fix: reuse recorded provider during incremental acquisition

src/ml4t/data/managers/storage_manager.py

@@ -508,6 +508,8 @@ def update(
                     f"Stored metadata provider for '{key}' must be a string, "
                     f"got {type(existing_provider).__name__}"
                 )
+            if not provider and existing_provider not in (None, "", "auto"):
+                provider = existing_provider
 
             # Get the date range from existing data
             _, last_timestamp = timestamp_bounds(existing_df)

tests/test_update_provider_reuse.py

@@ -0,0 +1,48 @@
+"""A recorded provider must control acquisition, not only rewritten metadata."""
+
+import pytest
+from polars.testing import assert_frame_equal
+
+from ml4t.data import DataManager
+from ml4t.data.providers.synthetic import SyntheticProvider
+from ml4t.data.storage.config import StorageConfig
+from ml4t.data.storage.flat import FlatStorage
+from ml4t.data.storage.hive import HiveStorage
+
+
+@pytest.fixture(params=[FlatStorage, HiveStorage])
+def stored_provider(request, tmp_path):
+    storage = request.param(StorageConfig(base_path=tmp_path))
+    with SyntheticProvider() as provider:
+        frame = provider.fetch_ohlcv("SPY", "2025-07-07", "2025-07-07", "daily")
+    storage.write(frame, "equities/daily/SPY", {"provider": "synthetic"})
+    return storage, frame
+
+
+def test_real_incremental_fetch_reuses_the_recorded_adapter_without_a_route(stored_provider):
+    storage, frame = stored_provider
+    with DataManager(storage=storage) as manager:
+        key = manager.update("SPY", fill_gaps=False)
+        assert key == "equities/daily/SPY"
+        assert manager.get_metadata_for_key(key)["provider"] == "synthetic"
+    assert storage.read(key).collect().height > frame.height
+
+
+def test_explicit_provider_still_overrides_the_recorded_adapter(stored_provider):
+    storage, frame = stored_provider
+    storage.write(frame, "equities/daily/SPY", {"provider": "no-such-recorded-provider"})
+    with DataManager(storage=storage) as manager:
+        key = manager.update("SPY", fill_gaps=False, provider="synthetic")
+        assert manager.get_metadata_for_key(key)["provider"] == "synthetic"
+
+
+def test_invalid_explicit_adapter_does_not_fall_back_to_the_recorded_one(stored_provider):
+    storage, frame = stored_provider
+    before = storage.get_metadata("equities/daily/SPY")
+    with (
+        DataManager(storage=storage) as manager,
+        pytest.raises(ValueError, match="not.*available|not found|Unknown|unknown"),
+    ):
+        manager.update("SPY", fill_gaps=False, provider="not-a-provider")
+    assert storage.get_metadata("equities/daily/SPY") == before
+    assert_frame_equal(storage.read("equities/daily/SPY").collect(), frame)