agent: Fix expand message editor while not focused (#28650)

Allow expanding the message editor while the agent panel is not focused,
right now there is no effect when you use the button from another focus

Release Notes:

- N/A

crates/agent/src/assistant_panel.rs

@@ -44,8 +44,8 @@ use crate::thread::{Thread, ThreadError, ThreadId, TokenUsageRatio};
 use crate::thread_history::{PastContext, PastThread, ThreadHistory};
 use crate::thread_store::ThreadStore;
 use crate::{
-    AgentDiff, InlineAssistant, NewTextThread, NewThread, OpenActiveThreadAsMarkdown,
+    AgentDiff, ExpandMessageEditor, InlineAssistant, NewTextThread, NewThread,
-    OpenAgentDiff, OpenHistory, ThreadEvent, ToggleContextPicker,
+    OpenActiveThreadAsMarkdown, OpenAgentDiff, OpenHistory, ThreadEvent, ToggleContextPicker,
 };
 
 pub fn init(cx: &mut App) {
@@ -90,6 +90,16 @@ pub fn init(cx: &mut App) {
                         let thread = panel.read(cx).thread.read(cx).thread().clone();
                         AgentDiff::deploy_in_workspace(thread, workspace, window, cx);
                     }
+                })
+                .register_action(|workspace, _: &ExpandMessageEditor, window, cx| {
+                    if let Some(panel) = workspace.panel::<AssistantPanel>(cx) {
+                        workspace.focus_panel::<AssistantPanel>(window, cx);
+                        panel.update(cx, |panel, cx| {
+                            panel.message_editor.update(cx, |editor, cx| {
+                                editor.expand_message_editor(&ExpandMessageEditor, window, cx);
+                            });
+                        });
+                    }
                 });
         },
     )

crates/agent/src/message_editor.rs

@@ -157,7 +157,7 @@ impl MessageEditor {
         cx.notify();
     }
 
-    fn expand_message_editor(
+    pub fn expand_message_editor(
         &mut self,
         _: &ExpandMessageEditor,
         _window: &mut Window,