spec: sequence protocol tests — 45 tests, all passing on JS and OCaml

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/javascript/platform.py

@@ -1659,6 +1659,10 @@ PLATFORM_JS_POST = '''
   var hasKey = PRIMITIVES["has-key?"];
   var vectorToList = PRIMITIVES["vector->list"];
   var listToVector = PRIMITIVES["list->vector"];
+  var isVector = PRIMITIVES["vector?"];
+  var vectorLength = PRIMITIVES["vector-length"];
+  var vectorRef = PRIMITIVES["vector-ref"];
+  var reverse = PRIMITIVES["reverse"];
   function zip(a, b) { var r = []; for (var i = 0; i < Math.min(a.length, b.length); i++) r.push([a[i], b[i]]); return r; }
   function append_b(arr, x) { arr.push(x); return arr; }
   var apply = function(f, args) {