Sometimes someone wants/needs to force a re-execution of a certain stage of a task manually.

Something like:

  task force (build SUBTASK_ID|arepo|install-check ...)

Why not, even if automatic detection of invalid cache would be correct?

However, automatic detection of invalid cache is not always correct:

* arepo doesn't notice the change of rpmrebuild-arepo;
* build doesn't (can't) correctly handle the situation when a changed contents_index would affect the built package.

An example of the latter case (contents_index should affect the result, but it didn't):

https://lists.altlinux.org/pipermail/sisyphus-incominger/2019-April/529123.html -- rpmrebuild-arepo was built before rpmquery-strictdep was added to the taks and missed the dependency (the same packages built in another task https://lists.altlinux.org/pipermail/sisyphus-incominger/2019-April/529122.html cause no problems.)

However, the latter case (when forcing a subtask rebuild is wanted) is easily worked around by removing the subtask and adding an identical one.

Forcing remaking arepo is not so easy to work around (without repeating a lot of builds).