* fix(keboola): per-table fallback to legacy Storage-API client
The DuckDB Keboola extension's per-table COPY fails with
`Schema '..."in.c-..."' does not exist or not authorized` on
projects whose Snowflake backend doesn't expose bucket schemas
to the storage-token-derived QueryService role
(keboola/duckdb-extension#17). ATTACH itself succeeds, so the
existing extension-level fallback in `_try_attach_extension`
never triggers — the table is just marked failed.
- Promote `kbcstorage>=0.9.0` from optional to core dep so the
legacy client import in `_extract_via_legacy` doesn't crash
default installs with `ModuleNotFoundError`.
- Wrap `_extract_via_extension` in a per-table try/except so a
scan failure retries via `_extract_via_legacy` instead of
recording `tables_failed` and moving on.
Slower than the extension path, but produces correct parquets
on affected projects while the upstream extension fix lands.
* test(keboola): cover per-table extension→legacy fallback
Two existing tests mocked _extract_via_extension to throw and asserted
the original message survived in result["errors"]. With per-table
fallback, the new flow retries via _extract_via_legacy — which on the
mock URLs would throw a different (404 / DNS-fail) error, replacing the
asserted message.
- Mock _extract_via_legacy alongside _extract_via_extension in
test_network_timeout_during_extraction +
test_partial_failure_continues +
test_all_tables_fail_returns_full_failure_stats so the assertion
observes the final propagated error from the fallback chain.
- Add test_extension_per_table_failure_falls_back_to_legacy that
exercises the new behavior directly: extension scan fails with the
QueryService schema-not-authorized message
(keboola/duckdb-extension#17), legacy succeeds, parquet ends up
queryable.
