A partition is an append-only daily NDJSON file of canonical masked events:
LAKE_DATA/events/runtime=<runtime>/date=<YYYY-MM-DD>/part-<12-hex-path-digest>.ndjsonRuntime and event-date directories make pruning and DuckDB scans predictable. The filename digest is derived from the full source path, so one source consistently lands in the same file for a runtime/day while the plaintext path is not encoded in the partition name. Events without a usable date use date=unknown.
Partitions are authoritative. Parquet mirrors and Oko per-session exports are derived. Never edit, truncate, merge, or replace a live partition by hand; preserve the root and rebuild from vendor-owned sources to a different empty destination.
DuckDB readers use an explicit schema and tolerate a torn final line during concurrent append. The stream writes complete batches before publishing their source cursor.
See cursor, architecture, and recovery runbook.