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_action_tool.rs

@@ -159,7 +159,7 @@ impl Tool for CodeActionTool {
             };
 
             action_log.update(cx, |action_log, cx| {
-                action_log.buffer_read(buffer.clone(), cx);
+                action_log.track_buffer(buffer.clone(), cx);
             })?;
 
             let range = {