# Workload Admission Contracts

This document records the `rustfs/backlog#660` PR-05 and PR-07 scheduler
preservation and runtime workload-class contract slice.

## Preservation Coverage

The `rustfs-concurrency` tests pin the current reusable scheduler and
admission-facing behavior before later snapshot extraction:

- Worker slot over-release remains clamped by the configured worker limit.
- Scheduler default buffer and priority thresholds remain unchanged.
- Scheduler priority boundaries remain high below the high threshold, normal at
  both thresholds, and low above the low threshold.
- Backpressure pipe metadata reads preserve buffer capacity and state without
  mutating the manager state.
- `GetObjectQueueSnapshot` preserves saturated, over-available, and zero-total
  permit semantics.

## Workload Class Contract

`WorkloadClass` defines the required future admission categories:

- Foreground read.
- Foreground write.
- Metadata.
- Scanner.
- Repair.
- Replication.

`AdmissionState`, `WorkloadAdmissionSnapshot`, and
`WorkloadAdmissionRegistrySnapshot` define read-only status shapes for later
runtime owners. They do not replace the current scheduler, request guard,
scanner, heal, replication, or ECStore placement behavior.

## Boundary Rules

- `rustfs-concurrency` owns this reusable contract surface.
- The contract does not depend on `rustfs-ecstore` or RustFS binary runtime
  state.
- No scheduler decision logic, queue capacity, Tokio runtime default, scanner
  admission, heal admission, replication admission, placement, membership, or
  NUMA behavior changes are part of this slice.