diff --git a/src/components/markdown.tsx b/src/components/markdown.tsx
index 742e49c6..dadb2fdf 100644
--- a/src/components/markdown.tsx
+++ b/src/components/markdown.tsx
@@ -7,6 +7,7 @@ interface MarkdownProps {
   isDark?: boolean
   size?: "base" | "sm" | "tight"
   disableHighlight?: boolean
+  onRendered?: () => void
 }
 
 export function Markdown(props: MarkdownProps) {
@@ -14,6 +15,10 @@ export function Markdown(props: MarkdownProps) {
   let containerRef: HTMLDivElement | undefined
   let latestRequestedText = ""
 
+  const notifyRendered = () => {
+    Promise.resolve().then(() => props.onRendered?.())
+  }
+
   createEffect(async () => {
     const part = props.part
     const rawText = typeof part.text === "string" ? part.text : ""
@@ -34,11 +39,13 @@ export function Markdown(props: MarkdownProps) {
 
         if (latestRequestedText === text) {
           setHtml(rendered)
+          notifyRendered()
         }
       } catch (error) {
         console.error("Failed to render markdown:", error)
         if (latestRequestedText === text) {
           setHtml(text)
+          notifyRendered()
         }
       }
       return
@@ -47,6 +54,7 @@ export function Markdown(props: MarkdownProps) {
     const cache = part.renderCache
     if (cache && cache.text === text && cache.theme === themeKey) {
       setHtml(cache.html)
+      notifyRendered()
       return
     }
 
@@ -56,12 +64,14 @@ export function Markdown(props: MarkdownProps) {
       if (latestRequestedText === text) {
         setHtml(rendered)
         part.renderCache = { text, html: rendered, theme: themeKey }
+        notifyRendered()
       }
     } catch (error) {
       console.error("Failed to render markdown:", error)
       if (latestRequestedText === text) {
         setHtml(text)
         part.renderCache = { text, html: text, theme: themeKey }
+        notifyRendered()
       }
     }
   })
@@ -110,6 +120,7 @@ export function Markdown(props: MarkdownProps) {
           setHtml(rendered)
           const themeKey = Boolean(props.isDark) ? "dark" : "light"
           part.renderCache = { text, html: rendered, theme: themeKey }
+          notifyRendered()
         }
       } catch (error) {
         console.error("Failed to re-render markdown after language load:", error)
diff --git a/src/components/message-stream.tsx b/src/components/message-stream.tsx
index f635a76a..3c1d8714 100644
--- a/src/components/message-stream.tsx
+++ b/src/components/message-stream.tsx
@@ -154,6 +154,7 @@ interface ToolCacheEntry {
   toolPart: any
   messageInfo?: any
   signature: string
+  contentKey: string
   item: ToolDisplayItem
 }
 
@@ -174,9 +175,26 @@ export default function MessageStream(props: MessageStreamProps) {
   function createToolSignature(message: Message, toolPart: any, toolIndex: number, messageInfo?: any): string {
     const messageId = message.id
     const partId = typeof toolPart?.id === "string" ? toolPart.id : `${messageId}-tool-${toolIndex}`
-    const status = toolPart?.state?.status ?? messageInfo?.state?.status ?? ""
-    const version = message.version ?? 0
-    return `${messageId}:${partId}:${status}:${version}`
+    return `${messageId}:${partId}`
+  }
+
+  function createToolContentKey(toolPart: any, messageInfo?: any): string {
+    const state = toolPart?.state ?? {}
+    const metadata = state?.metadata ?? {}
+    const input = state?.input ?? {}
+    const output = state?.output ?? {}
+    const error = state?.error ?? null
+    const title = state?.title ?? null
+    return JSON.stringify({
+      tool: toolPart?.tool ?? null,
+      status: state?.status ?? null,
+      title,
+      input,
+      output,
+      metadata,
+      error,
+      messageInfoState: messageInfo?.state ?? null,
+    })
   }
 
   const sessionInfo = createMemo(() => {
@@ -353,15 +371,27 @@ export default function MessageStream(props: MessageStreamProps) {
         const toolKey = typeof toolPart?.id === "string" ? toolPart.id : `${message.id}-tool-${toolIndex}`
 
