-- chat_turns: 端到端回合幂等权威表
CREATE TABLE IF NOT EXISTS chat_turns (
    id                      BIGSERIAL PRIMARY KEY,
    session_id              TEXT NOT NULL,
    client_turn_id          TEXT NOT NULL,
    user_id                 BIGINT,
    project_id              BIGINT,
    user_message_id         BIGINT REFERENCES chat_messages(id) ON DELETE SET NULL,
    assistant_message_id    BIGINT REFERENCES chat_messages(id) ON DELETE SET NULL,
    request_body_sha256     TEXT NOT NULL DEFAULT '',
    status                  TEXT NOT NULL DEFAULT 'accepted',
    owner_token             TEXT NOT NULL DEFAULT '',
    lease_expires_at        TIMESTAMPTZ,
    first_request_id        TEXT NOT NULL DEFAULT '',
    last_request_id         TEXT NOT NULL DEFAULT '',
    attempt_count           INT NOT NULL DEFAULT 1,
    created_at              TIMESTAMPTZ NOT NULL DEFAULT now(),
    updated_at              TIMESTAMPTZ NOT NULL DEFAULT now(),
    completed_at            TIMESTAMPTZ,
    CONSTRAINT uq_chat_turns_session_client UNIQUE (session_id, client_turn_id)
);

CREATE INDEX IF NOT EXISTS idx_chat_turns_session_status ON chat_turns(session_id, status);
CREATE INDEX IF NOT EXISTS idx_chat_turns_client ON chat_turns(client_turn_id);