BEGIN;

ALTER TABLE context_snapshot
    ADD COLUMN preparation_status varchar(16) NOT NULL DEFAULT 'READY',
    ADD COLUMN preparation_failure_code varchar(80),
    ADD CONSTRAINT context_snapshot_preparation_status_check
        CHECK (preparation_status IN ('READY', 'FAILED')),
    ADD CONSTRAINT context_snapshot_preparation_failure_check
        CHECK (
            (preparation_status = 'READY' AND preparation_failure_code IS NULL)
            OR
            (preparation_status = 'FAILED' AND NULLIF(btrim(preparation_failure_code), '') IS NOT NULL)
        );

COMMENT ON COLUMN context_snapshot.preparation_status IS
    'Whether the authorized context was prepared. FAILED snapshots retain only a sanitized diagnostic result.';

COMMIT;