feat(#462): add federation capabilities verb (#674)

apps/gateway/src/federation/federation.module.ts

@@ -4,12 +4,13 @@ import { CaService } from './ca.service.js';
 import { EnrollmentController } from './enrollment.controller.js';
 import { EnrollmentService } from './enrollment.service.js';
 import { FederationController } from './federation.controller.js';
+import { CapabilitiesController } from './server/verbs/capabilities.controller.js';
 import { GrantsService } from './grants.service.js';
 import { FederationClientService, QuerySourceService } from './client/index.js';
 import { FederationAuthGuard } from './server/index.js';
 
 @Module({
-  controllers: [EnrollmentController, FederationController],
+  controllers: [EnrollmentController, FederationController, CapabilitiesController],
   providers: [
     AdminGuard,
     CaService,

apps/gateway/src/federation/server/verbs/__tests__/capabilities.controller.spec.ts

@@ -0,0 +1,88 @@
+import 'reflect-metadata';
+import { RequestMethod } from '@nestjs/common';
+import { describe, expect, it } from 'vitest';
+import type { FastifyRequest } from 'fastify';
+import { FederationCapabilitiesResponseSchema, FEDERATION_VERBS } from '@mosaicstack/types';
+import { FederationScopeError } from '../../../scope-schema.js';
+import { FederationAuthGuard } from '../../federation-auth.guard.js';
+import { CapabilitiesController } from '../capabilities.controller.js';
+
+const VALID_SCOPE = {
+  resources: ['tasks', 'notes'],
+  excluded_resources: ['credentials'],
+  max_rows_per_query: 250,
+} as const;
+
+const DEFAULTED_SCOPE = {
+  resources: ['memory'],
+  max_rows_per_query: 10,
+} as const;
+
+function makeRequest(scope: Record<string, unknown>): FastifyRequest {
+  return {
+    federationContext: {
+      grantId: 'grant-1',
+      peerId: 'peer-1',
+      subjectUserId: 'user-1',
+      scope,
+    },
+  } as FastifyRequest;
+}
+
+describe('CapabilitiesController', () => {
+  it('declares GET /api/federation/v1/capabilities', () => {
+    expect(Reflect.getMetadata('path', CapabilitiesController)).toBe(
+      'api/federation/v1/capabilities',
+    );
+    expect(Reflect.getMetadata('path', CapabilitiesController.prototype.getCapabilities)).toBe('/');
+    expect(Reflect.getMetadata('method', CapabilitiesController.prototype.getCapabilities)).toBe(
+      RequestMethod.GET,
+    );
+  });
+
+  it('is protected only by FederationAuthGuard', () => {
+    const guards = Reflect.getMetadata('__guards__', CapabilitiesController) as unknown[];
+
+    expect(guards).toEqual([FederationAuthGuard]);
+  });
+
+  it('returns resources, excluded resources, max rows, and M3 supported verbs from the active grant scope', () => {
+    const controller = new CapabilitiesController();
+
+    const response = controller.getCapabilities(makeRequest(VALID_SCOPE));
+
+    expect(response).toEqual({
+      resources: ['tasks', 'notes'],
+      excluded_resources: ['credentials'],
+      max_rows_per_query: 250,
+      supported_verbs: [...FEDERATION_VERBS],
+    });
+    expect(FederationCapabilitiesResponseSchema.safeParse(response).success).toBe(true);
+  });
+
+  it('applies scope defaults without RBAC or resource filtering', () => {
+    const controller = new CapabilitiesController();
+
+    const response = controller.getCapabilities(makeRequest(DEFAULTED_SCOPE));
+
+    expect(response).toEqual({
+      resources: ['memory'],
+      excluded_resources: [],
+      max_rows_per_query: 10,
+      supported_verbs: ['list', 'get', 'capabilities'],
+    });
+  });
+
+  it('rejects invalid scope state instead of returning an invalid capabilities contract', () => {
+    const controller = new CapabilitiesController();
+
+    expect(() =>
+      controller.getCapabilities(
+        makeRequest({
+          resources: [],
+          max_rows_per_query: 0,
+        }),
+      ),
+    ).toThrow(FederationScopeError);
+  });
+});

apps/gateway/src/federation/server/verbs/capabilities.controller.ts

@@ -0,0 +1,38 @@
+/**
+ * Federation capabilities verb (FED-M3-07).
+ *
+ * Returns the read-only capability envelope for the active grant attached by
+ * FederationAuthGuard. This endpoint intentionally does not invoke native RBAC
+ * or ScopeService: an active grant is enough to ask what the grant allows.
+ */
+
+import { Controller, Get, Req, UseGuards } from '@nestjs/common';
+import type { FastifyRequest } from 'fastify';
+import {
+  FEDERATION_VERBS,
+  type FederationCapabilitiesResponse,
+  type FederationVerb,
+} from '@mosaicstack/types';
+import { parseFederationScope } from '../../scope-schema.js';
+import { FederationAuthGuard } from '../federation-auth.guard.js';
+import '../federation-context.js';
+
+@Controller('api/federation/v1/capabilities')
+@UseGuards(FederationAuthGuard)
+export class CapabilitiesController {
+  @Get()
+  getCapabilities(@Req() request: FastifyRequest): FederationCapabilitiesResponse {
+    if (!request.federationContext) {
+      throw new Error('Federation context missing after auth guard');
+    }
+
+    const scope = parseFederationScope(request.federationContext.scope);
+
+    return {
+      resources: [...scope.resources],
+      excluded_resources: [...scope.excluded_resources],
+      max_rows_per_query: scope.max_rows_per_query,
+      supported_verbs: [...FEDERATION_VERBS] satisfies FederationVerb[],
+    };
+  }
+}