fix(polars): fall back to plain collect when the streaming engine is rejected

CHANGELOG.md

@@ -7,6 +7,11 @@ adheres to [Semantic Versioning](https://semver.org/).
 ## [Unreleased]
 
 ### Fixed
+- The native Polars backend no longer raises on polars versions that reject
+  `collect(engine="streaming")` with a `ValueError` (polars 1.1–1.24): the
+  streaming collect now falls back to a plain `collect()` on those versions,
+  as it already did for the older `streaming=` keyword. Modern polars is
+  unaffected.
 - Explicit imputation (`impute="mean"`, `"median"`, `"mode"`, `"auto"`,
   `"missforest"` or an `impute_strategy` entry) no longer fills the declared
   `id_columns` or `target_column`, as documented. Those columns keep their

src/freshdata/execution/backends/_polars.py

@@ -557,7 +557,10 @@ def _collect(self, lf: Any, engine_config: EngineConfig | None, pl: Any) -> Any:
         # keyword first, then the legacy one, then a plain collect.
         try:
             return lf.collect(engine="streaming")
-        except TypeError:
+        except (TypeError, ValueError):
+            # Older polars either lacks the ``engine`` keyword (TypeError) or
+            # rejects the ``"streaming"`` value (ValueError: Invalid engine
+            # argument); fall through to the legacy switch, then plain collect.
             pass
         try:
             return lf.collect(streaming=True)

tests/test_execution/test_dispatch_and_config.py

@@ -78,3 +78,28 @@ def toPandas(self) -> pd.DataFrame:  # noqa: N802 - matches pyspark's API
 
     out = materialize_to_pandas(_FakeSparkFrame())
     pd.testing.assert_frame_equal(out, expected)
+
+
+def test_polars_collect_falls_back_when_streaming_engine_unsupported():
+    """Older polars rejects ``collect(engine="streaming")`` with ValueError (not
+    TypeError); the backend must fall back to a plain collect, not propagate it."""
+    from freshdata.execution._config import EngineConfig
+    from freshdata.execution.backends._polars import PolarsEngine
+
+    calls: list = []
+
+    class _FakeLazy:
+        def collect(self, **kwargs):
+            calls.append(kwargs)
+            if kwargs.get("engine") == "streaming":
+                raise ValueError("Invalid engine argument engine='streaming'")
+            if kwargs.get("streaming"):
+                raise TypeError("unexpected keyword argument 'streaming'")
+            return "collected"
+
+    class _Pl:
+        pass
+
+    out = PolarsEngine()._collect(_FakeLazy(), EngineConfig(), _Pl())
+    assert out == "collected"
+    assert {} in calls  # a plain collect() was reached