fix(config): reload AppConfig when config path or mtime changes (#1239)

* fix(config): reload AppConfig when config path or mtime changes

- Track resolved path + mtime; invalidate cache on change
- Preserve set_app_config() injection behavior
- Add regression tests (test_app_config_reload.py)
- Document behavior in README and backend/CLAUDE.md

Signed-off-by: Gao Mingfei <g199209@gmail.com>

* Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Signed-off-by: Gao Mingfei <g199209@gmail.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

README.md

@@ -160,6 +160,7 @@ make docker-start   # Start services (auto-detects sandbox mode from config.yaml
 ```
 
 `make docker-start` starts `provisioner` only when `config.yaml` uses provisioner mode (`sandbox.use: deerflow.community.aio_sandbox:AioSandboxProvider` with `provisioner_url`).
+Backend processes automatically pick up `config.yaml` changes on the next config access, so model metadata updates do not require a manual restart during development.
 
 **Production** (builds images locally, mounts runtime config and data):
 

backend/CLAUDE.md

@@ -172,6 +172,8 @@ Setup: Copy `config.example.yaml` to `config.yaml` in the **project root** direc
 
 **Config Versioning**: `config.example.yaml` has a `config_version` field. On startup, `AppConfig.from_file()` compares user version vs example version and emits a warning if outdated. Missing `config_version` = version 0. Run `make config-upgrade` to auto-merge missing fields. When changing the config schema, bump `config_version` in `config.example.yaml`.
 
+**Config Caching**: `get_app_config()` caches the parsed config, but automatically reloads it when the resolved config path changes or the file's mtime increases. This keeps Gateway and LangGraph reads aligned with `config.yaml` edits without requiring a manual process restart.
+
 Configuration priority:
 1. Explicit `config_path` argument
 2. `DEER_FLOW_CONFIG_PATH` environment variable

backend/packages/harness/deerflow/config/app_config.py

@@ -224,17 +224,65 @@ class AppConfig(BaseModel):
 
 
 _app_config: AppConfig | None = None
+_app_config_path: Path | None = None
+_app_config_mtime: float | None = None
+_app_config_is_custom = False
+
+
+def _get_config_mtime(config_path: Path) -> float | None:
+    """Get the modification time of a config file if it exists."""
+    try:
+        return config_path.stat().st_mtime
+    except OSError:
+        return None
+
+
+def _load_and_cache_app_config(config_path: str | None = None) -> AppConfig:
+    """Load config from disk and refresh cache metadata."""
+    global _app_config, _app_config_path, _app_config_mtime, _app_config_is_custom
+
+    resolved_path = AppConfig.resolve_config_path(config_path)
+    _app_config = AppConfig.from_file(str(resolved_path))
+    _app_config_path = resolved_path
+    _app_config_mtime = _get_config_mtime(resolved_path)
+    _app_config_is_custom = False
+    return _app_config
 
 
 def get_app_config() -> AppConfig:
     """Get the DeerFlow config instance.
 
-    Returns a cached singleton instance. Use `reload_app_config()` to reload
-    from file, or `reset_app_config()` to clear the cache.
+    Returns a cached singleton instance and automatically reloads it when the
+    underlying config file path or modification time changes. Use
+    `reload_app_config()` to force a reload, or `reset_app_config()` to clear
+    the cache.
     """
-    global _app_config
-    if _app_config is None:
-        _app_config = AppConfig.from_file()
+    global _app_config, _app_config_path, _app_config_mtime
+
+    if _app_config is not None and _app_config_is_custom:
+        return _app_config
+
+    resolved_path = AppConfig.resolve_config_path()
+    current_mtime = _get_config_mtime(resolved_path)
+
+    should_reload = (
+        _app_config is None
+        or _app_config_path != resolved_path
+        or _app_config_mtime != current_mtime
+    )
+    if should_reload:
+        if (
+            _app_config_path == resolved_path
+            and _app_config_mtime is not None
+            and current_mtime is not None
+            and _app_config_mtime != current_mtime
+        ):
+            logger.info(
+                "Config file has been modified (mtime: %s -> %s), reloading AppConfig",
