> ## Documentation Index
> Fetch the complete documentation index at: https://www.agentworldprotocol.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Preemption

> What a new action does to a running one — per-type policy.

Each action type declares its preemption policy in the manifest; the submitter selects one of the declared options per submission. `[AWP-PRE-001]`

| Policy    | Semantics                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| --------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `queue`   | New action enters the `queued` state and becomes `accepted` when the group frees, in submission order. Queue depth bounded by `max_queue` (manifest); overflow → `AWP_QUEUE_FULL`. Queued actions terminate per the [pre-execution rules](/spec/loop/action-lifecycle#terminal-rules-for-pre-execution-actions): cancel, e-stop, session close, safe-state entry, world reset → `cancelled`; deadline expiry → `rejected`. `[AWP-PRE-002]` |
| `replace` | Current `executing` action → `preempted` (after safe transition); current pre-execution actions in the group → `cancelled` (reason `superseded`); new action starts. `[AWP-PRE-003]`                                                                                                                                                                                                                                                       |
| `blend`   | World merges trajectories (continuous control); both actions report status, the replaced one ends `preempted` with `blended: true`. `[AWP-PRE-004]`                                                                                                                                                                                                                                                                                        |
| `reject`  | New submission is rejected with `AWP_BUSY` while one is `executing` or pre-execution in the group. `[AWP-PRE-005]`                                                                                                                                                                                                                                                                                                                         |

**Concurrency groups.** Each action type MAY name a `concurrency_group` (string) in its schema. Types sharing a group name preempt one another; types in different groups run concurrently (e.g. `base_motion` vs `gripper`). Types with no group form an implicit group per embodiment. `[AWP-PRE-006]`