pruneExact

Settle the exact-reverse index. Run by read once the file is exhausted — the earliest point where ambiguous and classN2I are both final, which is what both edits below need. One linear pass over rows we just parsed, cheaper than the parse itself, and both sit behind a download on a background thread.

• Drop every row whose runtime name is NOT ambiguous: reverseMethod answers those on its own, so the row would be a table entry nothing can ever read. A separator-less key goes too.

• Rewrite the descriptor into the runtime namespace (runtimeDesc): the file writes it in the file's own (named) terms, while every caller arrives holding one read off live reflection.