documents: reset keeps the caret and the top line

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/documents/document/mod.rs

@@ -206,10 +206,20 @@ impl MarkdownDocument {
             .update(cx, |editor, cx| editor.set_text(text, cx));
     }
 
-    /// Replaces the text, undo afresh; open typing drops.
+    /// New text, undo afresh; caret and top line stay.
     pub fn reset(&mut self, text: impl Into<String>, cx: &mut Context<Self>) {
+        let ((line, column), top) = (self.caret(cx), self.top_line(cx));
         self.drop_open(cx);
         self.editor.update(cx, |editor, cx| editor.reset(text, cx));
+        self.set_caret(line, column, cx);
+        // Placed once the new text is read.
+        self.asks += 1;
+        self.top = Some(Placement {
+            line: top,
+            ask: self.asks,
+            placing: false,
+        });
+        cx.notify();
     }
 
     /// The headings as last read, with lines from zero.

src/documents/document/tests/place.rs

@@ -180,3 +180,21 @@ x- one"
     });
     assert_eq!(outline, [("Lift".to_string(), 0)]);
 }
+
+#[gpui::test]
+fn a_reset_keeps_the_caret_and_the_top_line(cx: &mut TestAppContext) {
+    let lines: String = (0..60).map(|n| format!("Line {n}\n\n")).collect();
+    let (document, cx) = open(&lines, MarkdownMode::Source, cx);
+    document.update_in(cx, |document, window, cx| {
+        document.set_caret(40, 2, cx);
+        document.set_top_line(30, window, cx);
+    });
+    frames(cx);
+    let changed: String = (0..60).map(|n| format!("Row {n}\n\n")).collect();
+    document.update(cx, |document, cx| document.reset(changed, cx));
+    frames(cx);
+    let (caret, top) = document.read_with(cx, |document, cx| {
+        (document.caret(cx), document.top_line(cx))
+    });
+    assert_eq!((caret, top), ((40, 2), 30));
+}