KIP-1026 — Handling producer snapshot when upgrading from < v2.8.0 for Tiered Storage

Discussion Kafka 3.7.1 Tiered Storage

KIP-1026 changes the `LogSegmentData` passed to the Remote Storage Manager API to hold `Optional<Path>` for the producer snapshot index instead of a mandatory `Path`, allowing segments uploaded without an associated snapshot file to be handled gracefully. Users migrating from Kafka versions prior to 2.8.0 (which aligned producer snapshots to segment boundaries) encounter `NullPointerException`s when enabling Tiered Storage because older segments have no snapshot files, breaking the RSM contract.

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