feat: add SQLite session persistence

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/session/store.ts

@@ -0,0 +1,57 @@
+import Database from 'better-sqlite3';
+import type { Message } from '../models/types.js';
+
+export class SessionStore {
+  private db: Database.Database;
+
+  constructor(dbPath: string) {
+    this.db = new Database(dbPath);
+    this.init();
+  }
+
+  private init(): void {
+    this.db.exec(`
+      CREATE TABLE IF NOT EXISTS messages (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        session_id TEXT NOT NULL,
+        role TEXT NOT NULL,
+        content TEXT NOT NULL,
+        created_at INTEGER NOT NULL DEFAULT (unixepoch())
+      );
+      CREATE INDEX IF NOT EXISTS idx_messages_session ON messages(session_id);
+    `);
+  }
+
+  addMessage(sessionId: string, message: Message): void {
+    const stmt = this.db.prepare(
+      'INSERT INTO messages (session_id, role, content) VALUES (?, ?, ?)'
+    );
+    stmt.run(sessionId, message.role, message.content);
+  }
+
+  getMessages(sessionId: string): Message[] {
+    const stmt = this.db.prepare(
+      'SELECT role, content FROM messages WHERE session_id = ? ORDER BY id ASC'
+    );
+    const rows = stmt.all(sessionId) as Array<{ role: string; content: string }>;
+    return rows.map(row => ({
+      role: row.role as 'user' | 'assistant',
+      content: row.content,
+    }));
+  }
+
+  clearSession(sessionId: string): void {
+    const stmt = this.db.prepare('DELETE FROM messages WHERE session_id = ?');
+    stmt.run(sessionId);
+  }
+
+  listSessions(): string[] {
+    const stmt = this.db.prepare('SELECT DISTINCT session_id FROM messages');
+    const rows = stmt.all() as Array<{ session_id: string }>;
+    return rows.map(row => row.session_id);
+  }
+
+  close(): void {
+    this.db.close();
+  }
+}