* Take 2 at the upward messages

* Trying to restore stuff from unsuccesful rebase

* Fix whitespace

* Clean up

* Change rustdoc to comment

* Pivot to a less stricter, w.r.t. to acceptance, model

* Rename `max_upward_message_num_per_candidate`

* Update docs for DownwardMessage

* Apply suggestions from code review

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* Rephrase "Dispatchable objects ready to ..."

* Finish the sentence

* Add a note about imprecision of the current weight formula

* Elaborate on potential use-cases for the upward message kinds.

* s/later/below

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* guide: validation data refactoring

* address grumbles from review

* Update roadmap/implementers-guide/src/types/candidate.md

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* last comments from review

Co-authored-by: Sergei Shulepov <sergei@parity.io>
Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* sketch out provisioner basics

* handle provisionable data

* stub out select_inherent_data

* split runtime APIs into sub-chapters to improve linkability

* explain SignedAvailabilityBitfield semantics

* add internal link to further documentation

* some more work figuring out how the provisioner can do its thing

* fix broken link

* don't import enum variants where it's one layer deep

* make request_availability_cores a free fn in util

* document more precisely what should happen on block production

* finish first-draft implementation of provisioner

* start working on the full and proper backed candidate selection rule

* Pass number of block under construction via RequestInherentData

* Revert "Pass number of block under construction via RequestInherentData"

This reverts commit 850fe62c.

That initially looked like the better approach--it spent the time
budget for fetching the block number in the proposer, instead of
the provisioner, and that felt more appropriate--but it turns out
not to be obvious how to get the block number of the block under
construction from within the proposer. The Chain API may be less
ideal, but it should be easier to implement.

* wip: get the block under production from the Chain API

* add ChainApiMessage to AllMessages

* don't break the run loop if a provisionable data channel closes

* clone only those backed candidates which are coherent

* propagate chain_api subsystem through various locations

* add delegated_subsystem! macro to ease delegating subsystems

Unfortunately, it doesn't work right:

```
error[E0446]: private type `CandidateBackingJob` in public interface
   --> node/core/backing/src/lib.rs:775:1
    |
86  | struct CandidateBackingJob {
    | - `CandidateBackingJob` declared as private
...
775 | delegated_subsystem!(CandidateBackingJob as CandidateBackingSubsystem);
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't leak private type
```

I'm not sure precisely what's going wrong, here; I suspect the problem is
the use of `$job as JobTrait>::RunArgs` and `::ToJob`; the failure would be
that it's not reifying the types to verify that the actual types are public,
but instead referring to them via `CandidateBackingJob`, which is in fact private;
that privacy is the point.

Going to see if I can generic my way out of this, but we may be headed for a
quick revert here.

* fix delegated_subsystem

The invocation is a bit more verbose than I'd prefer, but it's also
more explicit about what types need to be public. I'll take it as a win.

* add provisioning subsystem; reduce public interface of provisioner

* deny missing docs in provisioner

* refactor core selection per code review suggestion

This is twice as much code when measured by line, but IMO it is
in fact somewhat clearer to read, so overall a win.

Also adds an improved rule for selecting availability bitfields,
which (unlike the previous implementation) guarantees that the
appropriate postconditions hold there.

* fix bad merge double-declaration

* update guide with (hopefully) complete provisioner candidate selection procedure

* clarify candidate selection algorithm

* Revert "clarify candidate selection algorithm"

This reverts commit c68a02ac.

* clarify candidate selection algorithm

* update provisioner to implement candidate selection per the guide

* add test that no more than one bitfield is selected per validator

* add test that each selected bitfield corresponds to an occupied core

* add test that more set bits win conflicts

* add macro for specializing runtime requests; specailize all runtime requests

* add tests harness for select_candidates tests

* add first real select_candidates test, fix test_harness

* add mock overseer and test that success is possible

* add test that the candidate selection algorithm picks the right ones

* make candidate selection test somewhat more stringent

* First stab at downward messages.

That also includes a notion of horizontal messages.

* Add some structure to the router.

* Update `ValidationOutputs`

* Add `processed_downward_messages` to `ValidationOutputs`.

Forgot to check that in.

* s/AccountId/ParaId

* DownwardMessage::ParachainSpecfic

* s/ensure_horizontal_messages_fits/ensure_horizontal_messages_fit

* Clarify that Router called for each candidate

* Update the preamble for Router.

* Rewrite the relay-chain extrinsic routines

* Update gloassary

* Add DMP to the glossary

* If the queue is empty, `processed_downward_messages` can be 0

* WIP

* Add condemned list

* Pivot to message-storing channel based HRMP

* Finished draft

* Tidy up

* Remove a duplicate glossary entry

* Fix typo

* Fix wording to emphasize that the channel is unidirectional

* Proper decrement `HrmpOpenChannelRequestCount`

* Add a comment for `HrmpOpenChannelRequestCount`.

