Python: resolve postponed @response_handler annotations

[CoralGarden52]

Motivation & Context

The introspection path of @response_handler reads raw values from inspect.signature(func). With from __future__ import annotations, valid request, response, and WorkflowContext[...] annotations are strings, so a valid executor class currently fails during decoration with ValueError and cannot be imported or instantiated. The existing @handler path already resolves these annotations; issue #8327 tracks the missing response-handler counterpart.

The bug was reproduced on clean upstream commit 3c670707766a8455da6491a9049cc9d575e019f0 with a four-parameter response handler using original_request: str, response: int, and ctx: WorkflowContext[str].

Description & Review Guide

• What are the major changes?
  • Resolve response-handler annotations with typing.get_type_hints(func) during signature validation, matching the existing @handler behavior.
  • Fall back to raw annotations when resolution fails, preserving the existing diagnostic path for unresolved references.
  • Add a future-annotation regression test that verifies request type, response type, and workflow output type registration.
• What is the impact of these changes?
  • Executors using postponed annotations can define and register @response_handler methods normally.
  • Existing handlers with evaluated annotations and explicit decorator type parameters retain their behavior.
  • Before the fix, the executor definition raised ValueError: Response handler parameter 'ctx' must be annotated ... got WorkflowContext[str]; after the fix it registers (str, int) with workflow output type str.
  • Verification evidence: the full core suite passed with 5044 passed, 131 skipped, 2 xfailed; relevant request-info, executor, and future-annotation tests passed; Ruff format/lint passed; Pyright reported 0 errors, 0 warnings for both changed files.
• What do you want reviewers to focus on?
  • Whether the response-handler resolution and fallback behavior correctly mirror _validate_handler_signature.
  • Whether the regression test covers the public decorator/discovery path without changing explicit-parameter behavior.

Related Issue

Fixes #8327

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]

🟡 Changes recommended

Add fallback-path coverage and verify workflow_output_types registration for two-argument contexts.

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Pull request overview

Fixes postponed-annotation handling for Python @response_handler methods.

Changes:

• Resolve annotations with typing.get_type_hints, with raw-annotation fallback.
• Add regression coverage for future annotations.

File summaries

File	Summary
python/packages/core/tests/workflow/test_executor_future.py	Tests response-handler registration with postponed annotations.
python/packages/core/agent_framework/_workflows/_request_info_mixin.py	Resolves response-handler parameter annotations.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Lite (auto)

Note

Copilot is running an experiment and ran this review at Lite.

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[CoralGarden52]

Implemented in commit cf3e412. Added regression coverage for the unresolved-annotation fallback path and verified that it produces the existing ValueError diagnostic. The postponed-annotation test now uses WorkflowContext[str, bool] and asserts both output_types and workflow_output_types. The targeted executor tests and full workflow test suite pass.

[Ricky-7-Yan]

Reviewed current head cf3e412. Resolving annotations with typing.get_type_hints() and using the same (NameError, AttributeError, RecursionError) raw-annotation fallback as the existing @handler and function-executor validation paths keeps the decorator behaviors aligned. The regression exercises the public class-decoration/discovery path, verifies request/response plus both WorkflowContext type arguments, and the added unresolved-reference case covers the fallback diagnostic. I found no blocking issue in the scoped diff.

The full upstream Python workflows have not run on this external branch; this approval relies on the current code/tests and the author's reported full core suite, Ruff, and Pyright results rather than treating the governance checks as full CI.