HS reset/first/last: defaultValue tracking, list-of-elements reset, find().first|last

Mock DOM:
- El now tracks defaultValue/defaultChecked/defaultSelected and a reset()
  method that walks descendant form controls, restoring them.
- setAttribute(value|checked|selected) sets the matching default-* too, so
  the initial HTML state can be restored later.
- parseHTMLFragments + _setInnerHTML capture a textarea's textContent as
  its value AND defaultValue.

Generator (pw-body):
- add_action / add_assertion extract .first() / .last() / .nth(N) modifiers
  into (nth (dom-query-all …) i) or a (let ((_all …)) (nth _all (- … 1)))
  tail so multi-match helpers hit the right element.

Compiler:
- emit-reset! with a .<class>/.<sel> query target now compiles to hs-query-all
  so 'reset .resettable' resets every matching control (not just the first).

Net: reset 1→8 (100%).

tests/playwright/generate-sx-tests.py

@@ -800,19 +800,24 @@ def parse_dev_body(body, elements, var_names):
 
     def add_action(stmt):
         am = re.search(
-            r"find\((['\"])(.+?)\1\)(?:\.(?:first|last)\(\)|\.nth\((\d+)\))?"
+            r"find\((['\"])(.+?)\1\)(?:\.(first|last)\(\)|\.nth\((\d+)\))?"
             r"\.(click|dispatchEvent|fill|check|uncheck|focus|selectOption)\(([^)]*)\)",
             stmt,
         )
         if not am or 'expect' in stmt:
             return False
         selector = am.group(2)
-        nth_idx = am.group(3)
-        action_type = am.group(4)
-        action_arg = am.group(5).strip("'\"")
+        first_last = am.group(3)
+        nth_idx = am.group(4)
+        action_type = am.group(5)
+        action_arg = am.group(6).strip("'\"")
         target = selector_to_sx(selector, elements, var_names)
         if nth_idx is not None:
             target = f'(nth (dom-query-all (dom-body) "{selector}") {nth_idx})'
+        elif first_last == 'last':
+            target = f'(let ((_all (dom-query-all (dom-body) "{selector}"))) (nth _all (- (len _all) 1)))'
+        elif first_last == 'first':
+            target = f'(nth (dom-query-all (dom-body) "{selector}") 0)'
         if action_type == 'click':
             ops.append(f'(dom-dispatch {target} "click" nil)')
         elif action_type == 'dispatchEvent':
@@ -837,7 +842,7 @@ def parse_dev_body(body, elements, var_names):
 
     def add_assertion(stmt):
         em = re.search(
-            r"expect\(find\((['\"])(.+?)\1\)(?:\.(?:first|last)\(\)|\.nth\((\d+)\))?\)\.(not\.)?"
+            r"expect\(find\((['\"])(.+?)\1\)(?:\.(first|last)\(\)|\.nth\((\d+)\))?\)\.(not\.)?"
             r"(toHaveText|toHaveClass|toHaveCSS|toHaveAttribute|toHaveValue|toBeVisible|toBeHidden|toBeChecked)"
             r"\(((?:[^()]|\([^()]*\))*)\)",
             stmt,
@@ -845,13 +850,18 @@ def parse_dev_body(body, elements, var_names):
         if not em:
             return False
         selector = em.group(2)
-        nth_idx = em.group(3)
-        negated = bool(em.group(4))
-        assert_type = em.group(5)
-        args_str = em.group(6)
+        first_last = em.group(3)
+        nth_idx = em.group(4)
+        negated = bool(em.group(5))
+        assert_type = em.group(6)
+        args_str = em.group(7)
         target = selector_to_sx(selector, elements, var_names)
         if nth_idx is not None:
             target = f'(nth (dom-query-all (dom-body) "{selector}") {nth_idx})'
+        elif first_last == 'last':
+            target = f'(let ((_all (dom-query-all (dom-body) "{selector}"))) (nth _all (- (len _all) 1)))'
+        elif first_last == 'first':
+            target = f'(nth (dom-query-all (dom-body) "{selector}") 0)'
         sx = pw_assertion_to_sx(target, negated, assert_type, args_str)
         if sx:
             ops.append(sx)