JwtAuthGuard), nie aus
+ * Body oder Params — verhindert Elevation of Privilege.
+ *
+ * T-15-03: Ohne `@UseModule(slug)`-Metadaten gibt der Guard bewusst
+ * `true` zurück (Durchsetzung hängt am Dekorator) — jeder neue
+ * Modul-Controller MUSS `@UseModule` tragen (Projektregel seit Phase 3).
  */
 @Injectable()
 export class ModuleGuard implements CanActivate {
   constructor(
     private readonly reflector: Reflector,
     private readonly moduleRegistryService: ModuleRegistryService,
+    private readonly moduleAccessService: ModuleAccessService,
   ) {}
 
   async canActivate(context: ExecutionContext): Promise<boolean> {
@@ -48,24 +56,45 @@ export class ModuleGuard implements CanActivate {
       throw new ForbiddenException('No tenant context');
     }
 
-    const isActive = await this.moduleRegistryService.isModuleActive(
-      tenantId,
-      moduleSlug,
-    );
+    const userId = request.user?.id;
+    const role = request.user?.role;
 
-    if (!isActive) {
+    if (!userId || !role) {
+      throw new ForbiddenException('No user context');
+    }
+
+    const module = await this.moduleRegistryService.findBySlug(moduleSlug);
+
+    if (!module) {
       throw new ForbiddenException(
         `Module '${moduleSlug}' is not activated for this tenant`,
       );
     }
 
+    const accessibleModuleIds = await this.moduleAccessService.getAccessibleModuleIds(
+      tenantId,
+      userId,
+      role,
+    );
+
+    if (!accessibleModuleIds.has(module.id)) {
+      throw new ForbiddenException(
+        `Module '${moduleSlug}' is not accessible for this user`,
+      );
+    }
+
+    // Per-Request-Memoisierung (D-09): ein nachfolgender Handler im
+    // selben Request bezahlt die Auflösung nicht ein zweites Mal. Über
+    // Request-Grenzen hinweg wird nichts zwischengespeichert.
+    request.moduleAccessIds = accessibleModuleIds;
+
     return true;
   }
 }
 
 /**
  * Decorator that protects a controller or route handler with the ModuleGuard.
- * Ensures the specified module is activated for the requesting tenant.
+ * Ensures the specified module is accessible for the requesting user.
  *
  * Usage:
  *   @UseModule('domaincheck')