diff --git a/app/engine/services/ai_service.py b/app/engine/services/ai_service.py
index 68e40fe..dbd4401 100644
--- a/app/engine/services/ai_service.py
+++ b/app/engine/services/ai_service.py
@@ -80,7 +80,13 @@ class PromptProvider:
     def from_config(cls, md: dict) -> "PromptProvider":
         """快照 prompts 组 → PromptProvider。缺键/非字符串显性炸带键名
         (DB 快照坏数据不留到 build_system 才炸)。"""
-        bad = [k for k in PROMPTS_KEYS if not isinstance((md or {}).get(k), str)]
+        if not isinstance(md, dict):
+            # 入口类型守卫(Task 6 的 PUT prompts 会接请求体): 字符串/
+            # 列表进来给 ValueError,不让 .get 的 AttributeError 漏成 500
+            raise ValueError(
+                f"prompts 必须是 dict: {{{', '.join(PROMPTS_KEYS)}}}: "
+                f"实际 {type(md).__name__}")
+        bad = [k for k in PROMPTS_KEYS if not isinstance(md.get(k), str)]
         if bad:
             raise ValueError(f"prompts 配置缺少(或非字符串)键: {', '.join(bad)}")
         return cls(
diff --git a/app/platform/tenant_source.py b/app/platform/tenant_source.py
index ba00fa8..f0906c8 100644
--- a/app/platform/tenant_source.py
+++ b/app/platform/tenant_source.py
@@ -16,10 +16,12 @@ registry 只认本模块的 TenantSource 协议(async load_all / load_tenant),
 ——旧路径 PromptProvider.from_dir 直读盘、不进快照;对齐后 DB 源(prompts
 嵌 config_json)与文件源输出形态一致,registry 不再感知源差异。
 
-错误契约(两源一致,registry 依赖):
+错误契约(registry 依赖,加载期显性失败不流入运行期):
 - 未知 slug → LookupError(registry_reload 映射为 UnknownTenantError);
-- 数据坏(缺版本/坏 JSON/零站点/缺 wall·prompts 组)→ ValueError 带
-  租户名(加载期显性失败,不流入运行期)。
+- DB 源数据坏(缺版本/坏 JSON/非对象/零站点/缺 wall·prompts 组)→
+  ValueError 带租户名(与版本号);
+- 文件源数据坏:坏 JSON/slug 与目录不一致/零站点 → ValueError 带路径,
+  wall/prompts 文件缺失 → FileNotFoundError 带路径(read_text 原样)。
 """
 import json
 import pathlib
diff --git a/tests/test_db_tenant_source.py b/tests/test_db_tenant_source.py
index 6635e45..6d3ec87 100644
--- a/tests/test_db_tenant_source.py
+++ b/tests/test_db_tenant_source.py
@@ -20,7 +20,7 @@ import pytest
 from sqlalchemy import text
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.engine.services.ai_service import PromptProvider
+from app.engine.services.ai_service import PROMPTS_KEYS, PromptProvider
 from app.platform.db import (
     Site,
     SiteDomain,
@@ -36,8 +36,6 @@ REPO_ROOT = Path(__file__).resolve().parents[1]
 SEED_DIR = REPO_ROOT / "seed_profiles"
 JC_DOMAIN = "db.jc.example.com"      # DB 源测试专属域名(不与文件源种子撞)
 
-_PROMPTS_KEYS = ("system", "company_facts", "extractor", "evaluator")
-
 
 def _jiancai_snapshot(prefix="ai-kefu-jc"):
     """版本 config_json 构造助手:seed jiancai 的 config 组 + wall.json +
@@ -51,7 +49,7 @@ def _jiancai_snapshot(prefix="ai-kefu-jc"):
         (SEED_DIR / "jiancai" / "wall.json").read_text(encoding="utf-8"))
     snapshot["prompts"] = {
         name: (prompts_dir / f"{name}.md").read_text(encoding="utf-8")
-        for name in _PROMPTS_KEYS
+        for name in PROMPTS_KEYS
     }
     return snapshot
 
diff --git a/tests/test_prompt_provider.py b/tests/test_prompt_provider.py
index 1f4891d..65251a6 100644
--- a/tests/test_prompt_provider.py
+++ b/tests/test_prompt_provider.py
@@ -153,6 +153,14 @@ def test_from_config_non_string_key_raises():
              "extractor": "e", "evaluator": "v"})
 
 
+def test_from_config_non_dict_raises():
+    # 入口类型守卫: Task 6 的 PUT prompts 会把请求体直传这里——字符串/
+    # 列表进来必须是 ValueError,不能让 .get 的 AttributeError 漏成 500
+    for bad in ("system=...", ["system", "company_facts"], 42, None):
+        with pytest.raises(ValueError, match="dict"):
+            PromptProvider.from_config(bad)
+
+
 def test_from_config_equals_from_dir():
     d = JC_PROMPTS
     cfg = {name: (d / f"{name}.md").read_text(encoding="utf-8")