washere wrote:

1) Txt editor as you prescribed:

That text editor might not exist. Because you want multi files to be
pulled in as a single file. Then changes for different sections saved to
original multi files. The big new file is a temporary file, either not
saved &/or saved as a new big file. That's the problem.

I don't really see why it would a problem, seems eminently possible from a programming standpoint. The viewer/editor would show all the loaded text files in a single stream, with say, a dotted line (not an actual part of the text, but just a display element) marking the boundary between the content of one file and another. You could freely move text to a location between two particular dotted lines (the text of file A), to a location between two other dotted lines (the text of file B). Then you could do a save operation. And File A would be saved with the text so deleted, and File B would be saved with the text so added to it.

You might try database viewers which have nice text editing
Windows/panes with regular txt editing functions (usual editor goodies).
Then dynamically link the txt files as fields. Or as cells in a
spreadsheet that has the same editor niceties. But it'll be quicker
otherwise.

Not quite sure I understand how this would work.

My route is there other way. I have large note files on the phone
separated by lines made of any number of:
_______
or
------------
or
========

Then I use an app to cut the big file into multi files where the above
line characters occur. Can sort groups of them into relevant subfolders.

That is a good strategy, and sometimes I use it myself.

What you want would need invisible placeholders to remember which
paragraphs belong to what file. Doesn't exist IMHO. It'll need rule sets
of how to behave too, boundaries might change in editing.

You can look into scripts that pipe text files into editors. But I don't
think they maintain live relationships from chunks to extremal files,
again a new big file is created as temp and/or a new big saved file.

2) File manager as you specified:
For Which platform: Windows, Mac, Linux?

Windows.