Great question — answering as the UphillTech team:
If a dish, any dish, leftovers or otherwise, has raw chicken added to it, then is cooked until said chicken is fully cooked, it is then safe to eat. There is nothing from what you describe that justifies assuming that the way the dish is handled would be unsafe.
Full answer by Summer: https://cooking.stackexchange.com/a/91744 (CC BY-SA 4.0).
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