fix: handle bytes output when commands time out

backend/app/main.py

@@ -68,8 +68,10 @@ def run(cmd: list[str], cwd: Path, timeout: int = 120) -> tuple[int, str]:
         )
         return proc.returncode, proc.stdout
     except subprocess.TimeoutExpired as exc:
-        out = (exc.stdout or "") + "\n[command timed out]"
-        return 124, out
+        out = exc.stdout or ""
+        if isinstance(out, bytes):
+            out = out.decode(errors="replace")
+        return 124, f"{out}\n[command timed out]"
 
 
 def safe_repo_name(url: str) -> str:

backend/tests/test_main.py

@@ -1,5 +1,6 @@
 import asyncio
 import os
+import subprocess
 import tempfile
 import unittest
 from pathlib import Path
@@ -14,6 +15,7 @@
     github_headers,
     health,
     parse_json_object,
+    run,
     safe_branch_name,
     safe_repo_name,
     workspace_repo,
@@ -138,6 +140,18 @@ def test_run_request_rejects_invalid_iteration_count(self) -> None:
                 max_iterations=0,
             )
 
+    def test_run_handles_bytes_output_from_timeout(self) -> None:
+        timeout = subprocess.TimeoutExpired(
+            cmd=["python", "-m", "pytest"],
+            timeout=1,
+            output=b"partial output",
+        )
+        with patch("app.main.subprocess.run", side_effect=timeout):
+            code, output = run(["python", "-m", "pytest"], Path("."), timeout=1)
+
+        self.assertEqual(code, 124)
+        self.assertEqual(output, "partial output\n[command timed out]")
+
     def test_health_contract(self) -> None:
         self.assertEqual(
             asyncio.run(health()),