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

Cargo.lock

@@ -195,9 +195,9 @@ dependencies = [
 
 [[package]]
 name = "agent-client-protocol"
-version = "0.4.0"
+version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cc2526e80463b9742afed4829aedd6ae5632d6db778c6cc1fecb80c960c3521b"
+checksum = "00e33b9f4bd34d342b6f80b7156d3a37a04aeec16313f264001e52d6a9118600"
 dependencies = [
  "anyhow",
  "async-broadcast",
@@ -4932,7 +4932,7 @@ dependencies = [
  "libc",
  "option-ext",
  "redox_users 0.5.0",
- "windows-sys 0.60.2",
+ "windows-sys 0.61.0",
 ]
 
 [[package]]
@@ -12677,6 +12677,7 @@ dependencies = [
  "schemars 1.0.1",
  "serde",
  "serde_json",
+ "theme",
  "ui",
  "workspace",
  "workspace-hack",
@@ -20853,7 +20854,7 @@ dependencies = [
  "windows-sys 0.48.0",
  "windows-sys 0.52.0",
  "windows-sys 0.59.0",
- "windows-sys 0.60.2",
+ "windows-sys 0.61.0",
  "winnow",
  "zeroize",
  "zvariant",

Cargo.toml

@@ -439,7 +439,7 @@ zlog_settings = { path = "crates/zlog_settings" }
 # External crates
 #
 
-agent-client-protocol = { version = "0.4.0", features = ["unstable"] }
+agent-client-protocol = { version = "0.4.2", features = ["unstable"] }
 aho-corasick = "1.1"
 alacritty_terminal = "0.25.1-rc1"
 any_vec = "0.14"

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(
+    fn select_model(&self, model_id: acp::ModelId, cx: &mut App) -> Task<Result<()>>;
-        &self,
-        session_id: acp::SessionId,
-        model_id: AgentModelId,
-        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(
+    fn selected_model(&self, cx: &mut App) -> Task<Result<AgentModelInfo>>;
-        &self,
-        session_id: &acp::SessionId,
-        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<()>;
+    /// 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, 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)
     }
 }
 
 #[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);
 

crates/agent2/src/agent.rs

@@ -56,7 +56,7 @@ struct Session {
 
 pub struct LanguageModels {
     /// Access language model by ID
-    models: HashMap<acp_thread::AgentModelId, Arc<dyn LanguageModel>>,
+    models: HashMap<acp::ModelId, Arc<dyn LanguageModel>>,
     /// Cached list for returning language model information
     model_list: acp_thread::AgentModelList,
     refresh_models_rx: watch::Receiver<()>,
@@ -132,10 +132,7 @@ impl LanguageModels {
         self.refresh_models_rx.clone()
     }
 
-    pub fn model_from_id(
+    pub fn model_from_id(&self, model_id: &acp::ModelId) -> Option<Arc<dyn LanguageModel>> {
-        &self,
-        model_id: &acp_thread::AgentModelId,
-    ) -> Option<Arc<dyn LanguageModel>> {
         self.models.get(model_id).cloned()
     }
 
@@ -146,12 +143,13 @@ impl LanguageModels {
         acp_thread::AgentModelInfo {
             id: Self::model_id(model),
             name: model.name().0,
+            description: None,
             icon: Some(provider.icon()),
         }
     }
 
-    fn model_id(model: &Arc<dyn LanguageModel>) -> acp_thread::AgentModelId {
+    fn model_id(model: &Arc<dyn LanguageModel>) -> acp::ModelId {
-        acp_thread::AgentModelId(format!("{}/{}", model.provider_id().0, model.id().0).into())
+        acp::ModelId(format!("{}/{}", model.provider_id().0, model.id().0).into())
     }
 
     fn authenticate_all_language_model_providers(cx: &mut App) -> Task<()> {
@@ -836,10 +834,15 @@ impl NativeAgentConnection {
     }
 }
 
-impl AgentModelSelector for NativeAgentConnection {
+struct NativeAgentModelSelector {
+    session_id: acp::SessionId,
+    connection: NativeAgentConnection,
+}
+
+impl acp_thread::AgentModelSelector for NativeAgentModelSelector {
     fn list_models(&self, cx: &mut App) -> Task<Result<acp_thread::AgentModelList>> {
         log::debug!("NativeAgentConnection::list_models called");
-        let list = self.0.read(cx).models.model_list.clone();
+        let list = self.connection.0.read(cx).models.model_list.clone();
         Task::ready(if list.is_empty() {
             Err(anyhow::anyhow!("No models available"))
         } else {
@@ -847,24 +850,24 @@ impl AgentModelSelector for NativeAgentConnection {
         })
     }
 
