Allow execution history in fallback isolation test

Why: execution history intentionally adds one source-external Git metadata path after every run

Evidence: focused fallback and history tests

Impact: preserves the no-canonical-implementation assertion while accepting the history record

Refs: feature/goal-first-delivery

tests/test_agent_exec.py

@@ -391,8 +391,15 @@ class AgentExecControllerTests(unittest.TestCase):
         self.assertTrue(all(a["terminal_status"] == "unavailable" for a in data["attempts"]))
         self.assertEqual(data.get("host_fallback_authorizations"), 1)
         # Controller must not implement the unit itself.
-        after = list(self.repo.rglob("*"))
+        history_root = self.repo / ".git" / "agent-exec"
+        after = [
+            path
+            for path in self.repo.rglob("*")
+            if path != history_root and history_root not in path.parents
+        ]
         self.assertEqual(before, after)
+        self.assertEqual(data["history"]["status"], "recorded")
+        self.assertTrue((history_root / "execution-history.jsonl").is_file())
         self.assertFalse((self.repo / "src" / "marker.txt").exists())
         self.assertIn("allowed_paths", data["host_scope"])
         self._assert_canonical_untouched()