feat: TenantSource 抽象——File源(测试/档案)与DB源(生产)，registry 数据源可切换+reload upsert

Co-Authored-By: Claude Code <noreply@anthropic.com>

tests/test_prompt_provider.py

@@ -136,6 +136,30 @@ def test_build_extractor_handles_none_info():
     assert "{}" in out                           # existing_info or {} 语义保留
 
 
+# ---- from_config(Phase 2 Task 4: 快照 prompts 组构造)----------------------
+
+def test_from_config_missing_key_raises():
+    # 缺一键 → 显性 ValueError 带键名(不留到 build_system 才炸)
+    with pytest.raises(ValueError, match="company_facts"):
+        PromptProvider.from_config(
+            {"system": "s", "extractor": "e", "evaluator": "v"})
+
+
+def test_from_config_non_string_key_raises():
+    # 值非字符串(JSON null 等)同样显性拒绝
+    with pytest.raises(ValueError, match="system"):
+        PromptProvider.from_config(
+            {"system": None, "company_facts": "c",
+             "extractor": "e", "evaluator": "v"})
+
+
+def test_from_config_equals_from_dir():
+    d = JC_PROMPTS
+    cfg = {name: (d / f"{name}.md").read_text(encoding="utf-8")
+           for name in ("system", "company_facts", "extractor", "evaluator")}
+    assert PromptProvider.from_config(cfg) == PromptProvider.from_dir(JC_PROMPTS)
+
+
 # ---- runtime 接线 --------------------------------------------------------
 
 def test_registry_runtime_carries_prompts(tmp_path):