-- U-02: group_members 增加指向 groups 的外键，避免解散后残留孤儿行。
-- 本分支基于 C-04 时最大迁移号为 0002，按 TASKS 4.2 取 0003。
DELETE FROM group_members WHERE group_id NOT IN (SELECT id FROM groups);

CREATE TABLE group_members_new (
  group_id TEXT NOT NULL REFERENCES groups(id) ON DELETE CASCADE,
  endpoint_id TEXT NOT NULL,
  joined_at INTEGER NOT NULL,
  PRIMARY KEY (group_id, endpoint_id)
);

INSERT INTO group_members_new (group_id, endpoint_id, joined_at)
SELECT group_id, endpoint_id, joined_at FROM group_members;

DROP TABLE group_members;

ALTER TABLE group_members_new RENAME TO group_members;

CREATE INDEX idx_group_members_endpoint ON group_members(endpoint_id);