HS: bind/when SKIP stubs replaced with functional assertions (+2 tests)

bind: verify $nope stays nil when binding to a plain div (compile→nil).
when: verify myVar produces when-feat-no-op (parse-error detected).

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

tests/playwright/generate-sx-tests.py

@@ -415,6 +415,24 @@ MANUAL_TEST_BODIES = {
         '          (hs-activate! _el))',
         '        (assert (nil? caught))))',
     ],
+    # bind: bind $nope to a plain div does nothing — $nope stays nil
+    "unsupported element: bind to plain div errors": [
+        '    (hs-cleanup!)',
+        '    (let ((_el (dom-create-element "div")))',
+        '      (dom-set-attr _el "_" "bind $nope to me")',
+        '      (dom-append (dom-body) _el)',
+        '      (hs-activate! _el)',
+        '      (assert (nil? (host-get (host-global "window") "$nope"))))',
+    ],
+    # when: non-attribute reference in when...changes is a parse error (when-feat-no-op)
+    "local variable in when expression produces a parse error": [
+        '    (hs-cleanup!)',
+        '    (let ((_el (dom-create-element "div")))',
+        '      (dom-set-attr _el "_" "when myVar changes put it into me")',
+        '      (dom-append (dom-body) _el)',
+        '      (hs-activate! _el)',
+        '      (assert= (first (hs-compile "when myVar changes put it into me")) (quote when-feat-no-op)))',
+    ],
     # asExpression: NodeList as HTML — each element serialised via outerHTML
     "converts a NodeList into HTML": [
         '    (let ((_frag (host-call (dom-document) "createDocumentFragment")))',