Python: Fix Agent Framework tool parameter defaults

[ump45nose]

Motivation and Context

KernelFunction.as_agent_framework_tool() currently builds a field with a parameter default and then immediately overwrites it with a required field. As a result, optional Semantic Kernel parameters become required in the Agent Framework tool schema.

Description

• preserve every optional field by using is_required as the source of truth, including explicit None defaults
• add a focused regression test that verifies both default=5 and default=None remain optional

Validation:

• uv run pytest tests/unit/functions/test_kernel_function_from_method.py -q — 37 passed
• uv run ruff check semantic_kernel/functions/kernel_function.py tests/unit/functions/test_kernel_function_from_method.py — passed
• uv run ruff format --check semantic_kernel/functions/kernel_function.py tests/unit/functions/test_kernel_function_from_method.py — passed
• git diff --check — passed

Contribution Checklist

• I added a focused regression test for the corrected behavior
• I reviewed the change against the SK Contribution Guidelines
• I didn't break anyone 😄

[Copilot]

Pull request overview

Fixes Python KernelFunction.as_agent_framework_tool() so Agent Framework tool input models preserve parameter defaults (instead of incorrectly making optional parameters required), and adds a regression test to validate the behavior.

Changes:

• Prevent overwriting Pydantic fields that already include a non-None default when building the Agent Framework tool input model.
• Add a unit test asserting a parameter with default=5 remains optional in the generated tool schema.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
python/semantic_kernel/functions/kernel_function.py	Adjusts field-building logic in as_agent_framework_tool() to avoid overwriting defaulted fields.
python/tests/unit/functions/test_kernel_function_from_method.py	Adds a regression test verifying optionality is preserved when a default value is present.

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[github-actions]

MAF Automated Review — Iteration 1

Result: No findings
Scope: full PR (1 commit(s)): a60b81246da8
Model: claude-opus-4.8

Overview

The PR converts an unconditional field-overwrite into an else branch in
KernelFunction.as_agent_framework_tool(), so a Semantic Kernel parameter carrying a
non-None default is preserved as an optional field instead of being clobbered into a
required one. The change is minimal, API-compatible, and touches no shared state,
serialization, or trust boundary. It is backed by a focused regression test that fails
against the pre-fix code and passes after, and the full test_kernel_function_from_method
suite stays green. No Critical/High/Medium defect introduced by the PR was found.

Reviewed the supplied pull-request change set across correctness, security/reliability, architecture, and failure behavior.
No publishable findings remained after source verification for this scope.