swe_agentic: ensure per-instance image before docker run

docker run's implicit pull prints nothing and the 120s start timeout
kills runs on slow mirrors; ensure_image brings the progress display,
mirror chain and watchdog to per-instance pulls (each sample = its own
image, 10 samples = 10 pulls).

Co-Authored-By: Claude <noreply@anthropic.com>

evalharness/agent/envs/swe_agentic.py

@@ -118,6 +118,15 @@ class SWEAgenticEnvironment(Environment):
 
     # ---- container lifecycle ----
     def _start(self, image: str) -> str:
+        # per-instance image: ensure (local check -> mirror-chain pull with
+        # progress) BEFORE docker run -- `docker run` auto-pulls with zero
+        # output and its 120s timeout kills runs on slow mirrors
+        from ...sandbox.docker import ensure_image
+
+        try:
+            ensure_image(image)
+        except RuntimeError as e:
+            raise RuntimeError(f'image {image} unavailable: {str(e)[:150]}')
         name = f'eh-swe-{uuid.uuid4().hex[:10]}'
         r = _docker(['run', '-d', '--name', name,
                      '-w', '/testbed',