Step 18 (part 3): Expand parser — expressions, commands, features

Tokenizer:
  * and % now emit as operators (were silently swallowed)
  Added keywords: install, measure, behavior, called
  5 new arithmetic operator tests

Parser — expression layer:
  Arithmetic (+, -, *, /, %) via parse-arith
  Unary not, no, unary minus
  the X of Y possessive (parse-the-expr)
  as Type conversion, X in Y membership, array literals [...]
  fetch URL parsing fixed — no longer consumes "as" meant for fetch

Parser — 8 new commands:
  return, throw, append...to, tell...end, for...in...end,
  make a Type, install Behavior, measure

Parser — 2 new features:
  def name(params)...end, behavior Name(params)...end

Parser — enhanced:
  wait for event [from target], on every event modifier

33 new parser tests (16 suites), 5 tokenizer tests.
3043/3043 full build, zero regressions.

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

spec/tests/test-hyperscript-tokenizer.sx

@@ -185,6 +185,43 @@
       (assert= "number" (get (hs-tok tokens 1) "type"))
       (assert= "bracket-close" (get (hs-tok tokens 2) "type")))))
 
+(defsuite
+  "hs-tokenize-arithmetic-ops"
+  (deftest
+    "multiply operator"
+    (let
+      ((toks (hs-tokenize "4 * 5")))
+      (assert= "number" (get (nth toks 0) "type"))
+      (assert= "op" (get (nth toks 1) "type"))
+      (assert= "*" (get (nth toks 1) "value"))
+      (assert= "number" (get (nth toks 2) "type"))))
+  (deftest
+    "modulo operator"
+    (let
+      ((toks (hs-tokenize "10 % 3")))
+      (assert= "op" (get (nth toks 1) "type"))
+      (assert= "%" (get (nth toks 1) "value"))))
+  (deftest
+    "star as style not operator"
+    (let
+      ((toks (hs-tokenize "*color")))
+      (assert= "style" (get (nth toks 0) "type"))
+      (assert= "color" (get (nth toks 0) "value"))))
+  (deftest
+    "division operator"
+    (let
+      ((toks (hs-tokenize "10 / 2")))
+      (assert= "op" (get (nth toks 1) "type"))
+      (assert= "/" (get (nth toks 1) "value"))))
+  (deftest
+    "mixed arithmetic"
+    (let
+      ((toks (hs-tokenize "1 + 2 * 3")))
+      (assert= "op" (get (nth toks 1) "type"))
+      (assert= "+" (get (nth toks 1) "value"))
+      (assert= "op" (get (nth toks 3) "type"))
+      (assert= "*" (get (nth toks 3) "value")))))
+
 (defsuite
   "hs-tokenize-comments"
   (deftest