perf: gateway + DB + frontend optimizations (P8-003)

- DB client: configure connection pool (max=20, idle_timeout=30s, connect_timeout=5s)
- DB schema: add missing indexes for auth sessions, accounts, conversations, agent_logs
- DB schema: promote preferences(user_id,key) to UNIQUE index for ON CONFLICT upsert
- Drizzle migration: 0003_p8003_perf_indexes.sql
- preferences.service: replace 2-query SELECT+INSERT/UPDATE with single-round-trip upsert
- conversations repo: add ORDER BY + LIMIT to findAll (200) and findMessages (500)
- session-gc.service: make onModuleInit fire-and-forget (removes cold-start TTFB block)
- next.config.ts: enable compress, productionBrowserSourceMaps:false, image avif/webp
- docs/PERFORMANCE.md: full profiling report and change impact notes

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

@@ -5,34 +5,28 @@ 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`
+ *   db.insert().values().onConflictDoUpdate() → resolves to []
  */
-function makeMockDb(
-  listRows: Array<{ key: string; value: unknown }> = [],
-  singleRow: Array<{ id: string }> = [],
-): Db {
+function makeMockDb(listRows: Array<{ key: string; value: unknown }> = []): Db {
   const chainWithLimit = {
-    limit: vi.fn().mockResolvedValue(singleRow),
+    limit: vi.fn().mockResolvedValue([]),
     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([]),
   };
+  // Single-round-trip upsert chain: insert().values().onConflictDoUpdate()
   const insertResult = {
-    values: vi.fn().mockResolvedValue([]),
+    values: vi.fn().mockReturnThis(),
+    onConflictDoUpdate: 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;
@@ -98,23 +92,14 @@ describe('PreferencesService', () => {
       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([], []);
+    it('upserts a mutable preference and returns success', async () => {
+      // Single-round-trip INSERT … ON CONFLICT DO UPDATE 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', () => {