Long messages are sent as `m.file` with part of the message as `body`

[maltee1]

I suppose signal sends long messages as attachments with a preview text in the caption. The attached file is "mimetype": "text/x-signal-plain". It contains the full message contents.

The bridge should probably look for that mimetype and send a regular message with the downloaded contents instead.

Mimicking that behavior for Matrix -> signal messages does not seem to be necessary. I sent one of those attachment messages in full from matrix and it was bridged just fine.