Cached concurrent LangGraph tasks need a release gate

A cache is meant to remove repeated work, but it can also change the timing of concurrent tasks. A fresh LangGraph issue reports that cached sync tasks running together in the Functional API can hit an internal write-queue mutation and abort a run. That is a release gate for teams depending on caching at production concurrency.

Reproduce with the deployment shape

Run a minimal workflow with several concurrent sync tasks, the same cache policy, and the installed version. Compare cold and warm cache runs. Capture the exception and run state without logging sensitive task inputs.

Protect side effects on retry

Classify each task as read-only or state-changing. Give state-changing work an idempotency key or deduplication record so a failed orchestration retry does not repeat external writes. Check whether completed cached outputs were committed before the exception.

Gate upgrades on both correctness and throughput

Test candidate SDK versions with cache-hit and cache-miss concurrency. If the reported path reproduces, reduce concurrency or disable caching for the affected workflow while tracking the upstream fix. Document the cost of the workaround.

Adovo’s view

Caching changes execution order, not just cost. A production agent should pass the same correctness test when work is reused and when it is computed. Treat the warm path as a separate release condition.