Restore file to original content when rejecting file recreated by agent (#29264)

Release Notes:

- Fixed a bug that could sometimes cause a file to be deleted when
rejecting an agent change.

crates/assistant_tools/src/code_symbols_tool.rs

@@ -174,7 +174,7 @@ pub async fn file_outline(
     };
 
     action_log.update(cx, |action_log, cx| {
-        action_log.buffer_read(buffer.clone(), cx);
+        action_log.track_buffer(buffer.clone(), cx);
     })?;
 
     // Wait until the buffer has been fully parsed, so that we can read its outline.