Release v0.21.1

Changes since v0.21.0.

New: Explode hierarchy node (#774)

Turns parent → child rows (a bill of materials, a chart of accounts) into every ancestor–descendant pair at any depth, with quantities multiplied along each route. Output is Totals, Levels or Paths. Available in the Python API as frame.explode_hierarchy(...) and in both code exports. See the docs.

Fixes

• A worker node that fails on its data now fails, instead of being re-run in core or sent to the worker a second time. Only failures in the worker itself (a missing UDF module, a plugin that won't load, the time limit) still fall back to core. Flows served as APIs follow the same rule. (#774)
• The filter docs now say that filter(ff.col(...) > x) becomes an editable Filter node. (#777)

Upgrade notes

• The Polars minimum is now 1.39, because polars-grouper 0.6.0 needs it.
• No database migration.