The C++ def/use harvester only recorded a def when an init_declarator's
declarator was a plain identifier, so a structured binding (auto [a,b] = mk(),
incl. the auto& reference form whose binding sits under a reference_declarator)
declared only the first name in phase 1 and emitted ZERO defs in phase 2 — a,b
were walked as spurious uses and later use(a)/use(b) resolved to a synthetic
module binding, silently corrupting REACHING_DEF/taint for an idiomatic C++17
shape. Unwrap the structured_binding_declarator in both phases and def every
identifier leaf; result-of-initializer flows to the whole list. Inert for C
(no structured bindings). Characterization tests added (plain + reference form).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>