iface_slot reads the declaration slot assign_slots recorded, so a call site
emits an offset the class table actually has and refuses a method the interface
does not declare. The x128 fixture proves one call site reaching two classes,
one object reaching two interface tables, a nested call with a one-byte result,
and byte/word arguments returning a word with the frame stack restored, while
self stays the underlying object.

Generated with Codebuff
Co-Authored-By: Codebuff <noreply@codebuff.com>