HS generator+runtime: nth() dispatch+expect, dom-query-all SX-list passthrough, nth-of-type selector

- generate-sx-tests.py: add_action/add_assertion accept .nth(N) in PW-body
  tests so 'find(sel).nth(1).dispatchEvent(...)' lands as a dispatch on
  the Nth matching element, and assertions target that same element.
- shared/static/wasm/sx/dom.sx: dom-query-all hands through an already-SX
  list unchanged — the bridge often pre-converts NodeLists/arrays to SX
  lists, so the host-get 'length' / host-call 'item' loop was returning
  empty. Guards node-list=nil and non-list types too.
- tests/hs-run-filtered.js (mock DOM): fnd() understands
  ':nth-of-type(N)', ':first-of-type', ':last-of-type' by matching the
  stripped base selector and returning the correct-indexed sibling.
  Covers upstream tests that write 'find("div:nth-of-type(2)")' to
  pick the HS-owning element.
- Runtime runtime.sx: hs-sorted-by, hs-fetch format normalizer (JSON/
  Object/etc.), nil-safe hs-joined-by/hs-split-by, emit-fetch chain sets
  the-result when wrapped in let((it …)).

Net: take 0→6, hide 11→12, show 15→16, fetch 11→15,
collectionExpressions 13→15 (remaining are a WASM JIT bug on
{…} literals inside arrays).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/playwright/generate-sx-tests.py

@@ -796,16 +796,19 @@ def parse_dev_body(body, elements, var_names):
 
     def add_action(stmt):
         am = re.search(
-            r"find\((['\"])(.+?)\1\)(?:\.(?:first|last)\(\))?"
+            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)
-        action_type = am.group(3)
-        action_arg = am.group(4).strip("'\"")
+        nth_idx = am.group(3)
+        action_type = am.group(4)
+        action_arg = am.group(5).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})'
         if action_type == 'click':
             ops.append(f'(dom-dispatch {target} "click" nil)')
         elif action_type == 'dispatchEvent':
@@ -830,7 +833,7 @@ def parse_dev_body(body, elements, var_names):
 
     def add_assertion(stmt):
         em = re.search(
-            r"expect\(find\((['\"])(.+?)\1\)(?:\.(?:first|last)\(\))?\)\.(not\.)?"
+            r"expect\(find\((['\"])(.+?)\1\)(?:\.(?:first|last)\(\)|\.nth\((\d+)\))?\)\.(not\.)?"
             r"(toHaveText|toHaveClass|toHaveCSS|toHaveAttribute|toHaveValue|toBeVisible|toBeHidden|toBeChecked)"
             r"\(((?:[^()]|\([^()]*\))*)\)",
             stmt,
@@ -838,10 +841,13 @@ def parse_dev_body(body, elements, var_names):
         if not em:
             return False
         selector = em.group(2)
-        negated = bool(em.group(3))
-        assert_type = em.group(4)
-        args_str = em.group(5)
+        nth_idx = em.group(3)
+        negated = bool(em.group(4))
+        assert_type = em.group(5)
+        args_str = em.group(6)
         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})'
         sx = pw_assertion_to_sx(target, negated, assert_type, args_str)
         if sx:
             ops.append(sx)