agent: Add ability to set a default_model per profile (#39220)

Split off from https://github.com/zed-industries/zed/pull/39175

Requires https://github.com/zed-industries/zed/pull/39219 to be merged
first

Adds support for `default_model` for profiles: 

```
      "my-profile": {
        "name": "Coding Agent",
        "tools": {},
        "enable_all_context_servers": false,
        "context_servers": {},
        "default_model": {
          "provider": "copilot_chat",
          "model": "grok-code-fast-1"
        }
      }
```

Which will then switch to the default model whenever the profile is
activated

![2025-09-30 17 09
06](https://github.com/user-attachments/assets/43f07b7b-85d9-4aff-82ce-25d6f5050d50)


Release Notes:

- Added `default_model` configuration to agent profile

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

crates/agent/src/tests/mod.rs

@@ -933,7 +933,7 @@ async fn test_profiles(cx: &mut TestAppContext) {
     // Test that test-1 profile (default) has echo and delay tools
     thread
         .update(cx, |thread, cx| {
-            thread.set_profile(AgentProfileId("test-1".into()));
+            thread.set_profile(AgentProfileId("test-1".into()), cx);
             thread.send(UserMessageId::new(), ["test"], cx)
         })
         .unwrap();
@@ -953,7 +953,7 @@ async fn test_profiles(cx: &mut TestAppContext) {
     // Switch to test-2 profile, and verify that it has only the infinite tool.
     thread
         .update(cx, |thread, cx| {
-            thread.set_profile(AgentProfileId("test-2".into()));
+            thread.set_profile(AgentProfileId("test-2".into()), cx);
             thread.send(UserMessageId::new(), ["test2"], cx)
         })
         .unwrap();
@@ -1002,8 +1002,8 @@ async fn test_mcp_tools(cx: &mut TestAppContext) {
     )
     .await;
     cx.run_until_parked();
-    thread.update(cx, |thread, _| {
-        thread.set_profile(AgentProfileId("test".into()))
+    thread.update(cx, |thread, cx| {
+        thread.set_profile(AgentProfileId("test".into()), cx)
     });
 
     let mut mcp_tool_calls = setup_context_server(
@@ -1169,8 +1169,8 @@ async fn test_mcp_tool_truncation(cx: &mut TestAppContext) {
     .await;
     cx.run_until_parked();
 
-    thread.update(cx, |thread, _| {
-        thread.set_profile(AgentProfileId("test".into()));
+    thread.update(cx, |thread, cx| {
+        thread.set_profile(AgentProfileId("test".into()), cx);
         thread.add_tool(EchoTool);
         thread.add_tool(DelayTool);
         thread.add_tool(WordListTool);

crates/agent/src/thread.rs

@@ -30,16 +30,17 @@ use gpui::{
 };
 use language_model::{
     LanguageModel, LanguageModelCompletionError, LanguageModelCompletionEvent, LanguageModelExt,
-    LanguageModelImage, LanguageModelProviderId, LanguageModelRegistry, LanguageModelRequest,
-    LanguageModelRequestMessage, LanguageModelRequestTool, LanguageModelToolResult,
-    LanguageModelToolResultContent, LanguageModelToolSchemaFormat, LanguageModelToolUse,
-    LanguageModelToolUseId, Role, SelectedModel, StopReason, TokenUsage, ZED_CLOUD_PROVIDER_ID,
+    LanguageModelId, LanguageModelImage, LanguageModelProviderId, LanguageModelRegistry,
+    LanguageModelRequest, LanguageModelRequestMessage, LanguageModelRequestTool,
+    LanguageModelToolResult, LanguageModelToolResultContent, LanguageModelToolSchemaFormat,
+    LanguageModelToolUse, LanguageModelToolUseId, Role, SelectedModel, StopReason, TokenUsage,
+    ZED_CLOUD_PROVIDER_ID,
 };
 use project::Project;
 use prompt_store::ProjectContext;
 use schemars::{JsonSchema, Schema};
 use serde::{Deserialize, Serialize};
-use settings::{Settings, update_settings_file};
+use settings::{LanguageModelSelection, Settings, update_settings_file};
 use smol::stream::StreamExt;
 use std::{
     collections::BTreeMap,
@@ -798,7 +799,8 @@ impl Thread {
         let profile_id = db_thread
             .profile
             .unwrap_or_else(|| AgentSettings::get_global(cx).default_profile.clone());
-        let model = LanguageModelRegistry::global(cx).update(cx, |registry, cx| {
+
+        let mut model = LanguageModelRegistry::global(cx).update(cx, |registry, cx| {
             db_thread
                 .model
                 .and_then(|model| {
@@ -811,6 +813,16 @@ impl Thread {
                 .or_else(|| registry.default_model())
                 .map(|model| model.model)
         });
+
+        if model.is_none() {
+            model = Self::resolve_profile_model(&profile_id, cx);
+        }
+        if model.is_none() {
+            model = LanguageModelRegistry::global(cx).update(cx, |registry, _cx| {
+                registry.default_model().map(|model| model.model)
+            });
+        }
+
         let (prompt_capabilities_tx, prompt_capabilities_rx) =
             watch::channel(Self::prompt_capabilities(model.as_deref()));
 
@@ -1007,8 +1019,17 @@ impl Thread {
         &self.profile_id
     }
 
-    pub fn set_profile(&mut self, profile_id: AgentProfileId) {
+    pub fn set_profile(&mut self, profile_id: AgentProfileId, cx: &mut Context<Self>) {
+        if self.profile_id == profile_id {
+            return;
+        }
+
         self.profile_id = profile_id;
+
+        // Swap to the profile's preferred model when available.
+        if let Some(model) = Self::resolve_profile_model(&self.profile_id, cx) {
+            self.set_model(model, cx);
+        }
     }
 
     pub fn cancel(&mut self, cx: &mut Context<Self>) {
@@ -1065,6 +1086,35 @@ impl Thread {
         })
     }
 
+    /// Look up the active profile and resolve its preferred model if one is configured.
+    fn resolve_profile_model(
+        profile_id: &AgentProfileId,
+        cx: &mut Context<Self>,
+    ) -> Option<Arc<dyn LanguageModel>> {
+        let selection = AgentSettings::get_global(cx)
+            .profiles
+            .get(profile_id)?
+            .default_model
+            .clone()?;
+        Self::resolve_model_from_selection(&selection, cx)
+    }
+
+    /// Translate a stored model selection into the configured model from the registry.
+    fn resolve_model_from_selection(
+        selection: &LanguageModelSelection,
+        cx: &mut Context<Self>,
+    ) -> Option<Arc<dyn LanguageModel>> {
+        let selected = SelectedModel {
+            provider: LanguageModelProviderId::from(selection.provider.0.clone()),
+            model: LanguageModelId::from(selection.model.clone()),
+        };
+        LanguageModelRegistry::global(cx).update(cx, |registry, cx| {
+            registry
+                .select_model(&selected, cx)
+                .map(|configured| configured.model)
+        })
+    }
+
     pub fn resume(
         &mut self,
         cx: &mut Context<Self>,