Enforce permissions in API guards and retire interim access (#52)

Every route now declares its access rule explicitly and is enforced through the shared resolution algorithm (permissions.md): - PermissionGuard + decorators (@RequiresPondRole, @RequiresPagePermission, @RequiresAttachmentPermission, @AuthenticatedOnly) applied to every route; a route-enumeration test proves full coverage alongside @Public()/Site-Admin-guarded routes. - 404/403 policy (documented in README conventions): denied reads answer 404 (existence hiding), denied writes on readable things answer 403; trash views need write capability (ADR 0013). - PermissionService resolves page/pond questions via the shared resolver, with an in-process pond-context cache (grants + label parents) that is invalidated on every grant/label-tree change and TTL-bounded as a multi-process safety net. Grant changes also fire pond_access_changed for collab revalidation (#39/#53). - shared: pond-scope resolution (hasPondRole, canSeePond) next to the page resolver; grant wire schemas + GrantView. - Owner Pond-Admin grants: migration backfill for all existing ponds, created transactionally with every new pond (shared + personal + seed). - Grant CRUD under /ponds/:id/grants (pond_admin-gated) with structural and referential validation, last-admin protection, audit logs. - InterimAccessService deleted; page lists, search, backlinks, phantom links, and trash listings are filtered per page through the resolver; collab tokens are now truly ro for readers. - Fixture-matrix e2e (reader/editor/pond admin/foreign, label-deny, authenticated-subject, revoke-then-immediate-deny cache test). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01PGdhRiwU1WRL4XxJfZYipY
2026-07-09 16:31:41 +02:00 · 2026-07-09 16:31:41 +02:00 · 0c6494f209
commit 0c6494f209
parent 4d48d72c40
50 changed files with 1825 additions and 337 deletions
--- a/apps/api/prisma/migrations/20260709140000_owner_admin_grants/migration.sql
+++ b/apps/api/prisma/migrations/20260709140000_owner_admin_grants/migration.sql
@ -0,0 +1,19 @@
+-- Seed the owner's Pond Admin grant for every existing pond (issue #52).
+-- From M5 on, access is decided solely by role_grants (permissions.md);
+-- without this backfill, owners of pre-M5 ponds would be locked out the
+-- moment the interim owner-or-siteadmin rule is retired. Raw SQL on purpose:
+-- the service-level rule "personal ponds get no additional pond_admin
+-- grants" does not apply here — the owner IS the one admin being seeded.
+-- Trashed ponds are included so a later restore restores access too.
+INSERT INTO "role_grants"
+  ("id", "pond_id", "subject_type", "subject_id", "role", "scope_type", "scope_id", "effect", "created_by")
+SELECT gen_random_uuid()::text, p."id", 'USER', p."owner_id", 'POND_ADMIN', 'POND', NULL, 'ALLOW', p."owner_id"
+FROM "ponds" p
+WHERE NOT EXISTS (
+  SELECT 1 FROM "role_grants" g
+  WHERE g."pond_id" = p."id"
+    AND g."subject_type" = 'USER'
+    AND g."subject_id" = p."owner_id"
+    AND g."role" = 'POND_ADMIN'
+    AND g."scope_type" = 'POND'
+);
--- a/apps/api/prisma/seed.ts
+++ b/apps/api/prisma/seed.ts
@ -66,6 +66,37 @@ const FIXTURES: FixtureUser[] = [
  },
 ];

+/**
+ * Every pond needs its owner's Pond Admin grant — access is decided solely
+ * by role_grants from M5 on (issue #52). Idempotent, matching the
+ * owner_admin_grants migration backfill.
+ */
+async function ensureOwnerAdminGrant(pondId: string, ownerId: string): Promise<void> {
+  const existing = await prisma.roleGrant.findFirst({
+    where: {
+      pondId,
+      subjectType: 'USER',
+      subjectId: ownerId,
+      role: 'POND_ADMIN',
+      scopeType: 'POND',
+    },
+    select: { id: true },
+  });
+  if (existing) return;
+  await prisma.roleGrant.create({
+    data: {
+      pondId,
+      subjectType: 'USER',
+      subjectId: ownerId,
+      role: 'POND_ADMIN',
+      scopeType: 'POND',
+      scopeId: null,
+      effect: 'ALLOW',
+      createdBy: ownerId,
+    },
+  });
+}
+
 async function upsertFixtureUser(fixture: FixtureUser): Promise<string> {
  const email = `${fixture.username}@dorfteich.test`;
  const user = await prisma.user.upsert({
@ -104,7 +135,7 @@ async function upsertFixtureUser(fixture: FixtureUser): Promise<string> {
      select: { id: true },
    });
    if (!existing) {
-      await prisma.pond.create({
+      const pond = await prisma.pond.create({
        data: {
          slug: slugify(fixture.displayName) || fixture.username,
          name: fixture.displayName,
@ -112,6 +143,7 @@ async function upsertFixtureUser(fixture: FixtureUser): Promise<string> {
          ownerId: user.id,
        },
      });
+      await ensureOwnerAdminGrant(pond.id, user.id);
    }
    // The instance default for additional_ponds is 0 (ADR 0011) — give
    // the fixtures headroom so pond flows are exercisable in dev/e2e.
@ -217,6 +249,7 @@ async function seedContentFixtures(ownerId: string): Promise<void> {
      },
    });
  }
+  await ensureOwnerAdminGrant(pond.id, ownerId);
  await prisma.quotaOverride.upsert({
    where: {
      subjectType_subjectId_quotaKey: {
--- a/apps/api/src/app.module.ts
+++ b/apps/api/src/app.module.ts
@ -15,6 +15,7 @@ import { LabelsModule } from './labels/labels.module';
 import { LinksModule } from './links/links.module';
 import { MailModule } from './mail/mail.module';
 import { PagesModule } from './pages/pages.module';
+import { PermissionsModule } from './permissions/permissions.module';
 import { PondsModule } from './ponds/ponds.module';
 import { PrismaModule } from './prisma/prisma.module';
 import { RateLimitModule } from './rate-limit/rate-limit.module';
@ -32,6 +33,7 @@ import { VersionsModule } from './versions/versions.module';
    MailModule,
    SettingsModule,
    UsersModule,
+    PermissionsModule,
    PondsModule,
    PagesModule,
    FilesModule,
--- a/apps/api/src/auth/auth.controller.ts
+++ b/apps/api/src/auth/auth.controller.ts
@ -14,12 +14,14 @@ import type { Response } from 'express';

 import { ZodValidationPipe } from '../common/zod-validation.pipe';
 import { AppConfig } from '../config/app-config.service';
+import { AuthenticatedOnly } from '../permissions/permission.decorators';
 import { RateLimit } from '../rate-limit/rate-limit.guard';
 import { InstanceSettingsService } from '../settings/instance-settings.service';
 import { AuthedRequest, Public, SESSION_COOKIE, toCurrentUser } from './auth.guard';
 import { AuthService } from './auth.service';
 import { SessionsService } from './sessions.service';

+@AuthenticatedOnly() // routes reachable without a session opt out via @Public
@Controller('auth')
 export class AuthController {
  constructor(
--- a/apps/api/src/files/files.controller.ts
+++ b/apps/api/src/files/files.controller.ts
@ -17,6 +17,10 @@ import { AttachmentView, MAX_UPLOAD_PARSE_BYTES } from '@dorfteich/shared';
 import type { Response } from 'express';

 import { AuthedRequest } from '../auth/auth.guard';
+import {
+  RequiresAttachmentPermission,
+  RequiresPondRole,
+} from '../permissions/permission.decorators';

 import { FilesService } from './files.service';

@ -26,6 +30,7 @@ export class FilesController {
  constructor(private readonly files: FilesService) {}

  @Post('ponds/:pondId/files')
+  @RequiresPondRole('editor', { idParam: 'pondId' })
  @UseInterceptors(FileInterceptor('file', { limits: { fileSize: MAX_UPLOAD_PARSE_BYTES } }))
  async upload(
    @Param('pondId') pondId: string,
@ -38,6 +43,7 @@ export class FilesController {

  /** Permission-checked file streaming (ADR 0011) — never served same-origin as executable content. */
  @Get('media/:fileId')
+  @RequiresAttachmentPermission('read', { idParam: 'fileId' })
  async download(
    @Param('fileId') fileId: string,
    @Req() request: AuthedRequest,
@ -55,6 +61,7 @@ export class FilesController {

  @Delete('files/:id')
  @HttpCode(204)
+  @RequiresAttachmentPermission('write', { idParam: 'id' })
  async remove(@Param('id') id: string, @Req() request: AuthedRequest): Promise<void> {
    await this.files.remove(request.user!, id);
  }
--- a/apps/api/src/files/files.service.ts
+++ b/apps/api/src/files/files.service.ts
@ -11,7 +11,6 @@ import { AttachmentView } from '@dorfteich/shared';
 import { Attachment, User } from '@prisma/client';
 import { PinoLogger } from 'nestjs-pino';

-import { InterimAccessService } from '../ponds/interim-access.service';
 import { PrismaService } from '../prisma/prisma.service';
 import { QuotaService } from '../quotas/quota.service';

@ -28,7 +27,6 @@ export interface FileDownload {
 export class FilesService {
  constructor(
    private readonly prisma: PrismaService,
-    private readonly access: InterimAccessService,
    private readonly quotas: QuotaService,
    private readonly storage: FileStorageService,
    private readonly logger: PinoLogger,
@ -54,7 +52,7 @@ export class FilesService {
    file: { buffer: Buffer; size: number; originalname: string },
  ): Promise<AttachmentView> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
-    this.access.assertCanModify(user, pond);
+    if (!pond) throw new NotFoundException();

    // Bytes decide, not the client-declared Content-Type or extension —
    // catches a renamed .html-as-.png (ADR 0011 acceptance criterion).
@ -106,23 +104,15 @@ export class FilesService {
    }
  }

-  async download(user: User, id: string): Promise<FileDownload> {
-    const attachment = await this.prisma.attachment.findFirst({
-      where: { id },
-      include: { pond: true },
-    });
+  async download(_user: User, id: string): Promise<FileDownload> {
+    const attachment = await this.prisma.attachment.findFirst({ where: { id } });
    if (!attachment) throw new NotFoundException();
-    this.access.assertCanSee(user, attachment.pond);
    return { attachment, stream: this.storage.createReadStream(attachment.pondId, attachment.id) };
  }

  async remove(user: User, id: string): Promise<void> {
-    const attachment = await this.prisma.attachment.findFirst({
-      where: { id },
-      include: { pond: true },
-    });
+    const attachment = await this.prisma.attachment.findFirst({ where: { id } });
    if (!attachment) throw new NotFoundException();
-    this.access.assertCanModify(user, attachment.pond);

    await this.prisma.attachment.delete({ where: { id: attachment.id } });
    await this.storage.delete(attachment.pondId, attachment.id);
--- a/apps/api/src/grants/grants.controller.ts
+++ b/apps/api/src/grants/grants.controller.ts
@ -0,0 +1,49 @@
+import { Body, Controller, Delete, Get, HttpCode, Param, Post, Req } from '@nestjs/common';
+import {
+  CreateGrantInput,
+  GrantView,
+  createGrantInputSchema,
+  grantOfInput,
+} from '@dorfteich/shared';
+
+import { AuthedRequest } from '../auth/auth.guard';
+import { ZodValidationPipe } from '../common/zod-validation.pipe';
+import { RequiresPondRole } from '../permissions/permission.decorators';
+import { GrantsService } from './grants.service';
+
+/**
+ * Grant management (issue #52): a pond's grants are its Pond Admins'
+ * business — members and their roles (permissions.md). The member-management
+ * UI on top of this arrives with #54.
+ */
+@Controller('ponds/:pondId/grants')
+export class GrantsController {
+  constructor(private readonly grants: GrantsService) {}
+
+  @Get()
+  @RequiresPondRole('pond_admin', { idParam: 'pondId' })
+  async list(@Param('pondId') pondId: string): Promise<GrantView[]> {
+    return this.grants.listGrants(pondId);
+  }
+
+  @Post()
+  @RequiresPondRole('pond_admin', { idParam: 'pondId' })
+  async create(
+    @Param('pondId') pondId: string,
+    @Body(new ZodValidationPipe(createGrantInputSchema)) input: CreateGrantInput,
+    @Req() request: AuthedRequest,
+  ): Promise<GrantView> {
+    return this.grants.createGrant(request.user!, pondId, grantOfInput(input));
+  }
+
+  @Delete(':grantId')
+  @HttpCode(204)
+  @RequiresPondRole('pond_admin', { idParam: 'pondId' })
+  async remove(
+    @Param('pondId') pondId: string,
+    @Param('grantId') grantId: string,
+    @Req() request: AuthedRequest,
+  ): Promise<void> {
+    await this.grants.deleteGrant(request.user!, pondId, grantId);
+  }
+}
--- a/apps/api/src/grants/grants.module.ts
+++ b/apps/api/src/grants/grants.module.ts
@ -2,15 +2,18 @@ import { Module } from '@nestjs/common';

 import { PondsModule } from '../ponds/ponds.module';

+import { GrantsController } from './grants.controller';
 import { GrantsService } from './grants.service';

 /**
- * Permission grants (issue #51). Exports `GrantsService` so the API guards and
- * collab token issuance (#52/#53) can resolve grants; the member-management
- * controller/UI arrives with #54.
+ * Permission grants (issues #51/#52): the management endpoints under
+ * `/ponds/:id/grants` (Pond-Admin-gated) and the service behind them.
+ * Resolution itself lives in PermissionsModule; the member-management UI
+ * arrives with #54.
 */
@Module({
  imports: [PondsModule],
+  controllers: [GrantsController],
  providers: [GrantsService],
  exports: [GrantsService],
 })
--- a/apps/api/src/grants/grants.service.db.test.ts
+++ b/apps/api/src/grants/grants.service.db.test.ts
@ -13,17 +13,11 @@ describe.skipIf(!hasTestDb)('GrantsService (db, issue #51)', () => {
  let grants: GrantsService;
  const suffix = uniqueSuffix();
  let owner: User;
+  let target: User;
  let shared: string;
  let personal: string;
-
-  const editorGrant: Grant = {
-    subjectType: 'user',
-    subjectId: 'target-user',
-    role: 'editor',
-    scopeType: 'pond',
-    scopeId: null,
-    effect: 'allow',
-  };
+  // Grants must point at an existing user (#52); filled in beforeAll.
+  let editorGrant: Grant;

  beforeAll(async () => {
    prisma = createTestPrisma();
@ -37,6 +31,21 @@ describe.skipIf(!hasTestDb)('GrantsService (db, issue #51)', () => {
        displayName: 'Grant Owner',
      },
    });
+    target = await prisma.user.create({
+      data: {
+        username: `grant-target-${suffix}`,
+        email: `grant-target-${suffix}@example.test`,
+        displayName: 'Grant Target',
+      },
+    });
+    editorGrant = {
+      subjectType: 'user',
+      subjectId: target.id,
+      role: 'editor',
+      scopeType: 'pond',
+      scopeId: null,
+      effect: 'allow',
+    };
    const s = await prisma.pond.create({
      data: { slug: `grant-shared-${suffix}`, name: 'Shared', type: 'SHARED', ownerId: owner.id },
    });
@ -55,7 +64,7 @@ describe.skipIf(!hasTestDb)('GrantsService (db, issue #51)', () => {
  afterAll(async () => {
    await prisma.roleGrant.deleteMany({ where: { pondId: { in: [shared, personal] } } });
    await prisma.pond.deleteMany({ where: { id: { in: [shared, personal] } } });
-    await prisma.user.deleteMany({ where: { id: owner.id } });
+    await prisma.user.deleteMany({ where: { id: { in: [owner.id, target.id] } } });
    await prisma.$disconnect();
    await app.close();
  });
@ -64,7 +73,7 @@ describe.skipIf(!hasTestDb)('GrantsService (db, issue #51)', () => {
    const created = await grants.createGrant(owner, shared, editorGrant);
    expect(created).toMatchObject({ role: 'editor', scopeType: 'pond', effect: 'allow' });
    const all = await grants.grantsForPond(shared);
-    expect(all).toContainEqual(expect.objectContaining({ subjectId: 'target-user' }));
+    expect(all).toContainEqual(expect.objectContaining({ subjectId: target.id }));
  });

  it('rejects a duplicate grant', async () => {
--- a/apps/api/src/grants/grants.service.ts
+++ b/apps/api/src/grants/grants.service.ts
@ -4,56 +4,107 @@ import {
  Injectable,
  NotFoundException,
 } from '@nestjs/common';
-import { Grant, grantValidationError } from '@dorfteich/shared';
-import { Pond, User } from '@prisma/client';
+import { Grant, GrantView, grantValidationError } from '@dorfteich/shared';
+import { Pond, RoleGrant, User } from '@prisma/client';
 import { PinoLogger } from 'nestjs-pino';

-import { InterimAccessService } from '../ponds/interim-access.service';
+import { PondPermissionCache } from '../permissions/pond-permission-cache';
+import { PondAccessNotifier } from '../ponds/pond-access-notifier.service';
 import { PrismaService } from '../prisma/prisma.service';
 import { toGrant, toGrantColumns } from './grant-mappers';

 /**
- * Writes and reads over the permission table (`role_grants`, issue #51). Grants
- * are validated against the shared structural rules before insertion (the DB
- * CHECK is a backstop for the pond_admin-scope rule). Who may manage grants is
- * still the interim rule (owner/Site Admin) until #52 wires the real Pond Admin
- * check; the member-management API/UI arrives with #54. `grantsForPond` is what
- * the resolver (#52/#53) reads.
+ * Writes and reads over the permission table (`role_grants`, issues #51/#52).
+ * Who may manage grants is the guard's job (Pond Admin); this service
+ * validates the grant itself — the shared structural rules, plus that the
+ * scope and subject actually exist in this pond. Every mutation invalidates
+ * the pond's permission context and notifies the collab server so live
+ * sessions revalidate (issue #39; full revocation UX is #53), and leaves an
+ * audit log line.
 */
@Injectable()
 export class GrantsService {
  constructor(
    private readonly prisma: PrismaService,
-    private readonly access: InterimAccessService,
+    private readonly permissionCache: PondPermissionCache,
+    private readonly accessNotifier: PondAccessNotifier,
    private readonly logger: PinoLogger,
  ) {
    this.logger.setContext(GrantsService.name);
  }

