fix(app): stabilize session timeline layout continuity (#34533)

packages/app/src/pages/session.tsx

@@ -26,6 +26,7 @@ import { FileProvider, selectionFromLines, useFile, type FileSelection, type Sel
 import { createStore } from "solid-js/store"
 import { ResizeHandle } from "@opencode-ai/ui/resize-handle"
 import { Select } from "@opencode-ai/ui/select"
+import { isScrollKeyTarget, scrollKey, scrollKeyOwner } from "@opencode-ai/ui/scroll-view"
 import { Tabs } from "@opencode-ai/ui/tabs"
 import { ButtonV2 } from "@opencode-ai/ui/v2/button-v2"
 import { createAutoScroll } from "@opencode-ai/ui/hooks"
@@ -940,9 +941,11 @@ export default function Page() {
       if (id && shouldFocusTerminalOnKeyDown(event) && focusTerminalById(id)) return
     }
 
-    // Only treat explicit scroll keys as potential "user scroll" gestures.
-    if (event.key === "PageUp" || event.key === "PageDown" || event.key === "Home" || event.key === "End") {
-      markScrollGesture()
+    const key = scrollKey(event)
+    if (key) {
+      if (!scroller || !isScrollKeyTarget(target ?? null, key)) return
+      if (scrollKeyOwner(scroller, target ?? null, key) !== scroller) return
+      markScrollGesture(scroller)
       return
     }
 

packages/app/src/pages/session/timeline/message-timeline.tsx

@@ -40,7 +40,7 @@ import { DialogFooter, DialogHeader, DialogTitleGroup, DialogV2 } from "@opencod
 import { InlineInput } from "@opencode-ai/ui/inline-input"
 import { ButtonV2 } from "@opencode-ai/ui/v2/button-v2"
 import { SessionRetry } from "@opencode-ai/session-ui/session-retry"
-import { ScrollView } from "@opencode-ai/ui/scroll-view"
+import { isScrollKeyTarget, scrollKey, scrollKeyOwner, ScrollView } from "@opencode-ai/ui/scroll-view"
 import { StickyAccordionHeader } from "@opencode-ai/ui/sticky-accordion-header"
 import { TextField } from "@opencode-ai/ui/text-field"
 import { TextReveal } from "@opencode-ai/ui/text-reveal"
@@ -441,6 +441,16 @@ export function MessageTimeline(props: {
     },
   })
   const resizeItem = virtualizer.resizeItem
+  let resizeAnchorScheduled = false
+  const anchorResizedBottom = () => {
+    if (resizeAnchorScheduled || props.hasScrollGesture()) return
+    resizeAnchorScheduled = true
+    queueMicrotask(() => {
+      resizeAnchorScheduled = false
+      if (!props.shouldAnchorBottom() || props.hasScrollGesture()) return
+      virtualizer.scrollToEnd()
+    })
+  }
   virtualizer.resizeItem = (index, size) => {
     const item = virtualizer.measurementsCache[index]
     const previous = item ? (virtualizer.itemSizeCache.get(item.key) ?? item.size) : undefined
@@ -462,9 +472,13 @@ export function MessageTimeline(props: {
       })
     }
     resizeItem(index, size)
+    if (root && props.shouldAnchorBottom()) anchorResizedBottom()
+  }
+  virtualizer.shouldAdjustScrollPositionOnItemSizeChange = (item) => {
+    if (props.shouldAnchorBottom()) return false
+    const first = virtualizer.range?.startIndex
+    return first !== undefined && item.index < first
   }
-  virtualizer.shouldAdjustScrollPositionOnItemSizeChange = (item, _delta, instance) =>
-    item.end <= instance.getLogicalScrollOffset()
   const virtualItemByKey = createMemo(
     () => new Map(virtualizer.getVirtualItems().map((item) => [item.key, item] as const)),
   )
@@ -491,24 +505,13 @@ export function MessageTimeline(props: {
     })
   })
 
-  let bottomAnchorSessionKey = ""
-  let bottomAnchorFrame: number | undefined
-
   const maybeAnchorBottom = () => {
-    const key = sessionKey()
-    if (bottomAnchorSessionKey === key) return
     if (timelineRows().length === 0) return
-    bottomAnchorSessionKey = key
-    if (!props.shouldAnchorBottom()) return
-    if (bottomAnchorFrame !== undefined) cancelAnimationFrame(bottomAnchorFrame)
+    if (!props.shouldAnchorBottom() || props.hasScrollGesture()) return
     if (resizePinFrame !== undefined) cancelAnimationFrame(resizePinFrame)
     clearPrependAnchor()
     if (prependAnchorFrame !== undefined) cancelAnimationFrame(prependAnchorFrame)
-    bottomAnchorFrame = requestAnimationFrame(() => {
-      bottomAnchorFrame = undefined
-      if (sessionKey() !== key) return
-      virtualizer.scrollToEnd()
-    })
+    virtualizer.scrollToEnd()
   }
 
