feat: show effective model in spawn agent event (#14944)

Show effective model after the full config layering for the sub agent

codex-rs/core/src/agent/control.rs

@@ -3,6 +3,7 @@ use crate::agent::guards::Guards;
 use crate::agent::role::DEFAULT_ROLE_NAME;
 use crate::agent::role::resolve_role_config;
 use crate::agent::status::is_final;
+use crate::codex_thread::ThreadConfigSnapshot;
 use crate::error::CodexErr;
 use crate::error::Result as CodexResult;
 use crate::find_thread_path_by_id_str;
@@ -360,6 +361,19 @@ impl AgentControl {
         ))
     }
 
+    pub(crate) async fn get_agent_config_snapshot(
+        &self,
+        agent_id: ThreadId,
+    ) -> Option<ThreadConfigSnapshot> {
+        let Ok(state) = self.upgrade() else {
+            return None;
+        };
+        let Ok(thread) = state.get_thread(agent_id).await else {
+            return None;
+        };
+        Some(thread.config_snapshot().await)
+    }
+
     /// Subscribe to status updates for `agent_id`, yielding the latest value and changes.
     pub(crate) async fn subscribe_status(
         &self,

codex-rs/core/src/tools/handlers/multi_agents/spawn.rs

@@ -98,15 +98,37 @@ impl ToolHandler for Handler {
             ),
             Err(_) => (None, AgentStatus::NotFound),
         };
-        let (new_agent_nickname, new_agent_role) = match new_thread_id {
-            Some(thread_id) => session
+        let agent_snapshot = match new_thread_id {
+            Some(thread_id) => {
+                session
+                    .services
+                    .agent_control
+                    .get_agent_config_snapshot(thread_id)
+                    .await
+            }
+            None => None,
+        };
+        let (new_agent_nickname, new_agent_role) = match (&agent_snapshot, new_thread_id) {
+            (Some(snapshot), _) => (
+                snapshot.session_source.get_nickname(),
+                snapshot.session_source.get_agent_role(),
+            ),
+            (None, Some(thread_id)) => session
                 .services
                 .agent_control
                 .get_agent_nickname_and_role(thread_id)
                 .await
                 .unwrap_or((None, None)),
-            None => (None, None),
+            (None, None) => (None, None),
         };
+        let effective_model = agent_snapshot
+            .as_ref()
+            .map(|snapshot| snapshot.model.clone())
+            .unwrap_or_else(|| args.model.clone().unwrap_or_default());
+        let effective_reasoning_effort = agent_snapshot
+            .as_ref()
+            .and_then(|snapshot| snapshot.reasoning_effort)
+            .unwrap_or(args.reasoning_effort.unwrap_or_default());
         let nickname = new_agent_nickname.clone();
         session
             .send_event(
@@ -118,8 +140,8 @@ impl ToolHandler for Handler {
                     new_agent_nickname,
                     new_agent_role,
                     prompt,
-                    model: args.model.clone().unwrap_or_default(),
-                    reasoning_effort: args.reasoning_effort.unwrap_or_default(),
+                    model: effective_model,
+                    reasoning_effort: effective_reasoning_effort,
                     status,
                 }
                 .into(),