-  /** All grants in a pond, as the shared resolver model (used by #52/#53). */
+  /** All grants in a pond, as the shared resolver model (kept for callers
+   * that resolve rather than manage; PermissionService reads its own copy). */
  async grantsForPond(pondId: string): Promise<Grant[]> {
    const rows = await this.prisma.roleGrant.findMany({ where: { pondId } });
    return rows.map(toGrant);
  }

-  private async requireModifiablePond(user: User, pondId: string): Promise<Pond> {
+  private static viewOf(row: RoleGrant): GrantView {
+    return {
+      ...toGrant(row),
+      id: row.id,
+      pondId: row.pondId,
+      createdBy: row.createdBy,
+      createdAt: row.createdAt.toISOString(),
+    };
+  }
+
+  private async requireLivePond(pondId: string): Promise<Pond> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
-    this.access.assertCanModify(user, pond);
+    if (!pond) throw new NotFoundException();
    return pond;
  }

+  /** A pond's grants for the management UI, newest last. */
+  async listGrants(pondId: string): Promise<GrantView[]> {
+    await this.requireLivePond(pondId);
+    const rows = await this.prisma.roleGrant.findMany({
+      where: { pondId },
+      orderBy: { createdAt: 'asc' },
+    });
+    return rows.map((row) => GrantsService.viewOf(row));
+  }
+
+  /** The grant must point at things that exist in this pond — a label/page
+   * from elsewhere would silently never match during resolution. */
+  private async assertScopeAndSubjectExist(pondId: string, grant: Grant): Promise<void> {
+    if (grant.scopeType === 'label' && grant.scopeId) {
+      const label = await this.prisma.label.findFirst({
+        where: { id: grant.scopeId, pondId },
+        select: { id: true },
+      });
+      if (!label) throw new BadRequestException({ code: 'grant_scope_not_found' });
+    }
+    if (grant.scopeType === 'page' && grant.scopeId) {
+      const page = await this.prisma.page.findFirst({
+        where: { id: grant.scopeId, pondId },
+        select: { id: true },
+      });
+      if (!page) throw new BadRequestException({ code: 'grant_scope_not_found' });
+    }
+    if (grant.subjectType === 'user' && grant.subjectId) {
+      const user = await this.prisma.user.findUnique({
+        where: { id: grant.subjectId },
+        select: { id: true },
+      });
+      if (!user) throw new BadRequestException({ code: 'grant_subject_not_found' });
+    }
+  }
+
  /**
   * Create a grant after validating its structural constraints (issue #51):
-   * pond_admin only at pond scope for a user subject, and no extra admins on a
-   * personal pond. Rejects duplicates. Returns the stored grant.
+   * pond_admin only at pond scope for a user subject, no extra admins on a
+   * personal pond, and scope/subject must exist here. Rejects duplicates.
   */
-  async createGrant(user: User, pondId: string, grant: Grant): Promise<Grant> {
-    const pond = await this.requireModifiablePond(user, pondId);
+  async createGrant(user: User, pondId: string, grant: Grant): Promise<GrantView> {
+    const pond = await this.requireLivePond(pondId);

    const invalid = grantValidationError(grant, {
      pondType: pond.type === 'PERSONAL' ? 'personal' : 'shared',
    });
    if (invalid) throw new BadRequestException({ code: invalid });
+    await this.assertScopeAndSubjectExist(pondId, grant);

    const columns = toGrantColumns(grant);
    const existing = await this.prisma.roleGrant.findFirst({
@ -65,19 +116,52 @@ export class GrantsService {
    const created = await this.prisma.roleGrant.create({
      data: { pondId, createdBy: user.id, ...columns },
    });
+    await this.accessChanged(pondId);
    this.logger.info(
-      { grantId: created.id, pondId, userId: user.id, role: grant.role, scope: grant.scopeType },
+      {
+        grantId: created.id,
+        pondId,
+        userId: user.id,
+        subject: grant.subjectType,
+        subjectId: grant.subjectId,
+        role: grant.role,
+        scope: grant.scopeType,
+        scopeId: grant.scopeId,
+        effect: grant.effect,
+      },
      'audit: grant created',
    );
-    return toGrant(created);
+    return GrantsService.viewOf(created);
  }

-  /** Remove a grant by id (member-management detail; permission is interim). */
-  async deleteGrant(user: User, grantId: string): Promise<void> {
-    const grant = await this.prisma.roleGrant.findUnique({ where: { id: grantId } });
+  /**
+   * Remove a grant by id within its pond. The last remaining Pond Admin
+   * grant is protected — deleting it would leave the pond unmanageable
+   * (only a Site Admin could recover it).
+   */
+  async deleteGrant(user: User, pondId: string, grantId: string): Promise<void> {
+    const grant = await this.prisma.roleGrant.findFirst({ where: { id: grantId, pondId } });
    if (!grant) throw new NotFoundException();
-    await this.requireModifiablePond(user, grant.pondId);
+
+    if (grant.role === 'POND_ADMIN') {
+      const admins = await this.prisma.roleGrant.count({
+        where: { pondId, role: 'POND_ADMIN', effect: 'ALLOW' },
+      });
+      if (admins <= 1) throw new ConflictException({ code: 'grant_last_admin' });
+    }
+
    await this.prisma.roleGrant.delete({ where: { id: grantId } });
-    this.logger.info({ grantId, userId: user.id }, 'audit: grant deleted');
+    await this.accessChanged(pondId);
+    this.logger.info(
+      { grantId, pondId, userId: user.id, subjectId: grant.subjectId, role: grant.role },
+      'audit: grant deleted',
+    );
+  }
+
+  /** Revoked/added permission takes effect immediately: drop the cached pond
+   * context and tell the collab server to revalidate its sessions. */
+  private async accessChanged(pondId: string): Promise<void> {
+    this.permissionCache.invalidate(pondId);
+    await this.accessNotifier.notifyAccessChanged(pondId);
  }
 }
--- a/apps/api/src/labels/labels.controller.ts
+++ b/apps/api/src/labels/labels.controller.ts
@ -25,11 +25,13 @@ import {

 import { AuthedRequest } from '../auth/auth.guard';
 import { ZodValidationPipe } from '../common/zod-validation.pipe';
+import { RequiresPagePermission, RequiresPondRole } from '../permissions/permission.decorators';
 import { LabelsService } from './labels.service';

 /**
- * Hierarchical label management (issue #43). Access rules live in
- * InterimAccessService, resolved per owning pond inside the service.
+ * Hierarchical label management (issue #43). Seeing a pond lets you read its
+ * label tree; managing the tree is Pond Admin work; assigning labels to a
+ * page is editing that page (permissions.md, enforced by the guard, #52).
 */
@Controller()
 export class LabelsController {
@ -37,6 +39,7 @@ export class LabelsController {

  /** The pond's label hierarchy in one call — sidebar tree and pickers. */
  @Get('ponds/:pondId/labels')
+  @RequiresPondRole('reader', { idParam: 'pondId' })
  async list(
    @Param('pondId') pondId: string,
    @Req() request: AuthedRequest,
@ -45,6 +48,7 @@ export class LabelsController {
  }

  @Post('ponds/:pondId/labels')
+  @RequiresPondRole('pond_admin', { idParam: 'pondId' })
  async create(
    @Param('pondId') pondId: string,
    @Body(new ZodValidationPipe(createLabelInputSchema)) input: CreateLabelInput,
@ -55,6 +59,7 @@ export class LabelsController {

  /** Rename and/or recolour a label. */
  @Patch('labels/:id')
+  @RequiresPondRole('pond_admin', { labelParam: 'id' })
  async update(
    @Param('id') id: string,
    @Body(new ZodValidationPipe(updateLabelInputSchema)) input: UpdateLabelInput,
@ -65,6 +70,7 @@ export class LabelsController {

  /** Move a label (with its subtree) to a new parent or to the root. */
  @Post('labels/:id/move')
+  @RequiresPondRole('pond_admin', { labelParam: 'id' })
  async move(
    @Param('id') id: string,
    @Body(new ZodValidationPipe(moveLabelInputSchema)) input: MoveLabelInput,
@ -76,6 +82,7 @@ export class LabelsController {
  /** Delete a label and its subtree; `?force=true` confirms detaching pages. */
  @Delete('labels/:id')
  @HttpCode(204)
+  @RequiresPondRole('pond_admin', { labelParam: 'id' })
  async remove(
    @Param('id') id: string,
    @Query('force') force: string | undefined,
@ -86,6 +93,7 @@ export class LabelsController {

  /** A page's assigned labels. */
  @Get('pages/:pageId/labels')
+  @RequiresPagePermission('read', { idParam: 'pageId' })
  async pageLabels(
    @Param('pageId') pageId: string,
    @Req() request: AuthedRequest,
@ -95,6 +103,7 @@ export class LabelsController {

  /** Assign a label to a page (idempotent). */
  @Post('pages/:pageId/labels')
+  @RequiresPagePermission('write', { idParam: 'pageId' })
  async assign(
    @Param('pageId') pageId: string,
    @Body(new ZodValidationPipe(assignLabelInputSchema)) input: AssignLabelInput,
@ -106,6 +115,7 @@ export class LabelsController {
  /** Unassign a label from a page (idempotent). */
  @Delete('pages/:pageId/labels/:labelId')
  @HttpCode(204)
+  @RequiresPagePermission('write', { idParam: 'pageId' })
  async unassign(
    @Param('pageId') pageId: string,
    @Param('labelId') labelId: string,
--- a/apps/api/src/labels/labels.service.db.test.ts
+++ b/apps/api/src/labels/labels.service.db.test.ts
@ -1,11 +1,6 @@
 import { randomUUID } from 'node:crypto';

-import {
-  BadRequestException,
-  ConflictException,
-  INestApplication,
-  NotFoundException,
-} from '@nestjs/common';
+import { BadRequestException, ConflictException, INestApplication } from '@nestjs/common';
 import { PrismaClient, User } from '@prisma/client';
 import { afterAll, beforeAll, describe, expect, it } from 'vitest';
 import * as Y from 'yjs';
@ -20,7 +15,6 @@ describe.skipIf(!hasTestDb)('LabelsService (db, issue #43)', () => {
  let labels: LabelsService;
  const suffix = uniqueSuffix();
  let owner: User;
-  let outsider: User;
  let pondId: string;
  let otherPondId: string;
  const pageIds: string[] = [];
@ -54,13 +48,6 @@ describe.skipIf(!hasTestDb)('LabelsService (db, issue #43)', () => {
        displayName: 'Label Owner',
      },
    });
-    outsider = await prisma.user.create({
-      data: {
-        username: `lbl-out-${suffix}`,
-        email: `lbl-out-${suffix}@example.test`,
-        displayName: 'Label Outsider',
-      },
-    });
    const pond = await prisma.pond.create({
      data: { slug: `lbl-pond-${suffix}`, name: 'Label Pond', type: 'PERSONAL', ownerId: owner.id },
    });
@ -80,7 +67,7 @@ describe.skipIf(!hasTestDb)('LabelsService (db, issue #43)', () => {
    if (pageIds.length > 0) await prisma.page.deleteMany({ where: { id: { in: pageIds } } });
    await prisma.label.deleteMany({ where: { pondId: { in: [pondId, otherPondId] } } });
    await prisma.pond.deleteMany({ where: { id: { in: [pondId, otherPondId] } } });
-    await prisma.user.deleteMany({ where: { id: { in: [owner.id, outsider.id] } } });
+    await prisma.user.deleteMany({ where: { id: owner.id } });
    await prisma.$disconnect();
    await app.close();
  });
@ -191,10 +178,6 @@ describe.skipIf(!hasTestDb)('LabelsService (db, issue #43)', () => {
    await prisma.label.deleteMany({ where: { id: label.id } });
  });

-  it('hides labels from users who cannot see the pond', async () => {
-    await expect(labels.list(outsider, pondId)).rejects.toBeInstanceOf(NotFoundException);
-    await expect(labels.create(outsider, pondId, { name: 'Nope' })).rejects.toBeInstanceOf(
-      NotFoundException,
-    );
-  });
+  // Hiding labels from users who cannot see the pond moved to the route
+  // guard with #52 — covered by the permission e2e pack.
 });
--- a/apps/api/src/labels/labels.service.ts
+++ b/apps/api/src/labels/labels.service.ts
@ -20,7 +20,7 @@ import {
 import { Label, Pond, Prisma, User } from '@prisma/client';
 import { PinoLogger } from 'nestjs-pino';

-import { InterimAccessService } from '../ponds/interim-access.service';
+import { PondPermissionCache } from '../permissions/pond-permission-cache';
 import { PrismaService } from '../prisma/prisma.service';
 import { SearchProvider } from '../search/search.provider';

@ -28,11 +28,14 @@ import { SearchProvider } from '../search/search.provider';
 type Tx = Prisma.TransactionClient;

 /**
- * Hierarchical labels within a pond (issue #43, data-model.md §labels). Access
- * is gated through {@link InterimAccessService} on the owning pond: seeing a
- * pond lets you read its labels, modifying it lets you manage them. The tree
- * logic (cycle prevention, depth limit) lives in `@dorfteich/shared` so the M5
- * permission resolver reuses the exact same hierarchy walk (permissions.md).
+ * Hierarchical labels within a pond (issue #43, data-model.md §labels).
+ * Permissions are enforced by the route guard (#52): seeing a pond lets you
+ * read its labels, Pond Admins manage the tree, label assignment is a page
+ * write. The tree logic (cycle prevention, depth limit) lives in
+ * `@dorfteich/shared` so the permission resolver uses the exact same
+ * hierarchy walk (permissions.md). Tree mutations invalidate the pond's
+ * permission context — grants on a label cover its descendants, so a move or
+ * delete changes what those grants mean.
 *
 * Writes that depend on the current tree (uniqueness, cycle, depth checks) run
 * inside a transaction holding a per-pond advisory lock, so check-then-write is
@ -44,7 +47,7 @@ type Tx = Prisma.TransactionClient;
 export class LabelsService {
  constructor(
    private readonly prisma: PrismaService,
-    private readonly access: InterimAccessService,
+    private readonly permissionCache: PondPermissionCache,
    private readonly logger: PinoLogger,
    private readonly search: SearchProvider,
  ) {
@ -84,29 +87,19 @@ export class LabelsService {
    });
  }

-  private async requireVisiblePond(user: User, pondId: string): Promise<Pond> {
+  private async requireLivePond(pondId: string): Promise<Pond> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
-    this.access.assertCanSee(user, pond);
+    if (!pond) throw new NotFoundException();
    return pond;
  }

-  private async requireModifiablePond(user: User, pondId: string): Promise<Pond> {
-    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
-    this.access.assertCanModify(user, pond);
-    return pond;
-  }
-
-  /** Loads a label and asserts the user may manage its pond; 404 if either is missing. */
-  private async requireModifiableLabel(
-    user: User,
-    labelId: string,
-  ): Promise<Label & { pond: Pond }> {
+  /** Loads a label in a live pond; permission is the guard's job (#52). */
+  private async requireLabel(labelId: string): Promise<Label & { pond: Pond }> {
    const label = await this.prisma.label.findUnique({
      where: { id: labelId },
      include: { pond: true },
    });
    if (!label || label.pond.deletedAt) throw new NotFoundException();
-    this.access.assertCanModify(user, label.pond);
    return label;
  }

@ -132,13 +125,13 @@ export class LabelsService {

  /** The whole label hierarchy of a pond in one call (issue #43 acceptance
   * criterion) — the sidebar tree and every label picker read this. */
-  async list(user: User, pondId: string): Promise<LabelTreeNode[]> {
-    await this.requireVisiblePond(user, pondId);
+  async list(_user: User, pondId: string): Promise<LabelTreeNode[]> {
+    await this.requireLivePond(pondId);
    return buildLabelTree(await this.allPondLabels(this.prisma, pondId));
  }

  async create(user: User, pondId: string, input: CreateLabelInput): Promise<LabelView> {
-    await this.requireModifiablePond(user, pondId);
+    await this.requireLivePond(pondId);
    const name = input.name;
    const parentId = input.parentId ?? null;

@ -163,13 +156,14 @@ export class LabelsService {
      });
    });

+    this.permissionCache.invalidate(pondId);
    this.logger.info({ labelId: label.id, pondId, userId: user.id }, 'audit: label created');
    return this.viewOf(label);
  }

  /** Rename and/or recolour a label (issue #43). */
-  async update(user: User, labelId: string, input: UpdateLabelInput): Promise<LabelView> {
-    const existing = await this.requireModifiableLabel(user, labelId);
+  async update(_user: User, labelId: string, input: UpdateLabelInput): Promise<LabelView> {
+    const existing = await this.requireLabel(labelId);
    const pondId = existing.pondId;

    const label = await this.withPondLock(pondId, async (tx) => {
@ -192,7 +186,7 @@ export class LabelsService {
  /** Move a label (with its subtree) to a new parent or to the root (issue #43).
   * Rejects cycles and any move that would push the subtree past the depth limit. */
  async move(user: User, labelId: string, input: MoveLabelInput): Promise<LabelView> {
-    const existing = await this.requireModifiableLabel(user, labelId);
+    const existing = await this.requireLabel(labelId);
    const pondId = existing.pondId;
    const parentId = input.parentId;

@ -219,6 +213,8 @@ export class LabelsService {
      return tx.label.update({ where: { id: labelId }, data: { parentId } });
    });

+    // Label grants cover descendants — a moved subtree changes their reach.
+    this.permissionCache.invalidate(pondId);
    this.logger.info({ labelId, pondId, parentId, userId: user.id }, 'audit: label moved');
    return this.viewOf(label);
  }
@ -231,7 +227,7 @@ export class LabelsService {
   * assignments and descendants.
   */
  async remove(user: User, labelId: string, force: boolean): Promise<void> {
-    const existing = await this.requireModifiableLabel(user, labelId);
+    const existing = await this.requireLabel(labelId);
    const pondId = existing.pondId;

    const affectedPageIds = await this.withPondLock(pondId, async (tx) => {
@ -253,33 +249,25 @@ export class LabelsService {
      return assignments.map((a) => a.pageId);
    });

+    this.permissionCache.invalidate(pondId);
    // Those pages lost a label → their search entries change (#49).
    for (const pageId of affectedPageIds) await this.search.indexPage(pageId);
    this.logger.info({ labelId, pondId, userId: user.id, force }, 'audit: label deleted');
  }

