Protect pull request workspace copies

Editor assessment

This commit patches CVE-2026-106486. The subject names the asset (pull request workspace copies) and the intent (protect), so the area is clear. But the body contains only a Signed-off-by trailer - no description of the traversal or disclosure risk, and no note on how copies are now protected. Understandable in outline, but the explanation never arrives. Style-wise the header is clean and the sign-off trailer is properly separated; the missing body is the whole gap, because the subject alone cannot explain the workspace-copy risk.