Remove lead/worker provider (#7989)

Signed-off-by: Douwe Osinga <douwe@squareup.com>
Co-authored-by: Douwe Osinga <douwe@squareup.com>

crates/goose/src/agents/agent.rs

@@ -158,7 +158,6 @@ pub struct Agent {
 pub enum AgentEvent {
     Message(Message),
     McpNotification((String, ServerNotification)),
-    ModelChange { model: String, mode: String },
     HistoryReplaced(Conversation),
 }
 
@@ -1230,27 +1229,6 @@ impl Agent {
                         Ok((response, usage)) => {
                             compaction_attempts = 0;
 
-                            // Emit model change event if provider is lead-worker
-                            let provider = self.provider().await?;
-                            if let Some(lead_worker) = provider.as_lead_worker() {
-                                if let Some(ref usage) = usage {
-                                    let active_model = usage.model.clone();
-                                    let (lead_model, worker_model) = lead_worker.get_model_info();
-                                    let mode = if active_model == lead_model {
-                                        "lead"
-                                    } else if active_model == worker_model {
-                                        "worker"
-                                    } else {
-                                        "unknown"
-                                    };
-
-                                    yield AgentEvent::ModelChange {
-                                        model: active_model,
-                                        mode: mode.to_string(),
-                                    };
-                                }
-                            }
-
                             if let Some(ref usage) = usage {
                                 self.update_session_metrics(&session_config.id, session_config.schedule_id.clone(), usage, false).await?;
                             }

crates/goose/src/agents/reply_parts.rs

@@ -208,8 +208,6 @@ impl Agent {
         Ok((tools, toolshim_tools, system_prompt))
     }
 
-    // Don't add gen_ai.request.model here — provider.get_model_config()
-    // returns the wrong model for LeadWorkerProvider.
     #[tracing::instrument(
         skip(provider, session_id, system_prompt, messages, tools, toolshim_tools),
         fields(session.id = %session_id)

crates/goose/src/agents/subagent_handler.rs

@@ -208,7 +208,7 @@ fn get_agent_messages(params: SubagentRunParams) -> AgentMessagesFuture {
                     }
                     conversation.push(msg);
                 }
-                Ok(AgentEvent::McpNotification(_)) | Ok(AgentEvent::ModelChange { .. }) => {}
+                Ok(AgentEvent::McpNotification(_)) => {}
                 Ok(AgentEvent::HistoryReplaced(updated_conversation)) => {
                     conversation = updated_conversation;
                 }