Flaky CI fix (#1647)

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

codex-rs/exec/src/event_processor.rs

@@ -1,15 +1,23 @@
+use std::path::Path;
+
 use codex_common::summarize_sandbox_policy;
 use codex_core::WireApi;
 use codex_core::config::Config;
 use codex_core::model_supports_reasoning_summaries;
 use codex_core::protocol::Event;
 
+pub(crate) enum CodexStatus {
+    Running,
+    InitiateShutdown,
+    Shutdown,
+}
+
 pub(crate) trait EventProcessor {
     /// Print summary of effective configuration and user prompt.
     fn print_config_summary(&mut self, config: &Config, prompt: &str);
 
     /// Handle a single event emitted by the agent.
-    fn process_event(&mut self, event: Event);
+    fn process_event(&mut self, event: Event) -> CodexStatus;
 }
 
 pub(crate) fn create_config_summary_entries(config: &Config) -> Vec<(&'static str, String)> {
@@ -35,3 +43,28 @@ pub(crate) fn create_config_summary_entries(config: &Config) -> Vec<(&'static st
 
     entries
 }
+
+pub(crate) fn handle_last_message(
+    last_agent_message: Option<&str>,
+    last_message_path: Option<&Path>,
+) {
+    match (last_message_path, last_agent_message) {
+        (Some(path), Some(msg)) => write_last_message_file(msg, Some(path)),
+        (Some(path), None) => {
+            write_last_message_file("", Some(path));
+            eprintln!(
+                "Warning: no last agent message; wrote empty content to {}",
+                path.display()
+            );
+        }
+        (None, _) => eprintln!("Warning: no file to write last message to."),
+    }
+}
+
+fn write_last_message_file(contents: &str, last_message_path: Option<&Path>) {
+    if let Some(path) = last_message_path {
+        if let Err(e) = std::fs::write(path, contents) {
+            eprintln!("Failed to write last message file {path:?}: {e}");
+        }
+    }
+}