Suicide trigger prevents later cycles starting

[wxtim]

Closes #6594

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[oliver-sanders]

Tested as working 👍.

I don't get why we would want to exclude self-edges in this function so I think this change makes sense.

[hjoliver]

I don't get why we would want to exclude self-edges in this function

Looking back at my original change (from 2022), the explanation at the time was something to do with the way suicide triggers work under SOD.

foo:fail => !bar

In Cylc 7, bar would be pre-spawned as waiting, and if foo fails the suicide trigger removes bar.

In Cylc 8, the suicide trigger is no longer necessary, but it still works because: if foo fails it spawns bar (on demand) and then the suicide trigger immediately removes it again.

Self-suicide (foo:fail => !foo) works the same way in Cylc 7, but there is a difference (from non-self suicide) in Cylc 8 because the trigger does not need to spawn foo (it was already spawned).

Anyhow, that change fixed a bug at the time, and this one, which partially reverts the change, fixes another without restoring the original bug (confirmed above), so I'm not going to blow any more time on this now.

[hjoliver]

Good, thanks @wxtim