-  /** Loads a live page and asserts the user may edit it (for assignment ops). */
-  private async requireModifiablePage(
-    user: User,
-    pageId: string,
-  ): Promise<{ id: string; pondId: string }> {
+  /** Loads a live page (assignment ops); permission is the guard's job (#52). */
+  private async requireLivePage(pageId: string): Promise<{ id: string; pondId: string }> {
    const page = await this.prisma.page.findFirst({
      where: { id: pageId, deletedAt: null },
-      include: { pond: true },
+      select: { id: true, pondId: true },
    });
    if (!page) throw new NotFoundException();
-    this.access.assertCanModify(user, page.pond);
    return page;
  }

-  /** A page's assigned labels (issue #43) — read requires seeing the pond. */
-  async pageLabels(user: User, pageId: string): Promise<LabelView[]> {
-    const page = await this.prisma.page.findFirst({
-      where: { id: pageId, deletedAt: null },
-      include: { pond: true },
-    });
-    if (!page) throw new NotFoundException();
-    this.access.assertCanSee(user, page.pond);
+  /** A page's assigned labels (issue #43). */
+  async pageLabels(_user: User, pageId: string): Promise<LabelView[]> {
+    await this.requireLivePage(pageId);
    const rows = await this.prisma.pageLabel.findMany({
      where: { pageId },
      include: { label: true },
@ -289,7 +277,7 @@ export class LabelsService {

  /** Assign a label to a page (idempotent). Rejects labels from another pond. */
  async assign(user: User, pageId: string, labelId: string): Promise<LabelView[]> {
-    const page = await this.requireModifiablePage(user, pageId);
+    const page = await this.requireLivePage(pageId);
    const label = await this.prisma.label.findUnique({ where: { id: labelId } });
    if (!label || label.pondId !== page.pondId) {
      throw new BadRequestException({ code: 'label_wrong_pond' });
@ -304,8 +292,8 @@ export class LabelsService {
  }

  /** Remove a label from a page (idempotent). */
-  async unassign(user: User, pageId: string, labelId: string): Promise<void> {
-    await this.requireModifiablePage(user, pageId);
+  async unassign(_user: User, pageId: string, labelId: string): Promise<void> {
+    await this.requireLivePage(pageId);
    await this.prisma.pageLabel.deleteMany({ where: { pageId, labelId } });
    await this.search.indexPage(pageId); // labels are a search field (#49)
  }
--- a/apps/api/src/links/links.controller.ts
+++ b/apps/api/src/links/links.controller.ts
@ -2,6 +2,7 @@ import { Controller, Get, Param, Req } from '@nestjs/common';
 import { BacklinkView, PhantomLinkView } from '@dorfteich/shared';

 import { AuthedRequest } from '../auth/auth.guard';
+import { RequiresPagePermission, RequiresPondRole } from '../permissions/permission.decorators';
 import { LinksService } from './links.service';

 /** Wikilink index reads (issue #47): backlinks and a pond's phantom links. */
@ -11,12 +12,14 @@ export class LinksController {

  /** Pages that link to this page (permission-filtered). */
  @Get('pages/:id/backlinks')
+  @RequiresPagePermission('read', { idParam: 'id' }) // sources are filtered per page
  async backlinks(@Param('id') id: string, @Req() request: AuthedRequest): Promise<BacklinkView[]> {
    return this.links.backlinks(request.user!, id);
  }

  /** Referenced-but-missing pages in the pond, with their referrers. */
  @Get('ponds/:pondId/phantom-links')
+  @RequiresPondRole('reader', { idParam: 'pondId' }) // referrers are filtered per page
  async phantomLinks(
    @Param('pondId') pondId: string,
    @Req() request: AuthedRequest,
--- a/apps/api/src/links/links.service.db.test.ts
+++ b/apps/api/src/links/links.service.db.test.ts
@ -1,13 +1,13 @@
 import { randomUUID } from 'node:crypto';

-import { INestApplication, NotFoundException } from '@nestjs/common';
+import { INestApplication } from '@nestjs/common';
 import { PrismaClient, User } from '@prisma/client';
 import { afterAll, beforeAll, describe, expect, it } from 'vitest';
 import * as Y from 'yjs';

 import { PagesService } from '../pages/pages.service';
 import { createTestApp } from '../testing/test-app';
-import { createTestPrisma, hasTestDb, uniqueSuffix } from '../testing/test-db';
+import { createTestPrisma, grantOwnerAdmin, hasTestDb, uniqueSuffix } from '../testing/test-db';
 import { LinksService } from './links.service';

 describe.skipIf(!hasTestDb)('LinksService (db, issue #47)', () => {
@ -70,6 +70,7 @@ describe.skipIf(!hasTestDb)('LinksService (db, issue #47)', () => {
      data: { slug: `lnk-pond-${suffix}`, name: 'Link Pond', type: 'PERSONAL', ownerId: owner.id },
    });
    pondId = pond.id;
+    await grantOwnerAdmin(prisma, pondId, owner.id);
    // Headroom for the pages the create test makes.
    await prisma.quotaOverride.create({
      data: { subjectType: 'USER', subjectId: owner.id, quotaKey: 'additional_ponds', value: 100 },
@ -97,9 +98,13 @@ describe.skipIf(!hasTestDb)('LinksService (db, issue #47)', () => {
    ]);
  });

-  it('hides backlinks from users who cannot see the pond', async () => {
+  it('filters backlink sources to pages the requester may read (#52)', async () => {
+    // Route-level 404s for invisible ponds are the guard's job (#52, covered
+    // by the permission e2e pack); the service filters the link *sources*.
    const target = await makePage(`hidden-${suffix}`);
-    await expect(links.backlinks(outsider, target)).rejects.toBeInstanceOf(NotFoundException);
+    const source = await makePage(`hidden-src-${suffix}`, 'Hidden Source');
+    await link(source, `hidden-${suffix}`, target);
+    expect(await links.backlinks(outsider, target)).toEqual([]);
  });

  it('aggregates phantom links by target slug', async () => {
--- a/apps/api/src/links/links.service.ts
+++ b/apps/api/src/links/links.service.ts
@ -2,15 +2,16 @@ import { Injectable, NotFoundException } from '@nestjs/common';
 import { BacklinkView, PhantomLinkView } from '@dorfteich/shared';
 import { User } from '@prisma/client';

-import { InterimAccessService } from '../ponds/interim-access.service';
+import { PermissionService } from '../permissions/permission.service';
 import { PrismaService } from '../prisma/prisma.service';

 /**
 * Reads over the wikilink index (`page_links`, issue #47). The index is written
 * by the collab server on every content change; here it is queried for a page's
 * backlinks and a pond's phantom (missing-target) links. Wikilinks resolve only
- * within a pond, so every backlink lives in the same pond as its target —
- * seeing the pond (InterimAccessService) is therefore the read permission.
+ * within a pond, so every link source lives in the same pond as its target;
+ * sources are filtered to the pages the user may read (issue #52) so a link
+ * never leaks a title or snippet from a page outside the user's slice.
 */
 /** Longest plain-text preview shown next to a backlink (issue #48). */
 const SNIPPET_LENGTH = 140;
@ -27,7 +28,7 @@ type LinkSource = {
 export class LinksService {
  constructor(
    private readonly prisma: PrismaService,
-    private readonly access: InterimAccessService,
+    private readonly permissions: PermissionService,
  ) {}

  private static viewOf(source: LinkSource): BacklinkView {
@ -41,10 +42,9 @@ export class LinksService {
  async backlinks(user: User, pageId: string): Promise<BacklinkView[]> {
    const page = await this.prisma.page.findFirst({
      where: { id: pageId, deletedAt: null },
-      include: { pond: true },
+      select: { id: true, pondId: true },
    });
    if (!page) throw new NotFoundException();
-    this.access.assertCanSee(user, page.pond);

    const links = await this.prisma.pageLink.findMany({
      where: { toPageId: pageId, fromPage: { deletedAt: null } },
@ -60,10 +60,16 @@ export class LinksService {
      },
      orderBy: { fromPage: { title: 'asc' } },
    });
+    const readable = await this.permissions.filterPages(
+      user,
+      page.pondId,
+      links.map((link) => ({ id: link.fromPage.id })),
+      'read',
+    );
    const seen = new Set<string>();
    const backlinks: BacklinkView[] = [];
    for (const link of links) {
-      if (seen.has(link.fromPage.id)) continue;
+      if (seen.has(link.fromPage.id) || !readable.has(link.fromPage.id)) continue;
      seen.add(link.fromPage.id);
      backlinks.push(LinksService.viewOf(link.fromPage));
    }
@ -73,7 +79,7 @@ export class LinksService {
  /** Referenced-but-missing targets in a pond, with the pages referencing them. */
  async phantomLinks(user: User, pondId: string): Promise<PhantomLinkView[]> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
-    this.access.assertCanSee(user, pond);
+    if (!pond) throw new NotFoundException();

    const rows = await this.prisma.pageLink.findMany({
      where: { toPageId: null, fromPage: { pondId, deletedAt: null } },
@ -90,8 +96,15 @@ export class LinksService {
      orderBy: [{ targetSlug: 'asc' }, { fromPage: { title: 'asc' } }],
    });

+    const readable = await this.permissions.filterPages(
+      user,
+      pondId,
+      rows.map((row) => ({ id: row.fromPage.id })),
+      'read',
+    );
    const grouped = new Map<string, PhantomLinkView>();
    for (const row of rows) {
+      if (!readable.has(row.fromPage.id)) continue;
      let entry = grouped.get(row.targetSlug);
      if (!entry) {
        entry = { targetSlug: row.targetSlug, referencedBy: [] };
--- a/apps/api/src/pages/pages.controller.ts
+++ b/apps/api/src/pages/pages.controller.ts
@ -28,14 +28,20 @@ import type { Response } from 'express';

 import { AuthedRequest } from '../auth/auth.guard';
 import { ZodValidationPipe } from '../common/zod-validation.pipe';
+import {
+  AuthenticatedOnly,
+  RequiresPagePermission,
+  RequiresPondRole,
+} from '../permissions/permission.decorators';
 import { PagesService } from './pages.service';

-/** Page CRUD and Yjs state persistence (issue #23). */
+/** Page CRUD and Yjs state persistence (issue #23; permission guard since #52). */
@Controller()
 export class PagesController {
  constructor(private readonly pages: PagesService) {}

  @Post('ponds/:pondId/pages')
+  @RequiresPondRole('editor', { idParam: 'pondId' })
  async create(
    @Param('pondId') pondId: string,
    @Body(new ZodValidationPipe(createPageInputSchema)) input: CreatePageInput,
@ -45,6 +51,7 @@ export class PagesController {
  }

  @Get('ponds/:pondId/pages')
+  @RequiresPondRole('reader', { idParam: 'pondId' }) // the service filters per page
  async list(
    @Param('pondId') pondId: string,
    @Req() request: AuthedRequest,
@ -53,12 +60,14 @@ export class PagesController {
  }

  @Get('pages/:id')
+  @RequiresPagePermission('read', { idParam: 'id' })
  async getState(@Param('id') id: string, @Req() request: AuthedRequest): Promise<PageStateView> {
    return this.pages.getState(request.user!, id);
  }

  /** Short-lived collaboration token for the collab server (issue #34). */
  @Get('pages/:id/collab-token')
+  @RequiresPagePermission('read', { idParam: 'id' }) // readers get an `ro` token
  async collabToken(
    @Param('id') id: string,
    @Req() request: AuthedRequest,
@ -68,6 +77,7 @@ export class PagesController {

  /** Markdown export (issue #30) — downloads `<slug>.md`. */
  @Get('pages/:id/export/markdown')
+  @RequiresPagePermission('read', { idParam: 'id' })
  async exportMarkdown(
    @Param('id') id: string,
    @Req() request: AuthedRequest,
@ -83,6 +93,7 @@ export class PagesController {
   * navigates to (issue #25); the pond id must already be known to the caller
   * (e.g. from `GET /ponds/:slug`). */
  @Get('ponds/:pondId/pages/:slug')
+  @RequiresPagePermission('read', { pondIdParam: 'pondId', slugParam: 'slug' })
  async getStateBySlug(
    @Param('pondId') pondId: string,
    @Param('slug') slug: string,
@ -98,6 +109,7 @@ export class PagesController {
   * remain. Kept as an explicit 410 so any stale client gets a clear signal.
   */
  @Put('pages/:id/state')
+  @AuthenticatedOnly() // always 410 — never touches the page
  saveState(): never {
    throw new GoneException({
      code: 'rest_state_write_retired',
@ -107,6 +119,7 @@ export class PagesController {

  /** Reposition a page in the manual sidebar order (issue #45). */
  @Patch('pages/:id/position')
+  @RequiresPagePermission('write', { idParam: 'id' })
  async reposition(
    @Param('id') id: string,
    @Body(new ZodValidationPipe(repositionPageInputSchema)) input: RepositionPageInput,
@ -116,6 +129,7 @@ export class PagesController {
  }

  @Patch('pages/:id')
+  @RequiresPagePermission('write', { idParam: 'id' })
  async update(
    @Param('id') id: string,
    @Body(new ZodValidationPipe(updatePageInputSchema)) input: UpdatePageInput,
@ -126,6 +140,7 @@ export class PagesController {

  @Delete('pages/:id')
  @HttpCode(204)
+  @RequiresPagePermission('write', { idParam: 'id' })
  async remove(@Param('id') id: string, @Req() request: AuthedRequest): Promise<void> {
    await this.pages.softDelete(request.user!, id);
  }
--- a/apps/api/src/pages/pages.service.ts
+++ b/apps/api/src/pages/pages.service.ts
@ -17,7 +17,7 @@ import { generateKeyBetween } from 'fractional-indexing';
 import { PinoLogger } from 'nestjs-pino';

 import { AppConfig } from '../config/app-config.service';
-import { InterimAccessService } from '../ponds/interim-access.service';
+import { PermissionService } from '../permissions/permission.service';
 import { PrismaService } from '../prisma/prisma.service';
 import { SearchProvider } from '../search/search.provider';
 import { evenlySpacedKeys, nextKeyOrRebalance } from './sort-key';
@ -43,7 +43,7 @@ const COLLAB_TOKEN_TTL_SECONDS = 60;
 export class PagesService {
  constructor(
    private readonly prisma: PrismaService,
-    private readonly access: InterimAccessService,
+    private readonly permissions: PermissionService,
    private readonly logger: PinoLogger,
    private readonly config: AppConfig,
    private readonly search: SearchProvider,
@ -86,23 +86,10 @@ export class PagesService {
    }
  }

-  private async findVisiblePage(user: User, id: string): Promise<Page> {
-    const page = await this.prisma.page.findFirst({
-      where: { id, deletedAt: null },
-      include: { pond: true },
-    });
+  /** Loads a live page; permission is the guard's job since #52. */
+  private async findLivePage(id: string): Promise<Page> {
+    const page = await this.prisma.page.findFirst({ where: { id, deletedAt: null } });
    if (!page) throw new NotFoundException();
-    this.access.assertCanSee(user, page.pond);
-    return page;
-  }
-
-  private async findModifiablePage(user: User, id: string): Promise<Page> {
-    const page = await this.prisma.page.findFirst({
-      where: { id, deletedAt: null },
-      include: { pond: true },
-    });
-    if (!page) throw new NotFoundException();
-    this.access.assertCanModify(user, page.pond);
    return page;
  }

@ -116,25 +103,35 @@ export class PagesService {
    };

  /** Sidebar page list, ordered per the pond's persisted sort mode (issue #26),
-   * each with its assigned label ids for chips and filtering (issue #44). */
+   * each with its assigned label ids for chips and filtering (issue #44).
+   * Filtered to the pages the user may read (issue #52) — a label- or
+   * page-scoped reader sees only their slice of the pond. */
  async list(user: User, pondId: string): Promise<PageListItemView[]> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
-    this.access.assertCanSee(user, pond);
+    if (!pond) throw new NotFoundException();
    const settings = pondSettingsSchema.parse(pond.settings ?? {});
    const pages = await this.prisma.page.findMany({
      where: { pondId, deletedAt: null },
      orderBy: PagesService.SORT_ORDER[settings.sidebarSort],
      include: { labels: { select: { labelId: true } } },
    });
-    return pages.map((page) => ({
-      ...this.viewOf(page),
-      labelIds: page.labels.map((l) => l.labelId),
-    }));
+    const readable = await this.permissions.filterPages(
+      user,
+      pondId,
+      pages.map((page) => ({ id: page.id, labelIds: page.labels.map((l) => l.labelId) })),
+      'read',
+    );
+    return pages
+      .filter((page) => readable.has(page.id))
+      .map((page) => ({
+        ...this.viewOf(page),
+        labelIds: page.labels.map((l) => l.labelId),
+      }));
  }

  async create(user: User, pondId: string, input: CreatePageInput): Promise<PageView> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
-    this.access.assertCanModify(user, pond);
+    if (!pond) throw new NotFoundException();

    const slug = await this.generateUniqueSlugInPond(pond.id, input.title);
    const last = await this.prisma.page.findFirst({
@ -179,28 +176,22 @@ export class PagesService {
        AND from_page_id IN (SELECT id FROM pages WHERE pond_id = ${pondId})`;
  }

-  async getState(user: User, id: string): Promise<PageStateView> {
-    const page = await this.findVisiblePage(user, id);
+  async getState(_user: User, id: string): Promise<PageStateView> {
+    const page = await this.findLivePage(id);
    return this.stateViewOf(page);
  }

  /**
   * Mint a collaboration token for a page (issue #34). The permission check
-   * runs here, in the api — the collab server never sees session cookies
-   * (ADR 0003). `mode` is `rw` for anyone who may modify the pond and `ro`
-   * otherwise; under the interim access model seeing and modifying coincide,
-   * so callers who can see a page currently always get `rw` (real read-only
-   * grants arrive with #53, which this endpoint is already shaped for).
+   * runs in the api — the guard requires read access, and the collab server
+   * never sees session cookies (ADR 0003). `mode` is `rw` for who may write
+   * the page per the real grant resolution (issue #52) and `ro` otherwise.
   */
  async issueCollabToken(user: User, id: string): Promise<CollabTokenResponse> {
-    const page = await this.prisma.page.findFirst({
-      where: { id, deletedAt: null },
-      include: { pond: true },
-    });
-    if (!page) throw new NotFoundException();
-    this.access.assertCanSee(user, page.pond);
+    const page = await this.findLivePage(id);

