[BREAKING] Python: clean up kwargs across agents, chat clients, tools, and sessions (#4581)

* Python: clean up kwargs across agents, chat clients, tools, and sessions (#3642)

Audit and refactor public **kwargs usage across core agents, chat clients,
tools, sessions, and provider packages per the migration strategy codified
in CODING_STANDARD.md.

Key changes:
- Add explicit runtime buckets: function_invocation_kwargs and client_kwargs
  on RawAgent.run() and chat client get_response() layers.
- Refactor FunctionTool to prefer explicit ctx: FunctionInvocationContext
  injection; legacy **kwargs tools still work via _forward_runtime_kwargs.
- Refactor Agent.as_tool() to use direct JSON schema, always-streaming
  wrapper, approval_mode parameter, and UserInputRequiredException
  propagation (integrates PR #4568 behavior).
- Remove implicit session bleeding into FunctionInvocationContext; tools
  that need a session must receive it via function_invocation_kwargs.
- Lower chat-client layers after FunctionInvocationLayer accept only
  compatibility **kwargs (client_kwargs flattened, function_invocation_kwargs
  ignored).
- Add layered docstring composition from Raw... implementations via
  _docstrings.py helper.
- Clean up provider constructors to use explicit additional_properties.
- Deprecation warnings on legacy direct kwargs paths.
- Update samples, tests, and typing across all 23 packages.

Resolves #3642

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

* clarified docstring

* feedback fixes

* Add unit tests for _docstrings.py build/apply helpers

Tests cover: no docstring source, no extra kwargs, appending to existing
Keyword Args section, inserting after Args, inserting in plain docstrings,
multiline descriptions, ordering, and apply_layered_docstring.

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

* Add test for propagate_session TypeError on non-AgentSession values

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

* Add tests for multi-content and empty UserInputRequiredException propagation

Cover the branching logic in _try_execute_function_calls for:
- Multiple user_input_request items in a single exception (extra_user_input_contents path)
- Empty contents list (fallback function_result path)

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

* Add tests for DurableAIAgent.get_session forwarding service_session_id

Verifies get_session correctly forwards service_session_id and session_id
to the executor's get_new_session, replacing the removed kwargs test.

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

* Simplify ag-ui test stub to read session from client_kwargs only

Remove dual-mode detection (client_kwargs vs raw kwargs fallback) from
the test mock. Session is now read exclusively from client_kwargs,
matching the settled public calling convention.

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

* updated create and get sessions in durable

* fixed docstrings

* fix test

* updated session handling

* updated from main

* updated tests

---------

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

python/CODING_STANDARD.md

@@ -127,7 +127,12 @@ def create_agent(name: str, tool_mode: Literal['auto', 'required', 'none'] | Cha
 Avoid `**kwargs` unless absolutely necessary. It should only be used as an escape route, not for well-known flows of data:
 
 - **Prefer named parameters**: If there are known extra arguments being passed, use explicit named parameters instead of kwargs
+- **Prefer purpose-specific buckets over generic kwargs**: If a flexible payload is still needed, use an explicit named parameter such as `additional_properties`, `function_invocation_kwargs`, or `client_kwargs` rather than a blanket `**kwargs`
 - **Subclassing support**: kwargs is acceptable in methods that are part of classes designed for subclassing, allowing subclass-defined kwargs to pass through without issues. In this case, clearly document that kwargs exists for subclass extensibility and not for passing arbitrary data
+- **Make known flows explicit first**: For abstract hooks, move known data flows into explicit parameters before leaving `**kwargs` behind for subclass extensibility (for example, prefer `state=` explicitly instead of passing it through kwargs)
+- **Prefer explicit metadata containers**: For constructors that expose metadata, prefer an explicit `additional_properties` parameter.
+- **Keep SDK passthroughs narrow and documented**: A kwargs escape hatch may be acceptable for provider helper APIs that pass through to a large or unstable external SDK surface, but it should be documented as SDK passthrough and revisited regularly
+- **Do not keep passthrough kwargs on wrappers that do not use them**: Convenience wrappers and session helpers should not accept generic kwargs merely to forward or ignore them
 - **Remove when possible**: In other cases, removing kwargs is likely better than keeping it
 - **Separate kwargs by purpose**: When combining kwargs for multiple purposes, use specific parameters like `client_kwargs: dict[str, Any]` instead of mixing everything in `**kwargs`
 - **Always document**: If kwargs must be used, always document how it's used, either by referencing external documentation or explaining its purpose