Python: Restore runtime tools on nested workflow response resume - #8345

Motivation & Context

A nested WorkflowExecutor forwards request-scoped runtime tools to its child during initial execution and nested cancellation, but currently omits them when resuming the child from a response.

As a result, the resumed child does not receive runtime tools supplied to the current parent continuation, leaving its response handling and subsequent child execution without that request-scoped context.

This restores the response-continuation propagation previously introduced in #7776 and later lost during the nested workflow invocation-kwargs changes in #7963.

Per the repository guidance for approval-resume-related changes, I am opening this as a draft so the concrete regression test and minimal fix are available for review while the core team confirms the intended direction.

Description & Review Guide

• What are the major changes?

  • Forward the active parent continuation's runtime tools when WorkflowExecutor._handle_response() resumes its child.
  • Add a provider-free regression test covering the nested propagated-response path.

• What is the impact of these changes?

  • Resumed nested workflows receive the request-scoped runtime tools supplied to the current parent continuation.
  • Existing child function_invocation_kwargs and client_kwargs continuation semantics remain unchanged.
  • Unknown or already-handled response validation remains unchanged.
  • There are no public API, checkpoint/storage-format, cancellation, serialization, or exception-handling changes.

• What do you want reviewers to focus on?

  • Whether forwarding the active continuation's runtime tools at _handle_response() is the intended restoration of the behavior introduced in Python: Fix AG-UI workflow-as-agent approval resumes #7776.
  • Whether the focused regression coverage captures the nested response-continuation boundary without expanding into the separate nested-cancellation kwargs behavior.

Related Issue

Fixes #8344

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and title prefix in sync automatically.