feat: add agent roles to collab tools (#9275)

Add `agent_type` parameter to the collab tool `spawn_agent` that
contains a preset to apply on the config when spawning this agent

codex-rs/core/src/codex.rs

@@ -541,24 +541,12 @@ impl Session {
             web_search_mode: per_turn_config.web_search_mode,
         });
 
-        let base_instructions = if per_turn_config.features.enabled(Feature::Collab) {
-            const COLLAB_INSTRUCTIONS: &str =
-                include_str!("../templates/collab/experimental_prompt.md");
-            let base = session_configuration
-                .base_instructions
-                .as_deref()
-                .unwrap_or(model_info.base_instructions.as_str());
-            Some(format!("{base}\n\n{COLLAB_INSTRUCTIONS}"))
-        } else {
-            session_configuration.base_instructions.clone()
-        };
-
         TurnContext {
             sub_id,
             client,
             cwd: session_configuration.cwd.clone(),
             developer_instructions: session_configuration.developer_instructions.clone(),
-            base_instructions,
+            base_instructions: session_configuration.base_instructions.clone(),
             compact_prompt: session_configuration.compact_prompt.clone(),
             user_instructions: session_configuration.user_instructions.clone(),
             approval_policy: session_configuration.approval_policy.value(),