fix(vscode): stabilize inline diff scrolling

.changeset/calm-diff-scroll.md

@@ -0,0 +1,5 @@
+---
+"kilo-code": patch
+---
+
+Keep the Agent Manager inline diff position stable while scrolling upward through large reviews

packages/kilo-ui/src/components/diff-ssr.tsx

@@ -24,6 +24,7 @@ export function Diff<T>(props: SSRDiffProps<T>) {
     "selectedLines",
     "commentedLines",
     "virtualized",
+    "sizeKey",
   ])
   const workerPool = useWorkerPool(props.diffStyle)
 

packages/kilo-ui/src/components/diff.tsx

@@ -23,6 +23,23 @@ const MIN_PLACEHOLDER_HEIGHT = 160
 const MAX_PLACEHOLDER_HEIGHT = 1200
 type Job = { run: () => void; cancelled: boolean }
 
+const sizes = new WeakMap<object, Map<number, number>>()
+const WIDTH_LIMIT = 8
+
+function remember(key: object | undefined, width: number, height: number) {
+  if (!key || width <= 0 || height <= 0) return
+  const widths = sizes.get(key) ?? new Map<number, number>()
+  widths.delete(width)
+  widths.set(width, height)
+  if (widths.size > WIDTH_LIMIT) widths.delete(widths.keys().next().value!)
+  sizes.set(key, widths)
+}
+
+function reserved(key: object | undefined, width: number) {
+  if (!key || width <= 0) return
+  return sizes.get(key)?.get(width)
+}
+
 // A review can contain many expanded diff components. Creating one
 // IntersectionObserver per diff showed up in profiles, so all deferred diffs
 // share a single observer and only register their element + render callback.
@@ -173,6 +190,7 @@ export function Diff<T>(props: DiffProps<T>) {
     "commentedLines",
     "onRendered",
     "virtualized",
+    "sizeKey",
   ])
 
   const mobile = createMediaQuery("(max-width: 640px)")
@@ -247,7 +265,7 @@ export function Diff<T>(props: DiffProps<T>) {
 
   createEffect(() => {
     if (visible()) return
-    container.style.minHeight = `${estimate()}px`
+    container.style.minHeight = `${reserved(local.sizeKey, container.clientWidth) ?? estimate()}px`
   })
 
   createEffect(() => {
@@ -266,6 +284,17 @@ export function Diff<T>(props: DiffProps<T>) {
     return root
   }
 
+  createEffect(() => {
+    if (typeof ResizeObserver === "undefined") return
+    const resize = new ResizeObserver(() => {
+      const root = getRoot()
+      if (!visible() || !current() || !root?.querySelector("[data-line]")) return
+      remember(local.sizeKey, container.clientWidth, container.offsetHeight)
+    })
+    resize.observe(container)
+    onCleanup(() => resize.disconnect())
+  })
+
   const applyScheme = () => {
     const host = container.querySelector("diffs-container")
     if (!(host instanceof HTMLElement)) return
@@ -370,6 +399,7 @@ export function Diff<T>(props: DiffProps<T>) {
         if (token !== renderToken) return
         // Clear the height pin now that Pierre has rendered new content.
         container.style.minHeight = ""
+        remember(local.sizeKey, container.clientWidth, container.offsetHeight)
         setSelectedLines(lastSelection)
         local.onRendered?.()
       })
@@ -411,6 +441,7 @@ export function Diff<T>(props: DiffProps<T>) {
     if (typeof MutationObserver === "undefined") {
       container.style.minHeight = ""
       if (!root || !isReady(root)) return
+      remember(local.sizeKey, container.clientWidth, container.offsetHeight)
       setSelectedLines(lastSelection)
       local.onRendered?.()
       return
@@ -777,6 +808,7 @@ export function Diff<T>(props: DiffProps<T>) {
         if (!instance) return
         instance.setLineAnnotations(annotations ?? [])
         instance.rerender()
+        notifyRendered()
       },
       { defer: true },
     ),

