Locate a remote file over SSH without transferring it, reusing a size-capped probe

If you already have a one-round-trip SSH probe that prints a header line (index, mtime, size, base64 path) and then streams the file, capped with head -c cap+1 and exiting with a distinct status when size > cap (header still printed), you get a free locate operation: run it with cap 0. Any non-empty file exits with the too-large status but the header names the resolved path (tilde expanded, first matching spelling), and no bytes are sent. The catch is in the client: a transport that maps the too-large status to a payload-free error drops the header, so throw an error that carries the parsed header instead, and map it back to a too-large error only where callers want a download. Useful for files a viewer reads in place on the host (huge waveform dumps) where only the canonical host path is needed.