fix(config): sync _memory_config with AppConfig auto-reload (#4208)

* fix(config): sync _memory_config with AppConfig auto-reload

get_memory_config() now calls get_app_config() before returning the
cached _memory_config singleton. get_app_config() auto-reloads when
the config file signature changes, and its _apply_singleton_configs()
calls load_memory_config_from_dict() to populate _memory_config.
Without this side effect, changing memory.mode in config.yaml (e.g.
from "middleware" to "tool") would never take effect at runtime
because _memory_config retained the stale value.

Only call get_app_config() when _app_config has already been loaded
to avoid picking up a config file as a side effect of the first
access to get_memory_config(), which would break callers that expect
module-level defaults (e.g. unit tests). Catch FileNotFoundError for
environments without a config file.

Closes #4204.

* fix(memory): broaden config-reload guard and add isolated-path tests

Addresses two review findings from willem-bd:

1. Broken-config crash risk: broaden the except from FileNotFoundError
   to Exception so transiently broken config.yaml (YAMLError,
   ValidationError, ValueError) falls back to the last-good singleton
   instead of crashing per-turn hot paths (memory_middleware,
   summarization_hook, lead_agent/prompt.py).

2. Missing regression test: add test_get_memory_config_self_syncs_...
   (calls get_memory_config() after file mutation with no intervening
   get_app_config() call) and test_get_memory_config_falls_back_on_...
   (verifies broken config does not crash, returns cached value).

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

@@ -121,7 +121,36 @@ _memory_config: MemoryConfig = MemoryConfig()
 
 
 def get_memory_config() -> MemoryConfig:
-    """Get the current memory configuration."""
+    """Get the current memory configuration.
+
+    ``_memory_config`` is only refreshed as a side effect of ``get_app_config()``
+    reloading (via ``_apply_singleton_configs`` -> ``load_memory_config_from_dict``).
+    A reader that reaches memory config without going through ``get_app_config()``
+    first -- e.g. the agent factory deciding whether to bind the memory tools --
+    would otherwise see a stale ``memory.mode`` after a ``config.yaml`` edit, even
+    though ``memory.*`` is documented as hot-reloadable. Trigger the same
+    signature-checked reload here so the singleton follows the config file.
+
+    If ``get_app_config()`` has never been called (``_app_config`` is ``None``),
+    there is no stale config to refresh, so we keep the pre-existing behaviour
+    of returning the in-memory singleton.  This avoids picking up a config file
+    as a side effect of the first access to ``get_memory_config()``, which would
+    break callers that expect module-level defaults (e.g. unit tests).
+    """
+    # Lazy import: app_config imports this module, so a top-level import cycles.
+    from .app_config import _app_config, get_app_config
+
+    if _app_config is not None:
+        try:
+            get_app_config()
+        except Exception:
+            # If the config file is transiently broken (invalid YAML, schema
+            # violation, missing env var, etc.), keep the last-good singleton
+            # so an in-flight turn completes normally instead of crashing.
+            logger.warning(
+                "Failed to reload app config from get_memory_config(); falling back to cached memory config.",
+                exc_info=True,
+            )
     return _memory_config
 
 

backend/tests/test_app_config_reload.py

@@ -611,3 +611,63 @@ def test_get_app_config_does_not_mutate_singletons_when_reload_validation_fails(
         assert get_store() is initial_store
     finally:
         _reset_config_singletons()
+
+
+def test_get_memory_config_self_syncs_without_prior_get_app_config(tmp_path, monkeypatch):
+    """get_memory_config() triggers reload when file changes without prior get_app_config().
+
+    Background memory paths (updater/queue/storage) never call get_app_config()
+    directly.  This test pins the fix: calling get_memory_config() in isolation
+    — after mutating the file, with no intervening get_app_config() — reflects
+    the new value.
+    """
+    config_path = tmp_path / "config.yaml"
+    extensions_path = tmp_path / "extensions_config.json"
+    _write_extensions_config(extensions_path)
+
+    _write_config_with_sections(config_path, {"memory": {"enabled": False}})
+
+    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_memory_config().enabled is False
+
+        _write_config_with_sections(config_path, {"memory": {"enabled": True}})
+        next_mtime = config_path.stat().st_mtime + 5
+        os.utime(config_path, (next_mtime, next_mtime))
+
+        assert get_memory_config().enabled is True
+    finally:
+        _reset_config_singletons()
+
+
+def test_get_memory_config_falls_back_on_broken_config(tmp_path, monkeypatch):
+    """get_memory_config() does not crash on transiently broken config.yaml.
+
+    get_app_config() can raise yaml.YAMLError, ValidationError, or ValueError.
+    get_memory_config() catches them and returns the last-good singleton.
+    """
+    config_path = tmp_path / "config.yaml"
+    extensions_path = tmp_path / "extensions_config.json"
+    _write_extensions_config(extensions_path)
+
+    _write_config_with_sections(config_path, {"memory": {"enabled": False}})
+
+    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_memory_config().enabled is False
+
+        config_path.write_text("memory: {enabled: true\n")
+        next_mtime = config_path.stat().st_mtime + 5
+        os.utime(config_path, (next_mtime, next_mtime))
+
+        assert get_memory_config().enabled is False
+    finally:
+        _reset_config_singletons()