acp: Support model selection for ACP agents (#38652)

It requires the agent to implement the (still unstable) model selection
API. Will allow us to test it out before stabilizing.

Release Notes:

- N/A

crates/acp_thread/src/connection.rs

@@ -68,7 +68,7 @@ pub trait AgentConnection {
     ///
     /// If the agent does not support model selection, returns [None].
     /// This allows sharing the selector in UI components.
-    fn model_selector(&self) -> Option<Rc<dyn AgentModelSelector>> {
+    fn model_selector(&self, _session_id: &acp::SessionId) -> Option<Rc<dyn AgentModelSelector>> {
         None
     }
 
@@ -177,61 +177,48 @@ pub trait AgentModelSelector: 'static {
     /// If the session doesn't exist or the model is invalid, it returns an error.
     ///
     /// # Parameters
-    /// - `session_id`: The ID of the session (thread) to apply the model to.
     /// - `model`: The model to select (should be one from [list_models]).
     /// - `cx`: The GPUI app context.
     ///
     /// # Returns
     /// A task resolving to `Ok(())` on success or an error.
-    fn select_model(
-        &self,
-        session_id: acp::SessionId,
-        model_id: AgentModelId,
-        cx: &mut App,
-    ) -> Task<Result<()>>;
+    fn select_model(&self, model_id: acp::ModelId, cx: &mut App) -> Task<Result<()>>;
 
     /// Retrieves the currently selected model for a specific session (thread).
     ///
     /// # Parameters
-    /// - `session_id`: The ID of the session (thread) to query.
     /// - `cx`: The GPUI app context.
     ///
     /// # Returns
     /// A task resolving to the selected model (always set) or an error (e.g., session not found).
-    fn selected_model(
-        &self,
-        session_id: &acp::SessionId,
-        cx: &mut App,
-    ) -> Task<Result<AgentModelInfo>>;
+    fn selected_model(&self, cx: &mut App) -> Task<Result<AgentModelInfo>>;
 
     /// Whenever the model list is updated the receiver will be notified.
-    fn watch(&self, cx: &mut App) -> watch::Receiver<()>;
-}
-
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct AgentModelId(pub SharedString);
-
-impl std::ops::Deref for AgentModelId {
-    type Target = SharedString;
-
-    fn deref(&self) -> &Self::Target {
-        &self.0
-    }
-}
-
-impl fmt::Display for AgentModelId {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.0.fmt(f)
+    /// Optional for agents that don't update their model list.
+    fn watch(&self, _cx: &mut App) -> Option<watch::Receiver<()>> {
+        None
     }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct AgentModelInfo {
-    pub id: AgentModelId,
+    pub id: acp::ModelId,
     pub name: SharedString,
+    pub description: Option<SharedString>,
     pub icon: Option<IconName>,
 }
 
+impl From<acp::ModelInfo> for AgentModelInfo {
+    fn from(info: acp::ModelInfo) -> Self {
+        Self {
+            id: info.model_id,
+            name: info.name.into(),
+            description: info.description.map(|desc| desc.into()),
+            icon: None,
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct AgentModelGroupName(pub SharedString);