-    const mode = this.access.canModifyPond(user, page.pond) ? 'rw' : 'ro';
+    const canWrite = await this.permissions.canAccessPage(user, page, 'write');
+    const mode = canWrite ? 'rw' : 'ro';
    const token = signCollabToken(
      { userId: user.id, pageId: page.id, mode },
      this.config.env.COLLAB_TOKEN_SECRET,
@ -211,26 +202,15 @@ export class PagesService {
    return { token, mode, expiresInSeconds: COLLAB_TOKEN_TTL_SECONDS };
  }

-  async getStateBySlug(user: User, pondId: string, slug: string): Promise<PageStateView> {
-    const page = await this.prisma.page.findFirst({
-      where: { pondId, slug },
-      include: { pond: true },
-    });
-    if (!page || !this.access.canSeePond(user, page.pond)) throw new NotFoundException();
-    if (page.deletedAt) {
-      // A plain 404 for anyone without edit rights — same as "does not
-      // exist" — but editors get a distinguishable code so the UI can
-      // offer a restore link instead of a dead end (issue #31).
-      if (this.access.canModifyPond(user, page.pond)) {
-        throw new NotFoundException({ code: 'page_trashed', details: { pageId: page.id } });
-      }
-      throw new NotFoundException();
-    }
+  /** The trashed-page hint for editors (issue #31) moved into the guard. */
+  async getStateBySlug(_user: User, pondId: string, slug: string): Promise<PageStateView> {
+    const page = await this.prisma.page.findFirst({ where: { pondId, slug, deletedAt: null } });
+    if (!page) throw new NotFoundException();
    return this.stateViewOf(page);
  }

-  async update(user: User, id: string, input: UpdatePageInput): Promise<PageView> {
-    const page = await this.findModifiablePage(user, id);
+  async update(_user: User, id: string, input: UpdatePageInput): Promise<PageView> {
+    const page = await this.findLivePage(id);

    let slug = page.slug;
    if (input.slug !== undefined) {
@ -267,8 +247,8 @@ export class PagesService {
   * same sequence. Requires write access; the sort mode does not have to be
   * `manual` (the key is stored regardless, just not applied in other modes).
   */
-  async reposition(user: User, id: string, input: RepositionPageInput): Promise<PageView> {
-    const page = await this.findModifiablePage(user, id);
+  async reposition(_user: User, id: string, input: RepositionPageInput): Promise<PageView> {
+    const page = await this.findLivePage(id);
    const { afterId, beforeId } = input;
    if (afterId === id || beforeId === id) {
      throw new ConflictException({ code: 'bad_request' });
@ -335,14 +315,14 @@ export class PagesService {
   * `page_content_cache.markdown` (refreshed on every state save, #23)
   * rather than re-decoding the Yjs state, so export always matches what
   * the app itself considers the page's current Markdown representation. */
-  async exportMarkdown(user: User, id: string): Promise<{ slug: string; markdown: string }> {
-    const page = await this.findVisiblePage(user, id);
+  async exportMarkdown(_user: User, id: string): Promise<{ slug: string; markdown: string }> {
+    const page = await this.findLivePage(id);
    const cache = await this.prisma.pageContentCache.findUnique({ where: { pageId: page.id } });
    return { slug: page.slug, markdown: cache?.markdown ?? '' };
  }

  async softDelete(user: User, id: string): Promise<void> {
-    const page = await this.findModifiablePage(user, id);
+    const page = await this.findLivePage(id);
    await this.prisma.page.update({
      where: { id: page.id },
      data: { deletedAt: new Date(), deletedBy: user.id },
--- a/apps/api/src/pages/reposition.db.test.ts
+++ b/apps/api/src/pages/reposition.db.test.ts
@ -3,7 +3,7 @@ import { PrismaClient, User } from '@prisma/client';
 import { afterAll, beforeAll, describe, expect, it } from 'vitest';

 import { createTestApp } from '../testing/test-app';
-import { createTestPrisma, hasTestDb, uniqueSuffix } from '../testing/test-db';
+import { createTestPrisma, grantOwnerAdmin, hasTestDb, uniqueSuffix } from '../testing/test-db';
 import { PagesService } from './pages.service';

