HS: targeted arith-only pseudo-cmd guard — allow all expr statements (+45 tests)

The previous callable check (0bef67dd) was too strict, rejecting legitimate
pseudo-commands like 'as' conversions, array literals, and property accesses.
The new approach:
- at-end? returns nil (trailing-then EOF guard, unchanged)
- arithmetic expressions (op symbols +/-/*//%) throw 'Pseudo-commands must
  be function calls', matching upstream _hyperscript behaviour
- everything else (literals, calls, as-expr, arrays, refs) passes through

Handles both hs-span-mode=false (raw list with op as first) and true (dict
with :kind "arith"). pseudoCommand 11/11, asExpression 36/42, arrayLiteral
8/8, breakpoint 2/2, evalStatically 8/8, regressions 16/16.

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

lib/hyperscript/parser.sx

@@ -2871,7 +2871,28 @@
                       (list (quote view-transition!) using body)))))
               ((and (= typ "keyword") (or (= val "on") (= val "init") (= val "def") (= val "behavior") (= val "live") (= val "when") (= val "bind")))
                 nil)
-              (true (if (at-end?) nil (parse-expr)))))))
+              (true
+                (if
+                  (at-end?)
+                  nil
+                  (let
+                    ((expr (parse-expr)))
+                    (if
+                      (if
+                        (and (dict? expr) (get expr :hs-ast))
+                        (= (get expr :kind) "arith")
+                        (and
+                          (list? expr)
+                          (let
+                            ((h (first expr)))
+                            (or
+                              (= h (quote +))
+                              (= h (quote -))
+                              (= h (quote *))
+                              (= h (quote /))
+                              (= h (make-symbol "%"))))))
+                      (error "Pseudo-commands must be function calls")
+                      expr))))))))
       (define
         parse-cmd-list
         (fn

shared/static/wasm/sx/hs-parser.sx

@@ -2871,7 +2871,28 @@
                       (list (quote view-transition!) using body)))))
               ((and (= typ "keyword") (or (= val "on") (= val "init") (= val "def") (= val "behavior") (= val "live") (= val "when") (= val "bind")))
                 nil)
-              (true (if (at-end?) nil (parse-expr)))))))
+              (true
+                (if
+                  (at-end?)
+                  nil
+                  (let
+                    ((expr (parse-expr)))
+                    (if
+                      (if
+                        (and (dict? expr) (get expr :hs-ast))
+                        (= (get expr :kind) "arith")
+                        (and
+                          (list? expr)
+                          (let
+                            ((h (first expr)))
+                            (or
+                              (= h (quote +))
+                              (= h (quote -))
+                              (= h (quote *))
+                              (= h (quote /))
+                              (= h (make-symbol "%"))))))
+                      (error "Pseudo-commands must be function calls")
+                      expr))))))))
       (define
         parse-cmd-list
         (fn