diff --git a/src/components/tool-call.tsx b/src/components/tool-call.tsx
index 413e9e3f..42043507 100644
--- a/src/components/tool-call.tsx
+++ b/src/components/tool-call.tsx
@@ -4,8 +4,6 @@ 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) {
@@ -37,27 +35,6 @@ function restoreScrollState(id: string, element: HTMLElement) {
   })
 }
 
-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
@@ -184,7 +161,6 @@ export default function ToolCall(props: ToolCallProps) {
     if (!id) return
 
     onCleanup(() => {
-      markdownPartCache.delete(id)
       toolScrollState.delete(id)
     })
   })
@@ -367,7 +343,7 @@ 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)
+    const markdownPart: TextPart = { type: "text", text: content }
 
     return (
       <div
@@ -390,7 +366,7 @@ export default function ToolCall(props: ToolCallProps) {
         onScroll={(event) => updateScrollState(toolCallId(), event.currentTarget)}
       >
         <Markdown
-          part={cachedPart}
+          part={markdownPart}
           isDark={isDark()}
           disableHighlight={disableHighlight}
           onRendered={handleMarkdownRendered}
diff --git a/src/stores/sessions.ts b/src/stores/sessions.ts
index c03d94ed..e58ccdc6 100644
--- a/src/stores/sessions.ts
+++ b/src/stores/sessions.ts
@@ -185,33 +185,17 @@ export function computeDisplayParts(message: Message, showThinking: boolean): Me
   return { text, tool, reasoning, combined, showThinking, version }
 }
 
-function ensurePartVersionsMap(message: Message) {
-  if (!message.partVersions) {
-    message.partVersions = new Map()
-  }
-  return message.partVersions
+function initializePartVersion(part: any, version = 0) {
+  if (!part || typeof part !== "object") return
+  const partAny = part as any
+  partAny.version = typeof partAny.version === "number" ? partAny.version : version
 }
 
-function initializePartVersion(message: Message, part: any) {
-  const partId = typeof part?.id === "string" ? part.id : null
-  if (!partId) return
-  const versions = ensurePartVersionsMap(message)
-  if (!versions.has(partId)) {
-    versions.set(partId, 0)
-  }
-  const partAny = part as any
-  partAny.__version = versions.get(partId)
-}
-
-function bumpPartVersion(message: Message, part: any): number | undefined {
-  const partId = typeof part?.id === "string" ? part.id : null
-  if (!partId) return undefined
-  const versions = ensurePartVersionsMap(message)
-  const next = (versions.get(partId) ?? 0) + 1
-  versions.set(partId, next)
-  const partAny = part as any
-  partAny.__version = next
-  return next
+function bumpPartVersion(previousPart: any, nextPart: any): number {
+  const prevVersion = typeof previousPart?.version === "number" ? previousPart.version : -1
+  const nextVersion = prevVersion + 1
+  initializePartVersion(nextPart, nextVersion)
+  return nextVersion
 }
 
 function withSession(instanceId: string, sessionId: string, updater: (session: Session) => void) {
@@ -836,10 +820,9 @@ async function loadMessages(instanceId: string, sessionId: string, force = false
         timestamp: info.time?.created || Date.now(),
         status: "complete" as const,
         version: 0,
-        partVersions: new Map(),
       }
 
-      parts.forEach((part: any) => initializePartVersion(message, part))
+      parts.forEach((part: any) => initializePartVersion(part))
 
       message.displayParts = computeDisplayParts(message, preferences().showThinkingBlocks)
 
@@ -956,10 +939,9 @@ function handleMessageUpdate(instanceId: string, event: any): void {
         timestamp: Date.now(),
         status: "streaming" as const,
         version: 0,
-        partVersions: new Map(),
       }
 
-      initializePartVersion(newMessage, part)
+      initializePartVersion(part)
       newMessage.displayParts = computeDisplayParts(newMessage, preferences().showThinkingBlocks)
 
       let insertIndex = session.messages.length
@@ -1017,11 +999,11 @@ function handleMessageUpdate(instanceId: string, event: any): void {
       const partIndex = partMap.get(part.id)
 
       if (partIndex === undefined) {
+        initializePartVersion(part)
         baseParts.push(part)
         if (part.id && typeof part.id === "string") {
           partMap.set(part.id, baseParts.length - 1)
         }
-        initializePartVersion(message, part)
         shouldIncrementVersion = true
         // Clear render cache for new text parts
         if (part.type === "text") {
@@ -1040,8 +1022,8 @@ function handleMessageUpdate(instanceId: string, event: any): void {
           return
         }
 
+        bumpPartVersion(previousPart, part)
         baseParts[partIndex] = part
-        bumpPartVersion(message, part)
         if (part.type !== "text" || !previousPart || previousPart.text !== part.text) {
           shouldIncrementVersion = true
           // Clear render cache when text changes
@@ -1347,10 +1329,9 @@ async function sendMessage(
     timestamp: Date.now(),
     status: "sending",
     version: 0,
-    partVersions: new Map(),
   }
 
-  optimisticParts.forEach((part: any) => initializePartVersion(optimisticMessage, part))
+  optimisticParts.forEach((part: any) => initializePartVersion(part))
 
   optimisticMessage.displayParts = computeDisplayParts(optimisticMessage, preferences().showThinkingBlocks)
 
diff --git a/src/types/message.ts b/src/types/message.ts
index d780a76c..ff686fa8 100644
--- a/src/types/message.ts
+++ b/src/types/message.ts
@@ -21,7 +21,6 @@ export interface Message {
   timestamp: number
   status: "sending" | "sent" | "streaming" | "complete" | "error"
   version: number
-  partVersions?: Map<string, number>
   displayParts?: MessageDisplayParts
 }
 
@@ -29,6 +28,7 @@ export interface TextPart {
   id?: string
   type: "text"
   text: string
+  version?: number
   synthetic?: boolean
   renderCache?: RenderCache
 }