fix: lock all-INFRA contract, idempotency tests, tuple units (algo #6)

app/harness/validate.py

@@ -809,7 +809,8 @@ class GateSpec:
         target_file: 解析后生效 skill 文件名(候选物化写此文件)。
         candidate_content: 候选 skill 全文。
         base_skill_content: 基线侧生效 skill 全文(skill_hash 作缓存键)。
-        units: 阶梯序单元列表(已排除案例单元、截断 gate_n_max)。
+        units: 阶梯序单元元组(已排除案例单元、截断 gate_n_max);元组,装配后
+            不可变,防 spec.units 与 run.slots 漂移。
         gate_run_prefix: run_id 前缀,必须含 "_gate_"(防泄露过滤依赖)。
     """
 
@@ -817,7 +818,7 @@ class GateSpec:
     target_file: str
     candidate_content: str
     base_skill_content: str
-    units: list[QuestionUnit]
+    units: tuple[QuestionUnit, ...]
     gate_run_prefix: str
 
 
@@ -884,6 +885,10 @@ def _advance_prefix(run: _GateRun, params: GateParams) -> None:
     瞬间返回、cand 臂必新鲜跑,两臂延迟不对称,若 cand 延迟与对错相关,早到翻转
     对系统性偏向 W 型 → e-值虚高假接受。前缀消费把判定顺序钉回预声明阶梯序,
     anytime-valid 无条件成立;INFRA 单元视为"已解决(剔除)"不阻塞前缀。
+
+    契约:全部单元被剔除时 verdict 保持 None、frozen 保持 False,由调度编排层
+    (Task 3 的 validate_skills_concurrent)检测 verdict None 并 raise
+    RuntimeError;本函数不负责该终态。
     """
     while not run.frozen and run.prefix_ptr < len(run.slots):
         slot = run.slots[run.prefix_ptr]
@@ -903,7 +908,9 @@ def _advance_prefix(run: _GateRun, params: GateParams) -> None:
                     run.frozen = True
             continue
         uid = slot.unit.unit_id
-        assert slot.base is not None and slot.cand_per_q is not None
+        assert slot.base is not None and slot.cand_per_q is not None, (
+            f"slot 未配齐即被消费: unit={slot.unit.unit_id}"
+        )
         c_units = unit_correctness_view([slot.unit], slot.cand_per_q)
         pair_result = pair_block({uid: slot.base}, c_units, [uid])
         run.candidate_per_q.update(slot.cand_per_q)