         const toolSignature = createToolSignature(message, toolPart, toolIndex, messageInfo)
+        const contentKey = createToolContentKey(toolPart, messageInfo)
         const toolEntry = toolItemCache.get(toolKey)
         if (toolEntry && toolEntry.signature === toolSignature) {
-          toolEntry.toolPart = toolPart
-          toolEntry.messageInfo = messageInfo
-          toolEntry.signature = toolSignature
-          toolEntry.item.toolPart = toolPart
-          toolEntry.item.messageInfo = messageInfo
-          newToolCache.set(toolKey, toolEntry)
-          items.push(toolEntry.item)
+          if (toolEntry.contentKey !== contentKey) {
+            const updatedItem: ToolDisplayItem = {
+              ...toolEntry.item,
+              toolPart,
+              messageInfo,
+            }
+            toolEntry.toolPart = toolPart
+            toolEntry.messageInfo = messageInfo
+            toolEntry.signature = toolSignature
+            toolEntry.contentKey = contentKey
+            toolEntry.item = updatedItem
+            console.debug("[ToolCall] update", toolKey, toolPart?.state?.status)
+            newToolCache.set(toolKey, toolEntry)
+            items.push(updatedItem)
+          } else {
+            newToolCache.set(toolKey, toolEntry)
+            items.push(toolEntry.item)
+          }
         } else {
           const toolItem: ToolDisplayItem = {
             type: "tool",
@@ -369,7 +399,8 @@ export default function MessageStream(props: MessageStreamProps) {
             toolPart,
             messageInfo,
           }
-          newToolCache.set(toolKey, { toolPart, messageInfo, signature: toolSignature, item: toolItem })
+          console.debug("[ToolCall] create", toolKey, toolPart?.state?.status)
+          newToolCache.set(toolKey, { toolPart, messageInfo, signature: toolSignature, contentKey, item: toolItem })
           items.push(toolItem)
         }
       }
@@ -568,7 +599,7 @@ export default function MessageStream(props: MessageStreamProps) {
                   <span>Tool Call</span>
                   <span class="tool-name">{toolPart?.tool || "unknown"}</span>
                 </div>
-                <ToolCall toolCall={toolPart} toolCallId={toolPart?.id} />
+                <ToolCall toolCall={toolPart} toolCallId={item.key} />
               </div>
             )
           }}
diff --git a/src/components/tool-call.tsx b/src/components/tool-call.tsx
index 05b9be7f..674ed493 100644
--- a/src/components/tool-call.tsx
+++ b/src/components/tool-call.tsx
@@ -1,7 +1,63 @@
-import { createSignal, Show, For, createEffect } from "solid-js"
+import { createSignal, Show, For, createEffect, onCleanup } from "solid-js"
 import { isToolCallExpanded, toggleToolCallExpanded, setToolCallExpanded } from "../stores/tool-call-state"
 import { Markdown } from "./markdown"
 import { useTheme } from "../lib/theme"
+import type { TextPart } from "../types/message"
+
+// Module-level cache for stable TextPart objects per tool call
+const markdownPartCache = new Map<string, TextPart>()
+const toolScrollState = new Map<string, { scrollTop: number; atBottom: boolean }>()
+
+function updateScrollState(id: string, element: HTMLElement) {
+  if (!id) return
+  const distanceFromBottom = element.scrollHeight - (element.scrollTop + element.clientHeight)
+  const atBottom = distanceFromBottom <= 2
+  toolScrollState.set(id, { scrollTop: element.scrollTop, atBottom })
+}
+
+function restoreScrollState(id: string, element: HTMLElement) {
+  if (!id) return
+  const state = toolScrollState.get(id)
+  if (!state) {
+    requestAnimationFrame(() => {
+      element.scrollTop = element.scrollHeight
+      updateScrollState(id, element)
+    })
+    return
+  }
+
+  requestAnimationFrame(() => {
+    if (state.atBottom) {
+      element.scrollTop = element.scrollHeight
+    } else {
+      const maxScrollTop = Math.max(element.scrollHeight - element.clientHeight, 0)
+      element.scrollTop = Math.min(state.scrollTop, maxScrollTop)
+    }
+    updateScrollState(id, element)
+  })
+}
+
+function getCachedMarkdownPart(id: string, text: string): TextPart {
+  if (!id) {
+    // No caching case - return fresh object
+    return { type: "text", text }
+  }
+
+  const part = markdownPartCache.get(id)
+  if (!part) {
+    const freshPart: TextPart = { type: "text", text }
+    markdownPartCache.set(id, freshPart)
+    return freshPart
+  }
+
+  if (part.text !== text) {
+    const freshPart: TextPart = { type: "text", text }
+    markdownPartCache.set(id, freshPart)
+    return freshPart
+  }
+
+  return part
+}
 
 interface ToolCallProps {
   toolCall: any
@@ -103,6 +159,14 @@ export default function ToolCall(props: ToolCallProps) {
   const expanded = () => isToolCallExpanded(toolCallId())
   const [initializedId, setInitializedId] = createSignal<string | null>(null)
 
