When user is on B42 and a mod requires the B41 mod_id (e.g.
truemusic_mixtape_megapack require=truemusic), the canonical wsid
(2613146550, B41-only) is rightly filtered out by the build guard —
but we were silently dropping the suggestion. Now we fall back to
MOD_ID_ALIASES: truemusic → TrueMoozic, suggest wsid 3632610172.
- _lookup_wsids_for_missing returns Dict[str, Tuple[wsid, suggested_mod_id]]
- build_warnings unpacks tuple, label clarifies rename when alias used
- adapters.build_response signature updated for new shape
