feat(gateway): PreferencesService + /preferences REST + /system Valkey override (P8-011)

- PreferencesService: platform defaults, user overrides, IMMUTABLE_KEYS enforcement
- PreferencesController: GET /api/preferences, POST /api/preferences, DELETE /api/preferences/:key
- PreferencesModule: global module exporting PreferencesService and SystemOverrideService
- SystemOverrideService: Valkey-backed session-scoped system prompt override with 5-min TTL + renew
- CommandRegistryService: register /system command (socket execution)
- CommandExecutorService: handle /system command via SystemOverrideService
- AgentService: inject system override before each prompt turn, renew TTL; store userId in session
- ChatGateway: pass userId when creating agent sessions
- PreferencesService unit tests: 11 tests covering defaults, overrides, enforcement wins, immutable key errors

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/gateway/src/preferences/preferences.controller.ts

@@ -0,0 +1,44 @@
+import {
+  Body,
+  Controller,
+  Delete,
+  Get,
+  HttpCode,
+  HttpStatus,
+  Inject,
+  Param,
+  Post,
+  UseGuards,
+} from '@nestjs/common';
+import { PreferencesService } from './preferences.service.js';
+import { AuthGuard } from '../auth/auth.guard.js';
+import { CurrentUser } from '../auth/current-user.decorator.js';
+
+@Controller('api/preferences')
+@UseGuards(AuthGuard)
+export class PreferencesController {
+  constructor(@Inject(PreferencesService) private readonly preferences: PreferencesService) {}
+
+  @Get()
+  async show(@CurrentUser() user: { id: string }): Promise<Record<string, unknown>> {
+    return this.preferences.getEffective(user.id);
+  }
+
+  @Post()
+  @HttpCode(HttpStatus.OK)
+  async set(
+    @CurrentUser() user: { id: string },
+    @Body() body: { key: string; value: unknown },
+  ): Promise<{ success: boolean; message: string }> {
+    return this.preferences.set(user.id, body.key, body.value);
+  }
+
+  @Delete(':key')
+  @HttpCode(HttpStatus.OK)
+  async reset(
+    @CurrentUser() user: { id: string },
+    @Param('key') key: string,
+  ): Promise<{ success: boolean; message: string }> {
+    return this.preferences.reset(user.id, key);
+  }
+}

apps/gateway/src/preferences/preferences.module.ts

@@ -0,0 +1,12 @@
+import { Global, Module } from '@nestjs/common';
+import { PreferencesService } from './preferences.service.js';
+import { PreferencesController } from './preferences.controller.js';
+import { SystemOverrideService } from './system-override.service.js';
+
+@Global()
+@Module({
+  controllers: [PreferencesController],
+  providers: [PreferencesService, SystemOverrideService],
+  exports: [PreferencesService, SystemOverrideService],
+})
+export class PreferencesModule {}

