send-aggregated output (#2364)

We want to send an aggregated output of stderr and stdout so we don't
have to aggregate it stderr+stdout as we lose order sometimes.

---------

Co-authored-by: Gabriel Peal <gpeal@users.noreply.github.com>

codex-rs/exec/src/event_processor_with_human_output.rs

@@ -287,8 +287,7 @@ impl EventProcessor for EventProcessorWithHumanOutput {
             EventMsg::ExecCommandOutputDelta(_) => {}
             EventMsg::ExecCommandEnd(ExecCommandEndEvent {
                 call_id,
-                stdout,
-                stderr,
+                aggregated_output,
                 duration,
                 exit_code,
                 ..
@@ -304,8 +303,7 @@ impl EventProcessor for EventProcessorWithHumanOutput {
                     ("".to_string(), format!("exec('{call_id}')"))
                 };
 
-                let output = if exit_code == 0 { stdout } else { stderr };
-                let truncated_output = output
+                let truncated_output = aggregated_output
                     .lines()
                     .take(MAX_OUTPUT_LINES_FOR_EXEC_TOOL_CALL)
                     .collect::<Vec<_>>()