Context

Found during PE audit of PR #892. Several security-critical code paths lack dedicated tests:

1. SandboxWorkspaceManager.validateDirectoryMount() — path traversal prevention
2. AgentJobService.retryDelivery() — retry logic for failed deliveries
3. UNSAFE_MARKDOWN_LINK regex in PullRequestCommentPoster — XSS prevention in PR comments
4. Git security env vars in DockerSandboxAdapter — config blocklist

Scope

Write focused unit tests for each of the 4 paths:

• Path traversal: symlinks, ../ sequences, absolute paths outside allowed root
• Retry: idempotency, max retries, state transitions
• Markdown sanitization: malicious links, JS injection, nested markdown
• Git env vars: verify all blocked configs present in container env

Files

Verification

• All 4 test classes pass
• Path traversal attacks caught by validateDirectoryMount()
• Unsafe markdown sanitized correctly
• Git config blocklist verified exhaustively