apps/gateway/src/preferences/preferences.service.spec.ts

@@ -0,0 +1,167 @@
+import { describe, it, expect, vi } from 'vitest';
+import { PreferencesService, PLATFORM_DEFAULTS, IMMUTABLE_KEYS } from './preferences.service.js';
+import type { Db } from '@mosaic/db';
+
+/**
+ * Build a mock Drizzle DB where the select chain supports:
+ *   db.select().from().where()            → resolves to `listRows`
+ *   db.select().from().where().limit(n)   → resolves to `singleRow`
+ */
+function makeMockDb(
+  listRows: Array<{ key: string; value: unknown }> = [],
+  singleRow: Array<{ id: string }> = [],
+): Db {
+  const chainWithLimit = {
+    limit: vi.fn().mockResolvedValue(singleRow),
+    then: (resolve: (v: typeof listRows) => unknown) => Promise.resolve(listRows).then(resolve),
+  };
+  const selectFrom = {
+    from: vi.fn().mockReturnThis(),
+    where: vi.fn().mockReturnValue(chainWithLimit),
+  };
+  const updateResult = {
+    set: vi.fn().mockReturnThis(),
+    where: vi.fn().mockResolvedValue([]),
+  };
+  const deleteResult = {
+    where: vi.fn().mockResolvedValue([]),
+  };
+  const insertResult = {
+    values: vi.fn().mockResolvedValue([]),
+  };
+
+  return {
+    select: vi.fn().mockReturnValue(selectFrom),
+    update: vi.fn().mockReturnValue(updateResult),
+    delete: vi.fn().mockReturnValue(deleteResult),
+    insert: vi.fn().mockReturnValue(insertResult),
+  } as unknown as Db;
+}
+
+describe('PreferencesService', () => {
+  describe('getEffective', () => {
+    it('returns platform defaults when user has no overrides', async () => {
+      const db = makeMockDb([]);
+      const service = new PreferencesService(db);
+      const result = await service.getEffective('user-1');
+
+      expect(result['agent.thinkingLevel']).toBe('auto');
+      expect(result['agent.streamingEnabled']).toBe(true);
+      expect(result['session.autoCompactEnabled']).toBe(true);
+      expect(result['session.autoCompactThreshold']).toBe(0.8);
+    });
+
+    it('applies user overrides for mutable keys', async () => {
+      const db = makeMockDb([
+        { key: 'agent.thinkingLevel', value: 'high' },
+        { key: 'response.language', value: 'es' },
+      ]);
+
+      const service = new PreferencesService(db);
+      const result = await service.getEffective('user-1');
+
+      expect(result['agent.thinkingLevel']).toBe('high');
+      expect(result['response.language']).toBe('es');
+    });
+
+    it('ignores user overrides for immutable keys — enforcement always wins', async () => {
+      const db = makeMockDb([
+        { key: 'limits.maxThinkingLevel', value: 'high' },
+        { key: 'limits.rateLimit', value: 9999 },
+      ]);
+
+      const service = new PreferencesService(db);
+      const result = await service.getEffective('user-1');
+
+      // Should still be null (platform default), not the user-supplied values
+      expect(result['limits.maxThinkingLevel']).toBeNull();
+      expect(result['limits.rateLimit']).toBeNull();
+    });
+  });
+
+  describe('set', () => {
+    it('returns error when attempting to override an immutable key', async () => {
+      const db = makeMockDb();
+      const service = new PreferencesService(db);
+
+      const result = await service.set('user-1', 'limits.maxThinkingLevel', 'high');
+      expect(result.success).toBe(false);
+      expect(result.message).toContain('platform enforcement');
+    });
+
+    it('returns error when attempting to override limits.rateLimit', async () => {
+      const db = makeMockDb();
+      const service = new PreferencesService(db);
+
+      const result = await service.set('user-1', 'limits.rateLimit', 100);
+      expect(result.success).toBe(false);
+      expect(result.message).toContain('platform enforcement');
+    });
+
+    it('upserts a mutable preference and returns success — insert path', async () => {
+      // singleRow=[] → no existing row → insert path
+      const db = makeMockDb([], []);
+      const service = new PreferencesService(db);
+      const result = await service.set('user-1', 'agent.thinkingLevel', 'high');
+      expect(result.success).toBe(true);
+      expect(result.message).toContain('"agent.thinkingLevel"');
+    });
+
+    it('upserts a mutable preference and returns success — update path', async () => {
+      // singleRow has an id → existing row → update path
+      const db = makeMockDb([], [{ id: 'existing-id' }]);
+      const service = new PreferencesService(db);
+      const result = await service.set('user-1', 'agent.thinkingLevel', 'low');
+      expect(result.success).toBe(true);
+      expect(result.message).toContain('"agent.thinkingLevel"');
+    });
+  });
+
+  describe('reset', () => {
+    it('returns error when attempting to reset an immutable key', async () => {
+      const db = makeMockDb();
+      const service = new PreferencesService(db);
+
+      const result = await service.reset('user-1', 'limits.rateLimit');
+      expect(result.success).toBe(false);
+      expect(result.message).toContain('platform enforcement');
+    });
+
+    it('deletes user override and returns default value in message', async () => {
+      const db = makeMockDb();
+      const service = new PreferencesService(db);
+      const result = await service.reset('user-1', 'agent.thinkingLevel');
+
+      expect(result.success).toBe(true);
+      expect(result.message).toContain('"auto"'); // platform default for agent.thinkingLevel
+    });
+  });
+
+  describe('IMMUTABLE_KEYS', () => {
+    it('contains only the enforcement keys', () => {
+      expect(IMMUTABLE_KEYS.has('limits.maxThinkingLevel')).toBe(true);
+      expect(IMMUTABLE_KEYS.has('limits.rateLimit')).toBe(true);
+      expect(IMMUTABLE_KEYS.has('agent.thinkingLevel')).toBe(false);
+    });
+  });
+
+  describe('PLATFORM_DEFAULTS', () => {
+    it('has all expected keys', () => {
+      const expectedKeys = [
+        'agent.defaultModel',
+        'agent.thinkingLevel',
+        'agent.streamingEnabled',
+        'response.language',
+        'response.codeAnnotations',
+        'safety.confirmDestructiveTools',
+        'session.autoCompactThreshold',
+        'session.autoCompactEnabled',
+        'limits.maxThinkingLevel',
+        'limits.rateLimit',
+      ];
+      for (const key of expectedKeys) {
+        expect(Object.prototype.hasOwnProperty.call(PLATFORM_DEFAULTS, key)).toBe(true);
+      }
+    });
+  });
+});

