Implement approval engine production readiness

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a05e2e-805b-7042-a750-71f473bceea2

tests/test_outbox.py

@@ -82,3 +82,19 @@ def test_failed_outbox_rolls_back_consume(engine):
         pass
     assert engine.get(obj.id).status == "approved"
     assert all(item["class"] != "use" for item in engine.undrained())
+
+
+def test_drain_failure_records_bounded_attempt_state(engine):
+    approve(engine)
+
+    class SensitiveFailure(Exception):
+        pass
+
+    result = engine.drain(lambda _payload: (_ for _ in ()).throw(SensitiveFailure("secret")))
+    assert result["failed"] == 1
+    pending = engine.undrained()
+    assert pending[0]["attempts"] == 1
+    assert pending[0]["last_error"] == "SensitiveFailure"
+    stats = engine.outbox_stats()
+    assert stats["failed_pending"] == 1
+    assert stats["attempts"] == 1