FlakyAgent's model throws on its first N calls.

no handler,           N=1: Attempt[outcome=threw IllegalStateException: model unavailable (attempt 1), modelCalls=1]
handler retry(),      N=2: Attempt[outcome=returned 'AI-101 Mumbai to Lisbon', modelCalls=3] (handler invoked 2 times)
handler result(".."), N=5: Attempt[outcome=returned 'no flight found, ask the traveler', modelCalls=1]
handler throwException(), N=5: Attempt[outcome=threw IllegalStateException: model unavailable (attempt 1), modelCalls=1]