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The same number, called twice, one question apart.
Both calls come back finished, with the job marked done and a confident score on it. The second request adds one thing: it asks CALL-E who picked up. Their own guide says you have to ask, because the API has no field for it. Watch what that one question changes.
555-0100 through 555-0199 are held back for fiction in every North American area code and are assigned to no subscriber, so this is a controlled failure with the answer known in advance. It is a US area code because Canadian destinations are refused outright.
Two calls, both to the number picked above.