AssetData::linked carries a LinkedSource (absolute and relative path, document,
size, fingerprint, content hash). Linked bytes load through a process-wide
single-flight LRU store (512 MiB, 1 GiB per file) and the Loader the engine
installs in Session:🆕 absolute path first, then relative; a changed
fingerprint is checked against the hash, and other bytes are Modified.
Proxy.data is an AssetData so its decodes have a key of their own.