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/unit/test_harness_pools.py

@@ -327,7 +327,6 @@ class TestBuildOrLoadPoolsFrozen:
             gate_delta_min=0.02,
             gate_lambda_dir=-0.642,
             gate_e_rollback=10.0,
-            gate_block=8,
             gate_n_max=40,
             gate_p_low=0.05,
             gate_p_high=0.95,
@@ -881,7 +880,6 @@ class TestRunHoldoutEvalConfig:
             gate_delta_min=0.02,
             gate_lambda_dir=-0.642,
             gate_e_rollback=10.0,
-            gate_block=8,
             gate_n_max=40,
             gate_p_low=0.05,
             gate_p_high=0.95,
@@ -932,7 +930,6 @@ class TestRunHoldoutEvalConfig:
             gate_delta_min=0.02,
             gate_lambda_dir=-0.642,
             gate_e_rollback=10.0,
-            gate_block=8,
             gate_n_max=40,
             gate_p_low=0.05,
             gate_p_high=0.95,