HS: viewTransition command (+9 tests)

Add 'start view transition [using EXPR] [then] BODY end' syntax.
- tokenizer: add 'view' as a keyword
- parser: add 'start' to cmd-kw? and dispatch to view-transition! AST node
- compiler: emit hs-view-transition! call from view-transition! node

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

lib/hyperscript/compiler.sx

@@ -1832,6 +1832,9 @@
                     (hs-to-sx (nth ast 2))))
                 ((= head (quote set-el!))
                   (list (quote hs-set-element!) (hs-to-sx (nth ast 1)) (hs-to-sx (nth ast 2))))
+                ((= head (quote view-transition!))
+                  (let ((body (nth ast 2)))
+                    (list (quote hs-view-transition!) (hs-to-sx (nth ast 1)) (if (nil? body) (quote nil) (hs-to-sx body)))))
                 ((= head (quote put!))
                   (let
                     ((val (hs-to-sx (nth ast 1)))

lib/hyperscript/parser.sx

@@ -2711,6 +2711,16 @@
                 (do (adv!) (list (quote exit))))
               ((and (= typ "keyword") (= val "js"))
                 (do (adv!) (parse-js-block)))
+              ((and (= typ "keyword") (= val "start"))
+                (do
+                  (adv!)
+                  (expect-kw! "view")
+                  (expect-kw! "transition")
+                  (let ((using (if (match-kw "using") (parse-expr) nil)))
+                    (match-kw "then")
+                    (let ((body (parse-cmd-list)))
+                      (match-kw "end")
+                      (list (quote view-transition!) using body)))))
               (true (parse-expr))))))
       (define
         parse-cmd-list
@@ -2767,7 +2777,8 @@
                 (= v "pick")
                 (= v "ask")
                 (= v "answer")
-                (= v "js"))))
+                (= v "js")
+                (= v "start"))))
           (define
             cl-collect
             (fn

lib/hyperscript/tokenizer.sx

@@ -131,6 +131,7 @@
     "append"
     "settle"
     "transition"
+    "view"
     "over"
     "closest"
     "next"