fix: preserve complete tool batches during compaction

[K-Mistele]

Summary

• Compute compaction cutoffs from the largest physical sequence in the discarded projected history.
• Prevent a reordered parallel tool result from surviving after compaction removes its matching assistant tool call.
• Add a regression test for out-of-order persisted tool results.

Validation

• bun vitest run in packages/fold-core
• bun run typecheck in packages/fold-core
• bunx oxfmt --check packages/fold-core/src/Compaction/CompactionLayer.ts packages/fold-core/test/Projection/Projection.vi.test.ts
• bunx oxlint --type-aware packages/fold-core/src/Compaction/CompactionLayer.ts packages/fold-core/test/Projection/Projection.vi.test.ts