js-on-sx: spread ... in array literals and call args

Parser: jp-array-loop and jp-call-args-loop detect punct "..."
and emit (js-spread inner).

Transpile: when any element is spread, build array/args via
js-array-spread-build with (list "js-value" v) and (list
"js-spread" xs) tags.

Runtime: js-array-spread-build walks items, appending values or
splicing spreads via js-iterable-to-list (handles list/string/dict).

Works in arrays, call args, variadic fns (Math.max(...arr)),
and string spread ([...'abc']).

414/416 unit (+5), 148/148 slice unchanged.

lib/js/test.sh

@@ -1059,6 +1059,18 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 2401)
 (eval "(js-eval \"'abcd'.slice('1', '3')\")")
 
+;; ── Phase 11.spread: ... in arrays and calls ───────────────────
+(epoch 2500)
+(eval "(js-eval \"var a=[1,2]; var b=[...a,3,4]; b.length\")")
+(epoch 2501)
+(eval "(js-eval \"var a=[1,2]; var b=[0,...a,3]; b.join(',')\")")
+(epoch 2502)
+(eval "(js-eval \"function f(a,b,c){ return a+b+c; } var args=[1,2,3]; f(...args)\")")
+(epoch 2503)
+(eval "(js-eval \"Math.max(...[1,5,3])\")")
+(epoch 2504)
+(eval "(js-eval \"var a=[...'abc']; a.length\")")
+
 EPOCHS
 
 
@@ -1629,6 +1641,13 @@ check 2307 "Array.from w/ map"             '"2,4,6"'
 check 2400 "charAt coerces string"         '"c"'
 check 2401 "slice coerces strings"         '"bc"'
 
+# ── Phase 11.spread ───────────────────────────────────────────
+check 2500 "spread in array length"        '4'
+check 2501 "spread middle of array"        '"0,1,2,3"'
+check 2502 "spread in call args"           '6'
+check 2503 "spread Math.max"               '5'
+check 2504 "spread string"                 '3'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "✓ $PASS/$TOTAL JS-on-SX tests passed"