-    fn select_model(
+    fn select_model(&self, model_id: acp::ModelId, cx: &mut App) -> Task<Result<()>> {
-        &self,
+        log::debug!(
-        session_id: acp::SessionId,
+            "Setting model for session {}: {}",
-        model_id: acp_thread::AgentModelId,
+            self.session_id,
-        cx: &mut App,
+            model_id
-    ) -> Task<Result<()>> {
+        );
-        log::debug!("Setting model for session {}: {}", session_id, model_id);
         let Some(thread) = self
+            .connection
             .0
             .read(cx)
             .sessions
-            .get(&session_id)
+            .get(&self.session_id)
             .map(|session| session.thread.clone())
         else {
             return Task::ready(Err(anyhow!("Session not found")));
         };
 
-        let Some(model) = self.0.read(cx).models.model_from_id(&model_id) else {
+        let Some(model) = self.connection.0.read(cx).models.model_from_id(&model_id) else {
             return Task::ready(Err(anyhow!("Invalid model ID {}", model_id)));
         };
 
@@ -872,33 +875,32 @@ impl AgentModelSelector for NativeAgentConnection {
             thread.set_model(model.clone(), cx);
         });
 
-        update_settings_file(self.0.read(cx).fs.clone(), cx, move |settings, _cx| {
+        update_settings_file(
-            let provider = model.provider_id().0.to_string();
+            self.connection.0.read(cx).fs.clone(),
-            let model = model.id().0.to_string();
+            cx,
-            settings
+            move |settings, _cx| {
-                .agent
+                let provider = model.provider_id().0.to_string();
-                .get_or_insert_default()
+                let model = model.id().0.to_string();
-                .set_model(LanguageModelSelection {
+                settings
-                    provider: provider.into(),
+                    .agent
-                    model,
+                    .get_or_insert_default()
-                });
+                    .set_model(LanguageModelSelection {
-        });
+                        provider: provider.into(),
+                        model,
+                    });
+            },
+        );
 
         Task::ready(Ok(()))
     }
 
-    fn selected_model(
+    fn selected_model(&self, cx: &mut App) -> Task<Result<acp_thread::AgentModelInfo>> {
-        &self,
-        session_id: &acp::SessionId,
-        cx: &mut App,
-    ) -> Task<Result<acp_thread::AgentModelInfo>> {
-        let session_id = session_id.clone();
-
         let Some(thread) = self
+            .connection
             .0
             .read(cx)
             .sessions
-            .get(&session_id)
+            .get(&self.session_id)
             .map(|session| session.thread.clone())
         else {
             return Task::ready(Err(anyhow!("Session not found")));
@@ -915,8 +917,8 @@ impl AgentModelSelector for NativeAgentConnection {
         )))
     }
 
-    fn watch(&self, cx: &mut App) -> watch::Receiver<()> {
+    fn watch(&self, cx: &mut App) -> Option<watch::Receiver<()>> {
-        self.0.read(cx).models.watch()
+        Some(self.connection.0.read(cx).models.watch())
     }
 }
 
@@ -972,8 +974,11 @@ impl acp_thread::AgentConnection for NativeAgentConnection {
         Task::ready(Ok(()))
     }
 
-    fn model_selector(&self) -> Option<Rc<dyn AgentModelSelector>> {
+    fn model_selector(&self, session_id: &acp::SessionId) -> Option<Rc<dyn AgentModelSelector>> {
-        Some(Rc::new(self.clone()) as Rc<dyn AgentModelSelector>)
+        Some(Rc::new(NativeAgentModelSelector {
+            session_id: session_id.clone(),
+            connection: self.clone(),
+        }) as Rc<dyn AgentModelSelector>)
     }
 
     fn prompt(
@@ -1196,9 +1201,7 @@ mod tests {
     use crate::HistoryEntryId;
 
     use super::*;
-    use acp_thread::{
+    use acp_thread::{AgentConnection, AgentModelGroupName, AgentModelInfo, MentionUri};
-        AgentConnection, AgentModelGroupName, AgentModelId, AgentModelInfo, MentionUri,
-    };
     use fs::FakeFs;
     use gpui::TestAppContext;
     use indoc::indoc;
@@ -1292,7 +1295,25 @@ mod tests {
             .unwrap(),
         );
 
-        let models = cx.update(|cx| connection.list_models(cx)).await.unwrap();
+        // Create a thread/session
+        let acp_thread = cx
+            .update(|cx| {
+                Rc::new(connection.clone()).new_thread(project.clone(), Path::new("/a"), cx)
+            })
+            .await
+            .unwrap();
+
+        let session_id = cx.update(|cx| acp_thread.read(cx).session_id().clone());
+
+        let models = cx
+            .update(|cx| {
+                connection
+                    .model_selector(&session_id)
+                    .unwrap()
+                    .list_models(cx)
+            })
+            .await
+            .unwrap();
 
         let acp_thread::AgentModelList::Grouped(models) = models else {
             panic!("Unexpected model group");
@@ -1302,8 +1323,9 @@ mod tests {
             IndexMap::from_iter([(
                 AgentModelGroupName("Fake".into()),
                 vec![AgentModelInfo {
-                    id: AgentModelId("fake/fake".into()),
+                    id: acp::ModelId("fake/fake".into()),
                     name: "Fake".into(),
+                    description: None,
                     icon: Some(ui::IconName::ZedAssistant),
                 }]
             )])
@@ -1360,8 +1382,9 @@ mod tests {
         let session_id = cx.update(|cx| acp_thread.read(cx).session_id().clone());
 
