[2.0 / next] isPending(s) reads true for a signal whose writes net to its committed value in the tick an action opens a hold (D-8) #4485

On next @ ab3d2ad, writes that net to a signal's committed value pend it when they happen in the same tick as an action that holds another write. A render effect reading isPending(s) shows true for the whole hold. It then runs once more at the landing with the same values.

const [s, setS] = createSignal(1);
const [x, setX] = createSignal(0);
createRoot(() => {
  createRenderEffect(x, () => {});
  createRenderEffect(() => [s(), isPending(s)], v => runs.push(v));
});
flush();
let release;
action(function* () {
  setX(1);
  setS(2);
  setS(1); // nets to the committed 1
  yield new Promise(r => (release = r));
})();
await tick(); // runs: [[1, true]]   ← isPending(s) is true; unowned isPending(s) is false
release();
await tick(); // runs: [[1, true], [1, false]]

The same thing happens when setS(2); setS(1) runs on the mainline just before the action, in the same tick. When the netted writes come in a later tick, or there is no hold at all, the reader shows [1, false] and is not re-run at the landing.

Rule. D-8: "A tick whose writes net to the slot's committed value made no proposal: the slot is not held, pends nothing." So isPending(s) should be false, and the screen should be [[1, false]].

Where. The re-run is the seat table's row V2: the stagedScreen seam in read runs before any netted check and lists the reader as a stale reader of the flush's hold. I haven't traced where the true verdict comes from yet. Found while reviewing #4472. It is in the same family as #4469's landing re-runs.