+  let markdownContainerRef: HTMLDivElement | undefined
+
+  const handleMarkdownRendered = () => {
+    const id = toolCallId()
+    if (!id || !markdownContainerRef) return
+    restoreScrollState(id, markdownContainerRef)
+  }
+
   createEffect(() => {
     const id = toolCallId()
     if (!id || initializedId() === id) return
@@ -114,6 +178,32 @@ export default function ToolCall(props: ToolCallProps) {
     setInitializedId(id)
   })
 
+  // Restore scroll position when content updates
+  createEffect(() => {
+    const id = toolCallId()
+    const element = markdownContainerRef
+    if (!id || !element) return
+
+    const tool = toolName()
+    if (tool === "todowrite" || tool === "task") return
+
+    const content = getMarkdownContent(tool, props.toolCall?.state || {})
+    if (!content) return
+
+    restoreScrollState(id, element)
+  })
+
+  // Cleanup cache entry when component unmounts or toolCallId changes
+  createEffect(() => {
+    const id = toolCallId()
+    if (!id) return
+
+    onCleanup(() => {
+      markdownPartCache.delete(id)
+      toolScrollState.delete(id)
+    })
+  })
+
   const statusIcon = () => {
     const status = props.toolCall?.state?.status || ""
     switch (status) {
@@ -292,12 +382,33 @@ export default function ToolCall(props: ToolCallProps) {
     const messageClass = `message-text tool-call-markdown${isLarge ? " tool-call-markdown-large" : ""}`
     const disableHighlight = state?.status === "running"
 
+    const cachedPart = getCachedMarkdownPart(toolCallId(), content)
+
     return (
-      <div class={messageClass}>
+      <div
+        class={messageClass}
+        ref={(element) => {
+          markdownContainerRef = element || undefined
+          const id = toolCallId()
+          if (!element || !id) return
+
+          if (!toolScrollState.has(id)) {
+            requestAnimationFrame(() => {
+              if (!markdownContainerRef || toolCallId() !== id) return
+              markdownContainerRef.scrollTop = markdownContainerRef.scrollHeight
+              updateScrollState(id, markdownContainerRef)
+            })
+          } else {
+            restoreScrollState(id, element)
+          }
+        }}
+        onScroll={(event) => updateScrollState(toolCallId(), event.currentTarget)}
+      >
         <Markdown
-          part={{ type: "text", text: content }}
+          part={cachedPart}
           isDark={isDark()}
           disableHighlight={disableHighlight}
+          onRendered={handleMarkdownRendered}
         />
       </div>
     )
diff --git a/src/styles/components.css b/src/styles/components.css
index a2ba9fed..b01a5c17 100644
--- a/src/styles/components.css
+++ b/src/styles/components.css
@@ -763,6 +763,15 @@ button.button-primary {
   padding: 0;
   font-size: var(--font-size-xs);
   line-height: var(--line-height-tight);
+  max-height: calc(15 * 1.4em);
+  overflow-y: auto;
+  scrollbar-width: thin;
+  scrollbar-color: var(--border-base) transparent;
+  scrollbar-gutter: stable both-edges;
+}
+
+.tool-call-markdown-large {
+  max-height: calc(50 * 1.4em);
 }
 
 .tool-call-markdown .markdown-code-block {
@@ -780,33 +789,25 @@ button.button-primary {
 .tool-call-markdown .markdown-code-block pre {
   margin: 0 !important;
   min-height: auto;
-  max-height: calc(15 * 1.4em);
-  overflow-y: auto;
-  scrollbar-width: thin;
-  scrollbar-color: var(--border-base) transparent;
-  scrollbar-gutter: stable both-edges;
+  max-height: none;
+  overflow-y: visible;
 }
 
-.tool-call-markdown .markdown-code-block pre::-webkit-scrollbar {
+.tool-call-markdown::-webkit-scrollbar {
   width: 8px;
 }
 
-.tool-call-markdown .markdown-code-block pre::-webkit-scrollbar-track {
+.tool-call-markdown::-webkit-scrollbar-track {
   background: transparent;
 }
 
-.tool-call-markdown .markdown-code-block pre::-webkit-scrollbar-thumb {
+.tool-call-markdown::-webkit-scrollbar-thumb {
   background-color: var(--border-base);
   border-radius: 4px;
   border: 2px solid transparent;
   background-clip: padding-box;
 }
 
-.tool-call-markdown-large .markdown-code-block pre {
-  min-height: auto;
-  max-height: calc(50 * 1.4em);
-}
-
 .tool-call-section h4 {
   font-size: var(--font-size-xs);
   font-weight: var(--font-weight-semibold);