D031 - A store is verified after it lands

Status: decided Date: 2026-09-26

After each store, transfer::upload reads the file's size back. A plain file counts as copied only when the size matches what was sent. A SELF container, recognised by selfish_abi::Generation::from_container_magic, counts when a size comes back at all, because the target reports the unwrapped payload's size. Anything else is recorded as not copied.

Why: a target with the title mounted, or an overlay that swallows the write, acknowledges the store and keeps the old file. A size read is one protocol line per file. The target unwraps a container on access, so its size can only confirm presence.

Rejected:

• Trusting the completion reply: the fault this exists to catch.
• Reading the whole file back: a large cost on every file for a rarer same-size fault.
• Computing the unwrapped size here: reimplements a format that belongs to SELFish.