fix filename length limit error

[YoYoJa]

Description

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• The pull request does not introduce [breaking changes]
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[Copilot]

Pull request overview

This PR improves the resiliency of inline-markdown image handling in azure-ai-evaluation by treating invalid/unresolvable local image references as plain text rather than raising, specifically covering OS/path edge cases (e.g., overly long filenames and embedded null bytes).

Changes:

• Added unit tests covering filename-too-long and null-byte path scenarios for _inline_image and mixed-content parsing.
• Updated _inline_image to catch OSError/ValueError during local path resolution and fall back to returning a text chunk instead of throwing.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
sdk/evaluation/azure-ai-evaluation/tests/unittests/test_inline_image_fallback.py	Adds regression tests for long/invalid local image paths and mixed-content parsing behavior.
sdk/evaluation/azure-ai-evaluation/azure/ai/evaluation/_legacy/prompty/_utils.py	Makes _inline_image handle invalid/too-long paths gracefully by returning text instead of raising.

Comments suppressed due to low confidence (1)

sdk/evaluation/azure-ai-evaluation/azure/ai/evaluation/_legacy/prompty/_utils.py:447

• This branch resolves Path/exists() up front, then local_to_base64() re-resolves the same path and performs another exists() check. Consider refactoring so the resolved Path is computed once (or so local_to_base64 accepts a Path) to avoid duplicate filesystem calls and duplicated path-resolution logic.

            return {"type": "text", "text": image}
        inlined_uri = local_to_base64(local_file, mime_type)