Where does “rusty” come from?

I notice there's a mismatch in your request. The chain provided traces "resty/restiff" but the headword you want me to write about is "rusty." These are different words with different etymologies. Could you clarify: Do you want me to write the etymology summary for "resty" (following the chain you provided), or do you have a different chain for "rusty"?

rusty (English): Marked or corroded by rust; Of the rust color,...