fs: a rename of the open file itself no longer drops the staged write

The pending commit moved to `to.join("")`, which has a trailing slash, so
the commit rename failed and the staged file was deleted.

cli/src/fs.rs

@@ -339,8 +339,12 @@ impl HostDescriptor for ActorFs<'_> {
         HostDescriptor::rename_at(&mut self.inner, fd, old_path, new_fd, new_path).await?;
         // Open writes and directories below a renamed folder move with it.
         if let Some((from, to)) = moved {
+            // `join("")` would add a trailing slash, so a renamed file itself
+            // needs its own case.
             let rebase = |p: &mut PathBuf| {
-                if let Ok(rest) = p.strip_prefix(&from) {
+                if *p == from {
+                    *p = to.clone();
+                } else if let Ok(rest) = p.strip_prefix(&from) {
                     *p = to.join(rest);
                 }
             };