Python: Add windows junction detection for skills

[westey-m]

Motivation & Context

Description & Review Guide

• What are the major changes?
• What is the impact of these changes?
• What do you want reviewers to focus on?

Related Issue

Fixes #

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).
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[Copilot]

🟡 Not ready to approve

A newly added test (test_link_probe_detects_windows_reparse_attribute) will fail on non-Windows platforms because it asserts a Windows-only stat constant without skipping.

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Pull request overview

This PR hardens Python skill and file-access path handling on Windows by treating directory junctions (and other reparse points) as disallowed “link-like” path segments, closing an escape vector similar to symlinks.

Changes:

• Added a shared private helper (is_link_or_reparse_point) for detecting symlinks, junctions, and Windows reparse points.
• Updated file-based skills discovery/validation to reject any path containing a symlink or reparse point segment (fail-closed on probe errors).
• Consolidated junction creation helpers in tests and added coverage for junction/reparse-point detection.

File summaries

File	Description
python/packages/core/agent_framework/_filesystem.py	Introduces shared link/reparse-point detection helper used by security checks.
python/packages/core/agent_framework/_skills.py	Extends skill resource/script scanning and resource validation to treat reparse points like symlinks (and fail closed on probe errors).
python/packages/core/agent_framework/_harness/_file_access.py	Reuses the shared helper to consistently filter/deny link-like filesystem entries.
python/packages/core/tests/core/conftest.py	Adds a reusable create_junction_or_skip test helper for Windows junction creation.
python/packages/core/tests/core/test_skills.py	Updates symlink tests to new API name and adds a junction guard test.
python/packages/core/tests/core/test_harness_file_access.py	Switches to shared junction helper and adds a unit test for the Windows reparse-attribute fallback.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 1
• Review effort level: Lite

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[github-actions]

Automated Code Review

Reviewers: 5 | Confidence: 55% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Failure Modes, Design Approach

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Automated review by westey-m's agents

[github-actions]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/core/agent_framework
_filesystem.py	13	1	92%	19
_skills.py	1356	70	94%	321, 591, 1109, 1124, 1126–1127, 1493–1494, 1736, 1765, 2281, 2471, 2989–2990, 3092, 3100, 3105, 3108, 3114, 3134, 3146, 3151, 3247, 3255, 3260, 3263, 3269, 3289, 3298, 3303, 3596–3597, 4061, 4064, 4066–4067, 4069, 4220, 4547, 4562, 4570, 4597, 4601, 4605, 4668–4669, 4671–4672, 4684, 4688, 4724–4725, 4729–4730, 4774–4776, 4782, 4831, 4835, 4839, 4849–4851, 5053–5054, 5076–5077, 5084–5085
packages/core/agent_framework/_harness
_file_access.py	626	49	92%	189, 220, 283, 393, 395, 407, 411, 439, 452–453, 460–467, 471, 475, 841–842, 867, 871, 926–928, 950–953, 992, 994, 1051, 1053, 1458–1459, 1470–1471, 1483–1484, 1498–1499, 1522–1523, 1538, 1543–1544, 1573
TOTAL	44743	4104	90%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
9150	36 💤	0 ❌	0 🔥	2m 10s ⏱️