edit and multi_edit read the file before matching, and reported ANY read
failure as "File not found … Use the 'write' tool to create new files." A
network blip or a folder at that path therefore invited the model to
recreate an existing file from memory with 'write', silently dropping
whatever it misremembered.
Use the not-found message only for a genuine not-found error; otherwise say
why the read failed, that nothing was changed, and to retry rather than
recreate the file.
