Native execution runtime

omni-runtime provides SerialScheduler for the Cua-S1, Open-Jev and Laya native workers. Their engines assemble a processor, one scheduler for the loaded executor, and the executor. HTTP handlers still coordinate prepare → execute → finish.

The scheduler owns FIFO admission and blocking dispatch. A caller waits asynchronously for one execution permit before entering Tokio's blocking pool. Cloning a scheduler shares that admission queue; separate loaded executors have separate queues. The model mutex remains a guard for Rust's mutable executor state. Waiting requests no longer occupy blocking threads waiting for that mutex.

Worker	Admitted unit	Work outside admission
Cua-S1	One question's unpadded Qwen forward. Release before admitting its next question.	Request preparation, CPU letter projection and response finishing.
Open-Jev	One complete request's independent candidate forwards and CPU scalar heads.	Request preparation and calibrated response finishing.
Laya	One complete padded request, including GPU scorer/action head and copyback.	Request preparation/padding and calibrated response finishing.

Models retain weights, heads, device state, scratch buffers and graph caches. The scheduler takes an owned closure and returns its result; it does not know model identifiers, question/candidate mappings, tensor layouts or backend APIs. The existing numerical, ordering, whole-request failure and readiness contracts remain in the processors, executors and worker handlers.

Cancellation while waiting removes the caller from admission without dispatch. After dispatch, the blocking closure retains the permit and its captured resources until completion, even if the caller disconnects or stops waiting. Executors must finish queued device work before returning; the current Qwen forward synchronizes the final hidden-state download. Errors and panics release admission when the blocking task finishes. Model mutex poisoning retains its existing failure behavior.

This implements serial admission per executor within a worker process. Admitted concurrency is one. Queue-length limits, token budgets, compatibility grouping, shared processing orchestration and GPU batching remain planned. The Qwen executor still accepts one prompt per forward; this scheduler does not pack inputs or coordinate separately running workers.

CPU tests cover FIFO serialization, queued cancellation, retention of admission and resources after dispatched cancellation, errors/panics, and independent loaded executors:

cargo test --locked -p omni-runtime

See the architecture contracts and benchmark protocol when changing admission policy.