perf(vscode): coalesce task timeline performance optimization

.changeset/calm-timeline-follow.md

@@ -0,0 +1,5 @@
+---
+"kilo-code": patch
+---
+
+Keep task timelines in place while reviewing earlier activity across Kilo chat surfaces, and resume following updates from the latest bar.

packages/kilo-vscode/tests/unit/timeline-sizes.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from "vitest"
-import { sizes, MAX_HEIGHT } from "../../webview-ui/src/utils/timeline/sizes"
+import { sizes, pinned, MAX_HEIGHT } from "../../webview-ui/src/utils/timeline/sizes"
 import type { Part, TextPart, ToolPart, StepFinishPart } from "../../webview-ui/src/types/messages"
 
 function mkText(text: string): TextPart {
@@ -89,4 +89,10 @@ describe("timeline sizes", () => {
       expect(Number.isInteger(bar.height)).toBe(true)
     }
   })
+
+  it("detects whether scrolling should follow new bars", () => {
+    expect(pinned({ scrollLeft: 100, scrollWidth: 200, clientWidth: 100 })).toBe(true)
+    expect(pinned({ scrollLeft: 88, scrollWidth: 200, clientWidth: 100 })).toBe(true)
+    expect(pinned({ scrollLeft: 87, scrollWidth: 200, clientWidth: 100 })).toBe(false)
+  })
 })

packages/kilo-vscode/webview-ui/src/components/chat/TaskTimeline.tsx

@@ -16,7 +16,7 @@ import { Component, Index, Show, createMemo, createEffect, createSignal, on, onC
 import { Portal } from "solid-js/web"
 import { useSession } from "../../context/session"
 import { color, label } from "../../utils/timeline/colors"
-import { sizes, MAX_HEIGHT } from "../../utils/timeline/sizes"
+import { sizes, pinned, MAX_HEIGHT } from "../../utils/timeline/sizes"
 import type { Part, Message } from "../../types/messages"
 
 export interface TimelineBar {
@@ -73,19 +73,34 @@ export const TaskTimeline: Component = () => {
   const bars = createMemo(() => collect(messages(), allParts()))
   const busy = () => session.status() === "busy"
 
-  // Auto-scroll to the latest bar when new bars appear
+  // Reading scrollWidth and writing scrollLeft synchronously for every appended bar can
+  // force repeated layout during streamed part updates. Batch those appends behind one
+  // animation frame, after Solid has applied the current DOM updates. Only follow while
+  // pinned so inspecting earlier activity is not interrupted by incoming bars.
   let prev = 0
+  let frame: number | undefined
+  let follow = true
+  const onScroll = () => {
+    if (ref) follow = pinned(ref)
+  }
   createEffect(
     on(
       () => bars().length,
       (len) => {
-        if (len > prev && ref) {
-          ref.scrollLeft = ref.scrollWidth
+        if (len > prev && ref && follow && frame === undefined) {
+          frame = requestAnimationFrame(() => {
+            frame = undefined
+            if (!ref || !follow) return
+            ref.scrollLeft = ref.scrollWidth
+          })
         }
         prev = len
       },
     ),
   )
+  onCleanup(() => {
+    if (frame !== undefined) cancelAnimationFrame(frame)
+  })
 
   const hideTip = () => {
     tipBar = undefined
@@ -161,6 +176,7 @@ export const TaskTimeline: Component = () => {
           onPointerUp={onPointerUp}
           onPointerCancel={onPointerUp}
           onPointerLeave={hideTip}
+          onScroll={onScroll}
         >
           <Index each={bars()}>
             {(bar) => {

packages/kilo-vscode/webview-ui/src/utils/timeline/sizes.ts

@@ -20,6 +20,17 @@ export interface BarSize {
   content: number
 }
 
+export interface TimelineScroll {
+  scrollLeft: number
+  scrollWidth: number
+  clientWidth: number
+}
+
+/** Keep following updates when the viewport is within one bar of the right edge. */
+export function pinned(scroll: TimelineScroll, slack = BAR_W): boolean {
+  return scroll.scrollWidth - scroll.clientWidth - scroll.scrollLeft <= slack
+}
+
 // ── Content length ───────────────────────────────────────────────────
 
 function content(part: Part): number {