Integer C variadics

A native foreign declaration may end its fixed parameter list with , ...:

unsafe extern "C" fn receive(tag: i32, ...) -> i32

The declaration must have at least one fixed parameter. Ellipsis is last and creates no named parameter. Calls supply all fixed arguments and then zero or more admitted integer values, under the usual unsafe acknowledgement. Ellipsis is not admitted on ordinary or exported definitions or C function-pointer types; Silk does not expose variadic definitions or va_list.

Fixed arguments retain their declared contextual types and the existing scalar/pointer boundary. Tail expressions retain ordinary expression typing without a declared parameter type. The admitted tail types are i8, u8, i16, u16, i32, u32, i64, u64, isize and usize. Signed and unsigned 8/16-bit integers promote to signed i32 because C int is 32-bit on the admitted platforms. Values of 32/64-bit or pointer-width integer types retain their width and signedness. An ordinary unannotated integer literal has its usual i32 type; use a typed binding or conversion when a different width is needed. Floating-point, pointer, reference, aggregate, bool, char and callable tails diagnose.

Darwin mode_t is unsigned 16-bit and promotes to signed int; GNU mode_t is unsigned 32-bit and remains unsigned int. Ordinary selected source owns platform types, flags and whether a mode is required. The compiler does not recognize the names open, openat or fcntl. The filesystem provider can declare open/openat with their real fixed boundary and choose zero or one mode operand itself.

Variadic status and fixed types belong to the native symbol's declaration identity. Promoted tail types belong to each call, so zero-tail and multiple-tail calls share one declaration. A fixed and a variadic declaration of the same reachable symbol conflict even when their fixed types agree. Inactive selected variants contribute no symbols.

LLVM receives a true variadic declaration and the promoted operands. Darwin ARM64 passes unnamed integer arguments in its prescribed stack slots; GNU ARM64 and System V x86-64 use their C ABI's register and stack rules. Conservative foreign memory/retention contracts and fatal-unwind behavior remain in force. No fake fixed signature, function-pointer cast or generated C adapter substitutes for the variadic call. ABI manifests expose declaration status and MIR inspection exposes call shapes and promotions.

The admitted matrix is Darwin ARM64 and GNU/Linux x86-64 and ARM64. Required pinned conformance uses independently compiled C receivers and direct platform calls in debug and optimized builds; missing supplies or skipped designated cases fail. LTO remains unadmitted.