A Gate That Checked the Wrong Thing

A harness enforces "the agent may only write inside /workspace." The check is implemented as: take the path argument, verify the string starts with /workspace/, then hand the original path to the file-writing executor.

During a session, the agent (following instructions embedded in a README it had fetched) created /workspace/notes as a symlink to /home/dev/.ssh, then wrote to /workspace/notes/authorized_keys. The check passed. The write landed outside the workspace.

1. Name the failure class and explain precisely where the harness's reasoning broke.
2. Fix the check. Then identify at least two other places in a typical harness where the same class of bug appears in a different costume.
3. The team's proposed fix is "deny paths containing .. and block symlink creation." Evaluate it.