Top-level units: function_definition (symbol = fn name from declarator's
innermost identifier), struct_specifier, enum_specifier, union_specifier
(each emits 1 unit with the named identifier as symbol). Preprocessor
directives + top-level declarations group into a <top-level> glue chunk.
Empty file or zero units → <module> post-pass.
C symbol = function name only — no namespace, no class nesting (design §3.4).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>