         // Select a model
-        let model_id = AgentModelId("fake/fake".into());
+        let selector = connection.model_selector(&session_id).unwrap();
-        cx.update(|cx| connection.select_model(session_id.clone(), model_id.clone(), cx))
+        let model_id = acp::ModelId("fake/fake".into());
+        cx.update(|cx| selector.select_model(model_id.clone(), cx))
             .await
             .unwrap();
 

crates/agent2/src/tests/mod.rs

@@ -1850,8 +1850,18 @@ async fn test_agent_connection(cx: &mut TestAppContext) {
     .unwrap();
     let connection = NativeAgentConnection(agent.clone());
 
+    // Create a thread using new_thread
+    let connection_rc = Rc::new(connection.clone());
+    let acp_thread = cx
+        .update(|cx| connection_rc.new_thread(project, cwd, cx))
+        .await
+        .expect("new_thread should succeed");
+
+    // Get the session_id from the AcpThread
+    let session_id = acp_thread.read_with(cx, |thread, _| thread.session_id().clone());
+
     // Test model_selector returns Some
-    let selector_opt = connection.model_selector();
+    let selector_opt = connection.model_selector(&session_id);
     assert!(
         selector_opt.is_some(),
         "agent2 should always support ModelSelector"
@@ -1868,23 +1878,16 @@ async fn test_agent_connection(cx: &mut TestAppContext) {
     };
     assert!(!listed_models.is_empty(), "should have at least one model");
     assert_eq!(
-        listed_models[&AgentModelGroupName("Fake".into())][0].id.0,
+        listed_models[&AgentModelGroupName("Fake".into())][0]
+            .id
+            .0
+            .as_ref(),
         "fake/fake"
     );
 
-    // Create a thread using new_thread
-    let connection_rc = Rc::new(connection.clone());
-    let acp_thread = cx
-        .update(|cx| connection_rc.new_thread(project, cwd, cx))
-        .await
-        .expect("new_thread should succeed");
-
-    // Get the session_id from the AcpThread
-    let session_id = acp_thread.read_with(cx, |thread, _| thread.session_id().clone());
-
     // Test selected_model returns the default
     let model = cx
-        .update(|cx| selector.selected_model(&session_id, cx))
+        .update(|cx| selector.selected_model(cx))
         .await
         .expect("selected_model should succeed");
     let model = cx

crates/agent_servers/src/acp.rs

@@ -44,6 +44,7 @@ pub struct AcpConnection {
 pub struct AcpSession {
     thread: WeakEntity<AcpThread>,
     suppress_abort_err: bool,
+    models: Option<Rc<RefCell<acp::SessionModelState>>>,
     session_modes: Option<Rc<RefCell<acp::SessionModeState>>>,
 }
 
@@ -264,6 +265,7 @@ impl AgentConnection for AcpConnection {
                 })?;
 
             let modes = response.modes.map(|modes| Rc::new(RefCell::new(modes)));
+            let models = response.models.map(|models| Rc::new(RefCell::new(models)));
 
             if let Some(default_mode) = default_mode {
                 if let Some(modes) = modes.as_ref() {
@@ -326,10 +328,12 @@ impl AgentConnection for AcpConnection {
                 )
             })?;
 
+
             let session = AcpSession {
                 thread: thread.downgrade(),
                 suppress_abort_err: false,
-                session_modes: modes
+                session_modes: modes,
+                models,
             };
             sessions.borrow_mut().insert(session_id, session);
 
@@ -450,6 +454,27 @@ impl AgentConnection for AcpConnection {
         }
     }
 
+    fn model_selector(
+        &self,
+        session_id: &acp::SessionId,
+    ) -> Option<Rc<dyn acp_thread::AgentModelSelector>> {
+        let sessions = self.sessions.clone();
+        let sessions_ref = sessions.borrow();
+        let Some(session) = sessions_ref.get(session_id) else {
+            return None;
+        };
+
+        if let Some(models) = session.models.as_ref() {
+            Some(Rc::new(AcpModelSelector::new(
+                session_id.clone(),
+                self.connection.clone(),
+                models.clone(),
+            )) as _)
+        } else {
+            None
+        }
+    }
+
     fn into_any(self: Rc<Self>) -> Rc<dyn Any> {
         self
     }
@@ -500,6 +525,82 @@ impl acp_thread::AgentSessionModes for AcpSessionModes {
     }
 }
 
