js-on-sx: switch/case/default/break

Parser: jp-parse-switch-stmt + jp-parse-switch-cases + jp-parse-switch-body.
AST: (js-switch discr (("case" val body) ("default" nil body) ...)).

Transpile: wraps body in (call/cc (fn (__break__) ...)). Each case
clause becomes (when (or __matched__ (js-strict-eq discr val))
(set! __matched__ true) body). Fall-through works naturally via
__matched__. Default appended as (when (not __matched__) body).

363/365 unit (+6), 148/148 slice unchanged.

lib/js/test.sh

@@ -937,6 +937,20 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1505)
 (eval "(js-eval \"Array.of(1,2,3).length\")")
 
+;; ── Phase 11.switch: switch/case/default/break ──────────────────
+(epoch 1600)
+(eval "(js-eval \"var r=0; switch(1){case 1: r=10; break;} r\")")
+(epoch 1601)
+(eval "(js-eval \"var r=0; switch(2){case 1: r=10; break; case 2: r=20; break;} r\")")
+(epoch 1602)
+(eval "(js-eval \"var r=0; switch(9){case 1: r=10; break; default: r=99;} r\")")
+(epoch 1603)
+(eval "(js-eval \"var r=0; switch(1){case 1: case 2: r=12; break;} r\")")
+(epoch 1604)
+(eval "(js-eval \"var r=''; switch('a'){case 'a': r='yes'; break;} r\")")
+(epoch 1605)
+(eval "(js-eval \"var r=0; switch(1){case 1: r=10; case 2: r=20; break;} r\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 180 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -1436,6 +1450,14 @@ check 1503 "Array.isArray yes"              'true'
 check 1504 "Array.isArray no"               'false'
 check 1505 "Array.of length"                '3'
 
+# ── Phase 11.switch ─────────────────────────────────────────────
+check 1600 "switch case 1 match"           '10'
+check 1601 "switch case 2 match"           '20'
+check 1602 "switch default"                '99'
+check 1603 "switch fallthrough stops on break" '12'
+check 1604 "switch on string"              '"yes"'
+check 1605 "switch fallthrough chains"     '20'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "✓ $PASS/$TOTAL JS-on-SX tests passed"