Python: Fix spurious Magentic custom manager warning (#6261)

* Fix magentic manager warning

* Use typing_extensions.Sentinel for _MISSING sentinel value

Replace the bare object() sentinel with typing_extensions.Sentinel per
PEP 661 (now final). Sentinel provides a proper name and repr
('<_MISSING>') and is the idiomatic approach going forward.

Refs #4306

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: correct Sentinel type annotation for max_stall_count param (#6261)

Use int | Sentinel for max_stall_count parameter type annotation instead
of int with cast(Any, _MISSING) to properly express that the parameter
can hold either an int or the _MISSING sentinel value. This fixes the
pyright reportUnnecessaryComparison errors caused by the types int and
Sentinel having no overlap.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Rename _MISSING sentinel to UNSET in orchestrations

The sentinel is user-visible as a default in public init signatures, so
use UNSET (no leading underscore) instead of the private _MISSING name.
Drop the now-unnecessary reportPrivateUsage ignores on the UNSET imports.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/packages/bedrock/agent_framework_bedrock/_chat_client.py

@@ -795,10 +795,7 @@ class BedrockChatClient(
             schema = copy.deepcopy(schema_src)
         else:
             if not isinstance(response_format, type) or not issubclass(response_format, BaseModel):
-                raise TypeError(
-                    "response_format must be None, a dict JSON schema, "
-                    "or a Pydantic BaseModel subclass."
-                )
+                raise TypeError("response_format must be None, a dict JSON schema, or a Pydantic BaseModel subclass.")
             # response_format is a Pydantic model class
             schema = response_format.model_json_schema()
             name = response_format.__name__
@@ -817,9 +814,7 @@ class BedrockChatClient(
         return {
             "textFormat": {
                 "type": "json_schema",
-                "structure": {
-                    "jsonSchema": json_schema
-                },
+                "structure": {"jsonSchema": json_schema},
             }
         }
 
@@ -840,9 +835,7 @@ class BedrockChatClient(
                 if node_id in visited:
                     return
                 visited.add(node_id)
-                if node.get("type") == "object" or (
-                    "properties" in node and "type" not in node
-                ):
+                if node.get("type") == "object" or ("properties" in node and "type" not in node):
                     existing = node.get("additionalProperties")
                     if existing is None or existing is True:
                         node["additionalProperties"] = False

python/packages/bedrock/tests/test_bedrock_structured_output.py

@@ -238,6 +238,7 @@ async def test_chat_response_value_populated_streaming() -> None:
 
 async def test_unsupported_model_validation_exception() -> None:
     """When a model doesn't support outputConfig, a clear error should be raised."""
+
     class _FailingStubBedrockRuntime:
         def converse(self, **kwargs: Any) -> dict[str, Any]:
             # Simulate botocore ClientError for ValidationException