[BUG] cuDF: shared-alias multi-pattern with relationship-property projection segfaults (exit 139)

[lmeyerov]

Summary

On cuDF (rapids 25.02 + 26.02), a Cypher query with shared aliases across comma-separated MATCH patterns and a relationship-property projection in RETURN crashes the Python process (SIGSEGV / exit 139).

Repro (rapids 25.02 / 26.02 GPU container)

import pandas as pd, graphistry, cudf
graphistry.register(api=3, server="hub.graphistry.com")

nodes = pd.DataFrame({"id":["a1","b1"],"label__A":[True,False],"label__B":[False,True]})
edges = pd.DataFrame({"s":["a1","b1"],"d":["b1","a1"],"type":["R","S"],"weight":[7,9]})
g = (graphistry.nodes(cudf.from_pandas(nodes),"id")
     .edges(cudf.from_pandas(edges),"s","d")
     .bind(edge_label="type"))

# Both of the following segfault with EXIT=139:

# A) WITH-form (goes through flatten path from #1341):
g.gfql(
    "MATCH (a:A {id: 'a1'})-[r:R]->(b:B) "
    "WITH a, b, r "
    "MATCH (b)-[:S]->(a) "
    "RETURN r.weight AS w",
    engine="cudf",
)

# B) Hand-flattened single-MATCH (does NOT go through flatten):
g.gfql(
    "MATCH (a:A {id: 'a1'})-[r:R]->(b:B), (b)-[:S]->(a) "
    "RETURN r.weight AS w",
    engine="cudf",
)

Both crash. Pandas equivalent works correctly and returns [{'w': 7}].

Suspected cause

cuDF row-pipeline shared-alias join with relationship-property projection — likely a C-level interop issue in cudf merge / pylibcudf. Stack trace dumps come from _PyRun_SimpleFileObject with pylibcudf.* extension modules loaded.

The issue is NOT specific to the new flatten_carried_endpoint_rebind path from #1341 — it reproduces equally on the hand-flattened single-MATCH form, so the cuDF bug is in shared-alias multi-pattern join with rel-property projection regardless of how the query reaches it.

Acceptance criteria

• The repro queries above execute without crashing on cuDF (rapids 25.02 + 26.02).
• Result rows match the pandas baseline ([{'w': 7}]).
• New parametrized test under graphistry/tests/compute/gfql/cypher/test_lowering.py covering shared-alias multi-pattern + rel-property projection on both engines.

Surfaced by

PR #1351 (#1341) test-amplification round-001. The corresponding cuDF parity test (test_string_cypher_executes_with_match_reentry_relationship_variable_carried_on_cudf) is currently @pytest.mark.skip'd with this issue as the link.