js-on-sx: Number.prototype methods unwrap Number wrappers, TypeError on non-Number

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.
 
+- 2026-05-09 — **`Number.prototype.toFixed`/`toString`/etc. unwrap Number wrappers and throw TypeError on non-Number receivers.** Was passing `(js-this)` straight through to `js-number-to-fixed`, so calling `Number.prototype.toFixed(1)` directly on `Number.prototype` (a Number wrapper dict) raised `"Expected number, got dict"`. Per spec, these methods must extract the Number primitive value (from primitive or wrapper) and throw TypeError otherwise. Added `js-number-this-val` helper that handles primitive number, rational, `__js_number_value__`-marked wrapper, and raises TypeError for everything else. Routed all six Number.prototype methods through it. Result: built-ins/Number/prototype/toFixed 5/13 → 7/13. Number 26/30 holds. conformance.sh: 148/148.
+
 - 2026-05-09 — **`Array.prototype` methods carry spec lengths and names.** Continuation of the same fix. `js-array-proto-fn` was returning bare lambdas → `Array.prototype.push.length === 0` instead of `1`. Added `js-array-proto-fn-length` (lookup table for the ~30 method names — `push:1`, `slice:2`, `splice:2`, `concat:1`, `forEach:1`, `every:1`, `flat:0`, etc.) and changed the helper to return the dict-with-`__callable__` form. Now `Array.prototype.push.length === 1`, `Array.prototype.slice.length === 2`. Array 27/50, Array.prototype 8/30, Object 30/30 unchanged. conformance.sh: 148/148.
 
 - 2026-05-09 — **`Number.prototype` and `String.prototype` methods carry spec lengths and names.** Same shape as the earlier Function.prototype fix. Number.prototype.{toFixed/toExponential/toPrecision/toString/valueOf/toLocaleString} were bare `(fn ...)` lambdas → length 0 → tests assert e.g. `Number.prototype.toExponential.length === 1`. Wrapped each in a dict-with-`__callable__` with `:length` and `:name`. For String.prototype, `js-string-proto-fn` was a single helper applied to ~30 method names; added `js-string-proto-fn-length` (lookup table for spec-defined lengths: `concat:1`, `indexOf:1`, `slice:2`, `substring:2`, `replace:2`, etc.) and changed the helper to return the dict form, so all string methods now report correctly. Result: built-ins/Number/prototype 18/30 → 20/30, String/prototype 18/30 → 21/30. Number 26/30 holds, String 29/30. conformance.sh: 148/148.