Cancellation should use a CANCELLING state type instead of state name

[zanieb]

First check

• I am a contributor to the Prefect codebase

Description

Cancellation is requested now with a transition from RUNNING -> Cancelling (CANCELLED). After cancellation completes, the state changes to Cancelled (CANCELLED). The state name is used as a filter at the agent level to avoid cancelling already cancelled runs.

There are some problems with this approach:

• Concurrency slots are released immediately on transition to Cancelling — but the run is still running
• The state name is being used to determine orchestration behavior — against our design for state types.

An alternative may be keeping the state name Cancelling (RUNNING), but this requires orchestration rules to allow RUNNING -> RUNNING transitions.

Impact

Improve the cancellation experience and internal coherence of orchestration.

Additional context

No response

[github-actions]

This issue is stale because it has been open 30 days with no activity. To keep this issue open remove stale label or comment.

[zanieb]

Resolved in #7794