-- AP1.5c: Rekursive Projects (parent_project_id, container_kind)

ALTER TABLE projects
    ADD COLUMN parent_project_id UUID NULL REFERENCES projects(id) ON DELETE SET NULL,
    ADD COLUMN container_kind VARCHAR(32) NULL
        CHECK (
            container_kind IS NULL
            OR container_kind IN ('project', 'stream', 'phase', 'release')
        );

CREATE INDEX idx_projects_parent ON projects(tenant_id, parent_project_id)
    WHERE parent_project_id IS NOT NULL;