* Remove old configuration values.

* Be more specific about the para{chain,thread} hrmp chan limits.

* Fix indentation so the lists are rendendered properly

* "to answer **the**" question instead of "a"

* Add a missing call to `check_processed_downward_messages`

* Clean more stuff during offboarding

* Fix typo

* Fix typo for the config

* Add a call to `prune_dmq`

* Add explicit invariants for ingress/egress indexes

* Add comments for the sender/reciever deposit config fields

* Document various fields and structs in Router module

* More docs

* Missing docs in Candidate.md

* Tabs to spaces in router.md

* Apply Rob's suggestion

* Add the hrmp_ prefix to the router messages

* Those are entry points

* Use SessionIndex type for the `age` field

* Use a struct to represent `HrmpChannelId`

* Put only MQCs into the LocalValidationData

* Close request can be initiated by the runtime directly

* Close request can be initiated by the runtime directly

* tabs/spaces

* Maintain the list of the outgoing paras in Router

* Update roadmap/implementers-guide/src/runtime/inclusion.md

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* fix typo

* Remove an unnecessary pair of code quotes

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* Add notes about contextual execution

* Clarify that `validation_data_hash` consists of global and local data

* Update roadmap/implementers-guide/src/runtime/inclusion.md

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Incorporate rphmeier's suggestion.

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Improve AVStore and Scheduler docs

* Update roadmap/implementers-guide/src/node/utility/availability-store.md

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* Bug in linking to README.md

* Update against new runtime apis

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* rename GlobalValidationSchedule to GlobalValidationData

* guide: update candidate descriptor to contain validation data hash

* guide: add note in inclusion module about checking validation data hash

* primitives: update CandidateDescriptor to contain new hash

* fix payload computation

* add helpers for computing validation data to runtime modules

* guide: note routines

* inclusion: check validation data hash and fix local_validation_data bug

* add a case to candidate_checks and improve that test substantially

* bump versions

* address review comments

* add a test for including code upgrade

* bump kusama version

* bump westend & polkadot versions

* create a README on Runtime APIs

* add ParaId type

* write up runtime APIs

* more preamble

* rename

* rejig runtime APIs

* add occupied_since to `BlockNumber`

* skeleton crate for runtime API subsystem

* improve group_for_core

* improve docs on availability cores runtime API

* guide: freed -> free

* add primitives for runtime APIs

* create a v1 ParachainHost API trait

* guide: make validation code return `Option`al.

* skeleton runtime API helpers

* make parachain-host runtime-generic

* skeleton for most runtime API implementation functions

* guide: add runtime API helper methods

* implement new helpers of the inclusion module

* guide: remove retries check, as it is unneeded

* implement helpers for scheduler module for Runtime APIs

* clean up `validator_groups` implementation

* implement next_rotation_at and last_rotation_at

* guide: more helpers on GroupRotationInfo

* almost finish implementing runtime APIs

* add explicit block parameter to runtime API fns

* guide: generalize number parameter

* guide: add group_responsible to occupied-core

* update primitives due to guide changes

* finishing touches on runtime API implementation; squash warnings

* break out runtime API impl to separate file

* add tests for next_up logic

* test group rotation info

* point to filed TODO

* remove unused TODO [now]

* indentation

* guide: para -> para_id

* rename para field to para_id for core meta

* remove reference to outdated AvailabilityCores type

* add an event in `inclusion` for candidates being included or timing out

* guide: candidate events

* guide: adjust language

* Candidate events type from guide and adjust inclusion event

* implement `candidate_events` runtime API

* fix runtime test compilation

* max -> min

* fix typos

* guide: add `RuntimeAPIRequest::CandidateEvents`

* inclusion: split PendingAvailability storage into descriptor and commitments

* inclusion: fix tests

* implementers-guide: update CandidatePendingAvailability type

* inclusion: simplify process_candidates a bit

* implementers-guide: more updates to the inclusion module

* inclusion: fix copy-paste errors in tests

* inclusion: revert some of the changes

* inclusion: lazy commitments loading and a test

* guide: revert enact_candidate changes

* inclusion: test process_bitfield for no commitments

* Grammar

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* create a README on Runtime APIs

* add ParaId type

* write up runtime APIs

* more preamble

* rename

* rejig runtime APIs

* add occupied_since to `BlockNumber`

* improve group_for_core

* improve docs on availability cores runtime API

* guide: freed -> free

* Update roadmap/implementers-guide/src/runtime-api/README.md

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* add explicit block parameter to runtime API fns

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* note that the initializer is responsible for buffering session changes

* amend initializer definition to include session change buffering

* support buffered changes before `on_initialize`

* implement and test session buffering

* Update roadmap/implementors-guide/src/runtime/README.md

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* expand on how this affects misbehavior reports

* fix typo

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* rename implementor's guide to implementer's guide

* fix typos in more places