Email replies truncated at code fences with tildes

[brad.king]

Code fences with ~~~ have been supported in the forum since at least 2017:

Fenced code blocks don't work with ~~~…~~~

Both triple ` and ~ should be supported as the start and end of fenced code blocks but only backticks seem to work here. This is a fenced code block This is a fenced code block

However, when replying by email the reply trimmer truncates messages on ~~~ lines, likely mistaking them for delimiters. For example, sending the literal source text

Prose before fenced code.

~~~
Fenced Code
~~~

Prose after fenced code.

results in a post containing just “Prose before fenced code.”. Using a fence of back-ticks works fine.

[brad.king]

IIUC discourse uses github.com/discourse/email_reply_trimmer to parse emails. The code here looks like it will consider a line of ~ characters to be a delimiter, and that is used here to remove everything following it.