fix(config): reset config-backed singletons on hot reload (#2588)

* Fix stale config singletons on reload

* fix(config): update checkpointer imports after runtime move

* Fix config reload singleton mutation on validation failure

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/tests/test_app_config_reload.py

@@ -4,10 +4,40 @@ import json
 import os
 from pathlib import Path
 
+import pytest
 import yaml
+from pydantic import ValidationError
 
-from deerflow.config.agents_api_config import get_agents_api_config
+import deerflow.config.app_config as app_config_module
+from deerflow.config.acp_config import load_acp_config_from_dict
+from deerflow.config.agents_api_config import get_agents_api_config, load_agents_api_config_from_dict
 from deerflow.config.app_config import AppConfig, get_app_config, reset_app_config
+from deerflow.config.checkpointer_config import get_checkpointer_config, load_checkpointer_config_from_dict
+from deerflow.config.guardrails_config import get_guardrails_config, load_guardrails_config_from_dict
+from deerflow.config.memory_config import get_memory_config, load_memory_config_from_dict
+from deerflow.config.stream_bridge_config import get_stream_bridge_config, load_stream_bridge_config_from_dict
+from deerflow.config.subagents_config import get_subagents_app_config, load_subagents_config_from_dict
+from deerflow.config.summarization_config import get_summarization_config, load_summarization_config_from_dict
+from deerflow.config.title_config import get_title_config, load_title_config_from_dict
+from deerflow.config.tool_search_config import get_tool_search_config, load_tool_search_config_from_dict
+from deerflow.runtime.checkpointer import get_checkpointer, reset_checkpointer
+from deerflow.runtime.store import get_store, reset_store
+
+
+def _reset_config_singletons() -> None:
+    load_title_config_from_dict({})
+    load_summarization_config_from_dict({})
+    load_memory_config_from_dict({})
+    load_agents_api_config_from_dict({})
+    load_subagents_config_from_dict({})
+    load_tool_search_config_from_dict({})
+    load_guardrails_config_from_dict({})
+    load_checkpointer_config_from_dict(None)
+    load_stream_bridge_config_from_dict(None)
+    load_acp_config_from_dict({})
+    reset_checkpointer()
+    reset_store()
+    reset_app_config()
 
 
 def _write_config(path: Path, *, model_name: str, supports_thinking: bool) -> None:
@@ -53,6 +83,23 @@ def _write_config_with_agents_api(
     path.write_text(yaml.safe_dump(config), encoding="utf-8")
 
 
+def _write_config_with_sections(path: Path, sections: dict | None = None) -> None:
+    config = {
+        "sandbox": {"use": "deerflow.sandbox.local:LocalSandboxProvider"},
+        "models": [
+            {
+                "name": "first-model",
+                "use": "langchain_openai:ChatOpenAI",
+                "model": "gpt-test",
+            }
+        ],
+    }
+    if sections:
+        config.update(sections)
+
+    path.write_text(yaml.safe_dump(config), encoding="utf-8")
+
+
 def _write_extensions_config(path: Path) -> None:
     path.write_text(json.dumps({"mcpServers": {}, "skills": {}}), encoding="utf-8")
 
