Reply missing from timeline: `This reply could not be found`

* https://archive.matrix.org/r/securemessagingapps:matrix.org/date/2023/05/29?at=$t2pNdVt1_9ViZNaSERJEB4qtGF3mRvZjhGCSHbcFiFY

```
{
"content": {
"body": "> <@memorysafetybelike:envs.net> I'm always skeptical of supposedly post-quantum messaging apps. There are a lot of fraudulent/scam messaging apps using post-quantum crypto as a marketing point\n\nSee messages around this point. If possible, add this to the chart/doc.",
"format": "org.matrix.custom.html",
"formatted_body": "

In reply to @memorysafetybelike:envs.net
I'm always skeptical of supposedly post-quantum messaging apps. There are a lot of fraudulent/scam messaging apps using post-quantum crypto as a marketing point

See messages around this point. If possible, add this to the chart/doc.",
"m.relates_to": {
"m.in_reply_to": {
"event_id": "$vofnzkokpJxtvNEGbZN9fWsCxFJc9UX2CIsQj4ZTW38"
}
},
"msgtype": "m.text"
},
"origin_server_ts": 1685362193658,
"sender": "@bkil:matrix.org",
"type": "m.room.message",
"unsigned": {
"age": 474,
"transaction_id": "m1685362193523.113"
},
"event_id": "$t2pNdVt1_9ViZNaSERJEB4qtGF3mRvZjhGCSHbcFiFY",
"room_id": "!sOLQNHloevPHIEWcYN:matrix.org"
}
```


## Potential solutions

### Reword error message

Ultimately, as a user, it is confusing that all I got was a generic error message. If it said `This reply could not be found within the last 100 messages`, I would be less worried.

https://github.com/matrix-org/matrix-public-archive/labels/Z-Confidence-High

### Show a permalink to the event if it can't be displayed in a reply

The event permalink is also missing in this error condition, while an in-reply-to link is present if no such error condition happens. A user could click this permalink to view what is being replied to if it can't be shown inline.

https://github.com/matrix-org/matrix-public-archive/labels/Z-Confidence-High

### Show reply fallback

If a message being replied to can't be shown, but the reply contains a reply fallback, show that fallback (with potentially a disclaimer that the wording might have been edited.

https://github.com/matrix-org/matrix-public-archive/labels/Z-Confidence-Medium

Start by reproducing the missing-reply state from the linked archive.matrix.org event and inspect the viewer's reply rendering path. Done means the interface gives users a useful way to understand or access the missing target, such as a clearer scope message, an event permalink, or the available reply fallback.

Written by the indexing model from the issue text.