docs(tools): clarify default httpx client behavior in factory docstrings

- Replace vague "today's behaviour"/"unchanged" with a concrete description of what None does.

Author: darshil3011

src/google/adk/tools/openapi_tool/openapi_spec_parser/openapi_toolset.py

@@ -139,8 +139,9 @@ def __init__(
         ``ssl_verify`` can't reach (proxies, HTTP/2, custom transports such as
         request signing). The returned client is used as an async context
         manager and closed after each request, so the factory must return a
-        fresh client on every call. Defaults to ``None``, which preserves
-        today's behaviour. Mirrors the pattern exposed for MCP by
+        fresh client on every call. Defaults to ``None``, in which case each
+        generated tool constructs its own ``httpx.AsyncClient`` per request.
+        Mirrors the pattern exposed for MCP by
         ``StreamableHTTPConnectionParams.httpx_client_factory``.
       preserve_property_names: If True, preserve the original property names
         from the OpenAPI spec instead of converting them to snake_case. This

src/google/adk/tools/openapi_tool/openapi_spec_parser/rest_api_tool.py

@@ -161,9 +161,9 @@ def __init__(
           request completes, so the factory must return a fresh client on each
           call. This lets callers configure proxies, HTTP/2, custom transports
           (e.g. request signing), or any other ``httpx.AsyncClient`` option
-          that ``ssl_verify`` can't reach. When ``None`` (default), behaviour
-          is unchanged: a fresh ``httpx.AsyncClient(verify=..., timeout=None)``
-          is created per request. Mirrors the pattern exposed for MCP by
+          that ``ssl_verify`` can't reach. When ``None`` (default), a fresh
+          ``httpx.AsyncClient(verify=..., timeout=None)`` is created per
+          request. Mirrors the pattern exposed for MCP by
           ``StreamableHTTPConnectionParams.httpx_client_factory``.
         credential_key: Optional stable key used for interactive auth and
           credential caching.