test(street-level): the gate waits for the photo line to be pickable

Draped lines build in a worker after their tile decoded: on a slow CI runner
the single pick scan ran before the line existed and the gate failed at
"a sequence line across the middle of the view". The scan now retries for up
to 30 s.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

scripts/qa-street-level.mjs

@@ -296,6 +296,20 @@ const findPick = (page, prefix, { box = null, step = 3 } = {}) =>
     step,
   );
 
+/**
+ * `findPick`, retried until a hit or `timeout`: draped lines build in a
+ * worker after their tile decoded, so a scan right after LOADING clears can
+ * come too early on a slow machine.
+ */
+async function findPickUntil(page, prefix, { timeout = 30_000 } = {}) {
+  const deadline = Date.now() + timeout;
+  for (;;) {
+    const hit = await findPick(page, prefix);
+    if (hit || Date.now() >= deadline) return hit;
+    await new Promise((resolve) => setTimeout(resolve, 500));
+  }
+}
+
 /** Park the camera over the photo line; a late startup flight can move it. */
 async function park(page) {
   for (let attempt = 0; attempt < 5; attempt++) {
@@ -455,7 +469,7 @@ async function main() {
         'a line selects its sequence, and a cone opens its photo with a caption',
         async () => {
           // Fixtures answer lookups for the photo sequence only.
-          const line = await findPick(
+          const line = await findPickUntil(
             page,
             fixtures ? `mly:seq:${PHOTO_SEQUENCE_ID}` : 'mly:seq:',
           );