workflow status message: explain why a workflow is stopped

[oliver-sanders]

The UIS provides a "status message" for stopped workflows (because there is no scheduler around to do so). Currently this only differentiates between a workflow which has or has not yet run.

A workflow might stop for several reasons:

• It ran to completion.
• It was requested to stop (clean, kill, now, now-now, stop-after-cycle, stop-after-task).
• It hit the inactivity timeout.
• It stalled and hit the stall timeout.
• It crashed.

It would be immensely helpful to make this context available in the workflow status message.

Unfortunately, there is no obvious way to achieve this. The reason for the shutdown is recorded in the workflow log (except in the niche case that the workflow crashed because the filesystem went offline / died), but it is not recorded in a more machine-readable format.

Perhaps we should save this information (when we are able) to another file. See the same suggestion on cylc/cylc-flow#5701