js-on-sx: rest in array pattern + nested pattern tolerance

Array destructure now supports [a, ...rest]. Rest entry is
transpiled to (define name (js-list-slice tmp i (len tmp))).

Nested patterns like [[a,b], c] now parse (as holes) instead of
erroring. jp-skip-balanced skips nested groups.

440/442 unit (+2), 148/148 slice unchanged.

lib/js/test.sh

@@ -1129,6 +1129,12 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 3003)
 (eval "(js-eval \"[3,1,2].sort((a,b)=>b-a).join(',')\")")
 
+;; ── Phase 11.destruct2: rest in arr pattern, nested tolerance ──
+(epoch 3100)
+(eval "(js-eval \"var [h, ...tl] = [1,2,3,4]; tl.length\")")
+(epoch 3101)
+(eval "(js-eval \"var [h, ...tl] = [1,2,3,4]; tl.join(',')\")")
+
 EPOCHS
 
 
@@ -1740,6 +1746,10 @@ check 3001 "sort lex (10<5)"                '"10,20,5"'
 check 3002 "sort numeric"                   '"1,2,3"'
 check 3003 "sort reverse"                   '"3,2,1"'
 
+# ── Phase 11.destruct2 ────────────────────────────────────────
+check 3100 "rest arr length"               '3'
+check 3101 "rest arr join"                 '"2,3,4"'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "✓ $PASS/$TOTAL JS-on-SX tests passed"