-- B09：任务范围与实际消费的不可变上下文快照。
-- 快照身份由载荷确定性派生，同一输入重复冻结幂等为一行；历史快照只读不改写。
DO $migration$
DECLARE
    namespace text;
BEGIN
    FOREACH namespace IN ARRAY ARRAY['public', 'evaluation'] LOOP
        EXECUTE format($ddl$
            CREATE TABLE %1$I.muse_context_snapshot (
                snapshot_id uuid PRIMARY KEY,
                run_purpose public.muse_purpose NOT NULL,
                task_id uuid NOT NULL REFERENCES %1$I.muse_task(task_id),
                work_id text NOT NULL,
                input_hash text NOT NULL,
                frozen_scope jsonb NOT NULL,
                assembly jsonb NOT NULL,
                source_bindings jsonb NOT NULL,
                created_by text NOT NULL,
                created_at timestamptz NOT NULL DEFAULT clock_timestamp(),
                UNIQUE (run_purpose, task_id, input_hash),
                CHECK (assembly ? ALL (ARRAY['入选','省略','字节数','文本哈希','文本'])),
                CHECK (jsonb_typeof(source_bindings) = 'array')
            );
            CREATE INDEX ON %1$I.muse_context_snapshot (task_id, created_at);
        $ddl$, namespace);
    END LOOP;
END
$migration$;