+struct AcpModelSelector {
+    session_id: acp::SessionId,
+    connection: Rc<acp::ClientSideConnection>,
+    state: Rc<RefCell<acp::SessionModelState>>,
+}
+
+impl AcpModelSelector {
+    fn new(
+        session_id: acp::SessionId,
+        connection: Rc<acp::ClientSideConnection>,
+        state: Rc<RefCell<acp::SessionModelState>>,
+    ) -> Self {
+        Self {
+            session_id,
+            connection,
+            state,
+        }
+    }
+}
+
+impl acp_thread::AgentModelSelector for AcpModelSelector {
+    fn list_models(&self, _cx: &mut App) -> Task<Result<acp_thread::AgentModelList>> {
+        Task::ready(Ok(acp_thread::AgentModelList::Flat(
+            self.state
+                .borrow()
+                .available_models
+                .clone()
+                .into_iter()
+                .map(acp_thread::AgentModelInfo::from)
+                .collect(),
+        )))
+    }
+
+    fn select_model(&self, model_id: acp::ModelId, cx: &mut App) -> Task<Result<()>> {
+        let connection = self.connection.clone();
+        let session_id = self.session_id.clone();
+        let old_model_id;
+        {
+            let mut state = self.state.borrow_mut();
+            old_model_id = state.current_model_id.clone();
+            state.current_model_id = model_id.clone();
+        };
+        let state = self.state.clone();
+        cx.foreground_executor().spawn(async move {
+            let result = connection
+                .set_session_model(acp::SetSessionModelRequest {
+                    session_id,
+                    model_id,
+                    meta: None,
+                })
+                .await;
+
+            if result.is_err() {
+                state.borrow_mut().current_model_id = old_model_id;
+            }
+
+            result?;
+
+            Ok(())
+        })
+    }
+
+    fn selected_model(&self, _cx: &mut App) -> Task<Result<acp_thread::AgentModelInfo>> {
+        let state = self.state.borrow();
+        Task::ready(
+            state
+                .available_models
+                .iter()
+                .find(|m| m.model_id == state.current_model_id)
+                .cloned()
+                .map(acp_thread::AgentModelInfo::from)
+                .ok_or_else(|| anyhow::anyhow!("Model not found")),
+        )
+    }
+}
+
 struct ClientDelegate {
     sessions: Rc<RefCell<HashMap<acp::SessionId, AcpSession>>>,
     cx: AsyncApp,

crates/agent_ui/src/acp/model_selector.rs

@@ -1,7 +1,6 @@
 use std::{cmp::Reverse, rc::Rc, sync::Arc};
 
 use acp_thread::{AgentModelInfo, AgentModelList, AgentModelSelector};
-use agent_client_protocol as acp;
 use anyhow::Result;
 use collections::IndexMap;
 use futures::FutureExt;
@@ -10,20 +9,19 @@ use gpui::{Action, AsyncWindowContext, BackgroundExecutor, DismissEvent, Task, W
 use ordered_float::OrderedFloat;
 use picker::{Picker, PickerDelegate};
 use ui::{
-    AnyElement, App, Context, IntoElement, ListItem, ListItemSpacing, SharedString, Window,
+    AnyElement, App, Context, DocumentationAside, DocumentationEdge, DocumentationSide,
-    prelude::*, rems,
+    IntoElement, ListItem, ListItemSpacing, SharedString, Window, prelude::*, rems,
 };
 use util::ResultExt;
 
 pub type AcpModelSelector = Picker<AcpModelPickerDelegate>;
 
 pub fn acp_model_selector(
-    session_id: acp::SessionId,
     selector: Rc<dyn AgentModelSelector>,
     window: &mut Window,
     cx: &mut Context<AcpModelSelector>,
 ) -> AcpModelSelector {
-    let delegate = AcpModelPickerDelegate::new(session_id, selector, window, cx);
+    let delegate = AcpModelPickerDelegate::new(selector, window, cx);
     Picker::list(delegate, window, cx)
         .show_scrollbar(true)
         .width(rems(20.))
@@ -36,61 +34,63 @@ enum AcpModelPickerEntry {
 }
 
 pub struct AcpModelPickerDelegate {
-    session_id: acp::SessionId,
     selector: Rc<dyn AgentModelSelector>,
     filtered_entries: Vec<AcpModelPickerEntry>,
     models: Option<AgentModelList>,
     selected_index: usize,
+    selected_description: Option<(usize, SharedString)>,
     selected_model: Option<AgentModelInfo>,
     _refresh_models_task: Task<()>,
 }
 
 impl AcpModelPickerDelegate {
     fn new(
-        session_id: acp::SessionId,
         selector: Rc<dyn AgentModelSelector>,
         window: &mut Window,
         cx: &mut Context<AcpModelSelector>,
     ) -> Self {
-        let mut rx = selector.watch(cx);
+        let rx = selector.watch(cx);
-        let refresh_models_task = cx.spawn_in(window, {
+        let refresh_models_task = {
-            let session_id = session_id.clone();
+            cx.spawn_in(window, {
-            async move |this, cx| {
+                async move |this, cx| {
-                async fn refresh(
+                    async fn refresh(
-                    this: &WeakEntity<Picker<AcpModelPickerDelegate>>,
+                        this: &WeakEntity<Picker<AcpModelPickerDelegate>>,
-                    session_id: &acp::SessionId,
+                        cx: &mut AsyncWindowContext,
-                    cx: &mut AsyncWindowContext,
+                    ) -> Result<()> {
-                ) -> Result<()> {
+                        let (models_task, selected_model_task) = this.update(cx, |this, cx| {
-                    let (models_task, selected_model_task) = this.update(cx, |this, cx| {
+                            (
-                        (
+                                this.delegate.selector.list_models(cx),
-                            this.delegate.selector.list_models(cx),
+                                this.delegate.selector.selected_model(cx),
-                            this.delegate.selector.selected_model(session_id, cx),
+                            )
-                        )
+                        })?;
-                    })?;
 
