Four overload-scoring lookups (cbm_registry_lookup_method_by_types/_by_args, _symbol_by_types/_by_args) linear-scanned the entire project registry on every call site, ignoring the pre-built method_buckets/func_qn_buckets hash index that the by-name lookups already use. On a large C++ header (e.g. 10989 defs) that is O(calls x project_funcs) per file (~34s/file), so big codebases never finish indexing. Add a hashed fast path (O(overloads)) when the registry is finalized; preserve first-match semantics via lowest registration index (equivalence verified over 1606 lookups, 0 divergence); keep the linear fallback for un-finalized single-file registries so normal files are unaffected. Adds tests/test_cpp_index_hang.sh (scale-tier subprocess+timeout repro, opt-in via CBM_RUN_HANG_TEST).
Martin Vogel