Stabilize cancellation and tracing tests (#58171)

## Why

The SIGTERM cleanup test depends on the OS scheduling the shell within the production grace period. Tracing tests also need fixture creation and cleanup to use the appropriate subscriber.

## What changed

- Pause Tokio time while waiting for the shell's cleanup marker, keeping the cancellation future runnable to prevent automatic clock advancement, then resume time after execution.
- Adjust subscriber setup and fixture lifetimes in session and tool dispatch tests so instrumented resources are created and dropped under the appropriate subscriber.

GitOrigin-RevId: 12c654a031a8a4e61fc66488a5f687852f5ca099

codex-rs/core/src/tools/parallel.rs

@@ -767,6 +767,17 @@ mod tests {
         dynamic: bool,
         critical_path_timing: bool,
     ) -> anyhow::Result<()> {
+        // Create and drop instrumented session resources under the same subscriber.
+        // A prior traced test may have installed a different global subscriber.
+        let buffer: &'static std::sync::Mutex<Vec<u8>> =
+            Box::leak(Box::new(std::sync::Mutex::new(Vec::new())));
+        let subscriber = tracing_subscriber::fmt()
+            .with_ansi(false)
+            .with_max_level(tracing::Level::INFO)
+            .with_writer(MockWriter::new(buffer))
+            .finish();
+        let _subscriber_guard = tracing::subscriber::set_default(subscriber);
+
         let (session, mut turn_context) = crate::session::tests::make_session_and_context().await;
         Arc::make_mut(&mut turn_context.config)
             .features
@@ -832,15 +843,6 @@ mod tests {
                 .expect("test should release the execution gate");
         });
 
-        let buffer: &'static std::sync::Mutex<Vec<u8>> =
-            Box::leak(Box::new(std::sync::Mutex::new(Vec::new())));
-        let subscriber = tracing_subscriber::fmt()
-            .with_ansi(false)
-            .with_max_level(tracing::Level::INFO)
-            .with_writer(MockWriter::new(buffer))
-            .finish();
-        let _subscriber_guard = tracing::subscriber::set_default(subscriber);
-
         let cancellation_token = CancellationToken::new();
         let call = ToolCall {
             tool_name,

codex-rs/core/src/tools/parallel_trace_tests.rs

@@ -61,8 +61,10 @@ async fn spawned_dispatch_preserves_caller_context(level: LevelFilter) -> anyhow
         tracing::Dispatch::new(tracing::subscriber::NoSubscriber::default());
     let _subscriber_guard = tracing::subscriber::set_default(subscriber);
     async {
+        // Retain the fixture until its ambient subscriber is restored.
         // The unknown-tool result still crosses the real spawned dispatch boundary.
         runtime
+            .clone()
             .handle_tool_call(
                 ToolCall {
                     tool_name: codex_tools::ToolName::plain("unknown_tool"),