Improve tracing for nested tool calls and exec processes (#41950)

## Why

Code-mode callbacks can outlive their initial request and run in separate tasks,
so their trace context must be preserved explicitly.

## What changed

- Preserve the execution context for code-mode callbacks and add spans for
  nested tool invocations in the runtime and dispatch broker.
- Propagate each tool invocation span as the parent of its streamed gRPC
  callback, falling back to the outer execution context when needed.
- Add a `codex.exec_server.process` span for each process lifetime, including
  its process ID and completion result, without retaining the request span.

GitOrigin-RevId: a6059e34d895416f5517e51dad6ca0078355adca

codex-rs/code-mode-runtime/src/service.rs

@@ -242,6 +242,17 @@ struct ProtocolDelegate {
 }
 
 impl runtime::SessionRuntimeDelegate for ProtocolDelegate {
+    #[tracing::instrument(
+        name = "code_mode.runtime.invoke_tool",
+        level = "info",
+        skip_all,
+        fields(
+            cell.id = %invocation.cell_id,
+            runtime_tool_call_id = invocation.runtime_tool_call_id.as_str(),
+            tool_name = invocation.tool_name.name.as_str(),
+            tool_namespace = invocation.tool_name.namespace.as_deref(),
+        )
+    )]
     async fn invoke_tool(
         &self,
         invocation: runtime::NestedToolCall,

codex-rs/code-mode-runtime/src/session_runtime/mod.rs

@@ -7,6 +7,7 @@ use std::sync::Arc;
 use std::sync::atomic::AtomicU64;
 use std::sync::atomic::Ordering;
 
+use opentelemetry::context::FutureExt;
 use serde_json::Value as JsonValue;
 use tokio::sync::Mutex;
 use tokio_util::sync::CancellationToken;
@@ -163,6 +164,7 @@ impl<D: SessionRuntimeDelegate> SessionRuntime<D> {
         let host = Arc::new(RuntimeCellHost {
             cell_id: cell_id.clone(),
             inner: Arc::clone(&self.inner),
+            execution_context: opentelemetry::Context::current(),
         });
         let mut cells = self.inner.cells.lock().await;
         if self.inner.shutdown_token.is_cancelled() {
@@ -235,6 +237,9 @@ impl PendingEvent {
 struct RuntimeCellHost<D: SessionRuntimeDelegate> {
     cell_id: CellId,
     inner: Arc<Inner<D>>,
+    // Callbacks outlive the initial request and run in separate tasks. Preserve
+    // their trace parent without retaining the request's tracing span.
+    execution_context: opentelemetry::Context,
 }
 
 impl<D: SessionRuntimeDelegate> CellHost for RuntimeCellHost<D> {
@@ -255,6 +260,7 @@ impl<D: SessionRuntimeDelegate> CellHost for RuntimeCellHost<D> {
                 },
                 cancellation_token,
             )
+            .with_context(self.execution_context.clone())
             .await
     }
 

codex-rs/code-mode-runtime/src/session_runtime/tests.rs

@@ -102,6 +102,7 @@ async fn termination_rejects_a_waiting_store_commit_before_the_next_cell_can_loa
     let host = RuntimeCellHost {
         cell_id: CellId::new("terminating-writer"),
         inner: Arc::clone(&runtime.inner),
+        execution_context: opentelemetry::Context::new(),
     };
     let completion = CellEvent::Completed {
         content_items: vec![OutputItem::Text {