* migrate subsystem expansion PR from w3f/research
As the file at this new location included changes not present in
https://github.com/w3f/research/pull/87, this is effectively a
rebase, applied manually. I believe that I have successfully retained
all of, and only, the intended changes.
* add section on collators
* note why the overseer is the terminal message point for the validation subsystem
* add detail about how the validitiy system gets PoV blocks
* rename to Validity Subsystems Overview
* get rid of changes to the implementor's guide
I think it makes most sense to track and review the subsystems
overview in a different PR than the one which adds content to
the implementor's guide.
* punt misbehavior arbitration details to the future
* empty commit to rerun CI
* file structure and initializer skeleton
* ensure session changes happen before initialization
* add a couple tests for initializer flow
* integrate with session handling
* configuration update logic
* configuration methods
* move test mock to its own module
* integrate configuration into initializer
* add note about initialization order
* integrate configuration module into mock
* add some tests for config module
* paras module storage
* implement paras session change operation
* amend past code pruning to fully cover acceptance period
* update guide again
* do pruning of historical validation code
* add weight to initialization
* integrate into mock & leave notes for next session
* clean up un-ended sentence
* alter test to account for double index in past code meta
* port over code-at logic test
* clarify checking for conflicting code upgrades
* add genesis for paras, include in mock, ensure incoming paras are processed
* note on return value of `validation_code_at`
* implement paras routines from implementor's guide
* bring over some existing tests and begin porting
* port over code upgrade tests
* test parachain registration
* test code_at with intermediate block
* fix warnings
* clean up docs and extract to separate struct
* adjust implementor's guide to include replacementtimes
* kill stray println
* rename expected_at to applied_after
* rewrite ParaPastCodeMeta to avoid reversal
* clarify and test interface of validation_code_at
* make FutureCode optional
* rename do_old_code_pruning
* add comment on Option<()> to answer FAQ
* address some more grumbles
* remove redundant resize instruction from guide
* amend past code pruning to fully cover acceptance period
* update guide again
* note on return value of `validation_code_at`
* rename execution cores to availability cores
* clarify terminology
* add ReplacementTimes to the guide
* fully decouple inclusion and scheduler
* clarify parathread scheduling substantially
* clarify validator group selection
Peter Goodspeed-Niklaus