Parser: catch/finally in on handlers, cmd terminators — 279/831 (34%)

- parse-cmd: catch/finally/end/else/otherwise are now terminators that
  stop parse-cmd-list (return nil from parse-cmd)
- parse-on-feat: optional catch var handler / finally handler clauses
  after the command body, before 'end'
- emit-on: scan-on passes catch-info/finally-info through recursion,
  wraps compiled body in (guard (var (true catch-body)) body) when
  catch clause is present
- Runtime: hs-put! handles "start" (afterbegin) and "end" (beforeend)
- Removed duplicate conformance-dev.sx (all 110 tests already in behavioral)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/hyperscript/parser.sx

@@ -1201,6 +1201,9 @@
           (let
             ((typ (tp-type)) (val (tp-val)))
             (cond
+              ;; Terminators — these end a command list, not start a command
+              ((and (= typ "keyword") (or (= val "catch") (= val "finally") (= val "end") (= val "else") (= val "otherwise")))
+                nil)
               ((and (= typ "keyword") (= val "add"))
                 (do (adv!) (parse-add-cmd)))
               ((and (= typ "keyword") (= val "remove"))
@@ -1298,6 +1301,18 @@
                   ((source (if (match-kw "from") (parse-expr) nil)))
                   (let
                     ((body (parse-cmd-list)))
+                    ;; Parse optional catch/finally
+                    (let
+                      ((catch-clause
+                        (if (match-kw "catch")
+                          (let ((var (let ((v (tp-val))) (adv!) v))
+                                (handler (parse-cmd-list)))
+                            (list var handler))
+                          nil))
+                       (finally-clause
+                        (if (match-kw "finally")
+                          (parse-cmd-list)
+                          nil)))
                     (match-kw "end")
                     (let
                       ((parts (list (quote on) event-name)))
@@ -1307,7 +1322,10 @@
                           ((parts (if flt (append parts (list :filter flt)) parts)))
                           (let
                             ((parts (if source (append parts (list :from source)) parts)))
-                            (append parts (list body)))))))))))))
+                            (let ((parts (if catch-clause (append parts (list :catch catch-clause)) parts)))
+                              (let ((parts (if finally-clause (append parts (list :finally finally-clause)) parts)))
+                                (let ((parts (append parts (list body))))
+                                  parts)))))))))))))))
       (define
         parse-init-feat
         (fn