README stated that a crate may only depend on layers to its left, but
nothing checked it, and the wording was self contradicting: the example
given for a cross layer jump was a reverse dependency. Clarify the rule,
add scripts/check-layers.sh to enforce it, run it in CI, and record the
boundary cases in docs/design/layers.md.
The cross-layer integration checks were examples containing assertions
that cargo test never ran, so a break in one layer's assumptions about
another could pass CI. Run them explicitly.
The benches/ and tests/ directories were empty placeholders that a virtual
workspace does not compile, and benches/criterion named a third party crate
this workspace forbids. Remove both and add a real zero dependency
benchmark as a facade example.
ApsisRS contributors