OpenMSX killed all my files!

@turbor, I do not understand completely.
As I mentioned, after I loaded a file, I have saved the file again..... After the messages appeared on screen.
Nothing was truncated or altered, except for the file I saved, the changes I made were saved correctly, not truncated, just saved, written to disk, as it should be.
Or am I missing something. For my point of view it works perfect, like it is now..

openMSX 18.0 was released last year in June 2022. It is included in Debian stable, which released very recently.
It is also in Ubuntu 22.10 and later.

I would always recommend to use the latest version of software, especially if it's older than a few months. It has the best support (and it's easier to support) and (hopefully) the least amount of bugs.

You really had bad luck to combine 17.0, a Sony machine, dir as dsk, your home folder and writing to it.

Ugh... Even if data IS properly backup up, losing 'production' data always sucks. By now it would make much difference anymore, but still: if you're using a old school hard drive, you might be able to recover things. If you are using an ssd just forget it. TRIM alone would by now have physically deleted the data.

I really want to give you some kudo's for the way you ended up handling this, as certainly it's beyond what people are supposed to be able to handle, losing MSX code is one, but pictures, letters maybe, or who knows what days you'd have on there. If only there was a beer emoticon here I'd share one with you

Dir as disk is not a very convenient thing unless it supports large volumes, so I tried it only once or twice.
Why not create a volume and use diskmanipulator command instead?