Centralize tool call scroll helpers

packages/ui/src/components/tool-call/renderers/task.tsx

@@ -40,7 +40,7 @@ export const taskRenderer: ToolRenderer = {
     }
     return base
   },
-  renderBody({ toolState, toolCall, messageVersion, partVersion }) {
+  renderBody({ toolState, toolCall, messageVersion, partVersion, scrollHelpers }) {
     const items = createMemo(() => {
       // Track the reactive change points so we only recompute when the part/message changes
       messageVersion?.()
@@ -63,7 +63,11 @@ export const taskRenderer: ToolRenderer = {
     if (items().length === 0) return null
 
     return (
-      <div class="message-text tool-call-markdown tool-call-task-container">
+      <div
+        class="message-text tool-call-markdown tool-call-task-container"
+        ref={(element) => scrollHelpers?.registerContainer(element)}
+        onScroll={scrollHelpers ? (event) => scrollHelpers.handleScroll(event as Event & { currentTarget: HTMLDivElement }) : undefined}
+      >
         <div class="tool-call-task-summary">
           <For each={items()}>
             {(item) => {
@@ -78,7 +82,9 @@ export const taskRenderer: ToolRenderer = {
             }}
           </For>
         </div>
+        {scrollHelpers?.renderSentinel?.()}
       </div>
     )
   },
 }
+

packages/ui/src/components/tool-call/types.ts

@@ -21,6 +21,12 @@ export interface DiffRenderOptions {
   label?: string
 }
 
+export interface ToolScrollHelpers {
+  registerContainer(element: HTMLDivElement | null, options?: { disableTracking?: boolean }): void
+  handleScroll(event: Event & { currentTarget: HTMLDivElement }): void
+  renderSentinel(options?: { disableTracking?: boolean }): JSXElement | null
+}
+
 export interface ToolRendererContext {
   toolCall: Accessor<ToolCallPart>
   toolState: Accessor<ToolState | undefined>
@@ -29,6 +35,7 @@ export interface ToolRendererContext {
   partVersion?: Accessor<number | undefined>
   renderMarkdown(options: MarkdownRenderOptions): JSXElement | null
   renderDiff(payload: DiffPayload, options?: DiffRenderOptions): JSXElement | null
+  scrollHelpers?: ToolScrollHelpers
 }
 
 export interface ToolRenderer {