fix(scm): resolve the editor's repository on the file's own machine

`scm_editor_target` paired the focused buffer's path with `spawn_host`,
the window's own machine. That was true of every file the tree could
open, but an SFTP buffer carries a path from somewhere else: with
`/home/me/proj` probed on both boxes, the panel would resolve the remote
file against the *local* repository and open a `.git` watch on it —
another machine's branch and status, shown for this file. The two
sibling targets already take the host from wherever the path came from.

Also drop a claim the watcher comment could not keep: a host that cannot
watch has no external-change detection at all, not a save-time check.
There is no such check, and adding one needs a "keep mine" that survives
to the next save, which the conflict banner does not have.

src/terminal/git_data.rs

@@ -885,7 +885,11 @@ impl Tty7App {
             return None;
         }
         let open = code.active_file()?;
-        let host = self.spawn_host(cx);
+        // The file's host, not the window's. They are the same for everything
+        // the tree can open, but a buffer read over SFTP carries a path from
+        // another machine, and pairing it with this one's host would resolve
+        // it against a local repository that merely shares the path.
+        let host = open.host.id();
         let root = cx
             .try_global::<crate::terminal::git_status::GitStatusCache>()?
             .repo_root_for(host, open.path.parent()?)?;

src/ui/code_editor.rs

@@ -294,8 +294,14 @@ impl Tty7App {
     fn editor_rebuild_watcher(&mut self, cx: &mut Context<Self>) {
         // Only files on the host the watch itself runs on. A path from
         // another machine — an SFTP file, say — does not exist under that
-        // watcher's feet, and hosts without watching (SFTP again) fall back
-        // to the save-time conflict check instead.
+        // watcher's feet, and would either miss or, worse, match a local file
+        // that happens to share its name.
+        //
+        // A host that cannot watch therefore gets no external-change
+        // detection at all: an SFTP buffer will not notice the file changing
+        // underneath it, and saving overwrites whatever is there. Catching
+        // that at save time needs a "keep mine" that survives to the next
+        // save, which the conflict banner does not have yet.
         let watch_host = self.spawn_host(cx);
         let files: HashSet<PathBuf> = self
             .tabs