[lakers-abing]

Motivation & Context

When a write hits a file/directory path collision, the file-access tool should tell the agent how to recover. The current generic OS error does not distinguish whether the parent path is a file or the target is a directory. The existing FileExistsError response is specific to exclusive create and should continue recommending overwrite=true only for that case.

Description & Review Guide

• What are the major changes? Return separate actionable messages for NotADirectoryError and IsADirectoryError, and add tool-level regression tests for both cases plus the existing exclusive-create response.
• What is the impact of these changes? Agents can choose a valid path after a collision while overwrite=false retains its existing behavior.
• What do you want reviewers to focus on? Confirm the guidance distinguishes path collisions from an existing file that can be overwritten.

Related Issue

Fixes #8567. This is complementary to open PR #8687: that PR adds the in-memory store path checks; this change handles the tool response and does not repeat those checks.

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

[Copilot]

Copilot review overview

🟡 Changes recommended

Filesystem-backed collisions can still be misclassified as overwriteable existing files.

Get a fresh assessment by requesting another Copilot review.

Review effort: Balanced
Findings: 1

Open (1)

• Filesystem collisions are misclassified as overwrite conflicts · New

What changed in this PR

Adds actionable file-write collision errors, complementing PR #8687’s in-memory path validation.

Changes:

• Distinguishes parent-file and target-directory collisions.
• Adds regression tests while preserving exclusive-create guidance.

File	Description
python/​packages/​core/​agent_framework/​_harness/​_file_access.py	Adds collision-specific write responses.
python/​packages/​core/​tests/​core/​test_harness_file_access.py	Tests collision and overwrite guidance.

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[lakers-abing]

@microsoft-github-policy-service agree