 describe.skipIf(!hasTestDb)('PagesService.reposition (db, issue #45)', () => {
@ -46,6 +46,7 @@ describe.skipIf(!hasTestDb)('PagesService.reposition (db, issue #45)', () => {
      },
    });
    pondId = pond.id;
+    await grantOwnerAdmin(prisma, pondId, owner.id);
    // Manual mode so `list` orders by sort_key.
    await prisma.pond.update({
      where: { id: pondId },
--- a/apps/api/src/permissions/permission.decorators.ts
+++ b/apps/api/src/permissions/permission.decorators.ts
@ -0,0 +1,82 @@
+import { SetMetadata, UseGuards, applyDecorators } from '@nestjs/common';
+import { PermissionAction } from '@dorfteich/shared';
+
+import { PermissionGuard } from './permission.guard';
+import { RequiredPondRole } from './permission.service';
+
+/**
+ * Route permission declarations (issue #52). Every route must carry exactly
+ * one of these markers — or `@Public()` / the Site-Admin guard — so the
+ * route-enumeration test can prove no endpoint ships without an explicit
+ * access decision (default-closed, security.md). The markers with a
+ * requirement also attach the {@link PermissionGuard} that enforces it.
+ *
+ * 404/403 policy (docs/architecture/README.md §Conventions): a denied read
+ * is a 404 — outsiders cannot probe what exists; a denied write on
+ * something the user may read is a 403.
+ */
+
+export const PERMISSION_KEY = 'permissionRequirement';
+
+/** Where the guard finds the pond: a route param carrying its id or slug, or
+ * a label id whose pond is meant (`/labels/:id` routes). */
+export interface PondParamSource {
+  idParam?: string;
+  slugParam?: string;
+  labelParam?: string;
+}
+
+/** Where the guard finds the page: its id param, or a pond-id + page-slug
+ * param pair (`/ponds/:pondId/pages/:slug`). */
+export interface PageParamSource {
+  idParam?: string;
+  pondIdParam?: string;
+  slugParam?: string;
+  /** Trash routes: the page must BE trashed, and access = write capability
+   * on the page (ADR 0013); live pages 404 here. */
+  inTrash?: boolean;
+}
+
+export type PermissionRequirement =
+  | { kind: 'pond'; role: RequiredPondRole; source: PondParamSource }
+  | { kind: 'page'; action: PermissionAction; source: PageParamSource }
+  | { kind: 'attachment'; action: PermissionAction; source: { idParam: string } }
+  | { kind: 'authenticated' };
+
+function requires(requirement: PermissionRequirement): MethodDecorator {
+  return applyDecorators(SetMetadata(PERMISSION_KEY, requirement), UseGuards(PermissionGuard));
+}
+
+/** The route needs `role` on the pond named by `source`. `reader` = may see
+ * the pond at all; `editor`/`pond_admin` are pond-wide roles. */
+export function RequiresPondRole(role: RequiredPondRole, source: PondParamSource): MethodDecorator {
+  return requires({ kind: 'pond', role, source });
+}
+
+/** The route needs `action` on the page named by `source`. */
+export function RequiresPagePermission(
+  action: PermissionAction,
+  source: PageParamSource,
+): MethodDecorator {
+  return requires({ kind: 'page', action, source });
+}
+
+/** The route needs `action` on the attachment named by `source` — permissions
+ * are inherited from its page, or from the pond for pond-level files
+ * (permissions.md §non-page objects). */
+export function RequiresAttachmentPermission(
+  action: PermissionAction,
+  source: { idParam: string },
+): MethodDecorator {
+  return requires({ kind: 'attachment', action, source });
+}
+
+/**
+ * The route needs a session but no pond/page permission — either it only
+ * touches the caller's own data (profile, sessions, pond list) or all
+ * filtering happens inside the service (search). Marker only: the global
+ * AuthGuard already enforces authentication.
+ */
+export function AuthenticatedOnly(): MethodDecorator & ClassDecorator {
+  return SetMetadata(PERMISSION_KEY, { kind: 'authenticated' } satisfies PermissionRequirement);
+}
--- a/apps/api/src/permissions/permission.guard.ts
+++ b/apps/api/src/permissions/permission.guard.ts
@ -0,0 +1,195 @@
+import {
+  CanActivate,
+  ExecutionContext,
+  ForbiddenException,
+  Injectable,
+  NotFoundException,
+} from '@nestjs/common';
+import { Reflector } from '@nestjs/core';
+import { PermissionAction } from '@dorfteich/shared';
+import { User } from '@prisma/client';
+
+import { AuthedRequest } from '../auth/auth.guard';
+import { PrismaService } from '../prisma/prisma.service';
+import {
+  PERMISSION_KEY,
+  PageParamSource,
+  PermissionRequirement,
+  PondParamSource,
+} from './permission.decorators';
+import { PermissionService, RequiredPondRole } from './permission.service';
+
+/** The columns the guard needs of a page under decision. */
+interface GuardedPage {
+  id: string;
+  pondId: string;
+  deletedAt: Date | null;
+  pond: { deletedAt: Date | null };
+}
+
+/**
+ * Enforces the permission requirement a route declares through the
+ * decorators in {@link ./permission.decorators} (issue #52). It resolves the
+ * pond/page/attachment from the route params, asks {@link PermissionService}
+ * (which delegates to the shared resolver — permissions.md), and applies the
+ * 404/403 policy: denied reads read as "not found" so existence is hidden;
+ * denied writes on things the user may read are 403.
+ */
+@Injectable()
+export class PermissionGuard implements CanActivate {
+  constructor(
+    private readonly reflector: Reflector,
+    private readonly prisma: PrismaService,
+    private readonly permissions: PermissionService,
+  ) {}
+
+  async canActivate(context: ExecutionContext): Promise<boolean> {
+    const requirement = this.reflector.getAllAndOverride<PermissionRequirement | undefined>(
+      PERMISSION_KEY,
+      [context.getHandler(), context.getClass()],
+    );
+    // No requirement (or a marker-only one): nothing for this guard to do.
+    if (!requirement || requirement.kind === 'authenticated') return true;
+
+    const request = context.switchToHttp().getRequest<AuthedRequest>();
+    const user = request.user ?? null;
+    const params = request.params as Record<string, string | undefined>;
+
+    switch (requirement.kind) {
+      case 'pond':
+        return this.checkPond(user, requirement.role, requirement.source, params);
+      case 'page':
+        return this.checkPage(user, requirement.action, requirement.source, params);
+      case 'attachment':
+        return this.checkAttachment(user, requirement.action, requirement.source, params);
+    }
+  }
+
+  private async checkPond(
+    user: User | null,
+    role: RequiredPondRole,
+    source: PondParamSource,
+    params: Record<string, string | undefined>,
+  ): Promise<boolean> {
+    const pond = await this.resolvePond(source, params);
+    if (!pond) throw new NotFoundException();
+
+    if (await this.permissions.hasPondRole(user, pond.id, role)) return true;
+    // Denied read → 404 (hide existence); denied write on a visible pond → 403.
+    if (role !== 'reader' && (await this.permissions.canSeePond(user, pond.id))) {
+      throw new ForbiddenException();
+    }
+    throw new NotFoundException();
+  }
+
+  /** The pond a pond-scoped route names — directly or via a label id. */
+  private async resolvePond(
+    source: PondParamSource,
+    params: Record<string, string | undefined>,
+  ): Promise<{ id: string } | null> {
+    if (source.labelParam) {
+      const label = await this.prisma.label.findFirst({
+        where: { id: params[source.labelParam], pond: { deletedAt: null } },
+        select: { pondId: true },
+      });
+      return label ? { id: label.pondId } : null;
+    }
+    const where = source.idParam
+      ? { id: params[source.idParam], deletedAt: null }
+      : { slug: params[source.slugParam!], deletedAt: null };
+    return this.prisma.pond.findFirst({ where, select: { id: true } });
+  }
+
+  private async checkPage(
+    user: User | null,
+    action: PermissionAction,
+    source: PageParamSource,
+    params: Record<string, string | undefined>,
+  ): Promise<boolean> {
+    const where = source.idParam
+      ? { id: params[source.idParam] }
+      : { pondId: params[source.pondIdParam!], slug: params[source.slugParam!] };
+    const page: GuardedPage | null = await this.prisma.page.findFirst({
+      where,
+      select: {
+        id: true,
+        pondId: true,
+        deletedAt: true,
+        pond: { select: { deletedAt: true } },
+      },
+    });
+    // A trashed pond hides its pages entirely (pond trash is Site-Admin land).
+    if (!page || page.pond.deletedAt) throw new NotFoundException();
+
+    if (source.inTrash) {
+      // Trash routes: only trashed pages, only for who could edit them
+      // (ADR 0013) — anyone else sees "not found", never "forbidden".
+      if (!page.deletedAt) throw new NotFoundException();
+      if (await this.permissions.canAccessTrashedPage(user, page)) return true;
+      throw new NotFoundException();
+    }
+
+    if (page.deletedAt) {
+      // Normal views never serve trashed pages; who could edit gets a
+      // distinguishable code so the UI can offer a restore link (issue #31).
+      if (await this.permissions.canAccessTrashedPage(user, page)) {
+        throw new NotFoundException({ code: 'page_trashed', details: { pageId: page.id } });
+      }
+      throw new NotFoundException();
+    }
+
+    if (!(await this.permissions.canAccessPage(user, page, 'read'))) {
+      throw new NotFoundException();
+    }
+    if (action === 'write' && !(await this.permissions.canAccessPage(user, page, 'write'))) {
+      // Write attempt on a readable page → 403 (README §Conventions).
+      throw new ForbiddenException();
+    }
+    return true;
+  }
+
+  private async checkAttachment(
+    user: User | null,
+    action: PermissionAction,
+    source: { idParam: string },
+    params: Record<string, string | undefined>,
+  ): Promise<boolean> {
+    const attachment = await this.prisma.attachment.findFirst({
+      where: { id: params[source.idParam] },
+      select: {
+        id: true,
+        pondId: true,
+        pageId: true,
+        pond: { select: { deletedAt: true } },
+      },
+    });
+    if (!attachment || attachment.pond.deletedAt) throw new NotFoundException();
+
+    // Attachments inherit their page's permissions (permissions.md §non-page
+    // objects). Deliberately without the trash rule: files of a soft-deleted
+    // page stay reachable until the purge removes them (issue #27).
+    if (attachment.pageId) {
+      const page = { id: attachment.pageId, pondId: attachment.pondId };
+      if (!(await this.permissions.canAccessPage(user, page, 'read'))) {
+        throw new NotFoundException();
+      }
+      if (action === 'write' && !(await this.permissions.canAccessPage(user, page, 'write'))) {
+        throw new ForbiddenException();
+      }
+      return true;
+    }
+
+    // Pond-level files (uploads not yet tied to a page): read follows pond
+    // visibility, write needs a pond-wide editor.
+    if (!(await this.permissions.canSeePond(user, attachment.pondId))) {
+      throw new NotFoundException();
+    }
+    if (
+      action === 'write' &&
+      !(await this.permissions.hasPondRole(user, attachment.pondId, 'editor'))
+    ) {
+      throw new ForbiddenException();
+    }
+    return true;
+  }
+}
--- a/apps/api/src/permissions/permission.service.ts
+++ b/apps/api/src/permissions/permission.service.ts
@ -0,0 +1,169 @@
+import { Injectable } from '@nestjs/common';
+import {
+  PermissionAction,
+  PermissionViewer,
+  PondRole,
+  canSeePond,
+  hasPondRole,
+  resolvePageCapability,
+} from '@dorfteich/shared';
+import { Prisma, User } from '@prisma/client';
+
+import { toGrant } from '../grants/grant-mappers';
+import { PrismaService } from '../prisma/prisma.service';
+import { PondPermissionCache, PondPermissionContext } from './pond-permission-cache';
+
+/** The role a permission decorator can require at pond level. `reader` means
+ * "may see the pond at all" — any allow grant, at any scope (shared
+ * `canSeePond`); `editor`/`pond_admin` are pond-wide roles. */
+export type RequiredPondRole = 'reader' | PondRole;
+
+/** What page filtering needs to know about one page; `labelIds` may be
+ * preloaded by the caller (one grouped query otherwise). */
+export interface FilterablePage {
+  id: string;
+  labelIds?: string[];
+}
+
+/**
+ * The API-side entry point for every permission question (issue #52). Pure
+ * resolution lives in `@dorfteich/shared` (permissions.md is normative); this
+ * service loads the inputs — grants and label hierarchy per pond (cached, see
+ * {@link PondPermissionCache}) and the page's labels (fresh) — and delegates.
+ * Nothing outside this module may answer an access question itself.
+ */
+@Injectable()
+export class PermissionService {
+  constructor(
+    private readonly prisma: PrismaService,
+    private readonly cache: PondPermissionCache,
+  ) {}
+
+  static viewerOf(user: User | null | undefined): PermissionViewer {
+    return { userId: user?.id ?? null, isSiteAdmin: user?.isSiteAdmin ?? false };
+  }
+
+  /** The pond's grants and label hierarchy, from cache or two indexed queries. */
+  async pondContext(pondId: string): Promise<PondPermissionContext> {
+    const cached = this.cache.get(pondId);
+    if (cached) return cached;
+    const [grantRows, labels] = await Promise.all([
+      this.prisma.roleGrant.findMany({ where: { pondId } }),
+      this.prisma.label.findMany({ where: { pondId }, select: { id: true, parentId: true } }),
+    ]);
+    const context: PondPermissionContext = {
+      grants: grantRows.map(toGrant),
+      labelParents: Object.fromEntries(labels.map((l) => [l.id, l.parentId])),
+    };
+    this.cache.set(pondId, context);
+    return context;
+  }
+
+  /** May the user see that the pond exists (metadata, shell)? */
+  async canSeePond(user: User | null, pondId: string): Promise<boolean> {
+    const { grants } = await this.pondContext(pondId);
+    return canSeePond(PermissionService.viewerOf(user), grants);
+  }
+
+  /** Does the user hold `role` pond-wide? (`reader` = may see the pond.) */
+  async hasPondRole(user: User | null, pondId: string, role: RequiredPondRole): Promise<boolean> {
+    if (role === 'reader') return this.canSeePond(user, pondId);
+    const { grants } = await this.pondContext(pondId);
+    return hasPondRole(role, PermissionService.viewerOf(user), grants);
+  }
+
+  /**
+   * May the user perform `action` on one live page? (Trash views go through
+   * {@link canAccessTrashedPage}.) The page's own labels are loaded fresh.
+   */
+  async canAccessPage(
+    user: User | null,
+    page: { id: string; pondId: string },
+    action: PermissionAction,
+  ): Promise<boolean> {
+    const allowed = await this.filterPages(user, page.pondId, [{ id: page.id }], action);
+    return allowed.has(page.id);
+  }
+
+  /** May the user see/restore/purge the page in trash views (= write capability,
+   * ADR 0013)? The trashed flag itself is the caller's routing decision. */
+  async canAccessTrashedPage(
+    user: User | null,
+    page: { id: string; pondId: string },
+  ): Promise<boolean> {
+    return this.canAccessPage(user, page, 'write');
+  }
+
+  /**
+   * Resolve `action` for many pages of one pond at once — the page-list,
+   * search, backlink, and trash filters. Returns the ids the user may access.
+   * Pages without preloaded `labelIds` get them in one grouped query.
+   */
+  async filterPages(
+    user: User | null,
+    pondId: string,
+    pages: FilterablePage[],
+    action: PermissionAction,
+  ): Promise<Set<string>> {
+    if (pages.length === 0) return new Set();
+    const viewer = PermissionService.viewerOf(user);
+    if (viewer.isSiteAdmin) return new Set(pages.map((p) => p.id));
+
+    const { grants, labelParents } = await this.pondContext(pondId);
+    const missing = pages.filter((p) => p.labelIds === undefined).map((p) => p.id);
+    const labelsByPage = new Map<string, string[]>();
+    if (missing.length > 0) {
+      const rows = await this.prisma.pageLabel.findMany({
+        where: { pageId: { in: missing } },
+        select: { pageId: true, labelId: true },
+      });
+      for (const row of rows) {
+        const list = labelsByPage.get(row.pageId) ?? [];
+        list.push(row.labelId);
+        labelsByPage.set(row.pageId, list);
+      }
+    }
+
+    const allowed = new Set<string>();
+    for (const page of pages) {
+      const pageLabelIds = page.labelIds ?? labelsByPage.get(page.id) ?? [];
+      const ok = resolvePageCapability(action, {
+        viewer,
+        grants,
+        pageId: page.id,
+        pageLabelIds,
+        labelParents,
+      });
+      if (ok) allowed.add(page.id);
+    }
+    return allowed;
+  }
+
+  /**
+   * The ponds the user may see, or `null` for "all" (Site Admin). Visibility
+   * is `canSeePond`: any matching allow grant, which this single indexed
+   * query expresses exactly (deny grants never *create* visibility).
+   */
+  async visiblePondIds(user: User): Promise<string[] | null> {
+    if (user.isSiteAdmin) return null;
+    const rows = await this.prisma.roleGrant.findMany({
+      where: {
+        effect: 'ALLOW',
+        OR: [
+          { subjectType: 'USER', subjectId: user.id },
+          { subjectType: 'AUTHENTICATED' },
+          { subjectType: 'PUBLIC' },
+        ],
+      },
+      select: { pondId: true },
+      distinct: ['pondId'],
+    });
+    return rows.map((row) => row.pondId);
+  }
+
+  /** Prisma `where` fragment restricting pond queries to visible rows. */
+  async visiblePondsWhere(user: User): Promise<Prisma.PondWhereInput> {
+    const ids = await this.visiblePondIds(user);
+    return ids === null ? {} : { id: { in: ids } };
+  }
+}
--- a/apps/api/src/permissions/permissions.e2e.db.test.ts
+++ b/apps/api/src/permissions/permissions.e2e.db.test.ts
@ -0,0 +1,388 @@
+import { INestApplication } from '@nestjs/common';
+import { CreateGrantInput } from '@dorfteich/shared';
+import { PrismaClient } from '@prisma/client';
+import request from 'supertest';
+import { afterAll, beforeAll, describe, expect, it } from 'vitest';
+
+import { PondsService } from '../ponds/ponds.service';
+import { createTestApp, sessionCookieOf } from '../testing/test-app';
+import { createTestPrisma, hasTestDb, uniqueSuffix } from '../testing/test-db';
+import { UsersService } from '../users/users.service';
+
+/**
+ * The fixture matrix for the real permission model (issue #52 acceptance
+ * criteria): reader / editor / pond admin / foreign user against one shared
+ * pond, exercised through HTTP so the guard, the resolver, the 404/403
+ * policy, and the cache invalidation are all proven end to end.
+ */
+describe.skipIf(!hasTestDb)('permission enforcement (e2e, issue #52)', () => {
+  let app: INestApplication;
+  let prisma: PrismaClient;
+  const suffix = uniqueSuffix();
+  const password = 'berechtigungen sind kein zufall 1';
+
+  const userIds: Record<string, string> = {};
+  const cookies: Record<string, string> = {};
+
+  let pondId: string;
+  let pondSlug: string;
+  let pageId: string;
+
+  const api = () => request(app.getHttpServer());
+
+  async function makeUser(handle: string): Promise<void> {
+    const users = app.get(UsersService);
+    const username = `perm-${handle}-${suffix}`;
+    const user = await users.createUser({
+      username,
+      email: `${username}@example.org`,
+      displayName: `Perm ${handle}`,
+      password,
+      locale: 'en',
+    });
+    userIds[handle] = user.id;
+    await users.markEmailVerified(user.id);
+    const res = await api()
+      .post('/api/v1/auth/login')
+      .send({ usernameOrEmail: username, password })
+      .expect(200);
+    cookies[handle] = sessionCookieOf(res);
+  }
+
+  function grantInput(overrides: Partial<CreateGrantInput>): CreateGrantInput {
+    return {
+      subjectType: 'user',
+      subjectId: undefined,
+      role: 'reader',
+      scopeType: 'pond',
+      scopeId: undefined,
+      effect: 'allow',
+      ...overrides,
+    };
+  }
+
+  async function createGrant(input: CreateGrantInput, as = 'owner'): Promise<string> {
+    const res = await api()
+      .post(`/api/v1/ponds/${pondId}/grants`)
+      .set('Cookie', cookies[as]!)
+      .send(input)
+      .expect(201);
+    return (res.body as { id: string }).id;
+  }
+
+  beforeAll(async () => {
+    prisma = createTestPrisma();
+    await prisma.rateLimit.deleteMany({});
+    app = await createTestApp();
+
+    for (const handle of ['owner', 'reader', 'editor', 'admin2', 'foreign']) {
+      await makeUser(handle);
+    }
+    // markEmailVerified bypasses the verification flow, so the personal pond
+    // (for the personal-pond grant rules below) and the shared-pond quota
+    // headroom are created explicitly.
+    await app
+      .get(PondsService)
+      .ensurePersonalPond(await prisma.user.findUniqueOrThrow({ where: { id: userIds.owner! } }));
+    await prisma.quotaOverride.create({
+      data: {
+        subjectType: 'USER',
+        subjectId: userIds.owner!,
+        quotaKey: 'additional_ponds',
+        value: 10,
+      },
+    });
+
+    const pond = await api()
+      .post('/api/v1/ponds')
+      .set('Cookie', cookies.owner!)
+      .send({ name: `Perm Pond ${suffix}` })
+      .expect(201);
+    pondId = (pond.body as { id: string }).id;
+    pondSlug = (pond.body as { slug: string }).slug;
+
+    const page = await api()
+      .post(`/api/v1/ponds/${pondId}/pages`)
+      .set('Cookie', cookies.owner!)
+      .send({ title: 'Guarded Page' })
+      .expect(201);
+    pageId = (page.body as { id: string }).id;
+
+    await createGrant(grantInput({ subjectId: userIds.reader!, role: 'reader' }));
+    await createGrant(grantInput({ subjectId: userIds.editor!, role: 'editor' }));
+    await createGrant(grantInput({ subjectId: userIds.admin2!, role: 'pond_admin' }));
+  });
+
+  afterAll(async () => {
+    await prisma.roleGrant.deleteMany({ where: { pondId } });
+    await prisma.pageLabel.deleteMany({ where: { page: { pondId } } });
+    await prisma.label.deleteMany({ where: { pondId } });
+    await prisma.pageContentCache.deleteMany({ where: { page: { pondId } } });
+    await prisma.pageUpdate.deleteMany({ where: { page: { pondId } } });
+    await prisma.page.deleteMany({ where: { pondId } });
+    await prisma.pond.deleteMany({ where: { id: pondId } });
+    // Personal ponds (and their grants) before their users.
+    const ids = Object.values(userIds);
+    await prisma.roleGrant.deleteMany({ where: { pond: { ownerId: { in: ids } } } });
+    await prisma.pond.deleteMany({ where: { ownerId: { in: ids } } });
+    await prisma.quotaOverride.deleteMany({ where: { subjectId: { in: ids } } });
+    await prisma.user.deleteMany({ where: { id: { in: ids } } });
+    await prisma.$disconnect();
+    await app.close();
+  });
+
+  it('owner (pond admin) sees and edits everything, including grants', async () => {
+    await api().get(`/api/v1/ponds/${pondSlug}`).set('Cookie', cookies.owner!).expect(200);
+    await api()
+      .patch(`/api/v1/pages/${pageId}`)
+      .set('Cookie', cookies.owner!)
+      .send({ title: 'Renamed by owner' })
+      .expect(200);
+    const grants = await api()
+      .get(`/api/v1/ponds/${pondId}/grants`)
+      .set('Cookie', cookies.owner!)
+      .expect(200);
+    // Owner admin grant + the three fixture grants.
+    expect((grants.body as unknown[]).length).toBeGreaterThanOrEqual(4);
+  });
+
+  it('reader reads but cannot write (403 on readable things)', async () => {
+    await api().get(`/api/v1/ponds/${pondSlug}`).set('Cookie', cookies.reader!).expect(200);
+    await api().get(`/api/v1/pages/${pageId}`).set('Cookie', cookies.reader!).expect(200);
+    // Write on a readable page → 403 (README §Conventions).
+    await api()
+      .patch(`/api/v1/pages/${pageId}`)
+      .set('Cookie', cookies.reader!)
+      .send({ title: 'Nope' })
+      .expect(403);
+    // Page creation needs a pond-wide editor.
+    await api()
+      .post(`/api/v1/ponds/${pondId}/pages`)
+      .set('Cookie', cookies.reader!)
+      .send({ title: 'Nope' })
+      .expect(403);
+    // History is gated like editing (ADR 0013).
+    await api().get(`/api/v1/pages/${pageId}/versions`).set('Cookie', cookies.reader!).expect(403);
+  });
+
+  it('reader gets a read-only collab token, editor a rw one (issue #52)', async () => {
+    const ro = await api()
+      .get(`/api/v1/pages/${pageId}/collab-token`)
+      .set('Cookie', cookies.reader!)
+      .expect(200);
+    expect((ro.body as { mode: string }).mode).toBe('ro');
+
+    const rw = await api()
+      .get(`/api/v1/pages/${pageId}/collab-token`)
+      .set('Cookie', cookies.editor!)
+      .expect(200);
+    expect((rw.body as { mode: string }).mode).toBe('rw');
+  });
+
+  it('editor edits pages but cannot manage members or labels', async () => {
+    await api()
+      .patch(`/api/v1/pages/${pageId}`)
+      .set('Cookie', cookies.editor!)
+      .send({ title: 'Renamed by editor' })
+      .expect(200);
+    await api().get(`/api/v1/ponds/${pondId}/grants`).set('Cookie', cookies.editor!).expect(403);
+    await api()
+      .post(`/api/v1/ponds/${pondId}/grants`)
+      .set('Cookie', cookies.editor!)
+      .send(grantInput({ subjectId: userIds.editor!, role: 'pond_admin' }))
+      .expect(403);
+    await api()
+      .post(`/api/v1/ponds/${pondId}/labels`)
+      .set('Cookie', cookies.editor!)
+      .send({ name: 'Nope' })
+      .expect(403);
+    // Pond settings are Pond Admin work too.
+    await api()
+      .patch(`/api/v1/ponds/${pondId}`)
+      .set('Cookie', cookies.editor!)
+      .send({ name: 'Nope' })
+      .expect(403);
+  });
+
+  it('a second pond admin manages grants and labels', async () => {
+    const id = await createGrant(
+      grantInput({ subjectType: 'authenticated', role: 'reader' }),
+      'admin2',
+    );
+    await api()
+      .delete(`/api/v1/ponds/${pondId}/grants/${id}`)
+      .set('Cookie', cookies.admin2!)
+      .expect(204);
+    await api()
+      .patch(`/api/v1/ponds/${pondId}`)
+      .set('Cookie', cookies.admin2!)
+      .send({ name: `Perm Pond ${suffix}` })
+      .expect(200);
+  });
+
+  it('foreign users consistently see 404 — existence stays hidden', async () => {
+    await api().get(`/api/v1/ponds/${pondSlug}`).set('Cookie', cookies.foreign!).expect(404);
+    await api().get(`/api/v1/pages/${pageId}`).set('Cookie', cookies.foreign!).expect(404);
+    await api()
+      .patch(`/api/v1/pages/${pageId}`)
+      .set('Cookie', cookies.foreign!)
+      .send({ title: 'Nope' })
+      .expect(404);
+    await api().get(`/api/v1/ponds/${pondId}/grants`).set('Cookie', cookies.foreign!).expect(404);
+    await api().get(`/api/v1/ponds/${pondId}/trash`).set('Cookie', cookies.foreign!).expect(404);
+    // Not in the pond list either.
+    const list = await api().get('/api/v1/ponds').set('Cookie', cookies.foreign!).expect(200);
+    expect((list.body as { id: string }[]).map((p) => p.id)).not.toContain(pondId);
+  });
+
+  it('an authenticated-subject grant opens the pond to signed-in users', async () => {
+    const id = await createGrant(grantInput({ subjectType: 'authenticated', role: 'reader' }));
+    await api().get(`/api/v1/pages/${pageId}`).set('Cookie', cookies.foreign!).expect(200);
+    await api()
+      .delete(`/api/v1/ponds/${pondId}/grants/${id}`)
+      .set('Cookie', cookies.owner!)
+      .expect(204);
+    await api().get(`/api/v1/pages/${pageId}`).set('Cookie', cookies.foreign!).expect(404);
+  });
+
+  it('a label-scope deny beats the pond-scope allow (most specific wins)', async () => {
+    const label = await api()
+      .post(`/api/v1/ponds/${pondId}/labels`)
+      .set('Cookie', cookies.owner!)
+      .send({ name: `confidential-${suffix}` })
+      .expect(201);
+    const labelId = (label.body as { id: string }).id;
+    await api()
+      .post(`/api/v1/pages/${pageId}/labels`)
+      .set('Cookie', cookies.owner!)
+      .send({ labelId })
+      .expect(201);
+
+    const denyId = await createGrant(
+      grantInput({
+        subjectId: userIds.reader!,
+        role: 'reader',
+        scopeType: 'label',
+        scopeId: labelId,
+        effect: 'deny',
+      }),
+    );
+    // The page reads as nonexistent for the denied reader; the pond stays visible.
+    await api().get(`/api/v1/pages/${pageId}`).set('Cookie', cookies.reader!).expect(404);
+    await api().get(`/api/v1/ponds/${pondSlug}`).set('Cookie', cookies.reader!).expect(200);
+    // …and it disappears from the sidebar list.
+    const pages = await api()
+      .get(`/api/v1/ponds/${pondId}/pages`)
+      .set('Cookie', cookies.reader!)
+      .expect(200);
+    expect((pages.body as { id: string }[]).map((p) => p.id)).not.toContain(pageId);
+
+    await api()
+      .delete(`/api/v1/ponds/${pondId}/grants/${denyId}`)
+      .set('Cookie', cookies.owner!)
+      .expect(204);
+    await api()
+      .delete(`/api/v1/pages/${pageId}/labels/${labelId}`)
+      .set('Cookie', cookies.owner!)
+      .expect(204);
+    await api().get(`/api/v1/pages/${pageId}`).set('Cookie', cookies.reader!).expect(200);
+  });
+
+  it('revoking a grant denies the very next request (cache invalidation)', async () => {
+    // Fill the cache with a granted read…
+    await api().get(`/api/v1/pages/${pageId}`).set('Cookie', cookies.reader!).expect(200);
+    // …revoke…
+    const grants = await api()
+      .get(`/api/v1/ponds/${pondId}/grants`)
+      .set('Cookie', cookies.owner!)
+      .expect(200);
+    const readerGrant = (grants.body as { id: string; subjectId: string | null }[]).find(
+      (g) => g.subjectId === userIds.reader,
+    );
+    expect(readerGrant).toBeDefined();
+    await api()
+      .delete(`/api/v1/ponds/${pondId}/grants/${readerGrant!.id}`)
+      .set('Cookie', cookies.owner!)
+      .expect(204);
+    // …and the immediately following request is already denied.
+    await api().get(`/api/v1/pages/${pageId}`).set('Cookie', cookies.reader!).expect(404);
+
+    // Restore for any later cases.
+    await createGrant(grantInput({ subjectId: userIds.reader!, role: 'reader' }));
+    await api().get(`/api/v1/pages/${pageId}`).set('Cookie', cookies.reader!).expect(200);
+  });
+
+  it('trash requires write capability, per page (ADR 0013)', async () => {
+    const page = await api()
+      .post(`/api/v1/ponds/${pondId}/pages`)
+      .set('Cookie', cookies.editor!)
+      .send({ title: 'Trash me' })
+      .expect(201);
+    const trashedId = (page.body as { id: string }).id;
+    await api().delete(`/api/v1/pages/${trashedId}`).set('Cookie', cookies.editor!).expect(204);
+
+    // Readers see an empty trash and cannot restore; editors can.
+    const readerTrash = await api()
+      .get(`/api/v1/ponds/${pondId}/trash`)
+      .set('Cookie', cookies.reader!)
+      .expect(200);
+    expect(readerTrash.body).toEqual([]);
+    await api()
+      .post(`/api/v1/pages/${trashedId}/restore`)
+      .set('Cookie', cookies.reader!)
+      .expect(404);
+
+    const editorTrash = await api()
+      .get(`/api/v1/ponds/${pondId}/trash`)
+      .set('Cookie', cookies.editor!)
+      .expect(200);
+    expect((editorTrash.body as { id: string }[]).map((p) => p.id)).toContain(trashedId);
+    await api()
+      .post(`/api/v1/pages/${trashedId}/restore`)
+      .set('Cookie', cookies.editor!)
+      .expect(201);
+    await api().delete(`/api/v1/pages/${trashedId}`).set('Cookie', cookies.editor!).expect(204);
+    await api()
+      .delete(`/api/v1/pages/${trashedId}/purge`)
+      .set('Cookie', cookies.editor!)
+      .expect(204);
+  });
+
+  it('grant validation: personal ponds refuse extra admins, last admin stays', async () => {
+    const personal = await prisma.pond.findFirstOrThrow({
+      where: { ownerId: userIds.owner!, type: 'PERSONAL' },
+    });
+    await api()
+      .post(`/api/v1/ponds/${personal.id}/grants`)
+      .set('Cookie', cookies.owner!)
+      .send(grantInput({ subjectId: userIds.editor!, role: 'pond_admin' }))
+      .expect(400);
+
+    // The personal pond's only admin grant (the owner's) cannot be deleted.
+    const grants = await api()
+      .get(`/api/v1/ponds/${personal.id}/grants`)
+      .set('Cookie', cookies.owner!)
+      .expect(200);
+    const adminGrant = (grants.body as { id: string; role: string }[]).find(
+      (g) => g.role === 'pond_admin',
+    );
+    expect(adminGrant).toBeDefined();
+    await api()
+      .delete(`/api/v1/ponds/${personal.id}/grants/${adminGrant!.id}`)
+      .set('Cookie', cookies.owner!)
+      .expect(409);
+  });
+
+  it('rejects grants pointing at foreign or missing scopes and subjects', async () => {
+    await api()
+      .post(`/api/v1/ponds/${pondId}/grants`)
+      .set('Cookie', cookies.owner!)
+      .send(grantInput({ subjectId: userIds.reader!, scopeType: 'label', scopeId: 'missing' }))
+      .expect(400);
+    await api()
+      .post(`/api/v1/ponds/${pondId}/grants`)
+      .set('Cookie', cookies.owner!)
+      .send(grantInput({ subjectId: 'no-such-user' }))
+      .expect(400);
+  });
+});
--- a/apps/api/src/permissions/permissions.module.ts
+++ b/apps/api/src/permissions/permissions.module.ts
@ -0,0 +1,19 @@
+import { Global, Module } from '@nestjs/common';
+
+import { PermissionGuard } from './permission.guard';
+import { PermissionService } from './permission.service';
+import { PondPermissionCache } from './pond-permission-cache';
+
+/**
+ * The permission layer (issue #52, permissions.md): the guard + decorators
+ * every route declares its access rule through, the service that answers
+ * permission questions via the shared resolver, and the pond-context cache.
+ * Global so `@UseGuards(PermissionGuard)` (applied by the decorators) can
+ * resolve its dependencies from any feature module without import churn.
+ */
+@Global()
+@Module({
+  providers: [PermissionService, PondPermissionCache, PermissionGuard],
+  exports: [PermissionService, PondPermissionCache, PermissionGuard],
+})
+export class PermissionsModule {}
--- a/apps/api/src/permissions/pond-permission-cache.test.ts
+++ b/apps/api/src/permissions/pond-permission-cache.test.ts
@ -0,0 +1,36 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { PondPermissionCache, PondPermissionContext } from './pond-permission-cache';
+
+const CTX: PondPermissionContext = { grants: [], labelParents: {} };
+
+describe('PondPermissionCache (issue #52)', () => {
+  beforeEach(() => vi.useFakeTimers());
+  afterEach(() => vi.useRealTimers());
+
+  it('serves a stored context and drops it on invalidate', () => {
+    const cache = new PondPermissionCache();
+    cache.set('pond-1', CTX);
+    expect(cache.get('pond-1')).toBe(CTX);
+
+    cache.invalidate('pond-1');
+    expect(cache.get('pond-1')).toBeUndefined();
+  });
+
+  it('invalidating one pond leaves others untouched', () => {
+    const cache = new PondPermissionCache();
+    cache.set('pond-1', CTX);
+    cache.set('pond-2', CTX);
+    cache.invalidate('pond-1');
+    expect(cache.get('pond-2')).toBe(CTX);
+  });
+
+  it('expires entries after the TTL (multi-process staleness bound)', () => {
+    const cache = new PondPermissionCache();
+    cache.set('pond-1', CTX);
+    vi.advanceTimersByTime(PondPermissionCache.TTL_MS - 1);
+    expect(cache.get('pond-1')).toBe(CTX);
+    vi.advanceTimersByTime(2);
+    expect(cache.get('pond-1')).toBeUndefined();
+  });
+});
--- a/apps/api/src/permissions/pond-permission-cache.ts
+++ b/apps/api/src/permissions/pond-permission-cache.ts
@ -0,0 +1,52 @@
+import { Injectable } from '@nestjs/common';
+import { Grant } from '@dorfteich/shared';
+
+/** Everything pond-wide that permission resolution needs (permissions.md
+ * §Performance): the pond's grants and its label hierarchy. Page labels are
+ * *not* cached — they change with everyday editing and are one indexed query. */
+export interface PondPermissionContext {
+  grants: Grant[];
+  /** Every label in the pond → its parent id (or null), for ancestor walks. */
+  labelParents: Record<string, string | null>;
+}
+
+interface CacheEntry {
+  context: PondPermissionContext;
+  expiresAt: number;
+}
+
+/**
+ * In-process cache for {@link PondPermissionContext} (issue #52). Explicitly
+ * invalidated whenever grants or the label tree change (GrantsService,
+ * LabelsService), so a revoked permission takes effect with the very next
+ * request. The short TTL is a safety net only — it bounds staleness if the
+ * API ever runs in multiple processes, where another instance's mutations
+ * cannot invalidate this map (collab sessions are separately revalidated via
+ * the `pond_access_changed` notification, issue #39).
+ */
+@Injectable()
+export class PondPermissionCache {
+  private readonly entries = new Map<string, CacheEntry>();
+
+  /** Staleness bound for changes this process did not see (see class docs). */
+  static readonly TTL_MS = 30_000;
+
+  get(pondId: string): PondPermissionContext | undefined {
+    const entry = this.entries.get(pondId);
+    if (!entry) return undefined;
+    if (entry.expiresAt <= Date.now()) {
+      this.entries.delete(pondId);
+      return undefined;
+    }
+    return entry.context;
+  }
+
+  set(pondId: string, context: PondPermissionContext): void {
+    this.entries.set(pondId, { context, expiresAt: Date.now() + PondPermissionCache.TTL_MS });
+  }
+
+  /** Drop a pond's context — call after any grant or label-tree mutation. */
+  invalidate(pondId: string): void {
+    this.entries.delete(pondId);
+  }
+}
--- a/apps/api/src/permissions/route-permissions.e2e.db.test.ts
+++ b/apps/api/src/permissions/route-permissions.e2e.db.test.ts
@ -0,0 +1,87 @@
+import 'reflect-metadata';
+
+import { INestApplication } from '@nestjs/common';
+// Nest's own metadata keys — the same ones its router reads.
+import { GUARDS_METADATA, METHOD_METADATA, PATH_METADATA } from '@nestjs/common/constants';
+import { ModulesContainer } from '@nestjs/core';
+import { afterAll, beforeAll, describe, expect, it } from 'vitest';
+
+import { SiteAdminGuard } from '../admin/site-admin.guard';
+import { createTestApp } from '../testing/test-app';
+import { hasTestDb } from '../testing/test-db';
+import { PERMISSION_KEY } from './permission.decorators';
+
+/**
+ * Every route must carry an explicit access declaration (issue #52 acceptance
+ * criterion, default-closed — security.md): a permission decorator from
+ * `permission.decorators.ts`, `@Public()`, or the Site-Admin guard, on the
+ * handler or its controller. A route added without one fails here, so no
+ * endpoint can ship with access control forgotten rather than decided.
+ */
+
+const IS_PUBLIC_KEY = 'isPublic'; // auth.guard.ts
+
+type Handler = (...args: unknown[]) => unknown;
+
+function hasOwnOrClassMetadata(key: string, handler: Handler, controller: object): boolean {
+  return (
+    Reflect.getMetadata(key, handler) !== undefined ||
+    Reflect.getMetadata(key, controller) !== undefined
+  );
+}
+
+function hasSiteAdminGuard(handler: Handler, controller: object): boolean {
+  const guards: unknown[] = [
+    ...((Reflect.getMetadata(GUARDS_METADATA, handler) as unknown[] | undefined) ?? []),
+    ...((Reflect.getMetadata(GUARDS_METADATA, controller) as unknown[] | undefined) ?? []),
+  ];
+  return guards.includes(SiteAdminGuard);
+}
+
+describe.skipIf(!hasTestDb)('route permission coverage (issue #52)', () => {
+  let app: INestApplication;
+
+  beforeAll(async () => {
+    app = await createTestApp();
+  });
+
+  afterAll(async () => {
+    await app.close();
+  });
+
+  it('every route declares its access rule explicitly', () => {
+    const modules = app.get(ModulesContainer);
+    const uncovered: string[] = [];
+    let routes = 0;
+
+    for (const module of modules.values()) {
+      for (const wrapper of module.controllers.values()) {
+        const controller = wrapper.metatype as (new () => unknown) | undefined;
+        if (!controller) continue;
+        const prototype = controller.prototype as Record<string, unknown>;
+        for (const name of Object.getOwnPropertyNames(prototype)) {
+          if (name === 'constructor') continue;
+          const handler = prototype[name];
+          if (typeof handler !== 'function') continue;
+          // Only actual routes: Nest stores the HTTP verb on the handler.
+          if (Reflect.getMetadata(METHOD_METADATA, handler) === undefined) continue;
+          routes += 1;
+
+          const covered =
+            hasOwnOrClassMetadata(PERMISSION_KEY, handler as Handler, controller) ||
+            hasOwnOrClassMetadata(IS_PUBLIC_KEY, handler as Handler, controller) ||
+            hasSiteAdminGuard(handler as Handler, controller);
+          if (!covered) {
+            const base = Reflect.getMetadata(PATH_METADATA, controller) as string;
+            const path = Reflect.getMetadata(PATH_METADATA, handler) as string;
+            uncovered.push(`${controller.name}.${name} (${base}/${path})`);
+          }
+        }
+      }
+    }
+
+    // Sanity: the enumeration actually saw the app's routes.
+    expect(routes).toBeGreaterThan(40);
+    expect(uncovered).toEqual([]);
+  });
+});
--- a/apps/api/src/ponds/interim-access.service.ts
+++ b/apps/api/src/ponds/interim-access.service.ts
@ -1,36 +0,0 @@
-import { Injectable, NotFoundException } from '@nestjs/common';
-import { Pond, Prisma, User } from '@prisma/client';
-
-/**
- * INTERIM access control, M2–M4 only: a pond is visible and editable for
- * its owner and for Site Admins, nobody else. The real role model
- * (docs/architecture/permissions.md) arrives with M5 and replaces this
- * service. Until then, every access question about ponds and their
- * content MUST be asked here and nowhere else — that keeps the M5 swap
- * confined to this one file (issue #21 acceptance criterion).
- */
-@Injectable()
-export class InterimAccessService {
-  canSeePond(user: User, pond: Pond): boolean {
-    return user.isSiteAdmin || pond.ownerId === user.id;
-  }
-
-  canModifyPond(user: User, pond: Pond): boolean {
-    // Interim rule: seeing and modifying coincide until M5 separates roles.
-    return this.canSeePond(user, pond);
-  }
-
-  /** Prisma `where` fragment restricting pond queries to visible rows. */
-  visiblePondsWhere(user: User): Prisma.PondWhereInput {
-    return user.isSiteAdmin ? {} : { ownerId: user.id };
-  }
-
-  /** 404 — not 403 — so outsiders cannot probe which slugs exist. */
-  assertCanSee(user: User, pond: Pond | null): asserts pond is Pond {
-    if (!pond || !this.canSeePond(user, pond)) throw new NotFoundException();
-  }
-
-  assertCanModify(user: User, pond: Pond | null): asserts pond is Pond {
-    if (!pond || !this.canModifyPond(user, pond)) throw new NotFoundException();
-  }
-}
--- a/apps/api/src/ponds/ponds.controller.ts
+++ b/apps/api/src/ponds/ponds.controller.ts
@ -23,14 +23,16 @@ import { Prisma } from '@prisma/client';
 import { SiteAdminGuard } from '../admin/site-admin.guard';
 import { AuthedRequest } from '../auth/auth.guard';
 import { ZodValidationPipe } from '../common/zod-validation.pipe';
+import { AuthenticatedOnly, RequiresPondRole } from '../permissions/permission.decorators';
 import { PondsService } from './ponds.service';

