Wrote a parser that reads the real 7,308‑line C header and verifies every call site, every enum constant and that every pointer‑owning class is final, after a hand‑written placeholder header let calls to three removed functions compile, link and crash.

Situation. Early in the project the C interface was represented by a hand‑written header describing the functions the application expected. That header compiled, the application linked, and calls to three functions that no longer existed in the core reached the point of being called and crashed. The compiler and the linker had both been satisfied by a description of the library rather than the library, and the gap only appeared at runtime.

Task. The real header — 7,308 lines and 268 declarations — had to become the authority, and every use of it in the Swift code had to be verified against it automatically rather than by review.

Action. The check is a parser that reads the actual upstream header and builds the set of functions, enum constants and types it declares, then reads the Swift source and resolves every call site and every constant reference against that set. A call to a function the header does not declare fails the build. A reference to an enum constant that has been renamed fails the build. The current count is 132 of the 268 declarations referenced, and knowing which 136 are unused is itself useful, because it says exactly how much of the core the client has not reached. The parser also enforces a rule the compiler cannot: every Swift class that owns a pointer into the core must be final. A non‑final pointer‑owning class can be subclassed, and a subclass that overrides deinitialisation or adds its own lifetime changes when the pointer is freed — a use‑after‑free with no unsafe keyword anywhere near it. The rule is checked by name across the whole tree.

Result. The class of defect that produced the original crash cannot recur, because a stale reference is now a build failure rather than a runtime one. The limitation is that the parser understands the header’s declarations and not its semantics: it proves a function exists with a matching name, and a function whose meaning or ownership rule changed upstream while keeping its signature passes without comment.