perf(ui): skip pacing for static markdown

packages/ui/src/components/message-part.tsx

@@ -230,6 +230,16 @@ function createPacedValue(getValue: () => string, live?: () => boolean) {
   return value
 }
 
+function PacedMarkdown(props: { text: () => string; cacheKey: string; streaming: () => boolean }) {
+  const value = createPacedValue(props.text, props.streaming)
+
+  return (
+    <Show when={value()}>
+      <Markdown text={value()} cacheKey={props.cacheKey} streaming={props.streaming()} />
+    </Show>
+  )
+}
+
 function relativizeProjectPath(path: string, directory?: string) {
   if (!path) return ""
   if (!directory) return path
@@ -1373,8 +1383,7 @@ PART_MAPPING["text"] = function TextPartDisplay(props) {
   const streaming = createMemo(
     () => props.message.role === "assistant" && typeof (props.message as AssistantMessage).time.completed !== "number",
   )
-  const displayText = () => (part().text ?? "").trim()
-  const throttledText = createPacedValue(displayText, streaming)
+  const text = () => (part().text ?? "").trim()
   const isLastTextPart = createMemo(() => {
     const last = (data.store.part?.[props.message.id] ?? [])
       .filter((item): item is TextPart => item?.type === "text" && !!item.text?.trim())
@@ -1390,7 +1399,7 @@ PART_MAPPING["text"] = function TextPartDisplay(props) {
   const [copied, setCopied] = createSignal(false)
 
   const handleCopy = async () => {
-    const content = displayText()
+    const content = text()
     if (!content) return
     await navigator.clipboard.writeText(content)
     setCopied(true)
@@ -1398,10 +1407,12 @@ PART_MAPPING["text"] = function TextPartDisplay(props) {
   }
 
   return (
-    <Show when={throttledText()}>
+    <Show when={text()}>
       <div data-component="text-part">
         <div data-slot="text-part-body">
-          <Markdown text={throttledText()} cacheKey={part().id} streaming={streaming()} />
+          <Show when={streaming()} fallback={<Markdown text={text()} cacheKey={part().id} streaming={false} />}>
+            <PacedMarkdown text={text} cacheKey={part().id} streaming={streaming} />
+          </Show>
         </div>
         <Show when={showCopy()}>
           <div data-slot="text-part-copy-wrapper" data-interrupted={interrupted() ? "" : undefined}>
@@ -1437,12 +1448,13 @@ PART_MAPPING["reasoning"] = function ReasoningPartDisplay(props) {
     () => props.message.role === "assistant" && typeof (props.message as AssistantMessage).time.completed !== "number",
   )
   const text = () => part().text.trim()
-  const throttledText = createPacedValue(text, streaming)
 
   return (
-    <Show when={throttledText()}>
+    <Show when={text()}>
       <div data-component="reasoning-part">
-        <Markdown text={throttledText()} cacheKey={part().id} streaming={streaming()} />
+        <Show when={streaming()} fallback={<Markdown text={text()} cacheKey={part().id} streaming={false} />}>
+          <PacedMarkdown text={text} cacheKey={part().id} streaming={streaming} />
+        </Show>
       </div>
     </Show>
   )

packages/ui/src/components/session-turn.tsx

@@ -343,14 +343,12 @@ export function SessionTurn(
   })
   const assistantDerived = createMemo(() => {
     let visible = 0
-    let tail: "text" | "other" | undefined
     let reason: string | undefined
     const show = showReasoningSummaries()
     for (const message of assistantMessages()) {
       for (const part of list(data.store.part?.[message.id], emptyParts)) {
         if (partState(part, show) === "visible") {
           visible++
-          tail = part.type === "text" ? "text" : "other"
         }
         if (part.type === "reasoning" && part.text) {
           const h = heading(part.text)
@@ -358,10 +356,9 @@ export function SessionTurn(
         }
       }
     }
-    return { visible, tail, reason }
+    return { visible, reason }
   })
   const assistantVisible = createMemo(() => assistantDerived().visible)
-  const assistantTailVisible = createMemo(() => assistantDerived().tail)
   const reasoningHeading = createMemo(() => assistantDerived().reason)
   const showThinking = createMemo(() => {
     if (!working() || !!error()) return false