-/** Pond CRUD (issue #21). Access rules live in InterimAccessService. */
+/** Pond CRUD (issue #21; permission guard since #52). */
@Controller('ponds')
 export class PondsController {
  constructor(private readonly ponds: PondsService) {}

  @Post()
+  @AuthenticatedOnly() // any signed-in user may create ponds; quotas gate how many
  async create(
    @Body(new ZodValidationPipe(createPondInputSchema)) input: CreatePondInput,
    @Req() request: AuthedRequest,
@ -39,6 +41,7 @@ export class PondsController {
  }

  @Get()
+  @AuthenticatedOnly() // the service filters to the caller's visible ponds
  async list(@Req() request: AuthedRequest): Promise<PondView[]> {
    return this.ponds.listVisible(request.user!);
  }
@ -51,11 +54,13 @@ export class PondsController {
  }

  @Get(':slug')
+  @RequiresPondRole('reader', { slugParam: 'slug' })
  async bySlug(@Param('slug') slug: string, @Req() request: AuthedRequest): Promise<PondView> {
    return this.ponds.getVisibleBySlug(request.user!, slug);
  }

  @Patch(':id')
+  @RequiresPondRole('pond_admin', { idParam: 'id' })
  async update(
    @Param('id') id: string,
    @Body(new ZodValidationPipe(updatePondInputSchema)) input: UpdatePondInput,
@ -66,6 +71,7 @@ export class PondsController {

  @Delete(':id')
  @HttpCode(204)
+  @RequiresPondRole('pond_admin', { idParam: 'id' })
  async remove(@Param('id') id: string, @Req() request: AuthedRequest): Promise<void> {
    await this.ponds.softDelete(request.user!, id);
  }
--- a/apps/api/src/ponds/ponds.module.ts
+++ b/apps/api/src/ponds/ponds.module.ts
@ -2,7 +2,6 @@ import { Module } from '@nestjs/common';

 import { QuotasModule } from '../quotas/quotas.module';

-import { InterimAccessService } from './interim-access.service';
 import { PondAccessNotifier } from './pond-access-notifier.service';
 import { PondsController } from './ponds.controller';
 import { PondsService } from './ponds.service';
@ -10,7 +9,7 @@ import { PondsService } from './ponds.service';
@Module({
  imports: [QuotasModule],
  controllers: [PondsController],
-  providers: [PondsService, InterimAccessService, PondAccessNotifier],
-  exports: [PondsService, InterimAccessService, PondAccessNotifier],
+  providers: [PondsService, PondAccessNotifier],
+  exports: [PondsService, PondAccessNotifier],
 })
 export class PondsModule {}
--- a/apps/api/src/ponds/ponds.service.ts
+++ b/apps/api/src/ponds/ponds.service.ts
@ -1,4 +1,4 @@
-import { ForbiddenException, Injectable } from '@nestjs/common';
+import { ForbiddenException, Injectable, NotFoundException } from '@nestjs/common';
 import {
  CreatePondInput,
  PondView,
@ -6,19 +6,19 @@ import {
  pondSettingsSchema,
  slugify,
 } from '@dorfteich/shared';
-import { Pond, User } from '@prisma/client';
+import { Pond, Prisma, User } from '@prisma/client';
 import { PinoLogger } from 'nestjs-pino';

+import { PermissionService } from '../permissions/permission.service';
 import { PrismaService } from '../prisma/prisma.service';
 import { QuotaService } from '../quotas/quota.service';
-import { InterimAccessService } from './interim-access.service';
 import { PondAccessNotifier } from './pond-access-notifier.service';

@Injectable()
 export class PondsService {
  constructor(
    private readonly prisma: PrismaService,
-    private readonly access: InterimAccessService,
+    private readonly permissions: PermissionService,
    private readonly quotas: QuotaService,
    private readonly accessNotifier: PondAccessNotifier,
    private readonly logger: PinoLogger,
@ -63,13 +63,34 @@ export class PondsService {
    }
  }

+  /**
+   * The owner's Pond Admin grant, created with the pond itself (issue #52) —
+   * access is decided solely by grants, so a pond without this row would be
+   * invisible even to its owner. Written directly (not through GrantsService)
+   * because the "no pond_admin grants on personal ponds" rule is about
+   * *additional* admins; the owner is the one admin every pond starts with.
+   */
+  private static ownerAdminGrant(pondId: string, ownerId: string): Prisma.RoleGrantCreateInput {
+    return {
+      pond: { connect: { id: pondId } },
+      subjectType: 'USER',
+      subjectId: ownerId,
+      role: 'POND_ADMIN',
+      scopeType: 'POND',
+      scopeId: null,
+      effect: 'ALLOW',
+      createdBy: ownerId,
+    };
+  }
+
  async createShared(owner: User, input: CreatePondInput): Promise<PondView> {
    const slug = await this.generateUniqueSlug(input.name, owner.username);
    // Quota check and create share one transaction — the advisory lock in
-    // the check makes concurrent creations by the same user race-safe.
+    // the check makes concurrent creations by the same user race-safe. The
+    // owner grant joins it so no pond ever exists without its admin.
    const pond = await this.prisma.$transaction(async (tx) => {
      await this.quotas.assertCanCreateSharedPond(tx, owner.id);
-      return tx.pond.create({
+      const created = await tx.pond.create({
        data: {
          slug,
          name: input.name,
@ -78,6 +99,8 @@ export class PondsService {
          ownerId: owner.id,
        },
      });
+      await tx.roleGrant.create({ data: PondsService.ownerAdminGrant(created.id, owner.id) });
+      return created;
    });
    this.logger.info({ pondId: pond.id, ownerId: owner.id }, 'audit: pond created');
    return this.viewOf(pond);
@ -94,34 +117,35 @@ export class PondsService {
      select: { id: true },
    });
    if (existing) return;
-    const pond = await this.prisma.pond.create({
-      data: {
-        slug: await this.generateUniqueSlug(user.displayName, user.username),
-        name: user.displayName,
-        type: 'PERSONAL',
-        ownerId: user.id,
-      },
+    const slug = await this.generateUniqueSlug(user.displayName, user.username);
+    const pond = await this.prisma.$transaction(async (tx) => {
+      const created = await tx.pond.create({
+        data: { slug, name: user.displayName, type: 'PERSONAL', ownerId: user.id },
+      });
+      await tx.roleGrant.create({ data: PondsService.ownerAdminGrant(created.id, user.id) });
+      return created;
    });
    this.logger.info({ pondId: pond.id, ownerId: user.id }, 'audit: personal pond created');
  }

  async listVisible(user: User): Promise<PondView[]> {
    const ponds = await this.prisma.pond.findMany({
-      where: { ...this.access.visiblePondsWhere(user), deletedAt: null },
+      where: { ...(await this.permissions.visiblePondsWhere(user)), deletedAt: null },
      orderBy: { name: 'asc' },
    });
    return ponds.map((pond) => this.viewOf(pond));
  }

