Issue #3616605: Make the gesture-after-the-answer test say which half broke when it fails

OfferStepperTest::testTheGestureFinishedAfterTheAnswerStillReachesTheServer asserted its outcome before its own precondition, so a red run said 1 is not 2 whether the queue had lost the gesture (the regression) or the window had never opened (a fault in the test).

• the setup records what it did as it happened: what the answer found in the field, whether the gesture was finished with at all, whether Drupal was still busy then, and what value was committed
• those are asserted in that order, each carrying the whole trace, and waitForHeld() runs last
• a count of the requests that leave after the commit tells apart "the queue never sent it" from "it was sent and not held"

Scope note. The issue as filed also proposed closing a race in the setup, a zero-delay timeout a loaded runner can starve. That was already fixed in #3616584, which landed while this was being written; the issue summary has been reworded to match what is left. No production code changes here.