deltaChannelHistoryTests

Conformance tests for BaseCheckpointSaver.getDeltaChannelHistory — the walk that reconstructs DeltaChannel state from checkpoint_writes.

This is the one checkpointer method with no coverage in the default spec suite, and it is intentionally opt-in: it is not run by specTest, so adding it does not raise the conformance bar for third-party savers (the method is Beta and inherits a default implementation from BaseCheckpointSaver). Each in-repo saver's .spec.ts calls it explicitly so the shared base walk is validated against every backend's real storage — Postgres, SQLite, Redis, MongoDB, and the MemorySaver override.

The scenarios target the per-backend behaviours the walk depends on: round-tripping DeltaSnapshot and plain-array seed blobs, following parentConfig up the ancestor chain, and — critically — replaying concurrent same-superstep writes in the canonical (task_id, idx) order regardless of how a given store happens to return pendingWrites (insertion order, locale collation, etc.).