Optional marker on RuntimeBackend objects exposing a zero-copy frame writer.
Why: Backends with shared frame memory (for example SAB worker transport)
can let drawlist builders write directly into backend-owned bytes, then
commit the exact byte length without an extra copy.
Optional marker on RuntimeBackend objects exposing a zero-copy frame writer.
Why: Backends with shared frame memory (for example SAB worker transport) can let drawlist builders write directly into backend-owned bytes, then commit the exact byte length without an extra copy.