packages/kilo-ui/src/pierre/index.ts

@@ -58,6 +58,9 @@ type DiffShared<T> = FileDiffOptions<T> & {
   // files so eager rendering does not expand full before/after content.
   // Defaults to virtualized.
   virtualized?: boolean
+  // Stable rendered-content identity used to preserve deferred height when a
+  // surrounding row virtualizer unmounts and later re-creates this diff.
+  sizeKey?: object
   class?: string
   classList?: ComponentProps<"div">["classList"]
 }

packages/kilo-vscode/tests/diff-scroll-preservation.spec.ts

@@ -2,11 +2,16 @@ import { expect, test, type Page } from "@playwright/test"
 
 const GLOBALS = "colorScheme:dark;theme:kilo-vscode;vscodeTheme:dark-modern"
 const STORY_ID = "agentmanager--full-screen-diff-agent-edit-scroll"
+const INLINE_STORY_ID = "agentmanager--diff-panel-scroll-up"
 
 function storyUrl() {
   return `/iframe.html?id=${STORY_ID}&viewMode=story&globals=${GLOBALS}`
 }
 
+function inlineStoryUrl() {
+  return `/iframe.html?id=${INLINE_STORY_ID}&viewMode=story&globals=${GLOBALS}`
+}
+
 async function disableAnimations(page: Page) {
   await page.addStyleTag({
     content: `
@@ -159,3 +164,60 @@ test("resets virtual measurements and scroll when the review context changes", a
   await expect.poll(async () => first.evaluate((el) => el.getBoundingClientRect().height)).toBe(1_200)
   await expect.poll(async () => scroller.evaluate((el) => el.scrollTop)).toBe(0)
 })
+
+test("keeps the inline diff position stable while scrolling upward", async ({ page }) => {
+  await page.setViewportSize({ width: 900, height: 760 })
+  await page.goto(inlineStoryUrl(), { waitUntil: "load" })
+  await disableAnimations(page)
+  await page.waitForSelector(".am-diff-content diffs-container", { state: "attached" })
+
+  const result = await page.locator(".am-diff-content").evaluate(async (el) => {
+    const frame = () => new Promise((resolve) => requestAnimationFrame(resolve))
+    const settle = async (count: number) => {
+      for (let i = 0; i < count; i++) await frame()
+    }
+    const seen = new Set(
+      Array.from(el.querySelectorAll("[data-file-path]"), (row) => row.getAttribute("data-file-path")),
+    )
+    let remounts = 0
+    const observer = new MutationObserver((records) => {
+      for (const record of records) {
+        for (const node of record.addedNodes) {
+          if (!(node instanceof HTMLElement)) continue
+          const rows = node.matches("[data-file-path]") ? [node] : Array.from(node.querySelectorAll("[data-file-path]"))
+          for (const row of rows) {
+            const file = row.getAttribute("data-file-path")
+            if (seen.has(file)) remounts++
+            seen.add(file)
+          }
+        }
+      }
+    })
+    observer.observe(el, { childList: true, subtree: true })
+
+    // Materialize every row once, then start from the settled bottom. The bug
+    // appears when upward scrolling re-creates rows above the viewport.
+    while (el.scrollTop < el.scrollHeight - el.clientHeight - 1) {
+      el.scrollTop = Math.min(el.scrollHeight - el.clientHeight, el.scrollTop + 120)
+      await frame()
+    }
+    await settle(30)
+
+    let correction = 0
+    let range = 0
+    while (el.scrollTop > 0) {
+      const height = el.scrollHeight
+      const intended = Math.max(0, el.scrollTop - 80)
+      el.scrollTop = intended
+      await settle(2)
+      correction = Math.max(correction, Math.abs(el.scrollTop - intended))
+      range = Math.max(range, Math.abs(el.scrollHeight - height))
+    }
+    observer.disconnect()
+    return { correction, range, remounts }
+  })
+
+  expect(result.remounts).toBeGreaterThan(0)
+  expect(result.correction).toBeLessThanOrEqual(1)
+  expect(result.range).toBeLessThanOrEqual(1)
+})

