<chatId>:<id> with % and :
percent-escaped in each part, so the single raw : always separates the
two. Ids without : or % (WhatsApp JIDs, Telegram/Discord numbers…) get
the exact same key as before; ids that do contain them (Twilio’s
whatsapp:+1555… chat ids) no longer collide — the former plain
${chatId}:${id} mapped ('a:b', 'c') and ('a', 'b:c') to one key.
Persistent stores that wrote keys in the old format read and delete through
legacyMessageKey as a fallback (see the store READMEs).
Parameters
Returns
string