エピソード記憶（セッションごとの履歴）

CREATE TABLE episodes (
    id BIGSERIAL PRIMARY KEY,
    user_id TEXT NOT NULL,
    session_id TEXT NOT NULL,
    role TEXT NOT NULL,        -- system/user/assistant/tool
    content TEXT NOT NULL,
    created_at TIMESTAMPTZ DEFAULT NOW(),
    metadata JSONB
);

def save_turn(user_id, session_id, role, content, metadata=None):
    conn.execute('''
        INSERT INTO episodes (user_id, session_id, role, content, metadata)
        VALUES (%s, %s, %s, %s, %s::jsonb)
    ''', (user_id, session_id, role, content, json.dumps(metadata or {})))

def load_session(session_id):
    rows = conn.execute('SELECT role, content FROM episodes WHERE session_id = %s ORDER BY id', (session_id,))
    return [{'role': r[0], 'content': r[1]} for r in rows]

def recent_sessions(user_id, n=5):
    rows = conn.execute('''
        SELECT DISTINCT session_id, MIN(created_at) AS started
        FROM episodes WHERE user_id = %s
        GROUP BY session_id ORDER BY started DESC LIMIT %s
    ''', (user_id, n))
    return [r[0] for r in rows]

def index_session(session_id):
    summary = summarise(load_session(session_id))
    vec = embed(summary)
    save_to_vector_db(session_id, vec, summary)

def search_episodes(user_id, query):
    qvec = embed(query)
    candidates = vector_db.query(qvec, k=10, filter={'user_id': user_id})
    return [load_session(c.id) for c in candidates]

if session_age_days > 30:
    summary = summarise(load_session(sid))
    conn.execute('UPDATE episodes SET content = %s WHERE session_id = %s', (summary, sid))
    conn.execute('DELETE FROM episodes WHERE session_id = %s AND created_at < NOW() - INTERVAL \'1 day\'', (sid,))