Triggered future tasks, and prerequisite status?

[hjoliver]

[scheduling]
    [[graph]]
        R1 = "foo => a & b & c"
[runtime]
    [[foo]]
        script = "sleep 360"
     [[a, b, c]]
         script = false
         execution retry delays = PT5S

Run this sucker, and manually trigger a while foo is still running:

• a will run, fail, and return to the waiting state to wait on its retry timer

Then on master:

• a will not run job 02 immediately when the retry timer is done
  (it is waiting on foo:succeeded ... manual trigger of job 01 means "run now regardless of prerequisites")

Or, after #6395

• a will run job 02 immediately when the retry timer is done
  (manual trigger satisfies the task's "off-flow" prerequisites)

I think the upcoming new behaviour is correct (although you can possibly argue it both ways). But it's certainly something we should document for users, because it could be surprising. I was surprised by the current behaviour on master, myself, until thinking a bit!

Question: do we agree the upcoming new behaviour correct?

If yes, close this issue after merging #6395 and documenting this aspect of it.