Pre batch processing task state (Option 1)

[dwsutherland]

closes #6567, closes #6861, closes #6859

Like #6859 but uses pre-existing task state.

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• Changelog entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

This state may well be incorrect leading to confusion.

[oliver-sanders]

We shouldn't be patching the data in this way, but moreover, I've managed to reproduce the bug (instructions) on this branch.

I'm not quite sure how this bug is working, but I think it's different to what we've assumed.

I'll close this to help tidy up open PRs.