Fix supervisor AI empty replies with fallback templates

Skip appending AI error strings to the session and use event-specific fallback commentary when the model returns empty content.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_hub_supervisor_lib.py

@@ -136,3 +136,25 @@ def test_normalize_supervisor_settings_env(monkeypatch):
     cfg = sup.normalize_supervisor_settings({})
     assert cfg["wechat_webhook"] == "https://example.com/hook"
     assert cfg["wechat_link_base"] == "https://hub.example/ai?mode=supervisor"
+
+
+def test_supervisor_fallback_reply_program_sl():
+    text = sup.build_supervisor_fallback_reply(
+        {
+            "event_type": sup.EVENT_PROGRAM_SL,
+            "symbol": "ZEC/USDT",
+            "pnl_amount": -0.9557,
+        }
+    )
+    assert "程序止损" in text
+    assert "AI 生成失败" not in text
+
+
+def test_supervisor_fallback_not_error_reply():
+    from hub_ai.text_util import is_ai_error_reply
+
+    text = sup.build_supervisor_fallback_reply(
+        {"event_type": sup.EVENT_MANUAL_CLOSE, "symbol": "ETH/USDT", "pnl_amount": -1}
+    )
+    assert text
+    assert not is_ai_error_reply(text)