feat(html): adoption-style hydration with mismatch reporting

hydrate(oldNode, newNode) normalizes the client tree to parser text-node
granularity, walks both trees to report the first server/client markup
disagreement (node, text, attribute, or child count, with a path), then
morphs — matching nodes are adopted in place, the client render wins.
choo.mount() now hydrates and console.warns on mismatch.

Building this surfaced two real isomorphism divergences, both fixed:
adjacent text nodes from template holes vs the parser's merged runs
(folded via Node.normalize), and the server serializing onclick="" where
the browser sets a property — event handlers now leave no trace in server
markup at all.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014NgfSjHE11oFpoSnLVKLXd

packages/html/server.js

@@ -11,6 +11,7 @@ const BOOL_PROPS = [
 ]
 
 const boolPropRx = new RegExp('([^-a-z](' + BOOL_PROPS.join('|') + '))=["\']?$', 'i')
+const handlerRx = /[^-a-z](on[a-z]+)=$/i
 const query = /(?:="|&)[^"]*=$/
 
 export default function html (pieces, ...values) {
@@ -19,6 +20,15 @@ export default function html (pieces, ...values) {
   for (let i = 0; i < pieces.length; i++) {
     const piece = pieces[i]
     if (i < pieces.length - 1) {
+      // Event handlers are behavior, not markup: `onclick=${fn}` renders
+      // nothing at all, matching the browser renderer (which sets the
+      // handler as a property). v7 serialized a useless onclick="".
+      const handlerMatch = handlerRx.exec(piece)
+      if (handlerMatch && typeof values[i] === 'function') {
+        output += piece.slice(0, handlerMatch.index + 1).replace(/\s+$/, ' ')
+        continue
+      }
+
       if ((boolMatch = boolPropRx.exec(piece))) {
         output += piece.slice(0, boolMatch.index)
         if (values[i]) {
@@ -59,6 +69,9 @@ function handleValue (value) {
   if (typeof value === 'object') {
     if (typeof value.outerHTML === 'string') return value.outerHTML
     return Object.keys(value).reduce(function (str, key) {
+      // handlers in spread objects are behavior too — never serialized
+      if (typeof value[key] === 'function') return str
+
       if (str.length > 0) str += ' '
 
       if (BOOL_PROPS.indexOf(key) !== -1) {