Zeren Wang 7cf0abe584
test(checkpoint): delta-history cache migration coverage + pin two open DeltaChannel defects (#5797)
* test(checkpoint): cover delta-history cache migration and pin two open DeltaChannel defects

- Extend the full -> delta migration contract to {cache disabled, cold, warm}
  with a differential raw-saver oracle; the warm state also asserts a
  cache-served re-read with no extra inner history walks.
- Pin two still-unfixed upstream DeltaChannel defects as tripwire regressions:
  #8382 (parallel-superstep delta replay order diverges from live order) and
  #8448 (Postgres paged delta walk hydrates old checkpoints empty). Each
  asserts the correct contract and skips, naming the issue and pinned version,
  while the defect is present - so a later dependency bump that lands the fix
  turns it into a live gate. The contract is never asserted as buggy behaviour
  (see backend/tests/AGENTS.md).

* test(checkpoint): scope the #8448 skip to the postgres parameter

The paged stage-1 walk that langgraph#8448 poisons only exists in
langgraph.checkpoint.postgres; memory and sqlite never paginate. An
unscoped skip let a future regression in long-chain materialization on
those backends hide behind the Postgres-only upstream issue instead of
failing the InMemorySaver differential oracle. Keep the assertion live
there and trip only where the defect can occur.
2026-09-24 15:16:08 +08:00
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