0266 — Key deletion is expressed in the payload; there is no schema-level tombstone

Context. Kafka defines a protocol-level tombstone marker so its background compactor — which physically deletes rows — can recognize a deletion generically across topics without understanding payload schemas, and eventually purge the tombstone itself.

Decision. No tombstone concept in the schema. “How do I delete a key” is answered entirely by what the producer puts in payload (for example an app-defined Deleted bool field). The claim-time filter already returns whatever the latest row is with zero special-casing, regardless of its contents, and nothing here physically deletes rows — so Kafka’s motivating reason does not apply.

Consequences. A tombstoned key still delivers its latest row on both claim paths like any other. Cost accepted: a future generic disk-space cleanup pass cannot recognize “this key is fully dead, purge every row for it” without understanding each topic’s payload schema — real, but currently unneeded. Rejected: a schema-level tombstone marker — machinery for a background deleter this design does not have.