Actually run the eval and fix a hang when retrieving outline (#28547)

Release Notes:

- Fixed a regression that caused the agent to hang sometimes.

---------

Co-authored-by: Thomas Mickley-Doyle <tmickleydoyle@gmail.com>
Co-authored-by: Nathan Sobo <nathan@zed.dev>
Co-authored-by: Michael Sloan <mgsloan@gmail.com>

crates/agent/src/agent_diff.rs

@@ -921,15 +921,16 @@ mod tests {
             })
             .unwrap();
 
-        let thread_store = cx.update(|cx| {
-            ThreadStore::new(
-                project.clone(),
-                Arc::default(),
-                Arc::new(PromptBuilder::new(None).unwrap()),
-                cx,
-            )
-            .unwrap()
-        });
+        let thread_store = cx
+            .update(|cx| {
+                ThreadStore::load(
+                    project.clone(),
+                    Arc::default(),
+                    Arc::new(PromptBuilder::new(None).unwrap()),
+                    cx,
+                )
+            })
+            .await;
         let thread = thread_store.update(cx, |store, cx| store.create_thread(cx));
         let action_log = thread.read_with(cx, |thread, _| thread.action_log().clone());