Python: Fix WorkflowAgent non-streaming return type

[WhaleTech (ryo-whaletech)]

Motivation & Context

WorkflowAgent.run(stream=False) currently exposes a ResponseStream[AgentResponseUpdate, AgentResponse] return type even though the runtime false branch returns the non-streaming _run_impl() awaitable. This disagrees with SupportsAgentRun, the method documentation, and nearby agent implementations, so type checkers and IDEs see the wrong public pre-await return type.

Runtime execution is already correct. This change aligns the overload with existing behavior and the common agent contract.

Description & Review Guide

• What are the major changes?
  • Correct the Literal[False] overload of WorkflowAgent.run() to return Awaitable[AgentResponse].
  • Add focused assert_type coverage for omitted/default stream, explicit stream=False, and stream=True.
• What is the impact of these changes?
  • Static typing now matches the existing runtime behavior.
  • stream=True typing and runtime execution are unchanged.
  • There are no changes to storage, serialization, checkpoints, workflow execution, network calls, or provider behavior.
  • Local validation passed all five core typing checkers, focused WorkflowAgent tests, strict Pyright, Ruff syntax checks, the full core check, package builds, and git diff --check.
• What do you want reviewers to focus on?
  • Whether the corrected overload matches the common SupportsAgentRun contract.
  • Whether the assert_type coverage is the preferred regression mechanism.
  • Whether any public or generated stub requires a matching edit; the root .pyi currently re-exports the concrete class directly.

Related Issue

Fixes #8286

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.

[Copilot]

🟢 Approval recommended

The typing fix matches runtime behavior and includes focused regression coverage.

Pull request overview

This pull request aligns WorkflowAgent.run() typing with runtime behavior and SupportsAgentRun.

Changes:

• Corrects non-streaming overload return types.
• Adds assertions for default, non-streaming, and streaming calls.

File summaries

File	Summary
python/packages/core/tests/workflow/test_workflow_agent.py	Adds overload regression assertions.
python/packages/core/agent_framework/_workflows/_agent.py	Fixes the non-streaming return annotation.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

---

💡 Add a code-review agent skill for context-aware, tailored reviews. Learn more in the docs.