js-on-sx: fix js-string-repeat arity collision, repeat() raises RangeError on neg/inf

lib/js/runtime.sx

@@ -3238,12 +3238,18 @@
 
 (define
   js-string-repeat
+  (fn
+    (s n)
+    (js-string-repeat-loop s n "")))
+
+(define
+  js-string-repeat-loop
   (fn
     (s n acc)
     (if
       (<= n 0)
       acc
-      (js-string-repeat s (- n 1) (str acc s)))))
+      (js-string-repeat-loop s (- n 1) (str acc s)))))
 
 (define
   js-string-pad
@@ -3383,7 +3389,16 @@
       ((= name "trimStart") (fn () (js-trim-left s)))
       ((= name "trimEnd") (fn () (js-trim-right s)))
       ((= name "repeat")
-        (fn (n) (js-string-repeat s (js-num-to-int n) "")))
+        (fn
+          (n)
+          (let
+            ((nn (js-to-number n)))
+            (cond
+              ((or (< nn 0) (= nn (js-infinity-value)))
+                (raise
+                  (js-new-call RangeError
+                    (js-args "Invalid count value"))))
+              (else (js-string-repeat-loop s (js-num-to-int nn) ""))))))
       ((= name "padStart")
         (fn
           (&rest args)
@@ -5732,12 +5747,6 @@
         (if (> (len sp) 10) (js-string-slice sp 0 10) sp))
       (else ""))))
 
-(define
-  js-string-repeat
-  (fn
-    (s n)
-    (if (<= n 0) "" (str s (js-string-repeat s (- n 1))))))
-
 (define
   js-json-unwrap-primitive
   (fn

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.
 
+- 2026-05-10 — **`String.prototype.repeat` no longer arity-collides with itself; raises RangeError on negative or +Infinity counts.** Earlier JSON.stringify iteration introduced a 2-arg `js-string-repeat` that shadowed the existing 3-arg `(s n acc)` accumulator implementation, breaking every `s.repeat(n)` call with "expects 2 args, got 3". Renamed the accumulator helper to `js-string-repeat-loop` and made `js-string-repeat` a 2-arg facade that delegates. Hooked the repeat method to raise RangeError when `count < 0` or `count = Infinity` per spec. Result: built-ins/String/prototype/repeat 7/13 → 11/13 (+4). conformance.sh: 148/148.
+
 - 2026-05-10 — **test262-runner inlines small upstream harness includes (`nans.js`, `sta.js`, `byteConversionValues.js`, `compareArray.js`) per-test.** The runner parsed `includes:` frontmatter but never used it, so tests like `built-ins/isNaN/return-true-nan.js` (which depends on `var NaNs = [...]`) failed with "ReferenceError: undefined symbol". Added `_load_harness_include` (cached) and `assemble_source` now prepends each allowlisted include's source to the test. Allowlist excludes large helpers like `propertyHelper.js` because per-test js-eval+JIT cost on a 371-line harness pushes tests over the 15s per-test timeout (regressed Math/abs 7/7 → 4/7 in a first-pass attempt before allowlisting). Result: built-ins/isNaN 2/7 → 3/7. conformance.sh: 148/148.
 
 - 2026-05-10 — **Real `Date.prototype.setFullYear/setMonth/setDate/setHours/setMinutes/setSeconds/setMilliseconds` (+ UTC variants) and a corrected `setTime`.** All Date setters were missing — only `setTime` existed and didn't validate. Added a unified `js-date-setter(d, field, args)` that decomposes the current ms into `(y mo da hh mm ss msv)` via `js-date-decompose`, splices in the `args` per the field's optional-arg contract (e.g. `setHours(h, m?, s?, ms?)`), recomposes via `js-date-civil-to-days`, and TimeClips at ±8.64e15. NaN args anywhere → ms set to NaN. Wired all 14 setters to the helper. Hit a parser gotcha: SX `cond` clause body is single-form only — multi-expression bodies like `(else (dict-set! ...) new-ms)` silently treat the second form as `(<first-result> new-ms)` ("Not callable: false"). Wrapped these in `(begin ...)`. Result: setFullYear 5/18 → 13/18 (+8). setHours 5/21 → 15/21 (+10). setMonth 3/15 → 9/15 (+6). setMinutes 4/16 → 10/16 (+6). setSeconds 3/15 → 9/15 (+6). setDate 2/12 → 6/12 (+4). setMilliseconds 2/12 → 6/12 (+4). setTime 4/9 → 6/9 (+2). conformance.sh: 148/148.