perf(gfql): route engine=auto to native polars for polars-frame graphs

resolve_engine(AUTO) maps polars frames to PANDAS (it predates
Engine.POLARS), so g.gfql(query) on a polars-frame graph silently
bridged to the generic pandas path: ~3-13x slower on cypher point
queries and pandas frames out. Route AUTO to the native polars engine;
an honest NotImplementedError (unsupported shape) falls back to the
legacy AUTO path — allowed because the user did not pin an engine.
Frames in = frames out: AUTO results on polars graphs are now polars.

Repro: 2k-node polars graph, seeded 1-hop cypher — AUTO 25.0ms/pandas
out before, 9.3ms/polars out after (engine='polars' = 8.8ms); polars-NIE
shapes (shortestPath) still answer via the pandas fallback.

Fixes the q5 finding in plans/gfql-benchmark-numbers (inferred-engine
13x penalty).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y6dQEcjdazEnzuvuwf73ZL

Author: lmeyerov

graphistry/compute/gfql_unified.py

@@ -1808,6 +1808,24 @@ def gfql(self: Plottable,
     :returns: Resulting Plottable
     :rtype: Plottable
     """
+    # engine inference: resolve_engine(AUTO) maps polars frames to PANDAS (polars predates
+    # Engine.POLARS there), silently bridging polars-frame graphs onto the generic pandas path
+    # (~13x slower on cypher point queries, pandas frames out). Route AUTO to the native polars
+    # engine instead; an honest NIE (unsupported shape) falls back to the legacy AUTO path, which
+    # is allowed here because the user did not pin an engine.
+    if (
+        (engine == EngineAbstract.AUTO or engine == EngineAbstract.AUTO.value)
+        and is_polars_df(self._edges) and (self._nodes is None or is_polars_df(self._nodes))
+    ):
+        try:
+            return gfql(
+                self, query, engine=Engine.POLARS.value, output=output, policy=policy,
+                where=where, language=language, params=params, validate=validate,
+                shortest_path_backend=shortest_path_backend,
+            )
+        except NotImplementedError:
+            logger.debug('AUTO polars-native attempt declined; falling back to generic path')
+
     context = ExecutionContext()
 
     if policy and context.policy_depth >= 1: