A buffer whose file was deleted on disk is dirty, and Del asks first

A file deleted under an open buffer left dirty 0 and let Del, Exit and the rest throw the only copy of its text away unasked. It now counts as dirty, as acme's does, and the refusals ask about it.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 3 insertions, 1 deletions

diff --git a/docs/fs.md b/docs/fs.md
index c72c0131..088d1c92 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -747,7 +747,9 @@ written to `addr` that goes from the current one (`.`, `+1`, `-/re/`), which
 there is none of, until an address that stands alone (`2`, `#0`, `/re/`) is.
 
 The three flag files `dirty`, `mark` and `scroll` read `0` or `1` and take
-`0` or `1`: whether the buffer differs from its file, whether a write pushes
+`0` or `1`: whether the buffer differs from its file (a file deleted on
+disk counts, as in acme: its text is only here now, and Del, Exit and the
+rest ask first), whether a write pushes
 an undo point (writing `1` pushes one now), and whether a write scrolls the
 pane. The writes of one open of `data`, `xdata` or `body` are one undo
 step while `mark` is 1 (so `printf 'a\nb\n' > data` is one, though a