car: cap road chain stitching to avoid Set overflow

vendor/clouds3d.js

@@ -4485,6 +4485,22 @@ function carMergeChains(polys, cfg) {
             eps.push(r);
         }
     }
+    // Safety valve: dense residential/tertiary cells can create far more
+    // endpoints than the join search can safely hold. In that case keep the
+    // roads as individual chains instead of trying to stitch everything.
+    var JOIN_ENDPOINT_LIMIT = 180000;
+    if (eps.length > JOIN_ENDPOINT_LIMIT) {
+        var isoOut = [], isoMax = 0;
+        for (i = 0; i < n; i++) {
+            if (polys[i] && polys[i].length > 1) {
+                isoOut.push(polys[i]);
+                var isoSpan = Math.max(polys[i][0].d, polys[i][polys[i].length - 1].d);
+                if (isoSpan > isoMax) isoMax = isoSpan;
+            }
+        }
+        return { out: isoOut, n: n, joins: 0,
+                 maxChainKm: n ? isoMax * cfg.KM_PER_TILE : 0 };
+    }
     // canonical numeric key for an endpoint pair (way index + end side)
     function pairKey(A, B) {
         var x = A.w * 2 + A.e, y = B.w * 2 + B.e;
@@ -4510,25 +4526,36 @@ function carMergeChains(polys, cfg) {
         var T = TIERS[t];
         var cands = candsByTier[t];
         var seenPair = new Set();
-        for (i = 0; i < eps.length; i++) {
+        var seenFull = false;
+        var SEEN_PAIR_LIMIT = 2000000;
+        var CAND_LIMIT = 1200000;
+        for (i = 0; i < eps.length && !seenFull; i++) {
             if ((i & 8191) === 8191) geoProgress('join tier ' + t, i, eps.length);
             var A2 = eps[i];
             var gx = Math.floor(A2.x / NEAR), gz = Math.floor(A2.z / NEAR);
-            for (var ox = -1; ox <= 1; ox++) {
-                for (var oz = -1; oz <= 1; oz++) {
+            for (var ox = -1; ox <= 1 && !seenFull; ox++) {
+                for (var oz = -1; oz <= 1 && !seenFull; oz++) {
                     var bucket = grid.get((gx + ox) + '_' + (gz + oz));
                     if (!bucket) continue;
-                    for (j = 0; j < bucket.length; j++) {
+                    for (j = 0; j < bucket.length && !seenFull; j++) {
                         var B2 = bucket[j];
                         if (B2.w === A2.w) continue;
                         var pk2 = pairKey(A2, B2);
                         if (seenPair.has(pk2)) continue;
+                        if (seenPair.size >= SEEN_PAIR_LIMIT) {
+                            seenFull = true;
+                            break;
+                        }
                         seenPair.add(pk2);
                         var gm = geomFor(A2, B2);
                         if (gm.dot <= T.dot) continue;
                         if (gm.lat > T.lat) continue;        // opposite carriageway: reject
                         if (gm.along < T.alongLo || gm.along > T.alongHi) continue;
                         cands.push({ a: A2, b: B2, s: gm.s });
+                        if (cands.length >= CAND_LIMIT) {
+                            seenFull = true;
+                            break;
+                        }
                     }
                 }
             }