perf: memoize message HTML to avoid re-parsing on every keystroke

marked.parse runs on all messages each render. With long conversations
this makes typing sluggish. useMemo caches rendered HTML per message,
only recomputing when messages or cwd change.

Also deferred textarea resize to requestAnimationFrame.

src/components/ChatPane.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useRef, useState } from 'preact/hooks'
+import { useEffect, useRef, useState, useMemo } from 'preact/hooks'
 import { marked } from 'marked'
 
 import mermaid from 'mermaid'
@@ -201,6 +201,15 @@ export function ChatPane({ session, cfg, messages, onSend, onStop, browsePath, b
   const [renaming, setRenaming] = useState(false)
   const [renameVal, setRenameVal] = useState('')
 
+  // Pre-render message HTML so typing in PromptBar doesn't re-parse everything
+  const renderedHtml = useMemo(() =>
+    messages.map(msg =>
+      (msg.role === 'user' || msg.role === 'assistant')
+        ? linkifyPaths((marked.parse(msg.content) as string), session.cwd)
+        : ''),
+    [messages, session.cwd]
+  )
+
   const startRename = () => { setRenaming(true); setRenameVal(sid) }
   const commitRename = () => {
     setRenaming(false)
@@ -251,7 +260,7 @@ export function ChatPane({ session, cfg, messages, onSend, onStop, browsePath, b
           <div key={i} class={`message ${msg.role}`}>
             <div class="msg-bubble">
               {msg.role === 'user' ? (
-                <div class="md" dangerouslySetInnerHTML={{ __html: linkifyPaths((marked.parse(msg.content) as string).replace(/^<p>/, '<p><span class="msg-prefix">u: </span>'), session.cwd) }} />
+                <div class="md" dangerouslySetInnerHTML={{ __html: renderedHtml[i].replace(/^<p>/, '<p><span class="msg-prefix">u: </span>') }} />
               ) : msg.role === 'call' ? (
                 <ToolCall name={msg.name ?? ''} args={msg.content} output={messages[i+1]?.role === 'tool' && messages[i+1]?.name === msg.name ? messages[i+1].content : ''} />
               ) : msg.role === 'tool' ? (
@@ -265,7 +274,7 @@ export function ChatPane({ session, cfg, messages, onSend, onStop, browsePath, b
               ) : (
                 <div
                   class="md"
-                  dangerouslySetInnerHTML={{ __html: linkifyPaths((marked.parse(msg.content) as string).replace(/^<p>/, '<p><span class="msg-prefix">a: </span>'), session.cwd) }}
+                  dangerouslySetInnerHTML={{ __html: renderedHtml[i].replace(/^<p>/, '<p><span class="msg-prefix">a: </span>') }}
                 />
               )}
             </div>

src/components/PromptBar.tsx

@@ -31,8 +31,11 @@ export function PromptBar({ running, onSend, onStop }: Props) {
   const handleInput = (e: Event) => {
     const el = e.target as HTMLTextAreaElement
     setValue(el.value)
-    el.style.height = 'auto'
+    // Use requestAnimationFrame to batch the resize reflow
-    el.style.height = Math.min(el.scrollHeight, 160) + 'px'
+    requestAnimationFrame(() => {
+      el.style.height = '0'
+      el.style.height = Math.min(el.scrollHeight, 160) + 'px'
+    })
   }
 
   return (