A replica carries the index alone, so titan's 99,137 tiles are invisible from
the Mac. The cache is machine-local because the thumbnail request answers with
a path the client maps, which is also why the client needs no change: fill a
local cache file for the remote volume and the same answer works.
Adds the fetch design (where a remote tile lands, why the identities already
line up, why the owner's version has to travel with the tile, FetchTile and
WebP on the wire) as P6, and the durable sidecar tier as P7 behind L5. Records
the deployed rebuild and thumbnail results in the register.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