apps/gateway/src/preferences/preferences.service.ts

@@ -0,0 +1,119 @@
+import { Inject, Injectable, Logger } from '@nestjs/common';
+import { eq, and, type Db, preferences as preferencesTable } from '@mosaic/db';
+import { DB } from '../database/database.module.js';
+
+export const PLATFORM_DEFAULTS: Record<string, unknown> = {
+  'agent.defaultModel': null,
+  'agent.thinkingLevel': 'auto',
+  'agent.streamingEnabled': true,
+  'response.language': 'auto',
+  'response.codeAnnotations': true,
+  'safety.confirmDestructiveTools': true,
+  'session.autoCompactThreshold': 0.8,
+  'session.autoCompactEnabled': true,
+  'limits.maxThinkingLevel': null,
+  'limits.rateLimit': null,
+};
+
+export const IMMUTABLE_KEYS = new Set<string>(['limits.maxThinkingLevel', 'limits.rateLimit']);
+
+@Injectable()
+export class PreferencesService {
+  private readonly logger = new Logger(PreferencesService.name);
+
+  constructor(@Inject(DB) private readonly db: Db) {}
+
+  /**
+   * Returns the effective preference set for a user:
+   * Platform defaults → user overrides (mutable keys only) → enforcements re-applied last
+   */
+  async getEffective(userId: string): Promise<Record<string, unknown>> {
+    const userPrefs = await this.getUserPrefs(userId);
+    const result: Record<string, unknown> = { ...PLATFORM_DEFAULTS };
+
+    for (const [key, value] of Object.entries(userPrefs)) {
+      if (!IMMUTABLE_KEYS.has(key)) {
+        result[key] = value;
+      }
+    }
+
+    // Re-apply immutable keys (enforcements always win)
+    for (const key of IMMUTABLE_KEYS) {
+      result[key] = PLATFORM_DEFAULTS[key];
+    }
+
+    return result;
+  }
+
+  async set(
+    userId: string,
+    key: string,
+    value: unknown,
+  ): Promise<{ success: boolean; message: string }> {
+    if (IMMUTABLE_KEYS.has(key)) {
+      return {
+        success: false,
+        message: `Cannot override "${key}" — this is a platform enforcement. Contact your admin.`,
+      };
+    }
+
+    await this.upsertPref(userId, key, value);
+    return { success: true, message: `Preference "${key}" set to ${JSON.stringify(value)}.` };
+  }
+
+  async reset(userId: string, key: string): Promise<{ success: boolean; message: string }> {
+    if (IMMUTABLE_KEYS.has(key)) {
+      return { success: false, message: `Cannot reset "${key}" — it is a platform enforcement.` };
+    }
+
+    await this.deletePref(userId, key);
+    const defaultVal = PLATFORM_DEFAULTS[key];
+    return {
+      success: true,
+      message: `Preference "${key}" reset to default: ${JSON.stringify(defaultVal)}.`,
+    };
+  }
+
+  private async getUserPrefs(userId: string): Promise<Record<string, unknown>> {
+    const rows = await this.db
+      .select({ key: preferencesTable.key, value: preferencesTable.value })
+      .from(preferencesTable)
+      .where(eq(preferencesTable.userId, userId));
+
+    const result: Record<string, unknown> = {};
+    for (const row of rows) {
+      result[row.key] = row.value;
+    }
+    return result;
+  }
+
+  private async upsertPref(userId: string, key: string, value: unknown): Promise<void> {
+    const existing = await this.db
+      .select({ id: preferencesTable.id })
+      .from(preferencesTable)
+      .where(and(eq(preferencesTable.userId, userId), eq(preferencesTable.key, key)))
+      .limit(1);
+
+    if (existing.length > 0) {
+      await this.db
+        .update(preferencesTable)
+        .set({ value: value as never, updatedAt: new Date() })
+        .where(and(eq(preferencesTable.userId, userId), eq(preferencesTable.key, key)));
+    } else {
+      await this.db.insert(preferencesTable).values({
+        userId,
+        key,
+        value: value as never,
+        mutable: true,
+      });
+    }
+    this.logger.debug(`Upserted preference "${key}" for user ${userId}`);
+  }
+
+  private async deletePref(userId: string, key: string): Promise<void> {
+    await this.db
+      .delete(preferencesTable)
+      .where(and(eq(preferencesTable.userId, userId), eq(preferencesTable.key, key)));
+    this.logger.debug(`Deleted preference "${key}" for user ${userId}`);
+  }
+}

apps/gateway/src/preferences/system-override.service.ts

@@ -0,0 +1,33 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { createQueue, type QueueHandle } from '@mosaic/queue';
+
+const SESSION_SYSTEM_KEY = (sessionId: string) => `mosaic:session:${sessionId}:system`;
+const TTL_SECONDS = 5 * 60; // 5 minutes, renewed on each turn
+
+@Injectable()
+export class SystemOverrideService {
+  private readonly logger = new Logger(SystemOverrideService.name);
+  private readonly handle: QueueHandle;
+
+  constructor() {
+    this.handle = createQueue();
+  }
+
+  async set(sessionId: string, override: string): Promise<void> {
+    await this.handle.redis.setex(SESSION_SYSTEM_KEY(sessionId), TTL_SECONDS, override);
+    this.logger.debug(`Set system override for session ${sessionId} (TTL=${TTL_SECONDS}s)`);
+  }
+
+  async get(sessionId: string): Promise<string | null> {
+    return this.handle.redis.get(SESSION_SYSTEM_KEY(sessionId));
+  }
+
+  async renew(sessionId: string): Promise<void> {
+    await this.handle.redis.expire(SESSION_SYSTEM_KEY(sessionId), TTL_SECONDS);
+  }
+
+  async clear(sessionId: string): Promise<void> {
+    await this.handle.redis.del(SESSION_SYSTEM_KEY(sessionId));
+    this.logger.debug(`Cleared system override for session ${sessionId}`);
+  }
+}