fix: replace mutable default arguments in Config.__init__ with None sentinels

Fixes #130 — default provider instances (StorageDefault, NotifyDefault, etc.)
were evaluated once at class definition time and shared across all Config()
calls. Any mutation to a default provider on one instance would bleed into
every subsequent Config() that relied on the default.

Replace each default with None and instantiate fresh providers inside __init__,
matching the standard Python pattern for mutable defaults.

Author: Austin Varga

dotflow/core/config.py

@@ -61,17 +61,19 @@ class Config:
 
     def __init__(
         self,
-        storage: Storage | None = StorageDefault(),
-        notify: Notify | None = NotifyDefault(),
-        log: Log | None = LogDefault(),
-        api: Api | None = ApiDefault(),
-        scheduler: Scheduler | None = SchedulerDefault(),
+        storage: Storage | None = None,
+        notify: Notify | None = None,
+        log: Log | None = None,
+        api: Api | None = None,
+        scheduler: Scheduler | None = None,
     ) -> None:
-        self.storage = storage
-        self.notify = notify
-        self.log = log
-        self.api = api
-        self.scheduler = scheduler
+        self.storage = storage if storage is not None else StorageDefault()
+        self.notify = notify if notify is not None else NotifyDefault()
+        self.log = log if log is not None else LogDefault()
+        self.api = api if api is not None else ApiDefault()
+        self.scheduler = (
+            scheduler if scheduler is not None else SchedulerDefault()
+        )
 
         self._validate()
 

tests/core/test_config.py

@@ -68,3 +68,18 @@ def test_custom_scheduler(self):
         config = Config(scheduler=scheduler)
 
         self.assertIs(config.scheduler, scheduler)
+
+    def test_default_providers_are_not_shared_between_instances(self):
+        config_a = Config()
+        config_b = Config()
+
+        self.assertIsNot(
+            config_a.storage,
+            config_b.storage,
+            "Each Config() call must produce a fresh StorageDefault instance",
+        )
+        self.assertIsNot(
+            config_a.notify,
+            config_b.notify,
+            "Each Config() call must produce a fresh NotifyDefault instance",
+        )