Addresses Copilot review on PR #392.
The previous fallback `normalizedChatId || 'unknown'` funneled every
message with a missing or malformed chat id into a single global queue
on `postUpsertMutex`, head-of-line blocking unrelated malformed inputs
behind a shared bucket.
Prefer `msg.key?.id` over the constant: it is unique per message so
unrelated malformed inputs no longer serialize together, while valid
messages continue to hit the normalized chat-id path — preserving the
per-chat ordering guarantee where it actually matters. The CodeRabbit
concern about `msg.key.id` fragmenting the queue applied to the primary
key derivation (where ordering matters); here it is purely a fallback
for a corruption edge case where there is no chat to order by anyway.
Renato Alcara
dc24e60e5b