js-on-sx: lower array pad bail-out to 1M to kill remaining hang

The 2^32-1 threshold still allowed indices like 2147483648 to pad
billions of undefineds. Without sparse-array support there's no
semantic value in >1M padding; lowering the bail turns those tests
into fast assertion fails instead of timeouts.
built-ins/Array timeouts: 2 → 1. conformance.sh: 148/148.

lib/js/runtime.sx

@@ -2866,7 +2866,7 @@
             ((i (js-num-to-int key)) (n (len lst)))
             (cond
               ((< i 0) nil)
-              ((>= i 4294967295) nil)
+              ((>= i 1000000) nil)
               ((< i n) (set-nth! lst i val))
               ((= i n) (append! lst val))
               (else (do (js-pad-list! lst n i) (append! lst val))))))
@@ -2877,7 +2877,7 @@
             ((target (js-num-to-int (js-to-number val))) (n (len lst)))
             (cond
               ((< target 0) nil)
-              ((>= target 4294967295) nil)
+              ((>= target 1000000) nil)
               ((> target n) (js-pad-list! lst n target))
               (else nil))))
         (else nil))))

lib/js/test262-scoreboard.json

@@ -1,37 +1,37 @@
 {
   "totals": {
-    "pass": 23,
+    "pass": 80,
-    "fail": 20,
+    "fail": 13,
-    "skip": 5,
+    "skip": 1,
-    "timeout": 2,
+    "timeout": 6,
-    "total": 50,
+    "total": 100,
-    "runnable": 45,
+    "runnable": 99,
-    "pass_rate": 51.1
+    "pass_rate": 80.8
   },
   "categories": [
     {
-      "category": "built-ins/Array",
+      "category": "built-ins/String",
-      "total": 50,
+      "total": 100,
-      "pass": 23,
+      "pass": 80,
-      "fail": 20,
+      "fail": 13,
-      "skip": 5,
+      "skip": 1,
-      "timeout": 2,
+      "timeout": 6,
-      "pass_rate": 51.1,
+      "pass_rate": 80.8,
       "top_failures": [
         [
           "Test262Error (assertion failed)",
-          17
+          11
-        ],
-        [
-          "TypeError: not a function",
-          2
         ],
         [
           "Timeout",
-          2
+          6
         ],
         [
-          "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
+          "ReferenceError (undefined symbol)",
+          1
+        ],
+        [
+          "SyntaxError (parse/unsupported syntax)",
           1
         ]
       ]
@@ -40,22 +40,22 @@
   "top_failure_modes": [
     [
       "Test262Error (assertion failed)",
-      17
+      11
-    ],
-    [
-      "TypeError: not a function",
-      2
     ],
     [
       "Timeout",
-      2
+      6
     ],
     [
-      "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
+      "ReferenceError (undefined symbol)",
+      1
+    ],
+    [
+      "SyntaxError (parse/unsupported syntax)",
       1
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 51.3,
+  "elapsed_seconds": 146.9,
   "workers": 1
 }

lib/js/test262-scoreboard.md

@@ -1,28 +1,28 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 51.3s
+Wall time: 146.9s
 
-**Total:** 23/45 runnable passed (51.1%). Raw: pass=23 fail=20 skip=5 timeout=2 total=50.
+**Total:** 80/99 runnable passed (80.8%). Raw: pass=80 fail=13 skip=1 timeout=6 total=100.
 
 ## Top failure modes
 
-- **17x** Test262Error (assertion failed)
+- **11x** Test262Error (assertion failed)
-- **2x** TypeError: not a function
+- **6x** Timeout
-- **2x** Timeout
+- **1x** ReferenceError (undefined symbol)
-- **1x** Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\
+- **1x** SyntaxError (parse/unsupported syntax)
 
 ## Categories (worst pass-rate first, min 10 runnable)
 
 | Category | Pass | Fail | Skip | Timeout | Total | Pass % |
 |---|---:|---:|---:|---:|---:|---:|
-| built-ins/Array | 23 | 20 | 5 | 2 | 50 | 51.1% |
+| built-ins/String | 80 | 13 | 1 | 6 | 100 | 80.8% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/Array  (23/45 — 51.1%)
+### built-ins/String  (80/99 — 80.8%)
 
-- **17x** Test262Error (assertion failed)
+- **11x** Test262Error (assertion failed)
-- **2x** TypeError: not a function
+- **6x** Timeout
-- **2x** Timeout
+- **1x** ReferenceError (undefined symbol)
-- **1x** Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\
+- **1x** SyntaxError (parse/unsupported syntax)

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 — **Lowered array padding bail-out from 2^32-1 to 1M.** Yesterday's 2^32-1 threshold still allowed indices like `2147483648` to pad billions of `js-undefined` entries, hanging the worker. Without sparse-array support there's no semantic value in supporting >1M sparse padding; lowering the bail to 1M turns those tests into fast assertion failures instead of timeouts. Removes another timeout (Array 7→1). built-ins/Array stays at 23/45, but the run is faster and no longer wall-time-bound. conformance.sh: 148/148.
+
 - 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.