ShellOperation continues running after cancelling a flow run when using process type work pool

[gediminasz]

Bug summary

Example flow:

from prefect import flow
from prefect_shell import ShellOperation


@flow
def sleepy():
    ShellOperation(commands=["sleep 9999"]).run()

Steps to reproduce:

# 1. set up project
uv init
uv add prefect[shell]
export PREFECT_API_URL=http://localhost:4200/api

# 2. start the prefect server
uv run prefect server start

# 3. set up a *process type* work pool and a worker
uv run prefect work-pool create --name test --type process
uv run prefect worker start --pool test

# 4. deploy and run the flow
uv run prefect --no-prompt deploy main.py:sleepy --name test --pool test
uv run prefect deployment run 'sleepy/test'

# 5. wait for the flow run to start

# 6. cancel the flow run via web UI

# 7. observe orphaned `sleep 9999` process is still running:
pgrep -a sleep

Possibly related: #17593

Version info

Version:              3.6.20
API version:          0.8.4
Python version:       3.14.2
Git commit:           395392ae
Built:                Fri, Feb 27, 2026 05:34 PM
OS/Arch:              linux/x86_64
Profile:              ephemeral
Server type:          ephemeral
Pydantic version:     2.12.5
Server:
  Database:           sqlite
  SQLite version:     3.50.4
Integrations:
  prefect-shell:      0.3.3

Additional context

I would look into having the prefect worker kill the process group instead.