Replacement events are inserted into the room based on the replacement timestamp rather the original event's?

I reconnected to my work server this morning, and noticed that an edit I'd made within a series of messages on Friday was out of sequence. I'd written four messages, and afterwards had edited the original message. At the time it was updated in-place; but after disconnecting and reconnecting the edited message was now being displayed as the last of the four messages.

I've been able to reproduce this in further testing, ending up with the likes of:

```plain
2024-01-15 (Monday)

13:01

phil:
13:01 two

phil:
13:01 one (edit) [edited]
```

I've tested on matrix.org as well. At first I thought I *wasn't* seeing the issue on matrix.org, but I suspect I failed to disconnect from that server the first time. After 'repeating' the disconnect/reconnect cycle for both servers, I saw the same/wrong outcome in both. (I mention this mostly in case I still don't understand, and you also can't replicate at first.)

The `m.relates_to` data in the edit event doesn't include a timestamp, and the `:origin-server-ts` value is for the edit, so I believe Ement needs to look up the timestamp in the original event (which AFAIR would only ever be a single-step away, as edit events are required to relate to the very first event in the chain).