diff --git a/evalharness/agent/envs/swe_agentic.py b/evalharness/agent/envs/swe_agentic.py
index c1f18cb..cbd78c1 100644
--- a/evalharness/agent/envs/swe_agentic.py
+++ b/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',