[Review] Path traversal in `_run_file_exists` — criterion `path` not confined to project_dir

[github-actions]

Review Finding

PR: #75 (feat: MCP server source control + 5 new session tools)
File: src/atlas_session/contract/verifier.py
Line: 100
Severity: must-fix

Description

full_path = Path(project_dir) / path where path is taken directly from the user-supplied criterion dict. A path of ../../etc/shadow would resolve outside the project. Add a check that full_path.resolve() is a descendant of Path(project_dir).resolve() before calling .exists().

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