refactor: read settings directly instead of getattr with a second default

About 85 call sites read a setting as getattr(settings, "NAME", fallback),
each carrying its own copy of the default. Every one of those names is a
field with a default on the model, so the fallback could never apply to
the real settings object; it only masked drift. Two had drifted:

- OPENAI_PROMPT_CACHE_KEY defaults to True on the model but the reader
  fell back to False, and two test stubs relied on that.
- SharePoint's MICROSOFT_AUTHORITY fallback to
  https://login.microsoftonline.com/<tenant> never fired, because the
  attribute always exists (as None), so MSAL got authority=None. The
  connector now derives the tenant authority when the setting is unset,
  as its test always assumed.

Four places read EMBEDDINGS_KEY straight from os.environ, skipping the
"None"/"" normalisation the model applies; they read the setting now.
Test stubs that replaced a module's settings with a SimpleNamespace list
every setting the code under test reads.

tests/llm/test_openai_responses.py

@@ -29,6 +29,9 @@ def _make_llm(monkeypatch, capabilities=None, store_responses=False):
             AZURE_DEPLOYMENT_NAME="dep",
             OPENAI_RESPONSES_STORE=store_responses,
             OPENAI_REASONING_SUMMARY="auto",
+            OPENAI_RESPONSES_TRUNCATION_AUTO=False,
+            OPENAI_PROMPT_CACHE_KEY=False,
+            OPENAI_PROMPT_CACHE_RETENTION=None,
         ),
     )
     from docsgpt.llm.openai import OpenAILLM

tests/llm/test_responses_chain_budget.py

@@ -24,18 +24,19 @@ def _make_llm(monkeypatch, store_responses=True, **extra_settings):
         "docsgpt.llm.openai.StorageCreator",
         types.SimpleNamespace(get_storage=lambda: None),
     )
-    monkeypatch.setattr(
-        "docsgpt.llm.openai.settings",
-        types.SimpleNamespace(
-            OPENAI_API_KEY="k",
-            API_KEY="k",
-            OPENAI_BASE_URL="",
-            AZURE_DEPLOYMENT_NAME="dep",
-            OPENAI_RESPONSES_STORE=store_responses,
-            OPENAI_REASONING_SUMMARY="auto",
-            **extra_settings,
-        ),
-    )
+    # Every setting the Responses path reads, with the hints off; tests opt in per case.
+    stub = {
+        "OPENAI_API_KEY": "k",
+        "API_KEY": "k",
+        "OPENAI_BASE_URL": "",
+        "AZURE_DEPLOYMENT_NAME": "dep",
+        "OPENAI_RESPONSES_STORE": store_responses,
+        "OPENAI_REASONING_SUMMARY": "auto",
+        "OPENAI_RESPONSES_TRUNCATION_AUTO": False,
+        "OPENAI_PROMPT_CACHE_KEY": False,
+        "OPENAI_PROMPT_CACHE_RETENTION": None,
+    }
+    monkeypatch.setattr("docsgpt.llm.openai.settings", types.SimpleNamespace(**{**stub, **extra_settings}))
     from docsgpt.llm.openai import OpenAILLM
 
     llm = OpenAILLM(api_key="k")
@@ -142,7 +143,7 @@ def _params(llm, **kwargs):
 
 
 @pytest.mark.unit
-def test_build_responses_params_defaults_omit_truncation_and_cache_hints(monkeypatch):
+def test_build_responses_params_omits_truncation_and_cache_hints_when_off(monkeypatch):
     llm = _make_llm(monkeypatch)
     llm._prompt_cache_key = "conv-123"
     params = _params(llm)

tests/parser/connectors/test_share_point_auth.py

@@ -14,8 +14,8 @@ def mock_settings():
     s.MICROSOFT_TENANT_ID = "tenant-id-123"
     s.CONNECTOR_REDIRECT_BASE_URI = "https://redirect.example.com/callback"
     s.MONGO_DB_NAME = "test_db"
-    # Delete MICROSOFT_AUTHORITY so getattr falls back to default
-    del s.MICROSOFT_AUTHORITY
+    # Unset, as in a real Settings object, so the tenant-derived authority is used.
+    s.MICROSOFT_AUTHORITY = None
     return s