-  async getVisibleBySlug(user: User, slug: string): Promise<PondView> {
+  /** Existence/permission are the guard's job (#52); this only loads. */
+  async getVisibleBySlug(_user: User, slug: string): Promise<PondView> {
    const pond = await this.prisma.pond.findFirst({ where: { slug, deletedAt: null } });
-    this.access.assertCanSee(user, pond);
+    if (!pond) throw new NotFoundException();
    return this.viewOf(pond);
  }

-  async update(user: User, id: string, input: UpdatePondInput): Promise<PondView> {
+  async update(_user: User, id: string, input: UpdatePondInput): Promise<PondView> {
    const pond = await this.prisma.pond.findFirst({ where: { id, deletedAt: null } });
-    this.access.assertCanModify(user, pond);
+    if (!pond) throw new NotFoundException();
    const settings =
      input.sidebarSort === undefined
        ? undefined
@ -135,7 +159,7 @@ export class PondsService {

  async softDelete(user: User, id: string): Promise<void> {
    const pond = await this.prisma.pond.findFirst({ where: { id, deletedAt: null } });
-    this.access.assertCanModify(user, pond);
+    if (!pond) throw new NotFoundException();
    if (pond.type === 'PERSONAL') {
      // The personal pond is the account's home — it cannot be trashed.
      throw new ForbiddenException({ code: 'personal_pond_undeletable' });
@ -145,9 +169,8 @@ export class PondsService {
      data: { deletedAt: new Date(), deletedBy: user.id },
    });
    this.logger.info({ pondId: id, userId: user.id }, 'audit: pond trashed');
-    // Trashing a pond is the interim access-relevant change: revalidate any
-    // live collaboration sessions on its pages (issue #39). Real per-user
-    // grant revocation reuses this same notification from M5 on (#53).
+    // Revalidate any live collaboration sessions on the pond's pages
+    // (issue #39); grant changes fire the same notification (#52/#53).
    await this.accessNotifier.notifyAccessChanged(id);
  }

--- a/apps/api/src/search/postgres-search.provider.ts
+++ b/apps/api/src/search/postgres-search.provider.ts
@ -9,6 +9,7 @@ import {
 } from '@dorfteich/shared';
 import { Prisma, User } from '@prisma/client';

+import { PermissionService } from '../permissions/permission.service';
 import { PrismaService } from '../prisma/prisma.service';
 import { SearchProvider } from './search.provider';

@ -45,7 +46,10 @@ interface SearchRow {
 */
@Injectable()
 export class PostgresSearchProvider extends SearchProvider {
-  constructor(private readonly prisma: PrismaService) {
+  constructor(
+    private readonly prisma: PrismaService,
+    private readonly permissions: PermissionService,
+  ) {
    super();
  }

@ -99,6 +103,15 @@ export class PostgresSearchProvider extends SearchProvider {
    // A phrase that folds to nothing (e.g. only punctuation) matches nothing.
    if (normalized.trim() === '') return [];

+    // Pond-level prefilter (visible ponds only) keeps the LIMIT meaningful;
+    // the exact per-page resolution happens below (issue #52, ADR 0010).
+    const visiblePondIds = await this.permissions.visiblePondIds(user);
+    if (visiblePondIds !== null && visiblePondIds.length === 0) return [];
+    const visibility =
+      visiblePondIds === null
+        ? Prisma.empty
+        : Prisma.sql`AND p.pond_id = ANY(${visiblePondIds}::text[])`;
+
    const scope = query.pondId ? Prisma.sql`AND p.pond_id = ${query.pondId}` : Prisma.empty;
    const labelFilter =
      query.labels && query.labels.length > 0
@ -120,21 +133,43 @@ export class PostgresSearchProvider extends SearchProvider {
        JOIN ponds po ON po.id = p.pond_id AND po.deleted_at IS NULL,
             websearch_to_tsquery('simple', ${normalized}) q
       WHERE c.search_vector @@ q
-         AND (${user.isSiteAdmin}::boolean OR po.owner_id = ${user.id})
+         ${visibility}
         ${scope}
         ${labelFilter}
       ORDER BY ts_rank(c.search_vector, q) DESC, p.updated_at DESC
       LIMIT ${SEARCH_RESULT_LIMIT}`);

-    return rows.map((row) => ({
-      pageId: row.pageId,
-      title: row.title,
-      slug: row.slug,
-      pondId: row.pondId,
-      pondSlug: row.pondSlug,
-      pondName: row.pondName,
-      labelIds: row.labelIds,
-      snippet: row.snippet,
-    }));
+    // Per-page resolution (label-/page-scope grants, deny-wins) per pond.
+    const rowsByPond = new Map<string, SearchRow[]>();
+    for (const row of rows) {
+      const group = rowsByPond.get(row.pondId) ?? [];
+      group.push(row);
+      rowsByPond.set(row.pondId, group);
+    }
+    const readableByPond = new Map<string, Set<string>>();
+    for (const [pondId, group] of rowsByPond) {
+      readableByPond.set(
+        pondId,
+        await this.permissions.filterPages(
+          user,
+          pondId,
+          group.map((row) => ({ id: row.pageId, labelIds: row.labelIds })),
+          'read',
+        ),
+      );
+    }
+
+    return rows
+      .filter((row) => readableByPond.get(row.pondId)?.has(row.pageId))
+      .map((row) => ({
+        pageId: row.pageId,
+        title: row.title,
+        slug: row.slug,
+        pondId: row.pondId,
+        pondSlug: row.pondSlug,
+        pondName: row.pondName,
+        labelIds: row.labelIds,
+        snippet: row.snippet,
+      }));
  }
 }
--- a/apps/api/src/search/reindex.cli.ts
+++ b/apps/api/src/search/reindex.cli.ts
@ -1,3 +1,5 @@
+import { PermissionService } from '../permissions/permission.service';
+import { PondPermissionCache } from '../permissions/pond-permission-cache';
 import { PrismaService } from '../prisma/prisma.service';
 import { PostgresSearchProvider } from './postgres-search.provider';

@ -12,7 +14,10 @@ import { PostgresSearchProvider } from './postgres-search.provider';
 */
 async function main(): Promise<void> {
  const prisma = new PrismaService();
-  const provider = new PostgresSearchProvider(prisma);
+  // Reindexing never asks permission questions, but the provider's search
+  // path needs the service — wire it manually like everything here.
+  const permissions = new PermissionService(prisma, new PondPermissionCache());
+  const provider = new PostgresSearchProvider(prisma, permissions);
  try {
    const count = await provider.reindexAll();
    console.log(`search:reindex — indexed ${count} page(s)`);
--- a/apps/api/src/search/search.controller.ts
+++ b/apps/api/src/search/search.controller.ts
@ -2,6 +2,7 @@ import { BadRequestException, Controller, Get, Query, Req } from '@nestjs/common
 import { SearchQuery, SearchResultView, searchQuerySchema } from '@dorfteich/shared';

 import { AuthedRequest } from '../auth/auth.guard';
+import { AuthenticatedOnly } from '../permissions/permission.decorators';
 import { SearchProvider } from './search.provider';

 /** Full-text search (issue #49, ADR 0010). */
@ -14,6 +15,7 @@ export class SearchController {
   * `labels` is a comma-separated list; scope defaults to all readable ponds.
   */
  @Get('search')
+  @AuthenticatedOnly() // results are permission-filtered inside the provider
  async query(
    @Query('q') q: string,
    @Query('pondId') pondId: string | undefined,
--- a/apps/api/src/search/search.service.db.test.ts
+++ b/apps/api/src/search/search.service.db.test.ts
@ -7,7 +7,7 @@ import { afterAll, beforeAll, describe, expect, it } from 'vitest';
 import * as Y from 'yjs';

 import { createTestApp } from '../testing/test-app';
-import { createTestPrisma, hasTestDb, uniqueSuffix } from '../testing/test-db';
+import { createTestPrisma, grantOwnerAdmin, hasTestDb, uniqueSuffix } from '../testing/test-db';
 import { SearchProvider } from './search.provider';

 describe.skipIf(!hasTestDb)('PostgresSearchProvider (db, issue #49)', () => {
@ -69,6 +69,7 @@ describe.skipIf(!hasTestDb)('PostgresSearchProvider (db, issue #49)', () => {
      },
    });
    pondId = pond.id;
+    await grantOwnerAdmin(prisma, pondId, owner.id);
  });

  afterAll(async () => {
@ -116,6 +117,7 @@ describe.skipIf(!hasTestDb)('PostgresSearchProvider (db, issue #49)', () => {
        ownerId: owner.id,
      },
    });
+    await grantOwnerAdmin(prisma, other.id, owner.id);
    const otherPage = await prisma.page.create({
      data: {
        id: randomUUID(),
--- a/apps/api/src/testing/test-db.ts
+++ b/apps/api/src/testing/test-db.ts
@ -15,3 +15,28 @@ export function createTestPrisma(): PrismaClient {
 export function uniqueSuffix(): string {
  return Math.random().toString(36).slice(2, 10);
 }
+
+/**
+ * The owner's Pond Admin grant for a pond created directly through Prisma.
+ * Production paths create it with the pond (PondsService, issue #52);
+ * fixtures that bypass the service need it too, or the owner cannot see
+ * their own pond under the grant-based resolution.
+ */
+export async function grantOwnerAdmin(
+  prisma: PrismaClient,
+  pondId: string,
+  ownerId: string,
+): Promise<void> {
+  await prisma.roleGrant.create({
+    data: {
+      pondId,
+      subjectType: 'USER',
+      subjectId: ownerId,
+      role: 'POND_ADMIN',
+      scopeType: 'POND',
+      scopeId: null,
+      effect: 'ALLOW',
+      createdBy: ownerId,
+    },
+  });
+}
--- a/apps/api/src/trash/trash.controller.ts
+++ b/apps/api/src/trash/trash.controller.ts
@ -2,6 +2,7 @@ import { Controller, Delete, Get, HttpCode, Param, Post, Req } from '@nestjs/com
 import { PageView } from '@dorfteich/shared';

 import { AuthedRequest } from '../auth/auth.guard';
+import { RequiresPagePermission, RequiresPondRole } from '../permissions/permission.decorators';

 import { TrashService } from './trash.service';

@ -11,17 +12,20 @@ export class TrashController {
  constructor(private readonly trash: TrashService) {}

  @Get('ponds/:pondId/trash')
+  @RequiresPondRole('reader', { idParam: 'pondId' }) // the service filters to editable pages
  async list(@Param('pondId') pondId: string, @Req() request: AuthedRequest): Promise<PageView[]> {
    return this.trash.list(request.user!, pondId);
  }

  @Post('pages/:id/restore')
+  @RequiresPagePermission('write', { idParam: 'id', inTrash: true })
  async restore(@Param('id') id: string, @Req() request: AuthedRequest): Promise<PageView> {
    return this.trash.restore(request.user!, id);
  }

  @Delete('pages/:id/purge')
  @HttpCode(204)
+  @RequiresPagePermission('write', { idParam: 'id', inTrash: true })
  async purge(@Param('id') id: string, @Req() request: AuthedRequest): Promise<void> {
    await this.trash.purgeNow(request.user!, id);
  }
--- a/apps/api/src/trash/trash.service.ts
+++ b/apps/api/src/trash/trash.service.ts
@ -5,7 +5,7 @@ import { PinoLogger } from 'nestjs-pino';

 import { ClockService } from '../common/clock.service';
 import { PagesService } from '../pages/pages.service';
-import { InterimAccessService } from '../ponds/interim-access.service';
+import { PermissionService } from '../permissions/permission.service';
 import { PrismaService } from '../prisma/prisma.service';
 import { QuotaService } from '../quotas/quota.service';
 import { InstanceSettingsService } from '../settings/instance-settings.service';
@ -24,7 +24,7 @@ const MS_PER_DAY = 24 * 60 * 60 * 1000;
 export class TrashService {
  constructor(
    private readonly prisma: PrismaService,
-    private readonly access: InterimAccessService,
+    private readonly permissions: PermissionService,
    private readonly pages: PagesService,
    private readonly settings: InstanceSettingsService,
    private readonly quotas: QuotaService,
@ -35,21 +35,27 @@ export class TrashService {
    this.logger.setContext(TrashService.name);
  }

-  /** A pond's trash — same access rule as restoring/purging from it. */
+  /** A pond's trash: the trashed pages the user could edit — trash access is
+   * write capability (ADR 0013), resolved per page (issue #52). */
  async list(user: User, pondId: string): Promise<PageView[]> {
    const pond = await this.prisma.pond.findFirst({ where: { id: pondId, deletedAt: null } });
-    this.access.assertCanModify(user, pond);
+    if (!pond) throw new NotFoundException();
    const pages = await this.prisma.page.findMany({
      where: { pondId, deletedAt: { not: null } },
      orderBy: { deletedAt: 'desc' },
    });
-    return pages.map((page) => this.pages.viewOf(page));
+    const editable = await this.permissions.filterPages(
+      user,
+      pondId,
+      pages.map((page) => ({ id: page.id })),
+      'write',
+    );
+    return pages.filter((page) => editable.has(page.id)).map((page) => this.pages.viewOf(page));
  }

  async restore(user: User, id: string): Promise<PageView> {
-    const page = await this.prisma.page.findFirst({ where: { id }, include: { pond: true } });
+    const page = await this.prisma.page.findFirst({ where: { id } });
    if (!page || !page.deletedAt) throw new NotFoundException();
-    this.access.assertCanModify(user, page.pond);
    const restored = await this.prisma.page.update({
      where: { id },
      data: { deletedAt: null, deletedBy: null },
@ -60,9 +66,8 @@ export class TrashService {

  /** Manual "purge single" (scope's third trash endpoint) — bypasses retention. */
  async purgeNow(user: User, id: string): Promise<void> {
-    const page = await this.prisma.page.findFirst({ where: { id }, include: { pond: true } });
+    const page = await this.prisma.page.findFirst({ where: { id } });
    if (!page || !page.deletedAt) throw new NotFoundException();
-    this.access.assertCanModify(user, page.pond);
    await this.purgePage(id);
    this.logger.info({ pageId: id, userId: user.id }, 'audit: page purged from trash');
  }
--- a/apps/api/src/users/users.controller.ts
+++ b/apps/api/src/users/users.controller.ts
@ -20,6 +20,7 @@ import {
 import { AuthedRequest, toCurrentUser } from '../auth/auth.guard';
 import { SessionsService } from '../auth/sessions.service';
 import { ZodValidationPipe } from '../common/zod-validation.pipe';
+import { AuthenticatedOnly } from '../permissions/permission.decorators';
 import { UsersService } from './users.service';

 export interface SessionView {
@ -30,7 +31,9 @@ export interface SessionView {
  current: boolean;
 }

-/** Self-service endpoints for the signed-in account (issues #17, #18). */
+/** Self-service endpoints for the signed-in account (issues #17, #18) —
+ * every route only touches the caller's own data. */
+@AuthenticatedOnly()
@Controller('users/me')
 export class UsersController {
  constructor(
--- a/apps/api/src/versions/versions.controller.ts
+++ b/apps/api/src/versions/versions.controller.ts
@ -8,6 +8,7 @@ import {

 import { AuthedRequest } from '../auth/auth.guard';
 import { ZodValidationPipe } from '../common/zod-validation.pipe';
+import { RequiresPagePermission } from '../permissions/permission.decorators';
 import { VersionsService } from './versions.service';

 /**
@ -20,12 +21,14 @@ export class VersionsController {

  /** List the page's versions, newest first. */
  @Get('pages/:id/versions')
+  @RequiresPagePermission('write', { idParam: 'id' }) // history = write (ADR 0013)
  async list(@Param('id') id: string, @Req() request: AuthedRequest): Promise<PageVersionView[]> {
    return this.versions.list(request.user!, id);
  }

  /** A single version rendered read-only, with Markdown for diffing. */
  @Get('pages/:id/versions/:versionId')
+  @RequiresPagePermission('write', { idParam: 'id' })
  async getContent(
    @Param('id') id: string,
    @Param('versionId') versionId: string,
@ -36,6 +39,7 @@ export class VersionsController {

  /** Create a named version of the page. */
  @Post('pages/:id/versions')
+  @RequiresPagePermission('write', { idParam: 'id' })
  async createNamed(
    @Param('id') id: string,
    @Body(new ZodValidationPipe(createVersionInputSchema)) input: CreateVersionInput,
@ -46,6 +50,7 @@ export class VersionsController {

  /** Restore the page to an earlier version (creates a pre-restore snapshot). */
  @Post('pages/:id/versions/:versionId/restore')
+  @RequiresPagePermission('write', { idParam: 'id' })
  async restore(
    @Param('id') id: string,
    @Param('versionId') versionId: string,
--- a/apps/api/src/versions/versions.service.db.test.ts
+++ b/apps/api/src/versions/versions.service.db.test.ts
@ -15,7 +15,6 @@ describe.skipIf(!hasTestDb)('VersionsService (db, issue #41)', () => {
  let versions: VersionsService;
  const suffix = uniqueSuffix();
  let owner: User;
-  let outsider: User;
  let pondId: string;
  const pageIds: string[] = [];

@ -48,13 +47,6 @@ describe.skipIf(!hasTestDb)('VersionsService (db, issue #41)', () => {
        displayName: 'Version Owner',
      },
    });
-    outsider = await prisma.user.create({
-      data: {
-        username: `ver-out-${suffix}`,
-        email: `ver-out-${suffix}@example.test`,
-        displayName: 'Version Outsider',
-      },
-    });
    const pond = await prisma.pond.create({
      data: {
        slug: `ver-pond-${suffix}`,
@ -69,7 +61,7 @@ describe.skipIf(!hasTestDb)('VersionsService (db, issue #41)', () => {
  afterAll(async () => {
    if (pageIds.length > 0) await prisma.page.deleteMany({ where: { id: { in: pageIds } } });
    await prisma.pond.deleteMany({ where: { id: pondId } });
-    await prisma.user.deleteMany({ where: { id: { in: [owner.id, outsider.id] } } });
+    await prisma.user.deleteMany({ where: { id: owner.id } });
    await prisma.$disconnect();
    await app.close();
  });
@ -121,18 +113,8 @@ describe.skipIf(!hasTestDb)('VersionsService (db, issue #41)', () => {
    expect(typeof content.markdown).toBe('string');
  });

