fix(qa): de-flake the Esri fallback check's fixed 50ms DOM settle

The last fixed sleep in this harness: after the controller commits
`activeId = 'osm'`, the fallback callback re-syncs the chips and Cesium
drops the "Powered by Esri" credit on a later render frame again. A flat
50ms covered that most runs and not a slow one — observed failing once in
12 runs on Windows with `creditVisible: true` after the fallback.

Same root cause and same remedy as the tray timers above: poll the
observable truth (credit gone AND the pressed chip is osm), bounded at 3s,
instead of guessing a duration.

0 failures in 15 consecutive runs after this, against 1-in-12 before.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01C3eGYgDYBo2BCUeDGwGvrp

scripts/qa-map-source-tray.mjs

@@ -158,9 +158,18 @@ try {
       await new Promise((resolve) => setTimeout(resolve, 25));
     }
     // The controller commits `activeId` before its fallback promise callback
-    // emits the terminal error state that re-syncs the chips. Give that
+    // emits the terminal error state that re-syncs the chips, and Cesium drops
-    // callback one turn so the DOM assertion observes the completed contract.
+    // the Esri credit on a later render frame again. A fixed delay races both:
-    await new Promise((resolve) => setTimeout(resolve, 50));
+    // 50ms was enough most runs and not enough on a slow one, which is the same
+    // flake as the tray timers above (#54). Poll the observable truth instead.
+    const domDeadline = performance.now() + 3000;
+    const settled = () => !document.body.innerText.includes('Powered by Esri')
+      && [...document.querySelectorAll('.map-stack-chip')]
+        .filter((chip) => chip.getAttribute('aria-pressed') === 'true')
+        .every((chip) => chip.dataset.stackId === 'osm');
+    while (!settled() && performance.now() < domDeadline) {
+      await new Promise((resolve) => setTimeout(resolve, 25));
+    }
     const afterTwo = {
       activeId: controller.getActiveId(),
       lastError: controller.getState().lastError,