diff --git a/pipeline_service/platform_model_tools.py b/pipeline_service/platform_model_tools.py
index 9e34fb4..07ed718 100644
--- a/pipeline_service/platform_model_tools.py
+++ b/pipeline_service/platform_model_tools.py
@@ -383,10 +383,16 @@ async def tool_invoke_model(params, org_id, user_id=""):
     cap2, desc = await _resolve_capability(model, org_id)
     cap = cap or cap2
     # 能力降级门禁换算：i2i/r2v 模型无媒体输入时按 t2i/t2v 契约校验
-    cap = _degrade_gate_cap(cap, biz)
-    gap = await judge_completeness(model, cap, task, biz,
-                                   description=desc, org_id=org_id or "0",
-                                   user_id=user_id or "")
+    cap_gate = _degrade_gate_cap(cap, biz)
+    if cap_gate != (cap or "").strip().lower():
+        # 降级执行：契约是确定性规则，直接代码表判定——LLM/模型技能层会按
+        # 模型自身能力（i2i 要源图）误判，实测 2026-09-08 拦截了合法文生图任务
+        gap = _check_completeness_code(cap_gate, task, biz)
+    else:
+        gap = await judge_completeness(model, cap_gate, task, biz,
+                                       description=desc, org_id=org_id or "0",
+                                       user_id=user_id or "")
+    cap = cap_gate
     if gap:
         logger.info("invoke_model 完备性门禁拦截（%s）: %s", cap or "?", gap[:80])
         return "QUESTION: " + gap