gfql cypher: WHERE on a single alias of a multi-alias MATCH is rejected as multi-source

[lmeyerov]

Repro (master @ 3fb216d, both engines)

import pandas as pd, graphistry
nodes_df = pd.DataFrame({'id': ['a','b','c','tx1','tx2'],'type': ['person','person','company','transaction','transaction']})
edges_df = pd.DataFrame({'src': ['a','b','a','tx1','tx2'],'dst': ['b','c','tx1','tx2','c'],'e_type': ['knows','works_at','sent','transfer','received']})
g = graphistry.edges(edges_df,'src','dst').nodes(nodes_df,'id')
g.gfql("MATCH (a)-[e]->(t) WHERE a.type IN ['person','company'] RETURN t.id AS id")

Raises GFQLValidationError [unsupported-cypher-query] Cypher row lowering currently supports one MATCH source alias at a time on engine='pandas' and 'polars'.

The same pattern with predicates on two aliases works on both engines:

g.gfql("MATCH (a)-[e]->(t) WHERE a.type IN ['person','company'] AND e.e_type IN ['sent','transfer'] RETURN t.id AS id")  # -> ['tx1']

So a WHERE that touches fewer aliases than the pattern is lowered as a multi-source query. Expected: filter on a, project t. Found while adding tested Cypher twins to gfql/about.rst examples (#2017 follow-up).

🤖 Generated with Claude Code

https://claude.ai/code/session_01WwMmVFo44ADiRRj5cxh7i1

[lmeyerov]

Disposition (0.60 landing phase): conformance gap, not a wrong answer (the query is rejected with a structured error). Backlog after the benchmark landing; fix belongs with the multi-alias WHERE lowering.