Core: specify the checked Core (abstract syntax + checking judgements)

[hyperpolymath]

Charter artefact (1) checked Core. Sketch area: src/core/ (src/core/README.adoc).

Specify the single checked target into which every accepted program projects. All guarantees are reasoned about in Core, never in a surface syntax.

Scope

• Core abstract syntax (terms, types; the substructural/affine fragment).
• The checking judgements — what well-formedness means and what facts a successful check establishes.
• The interface projections elaborate into and backends lower from.

Done when

• A written spec of the syntax + judgements exists under docs/ and/or src/core/.
• A successful check yields evidence (see Evidence issue), not just pass/fail.
• Core makes no global safety claim — it produces the facts that envelopes name.

Ref: docs/architecture/DESIGN-DISCIPLINE.adoc, docs/architecture/ARCHITECTURE.adoc.