Ensure thread's model is initialized once settings are loaded

Also, avoid showing token threshold warning when thread has no model.

Co-authored-by: Michael Sloan <mgsloan@gmail.com>

crates/agent/src/assistant_panel.rs

@@ -268,6 +268,7 @@ pub struct AssistantPanel {
     thread: Entity<ActiveThread>,
     message_editor: Entity<MessageEditor>,
     _active_thread_subscriptions: Vec<Subscription>,
+    _default_model_subscription: Subscription,
     context_store: Entity<assistant_context_editor::ContextStore>,
     prompt_store: Option<Entity<PromptStore>>,
     configuration: Option<Entity<AssistantConfiguration>>,
@@ -408,6 +409,20 @@ impl AssistantPanel {
             }
         });
 
+        let _default_model_subscription = cx.subscribe(
+            &LanguageModelRegistry::global(cx),
+            |this, _, event: &language_model::Event, cx| match event {
+                language_model::Event::DefaultModelChanged => {
+                    this.thread
+                        .read(cx)
+                        .thread()
+                        .clone()
+                        .update(cx, |thread, cx| thread.get_or_init_configured_model(cx));
+                }
+                _ => {}
+            },
+        );
+
         Self {
             active_view,
             workspace,
@@ -423,6 +438,7 @@ impl AssistantPanel {
                 active_thread_subscription,
                 message_editor_subscription,
             ],
+            _default_model_subscription,
             context_store,
             prompt_store,
             configuration: None,
@@ -1274,7 +1290,8 @@ impl AssistantPanel {
         let is_generating = thread.is_generating();
         let message_editor = self.message_editor.read(cx);
 
-        let conversation_token_usage = thread.total_token_usage();
+        let conversation_token_usage = thread.total_token_usage()?;
+
         let (total_token_usage, is_estimating) = if let Some((editing_message_id, unsent_tokens)) =
             self.thread.read(cx).editing_message_id()
         {

crates/agent/src/message_editor.rs

@@ -1134,8 +1134,11 @@ impl Focusable for MessageEditor {
 impl Render for MessageEditor {
     fn render(&mut self, window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
         let thread = self.thread.read(cx);
-        let total_token_usage = thread.total_token_usage();
-        let token_usage_ratio = total_token_usage.ratio();
+        let token_usage_ratio = thread
+            .total_token_usage()
+            .map_or(TokenUsageRatio::Normal, |total_token_usage| {
+                total_token_usage.ratio()
+            });
 
         let action_log = self.thread.read(cx).action_log();
         let changed_buffers = action_log.read(cx).changed_buffers(cx);

crates/agent/src/thread.rs

@@ -272,7 +272,11 @@ impl TotalTokenUsage {
         #[cfg(not(debug_assertions))]
         let warning_threshold: f32 = 0.8;
 
-        if self.total >= self.max {
+        // When the maximum is unknown because there is no selected model,
+        // avoid showing the token limit warning.
+        if self.max == 0 {
+            TokenUsageRatio::Normal
+        } else if self.total >= self.max {
             TokenUsageRatio::Exceeded
         } else if self.total as f32 / self.max as f32 >= warning_threshold {
             TokenUsageRatio::Warning
@@ -2323,19 +2327,17 @@ impl Thread {
         }
     }
 
-    pub fn total_token_usage(&self) -> TotalTokenUsage {
-        let Some(model) = self.configured_model.as_ref() else {
-            return TotalTokenUsage::default();
-        };
+    pub fn total_token_usage(&self) -> Option<TotalTokenUsage> {
+        let model = self.configured_model.as_ref()?;
 
         let max = model.model.max_token_count();
 
         if let Some(exceeded_error) = &self.exceeded_window_error {
             if model.model.id() == exceeded_error.model_id {
-                return TotalTokenUsage {
+                return Some(TotalTokenUsage {
                     total: exceeded_error.token_count,
                     max,
-                };
+                });
             }
         }
 
@@ -2344,7 +2346,7 @@ impl Thread {
             .unwrap_or_default()
             .total_tokens() as usize;
 
-        TotalTokenUsage { total, max }
+        Some(TotalTokenUsage { total, max })
     }
 
     fn token_usage_at_last_message(&self) -> Option<TokenUsage> {