js-on-sx: bail out of array set/length at 2^32-1 instead of padding

arr[4294967295] = 'x' and arr.length = 4294967295 were padding
the SX list with js-undefined for ~4 billion entries — instant
timeout. Per ES spec, indices >= 2^32-1 aren't array indices
anyway (regular properties, which we can't store on lists).
Added (>= i 4294967295) bail clauses to js-list-set! and the
length setter.
built-ins/Array: 21/45 → 23/45 (5 timeouts → 2).
conformance.sh: 148/148.

lib/js/runtime.sx

@@ -2866,6 +2866,7 @@
             ((i (js-num-to-int key)) (n (len lst)))
             (cond
               ((< i 0) nil)
+              ((>= i 4294967295) nil)
               ((< i n) (set-nth! lst i val))
               ((= i n) (append! lst val))
               (else (do (js-pad-list! lst n i) (append! lst val))))))
@@ -2876,6 +2877,7 @@
             ((target (js-num-to-int (js-to-number val))) (n (len lst)))
             (cond
               ((< target 0) nil)
+              ((>= target 4294967295) nil)
               ((> target n) (js-pad-list! lst n target))
               (else nil))))
         (else nil))))

lib/js/test262-scoreboard.json

@@ -1,35 +1,35 @@
 {
   "totals": {
-    "pass": 21,
-    "fail": 17,
+    "pass": 23,
+    "fail": 20,
     "skip": 5,
-    "timeout": 7,
+    "timeout": 2,
     "total": 50,
     "runnable": 45,
-    "pass_rate": 46.7
+    "pass_rate": 51.1
   },
   "categories": [
     {
       "category": "built-ins/Array",
       "total": 50,
-      "pass": 21,
-      "fail": 17,
+      "pass": 23,
+      "fail": 20,
       "skip": 5,
-      "timeout": 7,
-      "pass_rate": 46.7,
+      "timeout": 2,
+      "pass_rate": 51.1,
       "top_failures": [
         [
           "Test262Error (assertion failed)",
-          14
-        ],
-        [
-          "Timeout",
-          7
+          17
         ],
         [
           "TypeError: not a function",
           2
         ],
+        [
+          "Timeout",
+          2
+        ],
         [
           "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
           1
@@ -40,22 +40,22 @@
   "top_failure_modes": [
     [
       "Test262Error (assertion failed)",
-      14
-    ],
-    [
-      "Timeout",
-      7
+      17
     ],
     [
       "TypeError: not a function",
       2
     ],
+    [
+      "Timeout",
+      2
+    ],
     [
       "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
       1
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 123.5,
+  "elapsed_seconds": 51.3,
   "workers": 1
 }

lib/js/test262-scoreboard.md

@@ -1,28 +1,28 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 123.5s
+Wall time: 51.3s
 
-**Total:** 21/45 runnable passed (46.7%). Raw: pass=21 fail=17 skip=5 timeout=7 total=50.
+**Total:** 23/45 runnable passed (51.1%). Raw: pass=23 fail=20 skip=5 timeout=2 total=50.
 
 ## Top failure modes
 
-- **14x** Test262Error (assertion failed)
-- **7x** Timeout
+- **17x** Test262Error (assertion failed)
 - **2x** TypeError: not a function
+- **2x** Timeout
 - **1x** Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\
 
 ## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/Array | 21 | 17 | 5 | 7 | 50 | 46.7% |
+| built-ins/Array | 23 | 20 | 5 | 2 | 50 | 51.1% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/Array  (21/45 — 46.7%)
+### built-ins/Array  (23/45 — 51.1%)
 
-- **14x** Test262Error (assertion failed)
-- **7x** Timeout
+- **17x** Test262Error (assertion failed)
 - **2x** TypeError: not a function
+- **2x** Timeout
 - **1x** Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\

plans/js-on-sx.md

@@ -158,6 +158,8 @@ Each item: implement → tests → update progress. Mark `[x]` when tests green.
 
 Append-only record of completed iterations. Loop writes one line per iteration: date, what was done, test count delta.
 
+- 2026-05-08 — **Out-of-range array indices and lengths no longer hang.** `arr[4294967295] = 'x'` and `arr.length = 4294967295` were padding the SX list with `js-undefined` for ~4 billion entries — guaranteed timeout. Per ES spec, indices ≥ 2^32-1 aren't array indices (they're regular properties, which we can't store on a list). Added a `(>= i 4294967295)` bail-out clause to both `js-list-set!` (numeric index path) and the `length` setter; both now no-op at that bound. Removed 5 of the 7 Array timeouts. built-ins/Array: 21/45 → 23/45. conformance.sh: 148/148.
+
 - 2026-05-08 — **Built-in `.length` returns spec-defined values for variadic functions.** `String.fromCharCode.length`, `Math.max.length`, `Array.from.length` were all returning `0` because the underlying SX lambdas use `&rest args` with no required params — but the spec assigns each built-in a specific length (`fromCharCode === 1`, `max === 2`, etc.). Added `js-builtin-fn-length` that maps the unmapped JS name to its spec length (12 entries covering fromCharCode, fromCodePoint, raw, of, from, isArray, max, min, hypot, atan2, imul, pow). `js-fn-length` consults this table first and falls back to counting real params. built-ins/String: 79/99 → 80/99, built-ins/Array: 20/45 → 21/45. conformance.sh: 148/148.
 
 - 2026-05-08 — **`Object.prototype.toString` dispatches by [[Class]].** Was hardcoded to `"[object Object]"` for everything; per ES it should return `"[object Array]"`, `"[object Function]"`, `"[object Number]"`, etc. based on the receiver's class. Added `js-object-tostring-class` helper that switches on `(type-of v)` and on dict-internal markers (`__js_string_value__`, `__js_number_value__`, `__js_boolean_value__`, `__callable__`). Also added prototype-identity checks so `Object.prototype.toString.call(Number.prototype)` returns `"[object Number]"` (similar for String/Boolean/Array). built-ins/Array: 18/45 → 20/45, built-ins/Number: 43/50 → 44/50. conformance.sh: 148/148.