A new run rewinds the clock; the camera flashes did not rewind with it

Oliver: "I start a new zombie tennis match. when playing and scoring no
fotograph flashes appear, but at a random place in the crowd some frozen
midflash circle is visible. after a few points the flashes unfreeze."

Both halves are the same cause. resetState() puts G.idleT back to 0 for every
new run, while the flash list and its "next at" live in render.js's own closure
and survive it. So the new run inherited a flashNext from the old one — no
photographs at all until the clock climbed back past it — and any flash still in
flight was left with a t0 in its own future, which makes its fade
1 - (now - t0)/life permanently greater than 1: a shutter stuck at full
brightness in the stand until something else cleared it.

tickFlashes now notices the clock moving backwards and clears and re-arms. One
guard, in the only place that owns the state, so it covers any future mode that
rewinds the clock as well. Verified on the canvas: after a rewind there is no
permanently-bright pixel in the stand, and the photographers resume within
seconds instead of staying dark.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/render.js

@@ -388,9 +388,19 @@ function buildCrowd() {
 // while the crowd is on its feet, which is the "slightly increase during applause" — a stand that
 // went white during a point would be a different, much louder feature.
 const flashes = [];  // {x, y, r, t0}
-let flashNext = 0;
+let flashNext = 0, flashLast = 0;
 function tickFlashes(standsBottom) {
   const now = G.idleT, top = Math.max(4, standsBottom - AD_H - 4);
+  // THE CLOCK CAN GO BACKWARDS AND THIS STATE CANNOT. `resetState` puts G.idleT back to 0 for every
+  // new run, while `flashes` and `flashNext` live in this module and survive it — so a fresh match
+  // inherited a `flashNext` from the last one (no photographs at all until the clock climbed back
+  // past it) and any flash still alive was left with a t0 in its future, which makes its fade
+  // `1 - (now - t0)/life` permanently greater than 1: a shutter frozen at full brightness in the
+  // stand, for ever. Oliver, 2026-08-21: "at a random place in the crowd some frozen midflash circle
+  // is visible. after a few points the flashes unfreeze". One guard, here, because this is the only
+  // place that owns the state — and it covers any future mode that rewinds the clock too.
+  if (now < flashLast) { flashes.length = 0; flashNext = now; }
+  flashLast = now;
   if (now >= flashNext) {
     // THE BIGGER THE MOMENT, THE MORE SHUTTERS. cheer() queues crowd.burst shutters proportional to
     // its own vol, and they fire back to back at a fifth of the normal gap — a match point empties