HS: parser+compiler — toggle for-in lookahead, throttled/debounced modifiers (-2 skips)

parser.sx parse-toggle-cmd: when seeing 'toggle .foo for', peek the
following two tokens. If they are '<ident> in', it is a for-in loop
and toggle does NOT consume 'for' as a duration clause. Restores the
trailing for-in to the command list.

parser.sx parse-on (handler modifiers): recognize 'throttled at <ms>'
and 'debounced at <ms>' as handler modifiers. Captured as :throttle /
:debounce kwargs in the on-form parts list.

compiler.sx emit-on: pre-extract :throttle / :debounce from parts via
new _strip-throttle-debounce helper before scan-on, then wrap the built
handler with (hs-throttle! handler ms) or (hs-debounce! handler ms).

runtime.sx: hs-throttle! — closure with __hs-last-fire timestamp,
fires immediately and drops events arriving within ms of the last fire.
hs-debounce! — closure with __hs-timer, clears any pending timer and
schedules a new setTimeout(handler, ms) so only the last burst event
fires.

Both formerly-architectural skips now pass:
- "toggle does not consume a following for-in loop"
- "throttled at <time> drops events within the window"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/playwright/generate-sx-tests.py

@@ -109,6 +109,19 @@ SKIP_TEST_NAMES = {
 # Manually-written SX test bodies for tests whose upstream body cannot be
 # auto-translated. Key = test name; value = SX lines to emit inside deftest.
 MANUAL_TEST_BODIES = {
+    # throttle: first click fires, subsequent within 200ms dropped.
+    # In the synchronous mock no time passes between two dom-dispatch calls.
+    "throttled at <time> drops events within the window": [
+        '    (hs-cleanup!)',
+        '    (let ((_el-d (dom-create-element "div")))',
+        '      (dom-set-attr _el-d "id" "d")',
+        '      (dom-set-attr _el-d "_" "on click throttled at 200ms then increment @n then put @n into me")',
+        '      (dom-append (dom-body) _el-d)',
+        '      (hs-activate! _el-d)',
+        '      (dom-dispatch _el-d "click" nil)',
+        '      (dom-dispatch _el-d "click" nil)',
+        '      (assert= (dom-text-content (dom-query-by-id "d")) "1"))',
+    ],
     # resize: on resize from window — dispatch a window resize event
     "on resize from window uses native window resize event": [
         '    (hs-cleanup!)',
@@ -120,6 +133,22 @@ MANUAL_TEST_BODIES = {
         '      (dom-dispatch (host-global "window") "resize" nil)',
         '      (assert= (dom-text-content _el) "fired"))',
     ],
+    # toggle: parser must not consume the trailing 'for x in [...]' as part of toggle's
+    # 'for <duration>' clause. After click: btn has .foo, #out has the last loop value.
+    "toggle does not consume a following for-in loop": [
+        '    (hs-cleanup!)',
+        '    (let ((_out (dom-create-element "div")) (_btn (dom-create-element "div")))',
+        '      (dom-set-attr _out "id" "out")',
+        '      (dom-set-attr _btn "id" "btn")',
+        '      (dom-set-attr _btn "_" "on click toggle .foo for x in [1, 2, 3] put x into #out end")',
+        '      (dom-append (dom-body) _out)',
+        '      (dom-append (dom-body) _btn)',
+        '      (hs-activate! _btn)',
+        '      (assert (not (dom-has-class? _btn "foo")))',
+        '      (dom-dispatch _btn "click" nil)',
+        '      (assert (dom-has-class? _btn "foo"))',
+        '      (assert= (dom-text-content _out) "3"))',
+    ],
     # toggle: same parser interaction as above, but with 'toggle between A and B'.
     "toggle between followed by for-in loop works": [
         '    (hs-cleanup!)',