js-on-sx: built-in .length returns spec-defined values

String.fromCharCode.length, Math.max.length, Array.from.length
were returning 0 because their SX lambdas use &rest args with no
required params — but spec assigns each a specific length.
Added js-builtin-fn-length mapping JS name to spec length (12
entries). js-fn-length consults the 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.

lib/js/runtime.sx

@@ -113,13 +113,35 @@
     (let
       ((t (type-of f)))
       (cond
-        ((= t "lambda") (js-count-real-params (lambda-params f)))
+        ((= t "lambda")
+          (let
+            ((mapped (js-builtin-fn-length (js-unmap-fn-name (js-extract-fn-name f)))))
+            (if (>= mapped 0) mapped (js-count-real-params (lambda-params f)))))
         ((= t "function") 0)
         ((= t "component") 0)
         ((and (= t "dict") (contains? (keys f) "__callable__"))
           (js-fn-length (get f "__callable__")))
         (else 0)))))
 
+(define
+  js-builtin-fn-length
+  (fn
+    (name)
+    (cond
+      ((= name "fromCharCode") 1)
+      ((= name "fromCodePoint") 1)
+      ((= name "raw") 1)
+      ((= name "of") 0)
+      ((= name "from") 1)
+      ((= name "isArray") 1)
+      ((= name "max") 2)
+      ((= name "min") 2)
+      ((= name "hypot") 2)
+      ((= name "atan2") 2)
+      ((= name "imul") 2)
+      ((= name "pow") 2)
+      (else -1))))
+
 (define
   js-extract-fn-name
   (fn

lib/js/test262-scoreboard.json

@@ -1,45 +1,61 @@
 {
   "totals": {
-    "pass": 44,
-    "fail": 3,
-    "skip": 0,
-    "timeout": 3,
+    "pass": 21,
+    "fail": 17,
+    "skip": 5,
+    "timeout": 7,
     "total": 50,
-    "runnable": 50,
-    "pass_rate": 88.0
+    "runnable": 45,
+    "pass_rate": 46.7
   },
   "categories": [
     {
-      "category": "built-ins/Number",
+      "category": "built-ins/Array",
       "total": 50,
-      "pass": 44,
-      "fail": 3,
-      "skip": 0,
-      "timeout": 3,
-      "pass_rate": 88.0,
+      "pass": 21,
+      "fail": 17,
+      "skip": 5,
+      "timeout": 7,
+      "pass_rate": 46.7,
       "top_failures": [
         [
-          "Timeout",
-          3
+          "Test262Error (assertion failed)",
+          14
         ],
         [
-          "Test262Error (assertion failed)",
-          3
+          "Timeout",
+          7
+        ],
+        [
+          "TypeError: not a function",
+          2
+        ],
+        [
+          "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
+          1
         ]
       ]
     }
   ],
   "top_failure_modes": [
     [
-      "Timeout",
-      3
+      "Test262Error (assertion failed)",
+      14
     ],
     [
-      "Test262Error (assertion failed)",
-      3
+      "Timeout",
+      7
+    ],
+    [
+      "TypeError: not a function",
+      2
+    ],
+    [
+      "Unhandled: Not callable: {:2 43 :1 42 :0 41 :length 3}\\",
+      1
     ]
   ],
   "pinned_commit": "d5e73fc8d2c663554fb72e2380a8c2bc1a318a33",
-  "elapsed_seconds": 57.4,
+  "elapsed_seconds": 123.5,
   "workers": 1
 }

lib/js/test262-scoreboard.md

@@ -1,24 +1,28 @@
 # test262 scoreboard
 
 Pinned commit: `d5e73fc8d2c663554fb72e2380a8c2bc1a318a33`
-Wall time: 57.4s
+Wall time: 123.5s
 
-**Total:** 44/50 runnable passed (88.0%). Raw: pass=44 fail=3 skip=0 timeout=3 total=50.
+**Total:** 21/45 runnable passed (46.7%). Raw: pass=21 fail=17 skip=5 timeout=7 total=50.
 
 ## Top failure modes
 
-- **3x** Timeout
-- **3x** Test262Error (assertion failed)
+- **14x** Test262Error (assertion failed)
+- **7x** Timeout
+- **2x** TypeError: not a function
+- **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/Number | 44 | 3 | 0 | 3 | 50 | 88.0% |
+| built-ins/Array | 21 | 17 | 5 | 7 | 50 | 46.7% |
 
 ## Per-category top failures (min 10 runnable, worst first)
 
-### built-ins/Number  (44/50 — 88.0%)
+### built-ins/Array  (21/45 — 46.7%)
 
-- **3x** Timeout
-- **3x** Test262Error (assertion failed)
+- **14x** Test262Error (assertion failed)
+- **7x** Timeout
+- **2x** TypeError: not a function
+- **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 — **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.
 
 - 2026-05-08 — **`Math.X.name` returns the JS-style method name.** `Math.acos.name`, `Math.acosh.name`, `Math.asin.name` were returning the SX symbol name (`"js-math-acos"` etc.). `js-unmap-fn-name` had mappings for the older Math methods but not the trig/hyperbolic/log family added later. Added mappings for sin, cos, tan, asin, acos, atan, atan2, sinh, cosh, tanh, asinh, acosh, atanh, exp, log, log2, log10, expm1, log1p, clz32, imul, fround. built-ins/Math: 42/45 → 45/45 (100%). conformance.sh: 148/148.