js-on-sx: 10 new String.prototype methods (at, codePointAt, lastIndexOf, localeCompare, replaceAll, normalize, ...)

New methods added:
- at(i) — negative-index aware
- codePointAt(i) — returns char code at index
- lastIndexOf — walks right-to-left via js-string-last-index-of helper
- localeCompare — simple lexicographic (ignores locale)
- replaceAll — works with strings and regex-source
- normalize — no-op stub
- toLocaleLowerCase / toLocaleUpperCase — delegate to non-locale variants
- isWellFormed / toWellFormed — assume always well-formed

10 new unit tests, 489/491 total.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/js/test.sh

@@ -1213,6 +1213,28 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 3709)
 (eval "(js-eval \"var a=[1,2,3]; a.keys().join(',')\")")
 
+;; ── Phase 11.strmore: more String.prototype methods ─────────
+(epoch 3800)
+(eval "(js-eval \"'hello'.at(0)\")")
+(epoch 3801)
+(eval "(js-eval \"'hello'.at(-1)\")")
+(epoch 3802)
+(eval "(js-eval \"'hello'.codePointAt(0)\")")
+(epoch 3803)
+(eval "(js-eval \"'hello world hello'.lastIndexOf('hello')\")")
+(epoch 3804)
+(eval "(js-eval \"'abc'.localeCompare('abd')\")")
+(epoch 3805)
+(eval "(js-eval \"'abc'.localeCompare('abc')\")")
+(epoch 3806)
+(eval "(js-eval \"'hello hello'.replaceAll('hello', 'bye')\")")
+(epoch 3807)
+(eval "(js-eval \"'a,b,c'.replaceAll(',', '-')\")")
+(epoch 3808)
+(eval "(js-eval \"'hi'.toLocaleUpperCase()\")")
+(epoch 3809)
+(eval "(js-eval \"'HI'.toLocaleLowerCase()\")")
+
 ;; ── Phase 11.arrlike: Array.prototype.* on {length, 0:..., 1:...} ──
 (epoch 3500)
 (eval "(js-eval \"var a = {length: 3, 0: 41, 1: 42, 2: 43}; Array.prototype.slice.call(a).length\")")
@@ -1887,6 +1909,18 @@ check 3707 "arr.toReversed"                '"2,1,3"'
 check 3708 "arr.toSorted"                  '"1,1,3,4,5"'
 check 3709 "arr.keys"                      '"0,1,2"'
 
+# ── Phase 11.strmore: more String.prototype methods ───────────
+check 3800 "'hello'.at(0)"                 '"h"'
+check 3801 "'hello'.at(-1)"                '"o"'
+check 3802 "'hello'.codePointAt(0)"        '104'
+check 3803 "lastIndexOf found"             '12'
+check 3804 "localeCompare less"            '-1'
+check 3805 "localeCompare equal"           '0'
+check 3806 "replaceAll multiple"           '"bye bye"'
+check 3807 "replaceAll commas"             '"a-b-c"'
+check 3808 "toLocaleUpperCase"             '"HI"'
+check 3809 "toLocaleLowerCase"             '"hi"'
+
 # ── Phase 11.arrlike: array-like receivers on Array.prototype ─
 check 3500 "slice.call arrLike length"     '3'
 check 3501 "slice.call arrLike join"       '"41,42,43"'