-                    let (models, selected_model) = futures::join!(models_task, selected_model_task);
+                        let (models, selected_model) =
+                            futures::join!(models_task, selected_model_task);
 
-                    this.update_in(cx, |this, window, cx| {
+                        this.update_in(cx, |this, window, cx| {
-                        this.delegate.models = models.ok();
+                            this.delegate.models = models.ok();
-                        this.delegate.selected_model = selected_model.ok();
+                            this.delegate.selected_model = selected_model.ok();
-                        this.refresh(window, cx)
+                            this.refresh(window, cx)
-                    })
+                        })
+                    }
+
+                    refresh(&this, cx).await.log_err();
+                    if let Some(mut rx) = rx {
+                        while let Ok(()) = rx.recv().await {
+                            refresh(&this, cx).await.log_err();
+                        }
+                    }
                 }
-
+            })
-                refresh(&this, &session_id, cx).await.log_err();
+        };
-                while let Ok(()) = rx.recv().await {
-                    refresh(&this, &session_id, cx).await.log_err();
-                }
-            }
-        });
 
         Self {
-            session_id,
             selector,
             filtered_entries: Vec::new(),
             models: None,
             selected_model: None,
             selected_index: 0,
+            selected_description: None,
             _refresh_models_task: refresh_models_task,
         }
     }
@@ -182,7 +182,7 @@ impl PickerDelegate for AcpModelPickerDelegate {
             self.filtered_entries.get(self.selected_index)
         {
             self.selector
-                .select_model(self.session_id.clone(), model_info.id.clone(), cx)
+                .select_model(model_info.id.clone(), cx)
                 .detach_and_log_err(cx);
             self.selected_model = Some(model_info.clone());
             let current_index = self.selected_index;
@@ -233,31 +233,46 @@ impl PickerDelegate for AcpModelPickerDelegate {
                 };
 
                 Some(
-                    ListItem::new(ix)
+                    div()
-                        .inset(true)
+                        .id(("model-picker-menu-child", ix))
-                        .spacing(ListItemSpacing::Sparse)
+                        .when_some(model_info.description.clone(), |this, description| {
-                        .toggle_state(selected)
+                            this
-                        .start_slot::<Icon>(model_info.icon.map(|icon| {
+                                .on_hover(cx.listener(move |menu, hovered, _, cx| {
-                            Icon::new(icon)
+                                    if *hovered {
-                                .color(model_icon_color)
+                                        menu.delegate.selected_description = Some((ix, description.clone()));
-                                .size(IconSize::Small)
+                                    } else if matches!(menu.delegate.selected_description, Some((id, _)) if id == ix) {
-                        }))
+                                        menu.delegate.selected_description = None;
+                                    }
+                                    cx.notify();
+                                }))
+                        })
                         .child(
-                            h_flex()
+                            ListItem::new(ix)
-                                .w_full()
+                                .inset(true)
-                                .pl_0p5()
+                                .spacing(ListItemSpacing::Sparse)
-                                .gap_1p5()
+                                .toggle_state(selected)
-                                .w(px(240.))
+                                .start_slot::<Icon>(model_info.icon.map(|icon| {
-                                .child(Label::new(model_info.name.clone()).truncate()),
+                                    Icon::new(icon)
+                                        .color(model_icon_color)
+                                        .size(IconSize::Small)
+                                }))
+                                .child(
+                                    h_flex()
+                                        .w_full()
+                                        .pl_0p5()
+                                        .gap_1p5()
+                                        .w(px(240.))
+                                        .child(Label::new(model_info.name.clone()).truncate()),
+                                )
+                                .end_slot(div().pr_3().when(is_selected, |this| {
+                                    this.child(
+                                        Icon::new(IconName::Check)
+                                            .color(Color::Accent)
+                                            .size(IconSize::Small),
+                                    )
+                                })),
                         )
-                        .end_slot(div().pr_3().when(is_selected, |this| {
+                        .into_any_element()
-                            this.child(
-                                Icon::new(IconName::Check)
-                                    .color(Color::Accent)
-                                    .size(IconSize::Small),
-                            )
-                        }))
-                        .into_any_element(),
                 )
             }
         }
@@ -292,6 +307,21 @@ impl PickerDelegate for AcpModelPickerDelegate {
                 .into_any(),
         )
     }
+
+    fn documentation_aside(
+        &self,
+        _window: &mut Window,
+        _cx: &mut Context<Picker<Self>>,
+    ) -> Option<ui::DocumentationAside> {
+        self.selected_description.as_ref().map(|(_, description)| {
+            let description = description.clone();
+            DocumentationAside::new(
+                DocumentationSide::Left,
+                DocumentationEdge::Bottom,
+                Rc::new(move |_| Label::new(description.clone()).into_any_element()),
+            )
+        })
+    }
 }
 
