Feature: C-Header Ingestion (PFE)

Purpose

PFE (Proudly Found Elsewhere): C has perfected an enormous body of interface definitions — the Linux kernel’s own headers are the canonical corpus. Elseon must not re-declare them; it must ingest them. A C header imported into Elseon becomes a first-class semantic module, with Elseon’s safety guarantees applied at the boundary.

Requirements

• The language must provide an import form for C headers that is a semantic operation, not a textual #include.
• An imported header must expose, with Elseon semantics:
  • types, as nominal Elseon types with deterministic layout;
  • constants, as typed values;
  • function signatures, as checked call boundaries (arity, types, and nullability where the header or annotations make it knowable).
• The import must not require hand-written mirror declarations: Elseon uses the header as the single source of truth.
• The import boundary must be checked: mismatches between an Elseon call and the C signature must be compile-time errors.
• The mechanism must handle the kernel header corpus (including its preprocessor idiom: macros, conditional compilation, __attribute__, and type re-export chains) with a declared conformance subset.

Behavior

• The mechanism choice (libclang, clang AST dumps, or a dedicated C header parser) is recorded in the design document and TODO; the kernel headers are the conformance corpus.
• A conformance test must compile at least one real kernel-adjacent header and call one of its functions from Elseon, verifying the checked boundary.

Dependencies

• Feature 03-language-core.md (Language Core) — the import boundary must satisfy the Kernel Test (no hidden allocations, deterministic layout).