fix: correct 'clustering_key' to 'clustering' in column kind filter

[mykaul]

Summary

• Fix a latent bug in SchemaParserV3._build_table_metadata() where the column kind filter at cassandra/metadata.py:2744 used 'clustering_key' instead of 'clustering', causing clustering columns to not be excluded from the "other columns" loop and thus processed/added twice.

Details

The system_schema.columns table uses 'clustering' as the kind value for clustering key columns (not 'clustering_key'). The correct value 'clustering' is already used 6 lines above (line 2735) when building the clustering key list. The filter on line 2744, which is supposed to skip partition key and clustering columns when iterating "other" columns, was using the wrong string.

This bug is harmless in most cases because _build_column_metadata() overwrites column objects in a dict, but it causes unnecessary duplicate processing and could cause subtle issues with column ordering in edge cases.

Testing

All 55 metadata unit tests pass (tests/unit/test_metadata.py). The 1 pre-existing test failure in tests/unit/test_types.py::TypeTests::test_lookup_casstype is unrelated (broken test on master, to be fixed by PR #690).

[Copilot]

Pull request overview

Fixes a schema parsing bug in SchemaParserV3._build_table_columns() where clustering columns from system_schema.columns were not being filtered out of the “other columns” loop due to using the wrong kind value.

Changes:

• Corrected the kind filter from 'clustering_key' to 'clustering' when skipping key columns during non-key column processing.

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[mykaul]

It's not very clear to me it is the correct fix. In GoCQL we have both? https://github.com/scylladb/gocql/blob/2d8532c6f9e6047ef4c05e5705224dd618d76387/metadata_scylla.go#L509

AI says:

• ScyllaDB reports column kind as "clustering_key"
• Cassandra reports it as "clustering"

I think AI is wrong here. Nothing is sent over the write as such. Need to understand this and GoCQL better :-/

[mykaul]

AI again:

Writing (what drivers see): In db/schema_tables.cc:2298-2306, the serialize_kind function maps column_kind::clustering_key to the string "clustering":
case column_kind::clustering_key: return "clustering";