agent: Handle thread title generation errors (#30273)

The title of a (text) thread would get stuck in "Loading Summary..."
when the request to generate it failed. We now handle this case by
falling back to the default title, and letting the user manually edit
the title or retry generating it.



https://github.com/user-attachments/assets/898d26ad-d31f-4b62-9b05-519d923b1b22



Release Notes:

- agent: Handle thread title generation errors

---------

Co-authored-by: Richard Feldman <oss@rtfeldman.com>

crates/assistant_context_editor/src/context_editor.rs

@@ -1860,7 +1860,12 @@ impl ContextEditor {
     }
 
     pub fn title(&self, cx: &App) -> SharedString {
-        self.context.read(cx).summary_or_default()
+        self.context.read(cx).summary().or_default()
+    }
+
+    pub fn regenerate_summary(&mut self, cx: &mut Context<Self>) {
+        self.context
+            .update(cx, |context, cx| context.summarize(true, cx));
     }
 
     fn render_notice(&self, cx: &mut Context<Self>) -> Option<AnyElement> {