-  it('gates list, content, and restore on write access', async () => {
-    const pageId = await createPage();
-    const version = await versions.createNamed(owner, pageId, { label: 'v' });
-
-    await expect(versions.list(outsider, pageId)).rejects.toBeInstanceOf(NotFoundException);
-    await expect(versions.getContent(outsider, pageId, version.id)).rejects.toBeInstanceOf(
-      NotFoundException,
-    );
-    await expect(versions.restore(outsider, pageId, version.id)).rejects.toBeInstanceOf(
-      NotFoundException,
-    );
-  });
+  // Write-access gating of every history route moved to the route guard
+  // with #52 — covered by the permission e2e pack.

  it('restore returns the target version and emits without mutating history', async () => {
    const pageId = await createPage();
@ -150,14 +132,6 @@ describe.skipIf(!hasTestDb)('VersionsService (db, issue #41)', () => {
    );
  });

-  it('refuses a named version for a user without write access', async () => {
-    const pageId = await createPage();
-    await expect(versions.createNamed(outsider, pageId, { label: 'nope' })).rejects.toBeInstanceOf(
-      NotFoundException,
-    );
-    expect(await prisma.pageVersion.count({ where: { pageId } })).toBe(0);
-  });
-
  it('thins auto versions beyond the window to the newest per day, keeping the rest', async () => {
    const pageId = await createPage();
    const daysAgo = (days: number, hour: number): Date => {
--- a/apps/api/src/versions/versions.service.ts
+++ b/apps/api/src/versions/versions.service.ts
@ -7,12 +7,11 @@ import {
  PageVersionTrigger,
  PageVersionView,
 } from '@dorfteich/shared';
-import { Page, PageVersion, PageVersionTrigger as PrismaTrigger, Pond, User } from '@prisma/client';
+import { Page, PageVersion, PageVersionTrigger as PrismaTrigger, User } from '@prisma/client';
 import { PinoLogger } from 'nestjs-pino';
 import * as Y from 'yjs';

 import { deriveContent } from '../pages/yjs-content';
-import { InterimAccessService } from '../ponds/interim-access.service';
 import { PrismaService } from '../prisma/prisma.service';

 /**
@ -39,7 +38,6 @@ const TRIGGER_TO_VIEW: Record<PrismaTrigger, PageVersionTrigger> = {
 export class VersionsService {
  constructor(
    private readonly prisma: PrismaService,
-    private readonly access: InterimAccessService,
    private readonly logger: PinoLogger,
  ) {
    this.logger.setContext(VersionsService.name);
@ -58,23 +56,19 @@ export class VersionsService {
  }

  /**
-   * Load a page and assert the user may edit it. Viewing history requires the
-   * same permission as editing (permissions.md §UI obligations / ADR 0013), so
-   * every history operation gates on `assertCanModify`.
+   * Load a live page. Viewing history requires the same permission as
+   * editing (ADR 0013) — the guard enforces write access on every history
+   * route (#52); here only existence is checked.
   */
-  private async findModifiablePage(user: User, pageId: string): Promise<Page & { pond: Pond }> {
-    const page = await this.prisma.page.findFirst({
-      where: { id: pageId, deletedAt: null },
-      include: { pond: true },
-    });
+  private async findLivePage(pageId: string): Promise<Page> {
+    const page = await this.prisma.page.findFirst({ where: { id: pageId, deletedAt: null } });
    if (!page) throw new NotFoundException();
-    this.access.assertCanModify(user, page.pond);
    return page;
  }

  /** The page's versions, newest first (no snapshot bytes). Write access only. */
-  async list(user: User, pageId: string): Promise<PageVersionView[]> {
-    await this.findModifiablePage(user, pageId);
+  async list(_user: User, pageId: string): Promise<PageVersionView[]> {
+    await this.findLivePage(pageId);
    const versions = await this.prisma.pageVersion.findMany({
      where: { pageId },
      orderBy: { createdAt: 'desc' },
@ -85,8 +79,12 @@ export class VersionsService {
  }

  /** A single version rendered read-only (HTML) with its Markdown for diffing. */
-  async getContent(user: User, pageId: string, versionId: string): Promise<PageVersionContentView> {
-    await this.findModifiablePage(user, pageId);
+  async getContent(
+    _user: User,
+    pageId: string,
+    versionId: string,
+  ): Promise<PageVersionContentView> {
+    await this.findLivePage(pageId);
    const version = await this.prisma.pageVersion.findFirst({
      where: { id: versionId, pageId },
    });
@ -104,7 +102,7 @@ export class VersionsService {
   * Returns the version being restored.
   */
  async restore(user: User, pageId: string, versionId: string): Promise<PageVersionView> {
-    await this.findModifiablePage(user, pageId);
+    await this.findLivePage(pageId);
    const version = await this.prisma.pageVersion.findFirst({
      where: { id: versionId, pageId },
      omit: { ydocSnapshot: true },
@ -132,12 +130,7 @@ export class VersionsService {
    pageId: string,
    input: CreateVersionInput,
  ): Promise<PageVersionView> {
-    const page = await this.prisma.page.findFirst({
-      where: { id: pageId, deletedAt: null },
-      include: { pond: true },
-    });
-    if (!page) throw new NotFoundException();
-    this.access.assertCanModify(user, page.pond);
+    await this.findLivePage(pageId);

    const snapshot = await this.reconstructSnapshot(pageId);

--- a/docs/architecture/README.md
+++ b/docs/architecture/README.md
@ -103,3 +103,10 @@ flowchart LR
  (see ADR 0012), with German and English translations added in the same
  change.
 - Every story lists the ADRs it depends on; read them before starting.
+- Every API route declares its access rule explicitly (a permission
+  decorator, `@Public()`, or the Site-Admin guard — issue #52); permission
+  checks run only through the shared resolution (permissions.md), never ad
+  hoc. **404/403 policy:** a denied _read_ answers `404` so the existence
+  of ponds and pages is not revealed; a denied _write_ on something the
+  user may read answers `403`. Trash views require write capability and
+  answer `404` on denial (ADR 0013).
--- a/packages/shared/i18n/de/errors.json
+++ b/packages/shared/i18n/de/errors.json
@ -36,6 +36,9 @@
  "grant_pond_admin_personal_pond": "Der einzige Administrator eines persönlichen Teichs ist dessen Eigentümer.",
  "grant_subject_id_mismatch": "Das Subjekt der Berechtigung ist widersprüchlich.",
  "grant_scope_id_mismatch": "Der Geltungsbereich der Berechtigung ist widersprüchlich.",
+  "grant_scope_not_found": "Das Label oder die Seite, auf die sich diese Berechtigung bezieht, existiert in diesem Teich nicht.",
+  "grant_subject_not_found": "Diese Person existiert nicht.",
+  "grant_last_admin": "Die letzte Teich-Admin-Berechtigung kann nicht entfernt werden.",
  "validation": {
    "required": "Dieses Feld ist erforderlich.",
    "taken": "Dieser Wert ist bereits vergeben.",
--- a/packages/shared/i18n/en/errors.json
+++ b/packages/shared/i18n/en/errors.json
@ -36,6 +36,9 @@
  "grant_pond_admin_personal_pond": "A personal pond's only administrator is its owner.",
  "grant_subject_id_mismatch": "The grant's subject is inconsistent.",
  "grant_scope_id_mismatch": "The grant's scope is inconsistent.",
+  "grant_scope_not_found": "The label or page this grant points to does not exist in this pond.",
+  "grant_subject_not_found": "This user does not exist.",
+  "grant_last_admin": "The last Pond Admin cannot be removed.",
  "validation": {
    "required": "This field is required.",
    "taken": "This value is already taken.",
--- a/packages/shared/src/permissions/index.ts
+++ b/packages/shared/src/permissions/index.ts
@ -1,3 +1,5 @@
 export * from './types';
 export * from './resolve';
+export * from './pond';
+export * from './schemas';
 export * from './validate';
--- a/packages/shared/src/permissions/pond.test.ts
+++ b/packages/shared/src/permissions/pond.test.ts
@ -0,0 +1,107 @@
+import { describe, expect, it } from 'vitest';
+
+import { canSeePond, hasPondRole } from './pond';
+import type { Grant, GrantEffect, GrantRole, GrantScopeType, PermissionViewer } from './types';
+
+const UMA = 'uma';
+const VIEWER: PermissionViewer = { userId: UMA, isSiteAdmin: false };
+const ADMIN: PermissionViewer = { userId: 'root', isSiteAdmin: true };
+const ANONYMOUS: PermissionViewer = { userId: null, isSiteAdmin: false };
+
+/** Concise grant builder (mirrors resolve.test.ts). */
+function grant(
+  role: GrantRole,
+  scopeType: GrantScopeType,
+  scopeId: string | null,
+  effect: GrantEffect,
+  subject: { type: 'user'; id: string } | { type: 'authenticated' } | { type: 'public' } = {
+    type: 'user',
+    id: UMA,
+  },
+): Grant {
+  return {
+    subjectType: subject.type,
+    subjectId: subject.type === 'user' ? subject.id : null,
+    role,
+    scopeType,
+    scopeId,
+    effect,
+  };
+}
+
+describe('hasPondRole (issue #52)', () => {
+  it('is default-closed: no grants → no role', () => {
+    expect(hasPondRole('editor', VIEWER, [])).toBe(false);
+    expect(hasPondRole('pond_admin', VIEWER, [])).toBe(false);
+  });
+
+  it('a pond-scope editor grant answers the editor question', () => {
+    const grants = [grant('editor', 'pond', null, 'allow')];
+    expect(hasPondRole('editor', VIEWER, grants)).toBe(true);
+    expect(hasPondRole('pond_admin', VIEWER, grants)).toBe(false);
+  });
+
+  it('pond_admin implies editor', () => {
+    const grants = [grant('pond_admin', 'pond', null, 'allow')];
+    expect(hasPondRole('editor', VIEWER, grants)).toBe(true);
+    expect(hasPondRole('pond_admin', VIEWER, grants)).toBe(true);
+  });
+
+  it('a pond-scope reader grant gives no pond-wide editor capability', () => {
+    expect(hasPondRole('editor', VIEWER, [grant('reader', 'pond', null, 'allow')])).toBe(false);
+  });
+
+  it('only pond-scope grants count — a label-scoped editor is not pond-wide', () => {
+    expect(hasPondRole('editor', VIEWER, [grant('editor', 'label', 'docs', 'allow')])).toBe(false);
+  });
+
+  it('deny wins among matching pond-scope grants', () => {
+    const grants = [grant('editor', 'pond', null, 'allow'), grant('editor', 'pond', null, 'deny')];
+    expect(hasPondRole('editor', VIEWER, grants)).toBe(false);
+  });
+
+  it('grants for other subjects are ignored', () => {
+    const grants = [grant('editor', 'pond', null, 'allow', { type: 'user', id: 'somebody-else' })];
+    expect(hasPondRole('editor', VIEWER, grants)).toBe(false);
+  });
+
+  it('authenticated-subject grants apply to logged-in viewers only', () => {
+    const grants = [grant('editor', 'pond', null, 'allow', { type: 'authenticated' })];
+    expect(hasPondRole('editor', VIEWER, grants)).toBe(true);
+    expect(hasPondRole('editor', ANONYMOUS, grants)).toBe(false);
+  });
+
+  it('Site Admin bypasses', () => {
+    expect(hasPondRole('pond_admin', ADMIN, [])).toBe(true);
+  });
+});
+
+describe('canSeePond (issue #52)', () => {
+  it('is default-closed: no grants → invisible', () => {
+    expect(canSeePond(VIEWER, [])).toBe(false);
+  });
+
+  it('any allow grant makes the pond visible, even label- or page-scoped', () => {
+    expect(canSeePond(VIEWER, [grant('reader', 'label', 'docs', 'allow')])).toBe(true);
+    expect(canSeePond(VIEWER, [grant('editor', 'page', 'p1', 'allow')])).toBe(true);
+    expect(canSeePond(VIEWER, [grant('reader', 'pond', null, 'allow')])).toBe(true);
+  });
+
+  it('deny grants alone do not make a pond visible', () => {
+    expect(canSeePond(VIEWER, [grant('reader', 'label', 'docs', 'deny')])).toBe(false);
+  });
+
+  it('allow grants for other subjects do not', () => {
+    const grants = [grant('reader', 'pond', null, 'allow', { type: 'user', id: 'somebody-else' })];
+    expect(canSeePond(VIEWER, grants)).toBe(false);
+  });
+
+  it('public-subject grants make the pond visible to anonymous viewers', () => {
+    const grants = [grant('reader', 'pond', null, 'allow', { type: 'public' })];
+    expect(canSeePond(ANONYMOUS, grants)).toBe(true);
+  });
+
+  it('Site Admin bypasses', () => {
+    expect(canSeePond(ADMIN, [])).toBe(true);
+  });
+});
--- a/packages/shared/src/permissions/pond.ts
+++ b/packages/shared/src/permissions/pond.ts
@ -0,0 +1,49 @@
+import { subjectMatches } from './resolve';
+import type { Grant, PermissionViewer } from './types';
+
+/**
+ * Pond-scope permission questions (issue #52). Page access is decided by
+ * {@link ./resolve}; the questions answered here are about the pond as a
+ * whole: "may the viewer see that this pond exists?" and "does the viewer
+ * hold a pond-wide role?" (creating pages, managing the pond). Both are pure
+ * and share the grant model and deny-wins semantics of the page resolver.
+ */
+
+/** Roles a pond-wide capability check can ask for. `pond_admin` implies
+ * `editor`; `editor` implies nothing further here (pond-wide read is
+ * {@link canSeePond}, which any grant satisfies). */
+export type PondRole = 'editor' | 'pond_admin';
+
+/** Does a grant's role satisfy a pond-role question? Admin covers editor. */
+function roleSatisfies(grantRole: Grant['role'], asked: PondRole): boolean {
+  if (asked === 'pond_admin') return grantRole === 'pond_admin';
+  return grantRole === 'editor' || grantRole === 'pond_admin';
+}
+
+/**
+ * Does the viewer hold `role` pond-wide? Only pond-scope grants count — a
+ * label- or page-scoped editor may edit those pages but has no pond-wide
+ * capability (creating pages, managing the pond). Deny wins among matching
+ * grants; no matching grant → false (default-closed). Site Admin bypasses.
+ */
+export function hasPondRole(role: PondRole, viewer: PermissionViewer, grants: Grant[]): boolean {
+  if (viewer.isSiteAdmin) return true;
+  const matching = grants.filter(
+    (g) => g.scopeType === 'pond' && subjectMatches(g, viewer) && roleSatisfies(g.role, role),
+  );
+  if (matching.length === 0) return false;
+  return !matching.some((g) => g.effect === 'deny');
+}
+
+/**
+ * May the viewer see that the pond exists (its metadata, label tree, page
+ * list — individual pages still resolve per page)? Any `allow` grant whose
+ * subject matches makes the pond visible, at any scope and for any role: a
+ * label-scoped reader needs the pond shell to reach their pages. A viewer
+ * with only `deny` grants (or none) sees nothing (default-closed). Site
+ * Admin bypasses.
+ */
+export function canSeePond(viewer: PermissionViewer, grants: Grant[]): boolean {
+  if (viewer.isSiteAdmin) return true;
+  return grants.some((g) => g.effect === 'allow' && subjectMatches(g, viewer));
+}
--- a/packages/shared/src/permissions/resolve.ts
+++ b/packages/shared/src/permissions/resolve.ts
@ -11,8 +11,9 @@ import type { Grant, PageResolutionContext, PermissionAction, PermissionViewer }
 * → deny (default-closed). Site Admins bypass everything.
 */

-/** Does a grant's subject apply to the viewer? */
-function subjectMatches(grant: Grant, viewer: PermissionViewer): boolean {
+/** Does a grant's subject apply to the viewer? (Shared with the pond-scope
+ * resolution in {@link ./pond}.) */
+export function subjectMatches(grant: Grant, viewer: PermissionViewer): boolean {
  switch (grant.subjectType) {
    case 'public':
      return true;
--- a/packages/shared/src/permissions/schemas.ts
+++ b/packages/shared/src/permissions/schemas.ts
@ -0,0 +1,47 @@
+import { z } from 'zod';
+
+import type { Grant } from './types';
+
+/**
+ * Wire schemas and views for the grant-management API (`/ponds/:id/grants`,
+ * issue #52). The structural rules beyond shape (pond_admin only at pond
+ * scope, subject/scope id presence, personal-pond single admin) live in
+ * {@link ./validate} and are applied by the service after parsing.
+ */
+
+export const GRANT_SUBJECT_TYPES = ['user', 'authenticated', 'public'] as const;
+export const GRANT_ROLES = ['pond_admin', 'editor', 'reader'] as const;
+export const GRANT_SCOPE_TYPES = ['pond', 'label', 'page'] as const;
+export const GRANT_EFFECTS = ['allow', 'deny'] as const;
+
+export const createGrantInputSchema = z.object({
+  subjectType: z.enum(GRANT_SUBJECT_TYPES),
+  /** Required for `user` subjects, absent otherwise (validate.ts checks). */
+  subjectId: z.string().min(1).nullish(),
+  role: z.enum(GRANT_ROLES),
+  scopeType: z.enum(GRANT_SCOPE_TYPES),
+  /** The label/page id for those scopes, absent at pond scope. */
+  scopeId: z.string().min(1).nullish(),
+  effect: z.enum(GRANT_EFFECTS),
+});
+export type CreateGrantInput = z.infer<typeof createGrantInputSchema>;
+
+/** A stored grant as the API serves it. */
+export interface GrantView extends Grant {
+  id: string;
+  pondId: string;
+  createdBy: string;
+  createdAt: string;
+}
+
+/** The parsed input as the resolver's grant shape (nullish → null). */
+export function grantOfInput(input: CreateGrantInput): Grant {
+  return {
+    subjectType: input.subjectType,
+    subjectId: input.subjectId ?? null,
+    role: input.role,
+    scopeType: input.scopeType,
+    scopeId: input.scopeId ?? null,
+    effect: input.effect,
+  };
+}