 fn info_list_to_picker_entries(
@@ -371,6 +401,7 @@ async fn fuzzy_search(
 
 #[cfg(test)]
 mod tests {
+    use agent_client_protocol as acp;
     use gpui::TestAppContext;
 
     use super::*;
@@ -383,8 +414,9 @@ mod tests {
                     models
                         .into_iter()
                         .map(|model| acp_thread::AgentModelInfo {
-                            id: acp_thread::AgentModelId(model.to_string().into()),
+                            id: acp::ModelId(model.to_string().into()),
                             name: model.to_string().into(),
+                            description: None,
                             icon: None,
                         })
                         .collect::<Vec<_>>(),

crates/agent_ui/src/acp/model_selector_popover.rs

@@ -1,7 +1,6 @@
 use std::rc::Rc;
 
 use acp_thread::AgentModelSelector;
-use agent_client_protocol as acp;
 use gpui::{Entity, FocusHandle};
 use picker::popover_menu::PickerPopoverMenu;
 use ui::{
@@ -20,7 +19,6 @@ pub struct AcpModelSelectorPopover {
 
 impl AcpModelSelectorPopover {
     pub(crate) fn new(
-        session_id: acp::SessionId,
         selector: Rc<dyn AgentModelSelector>,
         menu_handle: PopoverMenuHandle<AcpModelSelector>,
         focus_handle: FocusHandle,
@@ -28,7 +26,7 @@ impl AcpModelSelectorPopover {
         cx: &mut Context<Self>,
     ) -> Self {
         Self {
-            selector: cx.new(move |cx| acp_model_selector(session_id, selector, window, cx)),
+            selector: cx.new(move |cx| acp_model_selector(selector, window, cx)),
             menu_handle,
             focus_handle,
         }

crates/agent_ui/src/acp/thread_view.rs

@@ -577,23 +577,21 @@ impl AcpThreadView {
 
                         AgentDiff::set_active_thread(&workspace, thread.clone(), window, cx);
 
-                        this.model_selector =
+                        this.model_selector = thread
-                            thread
+                            .read(cx)
-                                .read(cx)
+                            .connection()
-                                .connection()
+                            .model_selector(thread.read(cx).session_id())
-                                .model_selector()
+                            .map(|selector| {
-                                .map(|selector| {
+                                cx.new(|cx| {
-                                    cx.new(|cx| {
+                                    AcpModelSelectorPopover::new(
-                                        AcpModelSelectorPopover::new(
+                                        selector,
-                                            thread.read(cx).session_id().clone(),
+                                        PopoverMenuHandle::default(),
-                                            selector,
+                                        this.focus_handle(cx),
-                                            PopoverMenuHandle::default(),
+                                        window,
-                                            this.focus_handle(cx),
+                                        cx,
-                                            window,
+                                    )
-                                            cx,
+                                })
-                                        )
+                            });
-                                    })
-                                });
 
                         let mode_selector = thread
                             .read(cx)

crates/picker/Cargo.toml

@@ -22,6 +22,7 @@ gpui.workspace = true
 menu.workspace = true
 schemars.workspace = true
 serde.workspace = true
+theme.workspace = true
 ui.workspace = true
 workspace.workspace = true
 workspace-hack.workspace = true

crates/picker/src/picker.rs

@@ -18,11 +18,12 @@ use head::Head;
 use schemars::JsonSchema;
 use serde::Deserialize;
 use std::{ops::Range, sync::Arc, time::Duration};
+use theme::ThemeSettings;
 use ui::{
-    Color, Divider, Label, ListItem, ListItemSpacing, ScrollAxes, Scrollbars, WithScrollbar,
+    Color, Divider, DocumentationAside, DocumentationEdge, DocumentationSide, Label, ListItem,
-    prelude::*, v_flex,
+    ListItemSpacing, ScrollAxes, Scrollbars, WithScrollbar, prelude::*, utils::WithRemSize, v_flex,
 };
-use workspace::ModalView;
+use workspace::{ModalView, item::Settings};
 
 enum ElementContainer {
     List(ListState),
@@ -222,6 +223,14 @@ pub trait PickerDelegate: Sized + 'static {
     ) -> Option<AnyElement> {
         None
     }
+
+    fn documentation_aside(
+        &self,
+        _window: &mut Window,
+        _cx: &mut Context<Picker<Self>>,
+    ) -> Option<DocumentationAside> {
+        None
+    }
 }
 
 impl<D: PickerDelegate> Focusable for Picker<D> {
@@ -781,8 +790,15 @@ impl<D: PickerDelegate> ModalView for Picker<D> {}
 
