fwiw, after a bunch of trial and error on #mesonbuild, we found a way to prevent spam: set an exempt on the matrix irc bridge hostmask and set +R

```
/mode +e *!~*@2001:470:1af1:101::*
/msg ChanServ set #mesonbuild mlock +R
```

mlock +R must be set via ChanServ by someone who has CHANOP or higher, and mode +e must be set via an irc /mode command while OP

This will break if/when matrix changes the ipv6 host, so we should ask them / OFTC to get a cloak for the matrix IRC bridge, like it did on FreeNode