refactor: remove block-sequential gate path and gate_block knob (algo #6)

config/train_videomme.yaml 同时收录待入库的实验配置变更(run_id v2 /
concurrency 32 / batch_size 40)。tests/integration/test_v3_contract_e2e.py
的 run_id 断言按 Task 5 显式契约同步修正(原断言依赖旧隐式实例注入)。

tests/integration/test_v3_contract_e2e.py

@@ -338,7 +338,7 @@ class TestInferenceUnitAggregationEndToEnd:
 
     def _assert_all_persisted(self, log: HarnessLog, questions: list[GeneratedQuestion]) -> None:
         """逐题溯源保留：含被剔除的孤儿题在内，每题仍逐题落 predictions。"""
-        rows = log.query("SELECT * FROM predictions WHERE run_id = ?", ("test-run",))
+        rows = log.query("SELECT * FROM predictions WHERE run_id = ?", ("run-v3-contract",))
         persisted = {r["question_id"] for r in rows}
         assert "orphan_o" in persisted, "孤儿题未逐题落库（逐题溯源被破坏）"
         assert persisted == {q.question_id for q in questions}, "逐题落库题数与输入不符"