Module counters 

What the platform APIs moved, counted where this crate can see it.

These are not boundary bytes, and the distinction matters

blitz-wasm’s Counters count bytes crossing the guest boundary: read out of, or written into, wasm linear memory. The numbers here count bytes crossing the network and storage boundary: what a request body carried, what a response body brought back, what a storage value weighed.

For one fetch they are usually close and never guaranteed equal. A guest that starts a request and never reads the body moved 40 KB here and zero there. A guest that reads the same body twice moved 40 KB here and 80 KB there. Adding them would produce a number answering no question, which is why they are separate types in separate crates rather than more fields on one struct.

Both exist because the brief asks for fetch bytes to be attributable separately from DOM bytes in both directions. This half answers “what did the platform move”; the binding’s half answers “what did that cost at the boundary”.

No timing

Same reason blitz-wasm gives: a duration measured on one machine, in one build profile, is not evidence. A byte count is the same everywhere. A fetch duration is additionally dominated by the network, which is the one part of the system no design decision here changes.

Structs

PlatformCounters

Everything one PlatformHost has moved.