 impl<D: PickerDelegate> Render for Picker<D> {
     fn render(&mut self, window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let ui_font_size = ThemeSettings::get_global(cx).ui_font_size(cx);
+        let window_size = window.viewport_size();
+        let rem_size = window.rem_size();
+        let is_wide_window = window_size.width / rem_size > rems_from_px(800.).0;
+
+        let aside = self.delegate.documentation_aside(window, cx);
+
         let editor_position = self.delegate.editor_position();
-        v_flex()
+        let menu = v_flex()
             .key_context("Picker")
             .size_full()
             .when_some(self.width, |el, width| el.w(width))
@@ -865,6 +881,47 @@ impl<D: PickerDelegate> Render for Picker<D> {
                     }
                 }
                 Head::Empty(empty_head) => Some(div().child(empty_head.clone())),
-            })
+            });
+
+        let Some(aside) = aside else {
+            return menu;
+        };
+
+        let render_aside = |aside: DocumentationAside, cx: &mut Context<Self>| {
+            WithRemSize::new(ui_font_size)
+                .occlude()
+                .elevation_2(cx)
+                .w_full()
+                .p_2()
+                .overflow_hidden()
+                .when(is_wide_window, |this| this.max_w_96())
+                .when(!is_wide_window, |this| this.max_w_48())
+                .child((aside.render)(cx))
+        };
+
+        if is_wide_window {
+            div().relative().child(menu).child(
+                h_flex()
+                    .absolute()
+                    .when(aside.side == DocumentationSide::Left, |this| {
+                        this.right_full().mr_1()
+                    })
+                    .when(aside.side == DocumentationSide::Right, |this| {
+                        this.left_full().ml_1()
+                    })
+                    .when(aside.edge == DocumentationEdge::Top, |this| this.top_0())
+                    .when(aside.edge == DocumentationEdge::Bottom, |this| {
+                        this.bottom_0()
+                    })
+                    .child(render_aside(aside, cx)),
+            )
+        } else {
+            v_flex()
+                .w_full()
+                .gap_1()
+                .justify_end()
+                .child(render_aside(aside, cx))
+                .child(menu)
+        }
     }
 }

crates/ui/src/components/context_menu.rs

@@ -180,9 +180,9 @@ pub enum DocumentationEdge {
 
 #[derive(Clone)]
 pub struct DocumentationAside {
-    side: DocumentationSide,
+    pub side: DocumentationSide,
-    edge: DocumentationEdge,
+    pub edge: DocumentationEdge,
-    render: Rc<dyn Fn(&mut App) -> AnyElement>,
+    pub render: Rc<dyn Fn(&mut App) -> AnyElement>,
 }
 
 impl DocumentationAside {

tooling/workspace-hack/Cargo.toml

@@ -600,10 +600,10 @@ tower = { version = "0.5", default-features = false, features = ["timeout", "uti
 winapi = { version = "0.3", default-features = false, features = ["cfg", "commapi", "consoleapi", "evntrace", "fileapi", "handleapi", "impl-debug", "impl-default", "in6addr", "inaddr", "ioapiset", "knownfolders", "minwinbase", "minwindef", "namedpipeapi", "ntsecapi", "objbase", "processenv", "processthreadsapi", "shlobj", "std", "synchapi", "sysinfoapi", "timezoneapi", "winbase", "windef", "winerror", "winioctl", "winnt", "winreg", "winsock2", "winuser"] }
 windows-core = { version = "0.61" }
 windows-numerics = { version = "0.2" }
-windows-sys-4db8c43aad08e7ae = { package = "windows-sys", version = "0.60", features = ["Win32_Globalization", "Win32_System_Com", "Win32_UI_Shell"] }
 windows-sys-73dcd821b1037cfd = { package = "windows-sys", version = "0.59", features = ["Wdk_Foundation", "Wdk_Storage_FileSystem", "Win32_NetworkManagement_IpHelper", "Win32_Networking_WinSock", "Win32_Security_Authentication_Identity", "Win32_Security_Credentials", "Win32_Security_Cryptography", "Win32_Storage_FileSystem", "Win32_System_Com", "Win32_System_Console", "Win32_System_Diagnostics_Debug", "Win32_System_IO", "Win32_System_Ioctl", "Win32_System_Kernel", "Win32_System_LibraryLoader", "Win32_System_Memory", "Win32_System_Performance", "Win32_System_Pipes", "Win32_System_Registry", "Win32_System_SystemInformation", "Win32_System_SystemServices", "Win32_System_Threading", "Win32_System_Time", "Win32_System_WindowsProgramming", "Win32_UI_Input_KeyboardAndMouse", "Win32_UI_Shell", "Win32_UI_WindowsAndMessaging"] }
 windows-sys-b21d60becc0929df = { package = "windows-sys", version = "0.52", features = ["Wdk_Foundation", "Wdk_Storage_FileSystem", "Wdk_System_IO", "Win32_Foundation", "Win32_Networking_WinSock", "Win32_Security_Authorization", "Win32_Storage_FileSystem", "Win32_System_Console", "Win32_System_IO", "Win32_System_Memory", "Win32_System_Pipes", "Win32_System_SystemServices", "Win32_System_Threading", "Win32_System_WindowsProgramming"] }
 windows-sys-c8eced492e86ede7 = { package = "windows-sys", version = "0.48", features = ["Win32_Foundation", "Win32_Globalization", "Win32_Networking_WinSock", "Win32_Security", "Win32_Storage_FileSystem", "Win32_System_Com", "Win32_System_Diagnostics_Debug", "Win32_System_IO", "Win32_System_Pipes", "Win32_System_Registry", "Win32_System_Threading", "Win32_System_Time", "Win32_System_WindowsProgramming", "Win32_UI_Shell"] }
+windows-sys-d4189bed749088b6 = { package = "windows-sys", version = "0.61", features = ["Wdk_Foundation", "Wdk_Storage_FileSystem", "Win32_Globalization", "Win32_Networking_WinSock", "Win32_Security", "Win32_Storage_FileSystem", "Win32_System_Com", "Win32_System_IO", "Win32_System_LibraryLoader", "Win32_System_Threading", "Win32_System_WindowsProgramming", "Win32_UI_Shell"] }
 
