Persist t2→username mappings in reddit_users table

Adds a durable mapping so the UI never has to show raw t2_xxx IDs or
MXIDs just because the in-memory cache is cold after a restart.
ChatService seeds from the table on construction and writes through
every resolution path; cached chats whose username is still t2_xxx
get upgraded from the DB on loadCache.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/chat-service-username-persist.test.ts

@@ -0,0 +1,92 @@
+import { describe, it, expect } from 'vitest';
+import os from 'os';
+import path from 'path';
+import Database from 'better-sqlite3';
+import { runMigrations } from '../src/database/client.js';
+import { RedditUsersRepository } from '../src/database/repositories.js';
+import { ChatService } from '../src/services/chat/service.js';
+import { ChatCache } from '../src/services/chat/cache.js';
+import { MatrixClient } from '../src/services/chat/matrix/client.js';
+import { createMockLogger } from './mockLogger.js';
+
+const creds = {
+  homeserver: 'https://matrix.example.test',
+  accessToken: 'tok',
+  userId: '@me:example.test',
+  capturedAt: Date.now(),
+};
+
+function buildMatrix() {
+  const logger = createMockLogger();
+  const fetchImpl = (() =>
+    Promise.resolve(
+      new Response('{}', { status: 200, headers: { 'content-type': 'application/json' } }),
+    )) as typeof fetch;
+  return new MatrixClient(creds, logger, { minRequestIntervalMs: 0, fetchImpl });
+}
+
+describe('ChatService username persistence', () => {
+  it('seeds the in-memory cache from RedditUsersRepository on construction', () => {
+    const db = new Database(':memory:');
+    runMigrations(db);
+    const repo = new RedditUsersRepository(db);
+    repo.upsert({ t2Id: 't2_abc', username: 'alice' });
+
+    const logger = createMockLogger();
+    const svc = new ChatService(
+      buildMatrix(),
+      logger,
+      undefined, undefined, undefined, undefined, undefined, undefined,
+      repo,
+    );
+
+    expect(svc.resolveSenderDisplay('@t2_abc:reddit.com')).toBe('alice');
+    expect(svc.resolveSenderDisplay('t2_abc')).toBe('alice');
+    db.close();
+  });
+
+  it('falls back to t2 form when no mapping is known', () => {
+    const logger = createMockLogger();
+    const svc = new ChatService(buildMatrix(), logger);
+    expect(svc.resolveSenderDisplay('@t2_unknown:reddit.com')).toBe('t2_unknown');
+  });
+
+  it('upgrades cached chats with t2_ usernames from the db map on loadCache', async () => {
+    const db = new Database(':memory:');
+    runMigrations(db);
+    const repo = new RedditUsersRepository(db);
+    repo.upsert({ t2Id: 't2_abc', username: 'alice' });
+
+    const logger = createMockLogger();
+    const tmpFile = path.join(os.tmpdir(), `chat-cache-${Date.now()}-${Math.random()}.json`);
+    const cache = new ChatCache(logger, tmpFile);
+    cache.set([
+      {
+        username: 't2_abc',
+        roomName: 't2_abc',
+        lastMessageTime: Date.now(),
+        lastMessageSnippet: 'hi',
+        isFromUs: false,
+        unread: false,
+        url: 'https://chat.reddit.com/room/x',
+        roomId: '!room:reddit.com',
+        messages: [],
+      },
+    ]);
+
+    const svc = new ChatService(
+      buildMatrix(),
+      logger,
+      undefined, undefined, undefined, undefined,
+      cache,
+      undefined,
+      repo,
+    );
+
+    await svc.loadCache();
+    const chats = await svc.getCachedConversations();
+    expect(chats[0].username).toBe('alice');
+    expect(chats[0].roomName).toBe('alice');
+    db.close();
+  });
+});

tests/database.test.ts

@@ -103,8 +103,8 @@ describe('Database Client', () => {
       const tables = db
         .prepare("SELECT name FROM sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%'")
         .all() as { name: string }[];
-      // processed_posts, sent_messages, successful_messages, activity_log
-      expect(tables.length).toBe(4);
+      // processed_posts, sent_messages, successful_messages, activity_log, reddit_users
+      expect(tables.length).toBe(5);
     });
 
     it('processed_posts has correct schema', () => {

tests/reddit-users-repo.test.ts

@@ -0,0 +1,70 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import Database from 'better-sqlite3';
+import { runMigrations } from '../src/database/client.js';
+import { RedditUsersRepository } from '../src/database/repositories.js';
+
+describe('RedditUsersRepository', () => {
+  let db: Database.Database;
+  let repo: RedditUsersRepository;
+
+  beforeEach(() => {
+    db = new Database(':memory:');
+    db.pragma('foreign_keys = ON');
+    runMigrations(db);
+    repo = new RedditUsersRepository(db);
+  });
+
+  afterEach(() => {
+    db.close();
+  });
+
+  it('upserts a new user and reads it back', () => {
+    repo.upsert({ t2Id: 't2_abc', username: 'alice' });
+    const got = repo.getByT2('t2_abc');
+    expect(got?.username).toBe('alice');
+    expect(got?.t2Id).toBe('t2_abc');
+  });
+
+  it('normalizes a bare t2 id when looking up or writing', () => {
+    repo.upsert({ t2Id: 'abc', username: 'alice' });
+    expect(repo.getByT2('abc')?.username).toBe('alice');
+    expect(repo.getByT2('t2_abc')?.username).toBe('alice');
+  });
+
+  it('updates the username when the same t2 is upserted twice', () => {
+    repo.upsert({ t2Id: 't2_abc', username: 'old_name' });
+    repo.upsert({ t2Id: 't2_abc', username: 'new_name' });
+    expect(repo.getByT2('t2_abc')?.username).toBe('new_name');
+  });
+
+  it('refuses to store t2_-prefixed pseudo-usernames', () => {
+    repo.upsert({ t2Id: 't2_abc', username: 't2_abc' });
+    expect(repo.getByT2('t2_abc')).toBeNull();
+  });
+
+  it('refuses to store MXID-shaped pseudo-usernames', () => {
+    repo.upsert({ t2Id: 't2_abc', username: '@t2_abc:reddit.com' });
+    expect(repo.getByT2('t2_abc')).toBeNull();
+  });
+
+  it('looks up by username case-insensitively', () => {
+    repo.upsert({ t2Id: 't2_abc', username: 'Alice' });
+    expect(repo.getByUsername('alice')?.t2Id).toBe('t2_abc');
+    expect(repo.getByUsername('ALICE')?.t2Id).toBe('t2_abc');
+  });
+
+  it('preserves an existing mxid when a later upsert passes null', () => {
+    repo.upsert({ t2Id: 't2_abc', username: 'alice', mxid: '@t2_abc:reddit.com' });
+    repo.upsert({ t2Id: 't2_abc', username: 'alice' });
+    expect(repo.getByT2('t2_abc')?.mxid).toBe('@t2_abc:reddit.com');
+  });
+
+  it('bulk-inserts via upsertMany', () => {
+    repo.upsertMany([
+      { t2Id: 't2_a', username: 'alice' },
+      { t2Id: 't2_b', username: 'bob' },
+    ]);
+    const all = repo.getAll();
+    expect(all.map((u) => u.username).sort()).toEqual(['alice', 'bob']);
+  });
+});