Optionalcommit_Optional — the C.1 commit_batch(state, actions) extern. When a
primed bridge does not expose it (legacy single-commit adapters,
older test mocks) the queue degrades to N sequential
commit(state, action) calls, which is byte-identical by
construction (option-c doc §3.1) — the loop body IS the
single-envelope path.
The shadow bridge adapter the BatchedFlush queue drives. The single-commit
commit(state, action)is the pre-C.3 F-marshal.5 shadow surface (kept for theafterN === 1fast path and for adapters that have not adoptedcommit_batchyet);commit_batchis the C.1 batched extern (tools/engine-rs-bridge-{serde,gc}, PRs #1496/#1497).