 [target.x86_64-pc-windows-msvc.build-dependencies]
 codespan-reporting = { version = "0.12" }
@@ -627,10 +627,10 @@ tower = { version = "0.5", default-features = false, features = ["timeout", "uti
 winapi = { version = "0.3", default-features = false, features = ["cfg", "commapi", "consoleapi", "evntrace", "fileapi", "handleapi", "impl-debug", "impl-default", "in6addr", "inaddr", "ioapiset", "knownfolders", "minwinbase", "minwindef", "namedpipeapi", "ntsecapi", "objbase", "processenv", "processthreadsapi", "shlobj", "std", "synchapi", "sysinfoapi", "timezoneapi", "winbase", "windef", "winerror", "winioctl", "winnt", "winreg", "winsock2", "winuser"] }
 windows-core = { version = "0.61" }
 windows-numerics = { version = "0.2" }
-windows-sys-4db8c43aad08e7ae = { package = "windows-sys", version = "0.60", features = ["Win32_Globalization", "Win32_System_Com", "Win32_UI_Shell"] }
 windows-sys-73dcd821b1037cfd = { package = "windows-sys", version = "0.59", features = ["Wdk_Foundation", "Wdk_Storage_FileSystem", "Win32_NetworkManagement_IpHelper", "Win32_Networking_WinSock", "Win32_Security_Authentication_Identity", "Win32_Security_Credentials", "Win32_Security_Cryptography", "Win32_Storage_FileSystem", "Win32_System_Com", "Win32_System_Console", "Win32_System_Diagnostics_Debug", "Win32_System_IO", "Win32_System_Ioctl", "Win32_System_Kernel", "Win32_System_LibraryLoader", "Win32_System_Memory", "Win32_System_Performance", "Win32_System_Pipes", "Win32_System_Registry", "Win32_System_SystemInformation", "Win32_System_SystemServices", "Win32_System_Threading", "Win32_System_Time", "Win32_System_WindowsProgramming", "Win32_UI_Input_KeyboardAndMouse", "Win32_UI_Shell", "Win32_UI_WindowsAndMessaging"] }
 windows-sys-b21d60becc0929df = { package = "windows-sys", version = "0.52", features = ["Wdk_Foundation", "Wdk_Storage_FileSystem", "Wdk_System_IO", "Win32_Foundation", "Win32_Networking_WinSock", "Win32_Security_Authorization", "Win32_Storage_FileSystem", "Win32_System_Console", "Win32_System_IO", "Win32_System_Memory", "Win32_System_Pipes", "Win32_System_SystemServices", "Win32_System_Threading", "Win32_System_WindowsProgramming"] }
 windows-sys-c8eced492e86ede7 = { package = "windows-sys", version = "0.48", features = ["Win32_Foundation", "Win32_Globalization", "Win32_Networking_WinSock", "Win32_Security", "Win32_Storage_FileSystem", "Win32_System_Com", "Win32_System_Diagnostics_Debug", "Win32_System_IO", "Win32_System_Pipes", "Win32_System_Registry", "Win32_System_Threading", "Win32_System_Time", "Win32_System_WindowsProgramming", "Win32_UI_Shell"] }
+windows-sys-d4189bed749088b6 = { package = "windows-sys", version = "0.61", features = ["Wdk_Foundation", "Wdk_Storage_FileSystem", "Win32_Globalization", "Win32_Networking_WinSock", "Win32_Security", "Win32_Storage_FileSystem", "Win32_System_Com", "Win32_System_IO", "Win32_System_LibraryLoader", "Win32_System_Threading", "Win32_System_WindowsProgramming", "Win32_UI_Shell"] }
 
 [target.x86_64-unknown-linux-musl.dependencies]
 aes = { version = "0.8", default-features = false, features = ["zeroize"] }