* Sort out validation errors

* Typo

* Fixed wasm/android build

* Fixed bad merge

* chain-api subsystem skeleton

* chain-api subsystem: draft impl

* chain-api subsystem: mock testclient

* chain-api subsystem: impl HeaderBacked for TestClient

* chain-api subsystem: impl basic tests

* chain-api subsystem: tiny guide

* chain-api subsystem: rename ChainApiRequestMessage to ChainApiMessage

* chain-api subsystem: add the page to the ToC

* chain-api subsystem: proper error type

* chain-api subsystem: impl ancestors request

* chain-api subsystem: tests for ancestors request

* guide: fix ancestor return type

* runtime-api subsystem: remove unused dep

* fix fmt

* fix outdated comment

* chain-api subsystem: s/format/to_string

* lower-case subsystem names

* chain-api subsystem: resolve Finalized todo

* chain-api subsystem: remove TODO

* extract request errors into a module

* remove caching TODO

* fix imports

* skeleton for candidate-validation

* add to workspace

* implement candidate validation logic

* guide: note occupied-core assumption for candidate validation

* adjust message doc

* wire together `run` asynchronously

* add a Subsystem implementation

* clean up a couple warnings

* fix compilation errors due to merge

* improve candidate-validation.md

* remove old reference to subsystem-test helpers crate

* update Cargo.lock

* add a couple new Runtime API methods

* add a candidate validation message

* fetch validation data from the chain state

* some tests for assumption checking

* make spawn_validate_exhaustive mockable

* more tests on the error handling side

* fix all other grumbles except for wasm validation API change

* wrap a SpawnNamed in candidate-validation

* warn

* amend guide

* squanch warning

* remove duplicate after merge