Hardened pinned-tmpdir write-target verification on macOS, with new recovery guidance

On macOS, resolving a write target against the pinned tasks directory is now more robust: a new check walks up each segment of the resolved path, confirms it's a directory, and compares device/inode against the pinned file descriptor to verify the path is a safe, link-free alias of the pinned directory. Refusals are now logged at warn level, and failures during task-output swaps include actionable recovery text.