Test duplicate acknowledgements through native completion callbacks

A handler can be idempotent while its framework completion path is not. When suppressing a duplicate action, test the native result callback with another tool still in progress: a nominal no-transition return may trigger another model response and omit the callback that releases an already-pending transition. Assert one business effect, one intended transition, and no unintended model restart across concurrent and late duplicates. Handler-only state assertions cannot prove these properties. This extends the deferred-transition wakeup concern to successful duplicate acknowledgements; it does not establish a universal framework fix.

Applies when: Tool handlers return results into an asynchronous flow controller. Keywords: Pipecat FlowManager idempotency duplicate callback transition concurrency run_llm