Vector crash and concurrency study: kill -9 at controlled points, and writers plus readers during a rebuild #587

Problem

No study exists for crash consistency of the vector index. I want kill -9 at six controlled points on JDK 21 and 25, and concurrent writers and readers during a rebuild, on the engine API.

It decides requirement R3 of the vector program. The preparation and dry-run lines failed, and the study lines were retired because their gate could never be written.

Priority: P2.

Acceptance

• The seed bug in the preparation script is fixed and the preparation and dry-run lines pass
• The crash study and the concurrency study run and are scored by script against the pre-registered README
• An engine finding gets a Java repro on the engine API and goes upstream as a suggestion with the measurements

Results and the scorer output go in this issue as comments. Numbers are generated by script from the result files, never typed.