name refuses a directory, EISDIR, when written, not at the Save that could only fail

`name ~`, `name /` or `name foo/` renamed the pane to a directory, and
only its Save failed later. A name ending in `/`, the root, or one naming
a directory that is there is now refused at once, with words a mount
reads as EISDIR (`name: <path> is a directory, not a file`). The ctl word
name and a forwarded `pardes ~` go through the same check. fs.md says so.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/docs/fs.md b/docs/fs.md
index dacb49ba..041f3389 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -397,7 +397,8 @@ buffer (relative to the pane's directory) and marks nothing dirty; `Save`
 then writes under the new name. A name is one line; refused (EINVAL) are a
 second line, a blank at either end, control bytes and non-UTF-8 (`bad
 character in file name: a blank at its start`, ...). Up to 255 bytes a
-component.
+component. A directory (`/`, `~`, `foo/`) is no file name: refused, EISDIR
+(`name: /home/u is a directory, not a file`).
 
 **`body`** reads the text; a write appends; `>` (OTRUNC) replaces it all.
 A terminal's body is its history as plain text in logical lines (wrapped