Python: fix: stop treating backtick-quoted paths as resource references in Fi…

[max-montes]

fix: Stop treating backtick-quoted paths as resource references in
FileAgentSkillsProvider

Backtick-quoted filenames in SKILL.md bodies (e.g. config.json) were incorrectly
treated as resource file references by _RESOURCE_LINK_RE. When those files did not
exist in the skill directory, the entire skill was excluded with a warning.

Backticks are standard markdown inline code formatting and do not imply the referenced
file exists locally. Only explicit markdown links [text](path) should be validated
as resource references.

Changes:

• Update _RESOURCE_LINK_RE regex to match only markdown link syntax
• Update tests to verify backtick paths are ignored
• Add integration test for the reported scenario (issue Python: FileAgentSkillsProvider incorrectly treats backtick-quoted text in SKILL.md as resource references #4369)

Fixes #4369

Motivation and Context

FileAgentSkillsProvider incorrectly treats backtick-quoted filenames (e.g.
config.json) in SKILL.md as resource file references. When those files don't exist in
the skill directory, the entire skill is excluded. This makes it impossible to use
standard markdown inline code formatting to mention filenames in skill documentation
without also providing those files on disk. Fixes #4369.

Description

Updated _RESOURCE_LINK_RE to only match explicit markdown link syntax
([text](path/file.ext)), removing the backtick alternative. Backticks are standard
markdown code formatting and should not imply a file exists locally.

Updated two existing tests to reflect the new behavior and added an integration-level
test that verifies a skill with backtick-quoted filenames (that don't exist on disk)
still loads successfully.

Note: The .NET implementation has the same regex in FileAgentSkillLoader.cs
(line 48) and is affected by the same bug. Will open a separate issue for the .NET fix
after this PR lands.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution
  Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? Minor behavioral change: skills that relied on
  backtick-quoted paths to register resources will need to switch to markdown link syntax
  ([text](path)). Pre-GA.

[Copilot]

Pull request overview

This PR fixes an issue in the Python FileAgentSkillsProvider where backtick-quoted filenames in SKILL.md (inline code formatting like `config.json`) were incorrectly treated as resource references and could cause the entire skill to be excluded if the referenced files didn’t exist. The change narrows resource detection to explicit Markdown link syntax only, aligning behavior with standard Markdown semantics and resolving issue #4369.

Changes:

• Update _RESOURCE_LINK_RE to match only Markdown links ([text](path/file.ext)) and stop extracting backtick-quoted paths as resources.
• Update unit tests for _extract_resource_paths to ensure backtick-quoted filenames are ignored while Markdown links are still extracted.
• Add an integration-level test ensuring skills still load when SKILL.md contains non-existent backtick-quoted filenames, as long as linked resources are valid.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
python/packages/core/agent_framework/_skills.py	Restricts resource extraction to Markdown link syntax by removing backtick matching from _RESOURCE_LINK_RE.
python/packages/core/tests/core/test_skills.py	Updates existing tests to reflect new extraction rules and adds coverage for the reported scenario (issue #4369).

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_skills.py	225	11	95%	155–156, 169–170, 280–282, 317–318, 398, 585
TOTAL	22222	2758	87%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
4715	247 💤	0 ❌	0 🔥	1m 16s ⏱️

[max-montes]

@max-montes please read the following Contributor License Agreement(CLA). If you agree with the CLA, please reply with the following information.

@microsoft-github-policy-service agree [company="{your company}"]

Options:

• (default - no company specified) I have sole ownership of intellectual property rights to my Submissions and I am not making Submissions in the course of work for my employer.

@microsoft-github-policy-service agree

• (when company given) I am making Submissions in the course of work for my employer (or my employer has intellectual property rights in my Submissions by contract or applicable law). I have permission from my employer to make Submissions and enter into this Agreement on behalf of my employer. By signing below, the defined term “You” includes me and my employer.

@microsoft-github-policy-service agree company="Microsoft"

Contributor License Agreement

@microsoft-github-policy-service agree

[max-montes]

Closing this in favor of #4387, which restructures the skills module and addresses the backtick parsing issue as part of a broader refactor. Happy to help review or test if useful!