shortHashForRelay

32-character SHA-256 hex prefix of the raw network key. Used as the URL path component when downloading from the Bedrock relay (GET /rsp/bedrock/file/<hash>/<backendId>/<kind>) — the hoster stores files keyed by this hash and never sees / never stores the raw key on disk.

Returns null on null / too-short input so callers can detect malformed keys before issuing a request.