@@ -175,3 +222,168 @@ def test_get_app_config_resets_agents_api_config_when_section_removed(tmp_path,
         assert get_agents_api_config().enabled is False
     finally:
         reset_app_config()
+
+
+def test_get_app_config_resets_singleton_configs_when_sections_removed(tmp_path, monkeypatch):
+    config_path = tmp_path / "config.yaml"
+    extensions_path = tmp_path / "extensions_config.json"
+    _write_extensions_config(extensions_path)
+    _write_config_with_sections(
+        config_path,
+        {
+            "title": {"enabled": False, "max_words": 3},
+            "summarization": {"enabled": True},
+            "memory": {"enabled": False, "max_facts": 50},
+            "subagents": {"timeout_seconds": 42, "agents": {"reviewer": {"max_turns": 2}}},
+            "tool_search": {"enabled": True},
+            "guardrails": {"enabled": True, "fail_closed": False},
+            "checkpointer": {"type": "memory"},
+            "stream_bridge": {"type": "memory", "queue_maxsize": 12},
+        },
+    )
+
+    monkeypatch.setenv("DEER_FLOW_CONFIG_PATH", str(config_path))
+    monkeypatch.setenv("DEER_FLOW_EXTENSIONS_CONFIG_PATH", str(extensions_path))
+    reset_app_config()
+
+    try:
+        get_app_config()
+        assert get_title_config().enabled is False
+        assert get_summarization_config().enabled is True
+        assert get_memory_config().enabled is False
+        assert get_subagents_app_config().timeout_seconds == 42
+        assert get_tool_search_config().enabled is True
+        assert get_guardrails_config().enabled is True
+        assert get_checkpointer_config() is not None
+        assert get_stream_bridge_config() is not None
+
+        _write_config_with_sections(config_path)
+        next_mtime = config_path.stat().st_mtime + 5
+        os.utime(config_path, (next_mtime, next_mtime))
+
+        get_app_config()
+        assert get_title_config().enabled is True
+        assert get_summarization_config().enabled is False
+        assert get_memory_config().enabled is True
+        assert get_subagents_app_config().timeout_seconds == 900
+        assert get_tool_search_config().enabled is False
+        assert get_guardrails_config().enabled is False
+        assert get_checkpointer_config() is None
+        assert get_stream_bridge_config() is None
+    finally:
+        _reset_config_singletons()
+
+
+def test_get_app_config_resets_persistence_runtime_singletons_when_checkpointer_removed(tmp_path, monkeypatch):
+    config_path = tmp_path / "config.yaml"
+    extensions_path = tmp_path / "extensions_config.json"
+    _write_extensions_config(extensions_path)
+    _write_config_with_sections(config_path, {"checkpointer": {"type": "memory"}})
+
+    monkeypatch.setenv("DEER_FLOW_CONFIG_PATH", str(config_path))
+    monkeypatch.setenv("DEER_FLOW_EXTENSIONS_CONFIG_PATH", str(extensions_path))
+    reset_checkpointer()
+    reset_store()
+    reset_app_config()
+
+    try:
+        get_app_config()
+        initial_checkpointer = get_checkpointer()
+        initial_store = get_store()
+
+        _write_config_with_sections(config_path)
+        next_mtime = config_path.stat().st_mtime + 5
+        os.utime(config_path, (next_mtime, next_mtime))
+
+        get_app_config()
+
+        assert get_checkpointer_config() is None
+        assert get_checkpointer() is not initial_checkpointer
+        assert get_store() is not initial_store
+    finally:
+        _reset_config_singletons()
+
+
+def test_get_app_config_keeps_persistence_runtime_singletons_when_checkpointer_unchanged(tmp_path, monkeypatch):
+    config_path = tmp_path / "config.yaml"
+    extensions_path = tmp_path / "extensions_config.json"
+    _write_extensions_config(extensions_path)
+    _write_config_with_sections(
+        config_path,
+        {
+            "title": {"enabled": False},
+            "checkpointer": {"type": "memory"},
+        },
+    )
+
+    monkeypatch.setenv("DEER_FLOW_CONFIG_PATH", str(config_path))
+    monkeypatch.setenv("DEER_FLOW_EXTENSIONS_CONFIG_PATH", str(extensions_path))
+    _reset_config_singletons()
+
+    try:
+        get_app_config()
+        initial_checkpointer = get_checkpointer()
+        initial_store = get_store()
+
+        _write_config_with_sections(
+            config_path,
+            {
+                "title": {"enabled": True},
+                "checkpointer": {"type": "memory"},
+            },
+        )
+        next_mtime = config_path.stat().st_mtime + 5
+        os.utime(config_path, (next_mtime, next_mtime))
+
+        get_app_config()
+
+        assert get_checkpointer() is initial_checkpointer
+        assert get_store() is initial_store
+    finally:
+        _reset_config_singletons()
+
+
+def test_get_app_config_does_not_mutate_singletons_when_reload_validation_fails(tmp_path, monkeypatch):
+    config_path = tmp_path / "config.yaml"
+    extensions_path = tmp_path / "extensions_config.json"
+    _write_extensions_config(extensions_path)
+    _write_config_with_sections(
+        config_path,
+        {
+            "title": {"enabled": False},
+            "tool_search": {"enabled": True},
+            "checkpointer": {"type": "memory"},
+        },
+    )
+
+    monkeypatch.setenv("DEER_FLOW_CONFIG_PATH", str(config_path))
+    monkeypatch.setenv("DEER_FLOW_EXTENSIONS_CONFIG_PATH", str(extensions_path))
+    _reset_config_singletons()
+
+    try:
+        previous_app_config = get_app_config()
+        initial_checkpointer = get_checkpointer()
+        initial_store = get_store()
+
+        _write_config_with_sections(
+            config_path,
+            {
+                "title": False,
+                "tool_search": False,
+                "checkpointer": {"type": "memory"},
+            },
+        )
+        next_mtime = config_path.stat().st_mtime + 5
+        os.utime(config_path, (next_mtime, next_mtime))
+
+        with pytest.raises(ValidationError):
+            get_app_config()
+
+        assert app_config_module._app_config is previous_app_config
+        assert get_title_config().enabled is False
+        assert get_tool_search_config().enabled is True
+        assert get_checkpointer_config() is not None
+        assert get_checkpointer() is initial_checkpointer
+        assert get_store() is initial_store
+    finally:
+        _reset_config_singletons()