Flaky CI fix (#1647)

Flushing before sending `TaskCompleteEvent` and ending the submission
loop to avoid race conditions.

codex-rs/exec/src/event_processor_with_json_output.rs

@@ -1,18 +1,24 @@
 use std::collections::HashMap;
+use std::path::PathBuf;
 
 use codex_core::config::Config;
 use codex_core::protocol::Event;
 use codex_core::protocol::EventMsg;
+use codex_core::protocol::TaskCompleteEvent;
 use serde_json::json;
 
+use crate::event_processor::CodexStatus;
 use crate::event_processor::EventProcessor;
 use crate::event_processor::create_config_summary_entries;
+use crate::event_processor::handle_last_message;
 
-pub(crate) struct EventProcessorWithJsonOutput;
+pub(crate) struct EventProcessorWithJsonOutput {
+    last_message_path: Option<PathBuf>,
+}
 
 impl EventProcessorWithJsonOutput {
-    pub fn new() -> Self {
-        Self {}
+    pub fn new(last_message_path: Option<PathBuf>) -> Self {
+        Self { last_message_path }
     }
 }
 
@@ -33,15 +39,25 @@ impl EventProcessor for EventProcessorWithJsonOutput {
         println!("{prompt_json}");
     }
 
-    fn process_event(&mut self, event: Event) {
+    fn process_event(&mut self, event: Event) -> CodexStatus {
         match event.msg {
             EventMsg::AgentMessageDelta(_) | EventMsg::AgentReasoningDelta(_) => {
                 // Suppress streaming events in JSON mode.
+                CodexStatus::Running
             }
+            EventMsg::TaskComplete(TaskCompleteEvent { last_agent_message }) => {
+                handle_last_message(
+                    last_agent_message.as_deref(),
+                    self.last_message_path.as_deref(),
+                );
+                CodexStatus::InitiateShutdown
+            }
+            EventMsg::ShutdownComplete => CodexStatus::Shutdown,
             _ => {
                 if let Ok(line) = serde_json::to_string(&event) {
                     println!("{line}");
                 }
+                CodexStatus::Running
             }
         }
     }