diff --git a/app/main.js b/app/main.js
index d87f06a..0687011 100644
--- a/app/main.js
+++ b/app/main.js
@@ -215,8 +215,6 @@ function runCodex(model, prompt) {
       output.append(Buffer.from(`Codex execution timed out after ${timeoutMs} ms.\n`));
     }, timeoutMs);
 
-    child.stderr.pipe(process.stdout);
-
     child.stdout.on("data", (chunk) => {
       output.append(chunk);
     });
@@ -239,14 +237,11 @@ function runCodex(model, prompt) {
         output.append(Buffer.from(`Codex process terminated by signal ${signal}.\n`));
       }
 
-      let lastMessage = "";
-      try {
-        lastMessage = fs.readFileSync(lastMessageFile, "utf8");
-      } catch {
-        lastMessage = "";
-      }
+      const lastMessage = fs.existsSync(lastMessageFile) ? fs.readFileSync(lastMessageFile, "utf8") : null;
+      const diagnosticOutput = output.toString();
+      const resultOutput = code === 0 && lastMessage !== null ? lastMessage : diagnosticOutput || lastMessage || "";
 
-      resolve({ status: code ?? 1, output: lastMessage || output.toString() });
+      resolve({ status: code ?? 1, output: resultOutput });
     });
   });
 }
diff --git a/tests/entrypoint_test.sh b/tests/entrypoint_test.sh
index 97155ee..613d43a 100755
--- a/tests/entrypoint_test.sh
+++ b/tests/entrypoint_test.sh
@@ -70,7 +70,7 @@ while [ "$#" -gt 0 ]; do
   shift
 done
 
-printf '%s\n' 'codex' 'final answer' 'tokens used' '123' 'final answer'
+printf '%s\n' 'codex' 'final answer' 'tokens used' '123' 'final answer' >&2
 printf '%s\n' 'final answer' > "$last_message_file"
 SH
   chmod +x "$dir/codex"