feat: role metrics multi-agent (#12579)

add metrics for agent role

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

@@ -118,6 +118,9 @@ impl Guards {
             } else {
                 active_agents.used_agent_nicknames.clear();
                 active_agents.nickname_reset_count += 1;
+                if let Some(metrics) = codex_otel::metrics::global() {
+                    let _ = metrics.counter("codex.multi_agent.nickname_pool_reset", 1, &[]);
+                }
                 names.choose(&mut rand::rng())?.to_string()
             }
         };

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

@@ -13,7 +13,7 @@ use std::path::Path;
 use std::sync::LazyLock;
 use toml::Value as TomlValue;
 
-const DEFAULT_ROLE_NAME: &str = "default";
+pub const DEFAULT_ROLE_NAME: &str = "default";
 const AGENT_TYPE_UNAVAILABLE_ERROR: &str = "agent type is currently not available";
 
 /// Applies a role config layer to a mutable config and preserves unspecified keys.

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

@@ -93,6 +93,7 @@ impl ToolHandler for MultiAgentHandler {
 
 mod spawn {
     use super::*;
+    use crate::agent::role::DEFAULT_ROLE_NAME;
     use crate::agent::role::apply_role_to_config;
 
     use crate::agent::exceeds_thread_spawn_depth_limit;
@@ -201,6 +202,9 @@ mod spawn {
             )
             .await;
         let new_thread_id = result?;
+        let role_tag = role_name.unwrap_or(DEFAULT_ROLE_NAME);
+        turn.otel_manager
+            .counter("codex.multi_agent.spawn", 1, &[("role", role_tag)]);
 
         let content = serde_json::to_string(&SpawnAgentResult {
             agent_id: new_thread_id.to_string(),
@@ -409,6 +413,8 @@ mod resume_agent {
         if let Some(err) = error {
             return Err(err);
         }
+        turn.otel_manager
+            .counter("codex.multi_agent.resume", 1, &[]);
 
         let content = serde_json::to_string(&ResumeAgentResult { status }).map_err(|err| {
             FunctionCallError::Fatal(format!("failed to serialize resume_agent result: {err}"))