Function ingest_message 

pub fn ingest_message(
    state: &mut ChatState,
    opened: &OpenedMessage,
    my_pubkey: &PublicKey,
) -> Option<Message>

Ingest a verified Community message into STATE under its channel chat, creating the chat (as ChatType::Community) if absent. Returns the added Message (so the caller can persist + emit it), or None if it was a duplicate (dedup on the inner message id).