The gateway is the only thing standing between a shared key and the rest of
an owner's drive, so its SigV4 check, grant decisions and the BNS/deposit
proofs get tests that need no s3d to run.
s3d binds one Sia account per process, so the server runs one s3d per
person (pithos-hosted), started on demand and flushed and stopped when idle.
Only the connected s3d data folder moves between PC and server; the Sia
recovery phrase never leaves the PC and nothing is re-uploaded to Sia.
Because the server holds the connection key, local Pithos encrypts names and
contents before they leave the machine, with keys from the Theseus vault (or
a local key file elsewhere). What s3d cannot do on its own, the gateway now
enforces: public folders, expiring share links and S3 keys for other people
limited to one folder with read, add-only or edit rights. Files those reach
are stored readable, since visitors have no key, and go back to encrypted
when the rule is removed. Sign-up needs a BNS name signature, a deposit or
an invite, with a per-IP limit.