+                _app_config_mtime,
+                current_mtime,
+            )
+        _load_and_cache_app_config(str(resolved_path))
     return _app_config
 
 
@@ -251,9 +299,7 @@ def reload_app_config(config_path: str | None = None) -> AppConfig:
     Returns:
         The newly loaded AppConfig instance.
     """
-    global _app_config
-    _app_config = AppConfig.from_file(config_path)
-    return _app_config
+    return _load_and_cache_app_config(config_path)
 
 
 def reset_app_config() -> None:
@@ -263,8 +309,11 @@ def reset_app_config() -> None:
     `get_app_config()` to reload from file. Useful for testing
     or when switching between different configurations.
     """
-    global _app_config
+    global _app_config, _app_config_path, _app_config_mtime, _app_config_is_custom
     _app_config = None
+    _app_config_path = None
+    _app_config_mtime = None
+    _app_config_is_custom = False
 
 
 def set_app_config(config: AppConfig) -> None:
@@ -275,5 +324,8 @@ def set_app_config(config: AppConfig) -> None:
     Args:
         config: The AppConfig instance to use.
     """
-    global _app_config
+    global _app_config, _app_config_path, _app_config_mtime, _app_config_is_custom
     _app_config = config
+    _app_config_path = None
+    _app_config_mtime = None
+    _app_config_is_custom = True

backend/tests/test_app_config_reload.py

@@ -0,0 +1,81 @@
+from __future__ import annotations
+
+import json
+import os
+from pathlib import Path
+
+import yaml
+
+from deerflow.config.app_config import get_app_config, reset_app_config
+
+
+def _write_config(path: Path, *, model_name: str, supports_thinking: bool) -> None:
+    path.write_text(
+        yaml.safe_dump(
+            {
+                "sandbox": {"use": "deerflow.sandbox.local:LocalSandboxProvider"},
+                "models": [
+                    {
+                        "name": model_name,
+                        "use": "langchain_openai:ChatOpenAI",
+                        "model": "gpt-test",
+                        "supports_thinking": supports_thinking,
+                    }
+                ],
+            }
+        ),
+        encoding="utf-8",
+    )
+
+
+def _write_extensions_config(path: Path) -> None:
+    path.write_text(json.dumps({"mcpServers": {}, "skills": {}}), encoding="utf-8")
+
+
+def test_get_app_config_reloads_when_file_changes(tmp_path, monkeypatch):
+    config_path = tmp_path / "config.yaml"
+    extensions_path = tmp_path / "extensions_config.json"
+    _write_extensions_config(extensions_path)
+    _write_config(config_path, model_name="first-model", supports_thinking=False)
+
+    monkeypatch.setenv("DEER_FLOW_CONFIG_PATH", str(config_path))
+    monkeypatch.setenv("DEER_FLOW_EXTENSIONS_CONFIG_PATH", str(extensions_path))
+    reset_app_config()
+
+    try:
+        initial = get_app_config()
+        assert initial.models[0].supports_thinking is False
+
+        _write_config(config_path, model_name="first-model", supports_thinking=True)
+        next_mtime = config_path.stat().st_mtime + 5
+        os.utime(config_path, (next_mtime, next_mtime))
+
+        reloaded = get_app_config()
+        assert reloaded.models[0].supports_thinking is True
+        assert reloaded is not initial
+    finally:
+        reset_app_config()
+
+
+def test_get_app_config_reloads_when_config_path_changes(tmp_path, monkeypatch):
+    config_a = tmp_path / "config-a.yaml"
+    config_b = tmp_path / "config-b.yaml"
+    extensions_path = tmp_path / "extensions_config.json"
+    _write_extensions_config(extensions_path)
+    _write_config(config_a, model_name="model-a", supports_thinking=False)
+    _write_config(config_b, model_name="model-b", supports_thinking=True)
+
+    monkeypatch.setenv("DEER_FLOW_EXTENSIONS_CONFIG_PATH", str(extensions_path))
+    monkeypatch.setenv("DEER_FLOW_CONFIG_PATH", str(config_a))
+    reset_app_config()
+
+    try:
+        first = get_app_config()
+        assert first.models[0].name == "model-a"
+
+        monkeypatch.setenv("DEER_FLOW_CONFIG_PATH", str(config_b))
+        second = get_app_config()
+        assert second.models[0].name == "model-b"
+        assert second is not first
+    finally:
+        reset_app_config()