packages/kilo-vscode/tests/unit/agent-manager-diff-state.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "bun:test"
-import { mergeWorktreeDiffs } from "../../webview-ui/diff-viewer/diff-state"
+import { diffSizeKey, mergeWorktreeDiffs } from "../../webview-ui/diff-viewer/diff-state"
 import {
   EXTREME_DIFF_CHANGED_LINES,
   allOpenFiles,
@@ -28,6 +28,18 @@ function diff(overrides: Partial<WorktreeFileDiff>): WorktreeFileDiff {
   }
 }
 
+describe("diffSizeKey", () => {
+  it("changes with rendered content, style, and review context", () => {
+    const base = diff({ summarized: false, patch: "@@ -1 +1 @@\n-old\n+new\n" })
+    const key = diffSizeKey("review-a", base, "unified")
+
+    expect(diffSizeKey("review-a", base, "unified")).toBe(key)
+    expect(diffSizeKey("review-b", base, "unified")).not.toBe(key)
+    expect(diffSizeKey("review-a", base, "split")).not.toBe(key)
+    expect(diffSizeKey("review-a", { ...base, patch: "@@ -1 +1 @@\n-old\n+newer\n" }, "unified")).not.toBe(key)
+  })
+})
+
 describe("agent manager diff state", () => {
   it("preserves loaded detail and patch when summary metadata is unchanged", () => {
     const prev = [diff({ summarized: false, before: "old\n", after: "new\n", patch: "@@ -1 +1 @@\n-old\n+new\n" })]

packages/kilo-vscode/webview-ui/agent-manager/DiffPanel.tsx

@@ -60,7 +60,7 @@ import { VirtualDiffList } from "../diff-viewer/VirtualDiffList"
 import { treeOrder } from "../diff-viewer/file-tree-utils"
 import { isMarkdownFile, MarkdownDiffView } from "../diff-viewer/MarkdownDiffView"
 import { ImageDiffView } from "../diff-viewer/ImageDiffView"
-import { createDiffRows } from "../diff-viewer/diff-state"
+import { createDiffRows, diffSizeKey } from "../diff-viewer/diff-state"
 import { createDiffRequests } from "../diff-viewer/diff-requests"
 
 // --- Data model ---
@@ -728,6 +728,7 @@ export const DiffPanel: Component<DiffPanelProps> = (props) => {
                                     after={{ name: diff.file, contents: diff.after }}
                                     patch={diff.patch}
                                     diffStyle={props.diffStyle ?? "unified"}
+                                    sizeKey={diffSizeKey(props.sessionKey, diff, props.diffStyle ?? "unified")}
                                     virtualized={shouldVirtualizeDiff(diff)}
                                     annotations={annotationsForFile(diff.file)}
                                     renderAnnotation={buildAnnotation}

packages/kilo-vscode/webview-ui/diff-viewer/FullScreenDiffView.tsx

@@ -61,7 +61,7 @@ import { DiffEndMarker } from "./DiffEndMarker"
 import { VirtualDiffList } from "./VirtualDiffList"
 import { isMarkdownFile, MarkdownDiffView } from "./MarkdownDiffView"
 import { ImageDiffView } from "./ImageDiffView"
-import { createDiffRows } from "./diff-state"
+import { createDiffRows, diffSizeKey } from "./diff-state"
 import { createDiffRequests } from "./diff-requests"
 
 type DiffStyle = "unified" | "split"
@@ -802,6 +802,7 @@ export const FullScreenDiffView: Component<FullScreenDiffViewProps> = (props) =>
                                         after={{ name: diff.file, contents: diff.after }}
                                         patch={diff.patch}
                                         diffStyle={props.diffStyle}
+                                        sizeKey={diffSizeKey(props.sessionKey, diff, props.diffStyle)}
                                         virtualized={shouldVirtualizeDiff(diff)}
                                         annotations={annotationsForFile(diff.file)}
                                         renderAnnotation={buildAnnotation}

packages/kilo-vscode/webview-ui/diff-viewer/diff-state.ts

@@ -1,6 +1,18 @@
 import { createMemo, createSignal } from "solid-js"
 import type { WorktreeFileDiff } from "../src/types/messages"
 
