Boss fight: composition under fire

Repair lab (Module 6, L6.8, the boss fight): one run composes the compaction transaction and its immutable archive, the parity check and the append-only history across 3 compactions. An attacker edits compaction 2 to drop claim C1; every status still says ok and a status-reading checker says clean, while a recomputing verify() names (2, C1) and refuses to resume. Restore C1 byte-for-byte from the archive as an appended correction, prove the run clean, and catch the refactor that silently stopped calling parity with a spy-count seam test. In-memory only; no model.

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