entrypoint override passes only the script path

With --entrypoint python3, our 'python /work/main.py' runner became
interpreter args: python3 tried to open a FILE named 'python'
("can't open file '/app/python'"). When an entrypoint is set it IS
the interpreter -- pass just /work/<entry>.

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

evalharness/sandbox/docker.py

@@ -91,13 +91,17 @@ class DockerSandbox(Sandbox):
                     out_host = Path(hpath).expanduser()
                     out_host.mkdir(parents=True, exist_ok=True)
                     cmd += ['-v', f'{out_host}:{cpath}:rw']
-            runner = ['python', f'/work/{entry}'] if entry.endswith('.py') \
-                else ['sh', f'/work/{entry}']
             if entrypoint:
                 # images with an official-evaluator ENTRYPOINT (bigcodebench:
                 # python3 -m bigcodebench.evaluate) swallow our runner as
-                # CLI args -> override it so main.py actually executes
+                # CLI args -> override it. The entrypoint IS the interpreter
+                # now: pass only the script path, else 'python3 python
+                # /work/main.py' tries to open a file named 'python'
                 cmd += ['--entrypoint', entrypoint]
+                runner = [f'/work/{entry}']
+            else:
+                runner = ['python', f'/work/{entry}'] if entry.endswith('.py') \
+                    else ['sh', f'/work/{entry}']
             # Named + retried runs. A timed-out/killed `docker run` only kills
             # the CLI client -- the container lives on (--rm fires on EXIT)
             # and leaked containers slowly drown the daemon; the name gives