# KvCas contracts (strong consistency)

## CompareAndSwap
- **RPC**: `kvrpc.KvCas/CompareAndSwap`
- **Request**:
  - `namespace: string` (empty => `default`)
  - `key: bytes`
  - `value: bytes`
  - `expected_version: uint64`
- **Response**:
  - `success: bool`
  - `current_version: uint64`
  - `new_version: uint64`
- **Semantics**:
  - Allowed only for `strong` namespaces; returns `FailedPrecondition` otherwise or when not leader (redirect required).
  - Proposes via Raft; state machine applies with LWW timestamp wrapper.

## Get
- **RPC**: `kvrpc.KvCas/Get`
- **Request**:
  - `namespace: string` (empty => `default`)
  - `key: bytes`
- **Response**:
  - `found: bool`
  - `value: bytes`
  - `version: uint64`
- **Semantics**:
  - Allowed only for `strong` namespaces; returns `FailedPrecondition` if not leader.
  - Reads versioned value (timestamp-prefixed) and returns decoded value plus version.