Python: Replace Pydantic Settings with TypedDict + load_settings() (#3843)

* Replace Pydantic Settings with TypedDict + load_settings()

- Remove pydantic-settings dependency, add python-dotenv
- Delete _pydantic.py (AFBaseSettings, HTTPsUrl)
- Add _settings.py with generic load_settings() function, SecretString,
  type coercion, and Required field validation (SettingNotFoundError)
- Convert all 13 settings classes from AFBaseSettings subclasses to
  TypedDict definitions with load_settings() calls
- Update all consumers from attribute access to dict access
- Add 20 unit tests for load_settings() covering basic loading, dotenv,
  SecretString, type coercion, and required field validation
- Update all existing tests for new settings patterns

* Fix mypy type errors from settings conversion

- Fix str | None attribute access in responses_client (walrus operator)
- Fix SecretString | None narrowing in bedrock (type: ignore after guard)
- Convert _context_provider.py attribute access to dict access (missed file)
- Fix endpoint type narrowing in search_provider and context_provider
- Fix purview: str | None .rstrip(), int | None defaults, urlparse bytes

* Address PR review: required_fields param, type validation, fixes

- Move required field validation from TypedDict annotations (Required)
  to a required_fields parameter on load_settings(), enabling runtime
  decisions about which fields are required
- Remove Required imports and restore from __future__ import annotations
  in ollama and foundry_local
- Add _check_override_type() for deterministic ServiceInitializationError
  on invalid override types (e.g. dict passed for str field)
- Fix all multi-exception test catches back to single exception type
- Fix Ollama host=None: use .get() so None is passed through to SDK default
- Fix Purview processor: use explicit is-None checks instead of or operator
- Remove unused BaseModel import from openai/_shared.py
- Add 4 new tests (24 total): required_fields param, type validation

* Fix type validation: allow int for float fields

_check_override_type now permits int values for float-typed fields,
matching Python's standard numeric promotion behavior.

* fix: wrap urlparse arg with str() to fix mypy bytes endswith error

python/packages/purview/tests/purview/test_chat_middleware.py

@@ -125,7 +125,7 @@ class TestPurviewChatPolicyMiddleware:
     ) -> None:
         """Test that exceptions in post-check are logged but don't affect result when ignore_exceptions=True."""
         # Set ignore_exceptions to True to test exception suppression
-        middleware._settings.ignore_exceptions = True
+        middleware._settings["ignore_exceptions"] = True
 
         call_count = 0
 

python/packages/purview/tests/purview/test_middleware.py

@@ -119,7 +119,7 @@ class TestPurviewPolicyMiddleware:
     ) -> None:
         """Test middleware handles result that doesn't have messages attribute."""
         # Set ignore_exceptions to True so AttributeError is caught and logged
-        middleware._settings.ignore_exceptions = True
+        middleware._settings["ignore_exceptions"] = True
 
         context = AgentContext(agent=mock_agent, messages=[Message(role="user", text="Hello")])
 
@@ -216,7 +216,7 @@ class TestPurviewPolicyMiddleware:
         self, middleware: PurviewPolicyMiddleware, mock_agent: MagicMock
     ) -> None:
         """Test that post-check exceptions are propagated when ignore_exceptions=False."""
-        middleware._settings.ignore_exceptions = False
+        middleware._settings["ignore_exceptions"] = False
 
         context = AgentContext(agent=mock_agent, messages=[Message(role="user", text="Hello")])
 
@@ -242,7 +242,7 @@ class TestPurviewPolicyMiddleware:
     ) -> None:
         """Test that exceptions in pre-check are logged but don't stop processing when ignore_exceptions=True."""
         # Set ignore_exceptions to True
-        middleware._settings.ignore_exceptions = True
+        middleware._settings["ignore_exceptions"] = True
 
         context = AgentContext(agent=mock_agent, messages=[Message(role="user", text="Test")])
 
@@ -265,7 +265,7 @@ class TestPurviewPolicyMiddleware:
     ) -> None:
         """Test that exceptions in post-check are logged but don't affect result when ignore_exceptions=True."""
         # Set ignore_exceptions to True
-        middleware._settings.ignore_exceptions = True
+        middleware._settings["ignore_exceptions"] = True
 
         context = AgentContext(agent=mock_agent, messages=[Message(role="user", text="Test")])
 

python/packages/purview/tests/purview/test_processor.py

@@ -636,7 +636,6 @@ class TestScopedContentProcessorCaching:
         return PurviewSettings(
             app_name="Test App",
             tenant_id="12345678-1234-1234-1234-123456789012",
-            default_user_id="12345678-1234-1234-1234-123456789012",
             purview_app_location=location,
         )
 

python/packages/purview/tests/purview/test_purview_client.py

@@ -47,7 +47,7 @@ class TestPurviewClient:
     @pytest.fixture
     def settings(self) -> PurviewSettings:
         """Create test settings."""
-        return PurviewSettings(app_name="Test App", tenant_id="test-tenant", default_user_id="test-user")
+        return PurviewSettings(app_name="Test App", tenant_id="test-tenant")
 
     @pytest.fixture
     async def client(

python/packages/purview/tests/purview/test_settings.py

@@ -4,7 +4,7 @@
 
 import pytest
 
-from agent_framework_purview import PurviewAppLocation, PurviewLocationType, PurviewSettings
+from agent_framework_purview import PurviewAppLocation, PurviewLocationType, PurviewSettings, get_purview_scopes
 
 
 class TestPurviewSettings:
@@ -14,10 +14,10 @@ class TestPurviewSettings:
         """Test PurviewSettings with default values."""
         settings = PurviewSettings(app_name="Test App")
 
-        assert settings.app_name == "Test App"
-        assert settings.graph_base_uri == "https://graph.microsoft.com/v1.0/"
-        assert settings.tenant_id is None
-        assert settings.purview_app_location is None
+        assert settings["app_name"] == "Test App"
+        assert settings.get("graph_base_uri") is None
+        assert settings.get("tenant_id") is None
+        assert settings.get("purview_app_location") is None
 
     def test_settings_with_custom_values(self) -> None:
         """Test PurviewSettings with custom values."""
@@ -30,9 +30,9 @@ class TestPurviewSettings:
             purview_app_location=app_location,
         )
 
-        assert settings.graph_base_uri == "https://graph.microsoft-ppe.com"
-        assert settings.tenant_id == "test-tenant-id"
-        assert settings.purview_app_location.location_value == "app-123"
+        assert settings["graph_base_uri"] == "https://graph.microsoft-ppe.com"
+        assert settings["tenant_id"] == "test-tenant-id"
+        assert settings["purview_app_location"].location_value == "app-123"
 
     @pytest.mark.parametrize(
         "graph_uri,expected_scope",
@@ -44,7 +44,7 @@ class TestPurviewSettings:
     def test_get_scopes(self, graph_uri: str, expected_scope: str) -> None:
         """Test get_scopes returns correct scope for different URIs."""
         settings = PurviewSettings(app_name="Test App", graph_base_uri=graph_uri)
-        scopes = settings.get_scopes()
+        scopes = get_purview_scopes(settings)
 
         assert len(scopes) == 1
         assert expected_scope in scopes