+const sizeKeys = new WeakMap<
+  WorktreeFileDiff,
+  {
+    context: string | undefined
+    style: string
+    patch: string | undefined
+    before: string
+    after: string
+    key: object
+  }
+>()
+
 export function sameDiffMeta(left: WorktreeFileDiff, right: WorktreeFileDiff) {
   return (
     left.file === right.file &&
@@ -20,6 +32,23 @@ export function diffToken(diff: WorktreeFileDiff) {
   return diff.stamp ?? parts.join(":")
 }
 
+export function diffSizeKey(context: string | undefined, diff: WorktreeFileDiff, style: string) {
+  const cached = sizeKeys.get(diff)
+  if (
+    cached &&
+    cached.context === context &&
+    cached.style === style &&
+    cached.patch === diff.patch &&
+    cached.before === diff.before &&
+    cached.after === diff.after
+  )
+    return cached.key
+
+  const key = {}
+  sizeKeys.set(diff, { context, style, patch: diff.patch, before: diff.before, after: diff.after, key })
+  return key
+}
+
 // Keep each rendered row mounted while live detail refreshes replace its data.
 // Otherwise Solid's keyed <For> remounts the row and deferred rendering swaps a
 // previously rendered diff above the viewport for a short placeholder.

packages/kilo-vscode/webview-ui/src/stories/agent-manager.stories.tsx

@@ -87,13 +87,13 @@ const foldedDiffs: WorktreeFileDiff[] = [
 ]
 
 const ROWS = 140
-function edited(seed: string): WorktreeFileDiff {
+function edited(seed: string, file = "src/agent-edit.ts"): WorktreeFileDiff {
   const before = Array.from({ length: ROWS }, (_, i) => `const row${i} = "${seed}-old-${i}"\n`).join("")
   const after = Array.from({ length: ROWS }, (_, i) => `const row${i} = "${seed}-new-${i}"\n`).join("")
   const patch = [
-    "diff --git a/src/agent-edit.ts b/src/agent-edit.ts",
-    "--- a/src/agent-edit.ts",
-    "+++ b/src/agent-edit.ts",
+    `diff --git a/${file} b/${file}`,
+    `--- a/${file}`,
+    `+++ b/${file}`,
     `@@ -1,${ROWS} +1,${ROWS} @@`,
     ...before
       .trimEnd()
@@ -107,7 +107,7 @@ function edited(seed: string): WorktreeFileDiff {
   ].join("\n")
 
   return {
-    file: "src/agent-edit.ts",
+    file,
     status: "modified",
     additions: ROWS,
     deletions: ROWS,
@@ -322,6 +322,29 @@ export const DiffPanelWithDiffs: Story = {
   ),
 }
 
+export const DiffPanelScrollUp: Story = {
+  name: "DiffPanel - scroll upward through large diffs",
+  render: () => {
+    const diffs = Array.from({ length: 5 }, (_, i) => edited(`review-${i}`, `src/review-${i}.ts`))
+    return (
+      <StoryProviders noPadding>
+        <div style={{ height: "700px", display: "flex", "flex-direction": "column" }}>
+          <DiffPanel
+            diffs={diffs}
+            loading={false}
+            sessionKey="inline-scroll-up"
+            diffStyle="unified"
+            onDiffStyleChange={() => {}}
+            comments={[]}
+            onCommentsChange={() => {}}
+            onClose={() => {}}
+          />
+        </div>
+      </StoryProviders>
+    )
+  },
+}
+
 const buttonFixtureStyle: JSX.CSSProperties = {
   display: "inline-flex",
   "align-items": "center",