   let measuredSessionKey = sessionKey()
@@ -527,7 +530,6 @@ export function MessageTimeline(props: {
     timelineCache.delete(ownerSessionKey)
     timelineCache.set(ownerSessionKey, { measurements: virtualizer.takeSnapshot(), toolOpen: { ...toolOpen } })
     while (timelineCache.size > 16) timelineCache.delete(timelineCache.keys().next().value!)
-    if (bottomAnchorFrame !== undefined) cancelAnimationFrame(bottomAnchorFrame)
     if (resizePinFrame !== undefined) cancelAnimationFrame(resizePinFrame)
     if (overscanFrame !== undefined) cancelAnimationFrame(overscanFrame)
     props.setRevealMessage?.(() => {})
@@ -600,6 +602,15 @@ export function MessageTimeline(props: {
     props.onMarkScrollGesture(event.currentTarget)
   }
 
+  const handleListKeyDown = (event: KeyboardEvent & { currentTarget: HTMLDivElement }) => {
+    const key = scrollKey(event)
+    if (!key) return
+    if (!isScrollKeyTarget(event.target, key)) return
+    if (scrollKeyOwner(event.currentTarget, event.target, key) !== event.currentTarget) return
+    if (!prependLoading) clearPrependAnchor()
+    props.onMarkScrollGesture(event.currentTarget)
+  }
+
   const handleListScroll = (event: Event & { currentTarget: HTMLDivElement }) => {
     if (prependLoading) updatePrependAnchor()
     props.onScheduleScrollState(event.currentTarget)
@@ -976,10 +987,16 @@ export function MessageTimeline(props: {
           .map((ref) => getMsgPart(ref.messageID, ref.partID))
           .filter((part): part is ToolPart => part?.type === "tool")
       })
+      const contextOpenKey = () => `context:${row().group.key}`
+      const open = createMemo(() => {
+        return toolOpen[contextOpenKey()] === true
+      })
 
       return (
         <ContextToolGroup
           parts={parts()}
+          open={open()}
+          onOpenChange={(value) => setToolOpen(contextOpenKey(), value)}
           busy={
             workingTurn(row().userMessageID) && lastAssistantGroupKey().get(row().userMessageID) === row().group.key
           }
@@ -1339,6 +1356,7 @@ export function MessageTimeline(props: {
         onTouchEnd={handleListTouchEnd}
         onTouchCancel={handleListTouchEnd}
         onPointerDown={handleListPointerDown}
+        onKeyDown={handleListKeyDown}
         onScroll={handleListScroll}
         onClick={props.onAutoScrollInteraction}
         class="relative min-w-0 w-full h-full"

packages/app/src/pages/session/timeline/projection.test.ts

@@ -0,0 +1,96 @@
+import { describe, expect, test } from "bun:test"
+import type { PartGroup } from "@opencode-ai/session-ui/message-part"
+import { reuseTimelineRows } from "./row-reconciliation"
+import { TimelineRow } from "./timeline-row"
+
+const context = (key: string, partIDs: string[], userMessageID = "user-1") =>
+  new TimelineRow.AssistantPart({
+    userMessageID,
+    group: {
+      key,
+      type: "context",
+      refs: partIDs.map((partID) => ({ messageID: "assistant-1", partID })),
+    } satisfies PartGroup,
+    previousAssistantPart: false,
+  })
+
+const user = (userMessageID = "user-1") => new TimelineRow.UserMessage({ userMessageID, anchor: true })
+const keys = (rows: TimelineRow.TimelineRow[]) => rows.map(TimelineRow.key)
+
+describe("reuseTimelineRows", () => {
+  test.each([
+    {
+      name: "reuses an unchanged context group",
+      previous: [context("context:a", ["a", "b"])],
+      rows: [context("context:a", ["a", "b"])],
+      expected: ["assistant-part:user-1:context:a"],
+      reused: [[0, 0]],
+    },
+    {
+      name: "preserves the group key when a member is appended",
+      previous: [context("context:a", ["a"])],
+      rows: [context("context:a", ["a", "b"])],
+      expected: ["assistant-part:user-1:context:a"],
+      reused: [],
+    },
+    {
+      name: "preserves the group key when the first member is removed",
+      previous: [context("context:a", ["a", "b"])],
+      rows: [context("context:b", ["b"])],
+      expected: ["assistant-part:user-1:context:a"],
+      reused: [],
+    },
+    {
+      name: "lets only the natural owner retain an old key after a split",
+      previous: [context("context:a", ["a", "b"])],
+      rows: [context("context:a", ["a"]), context("context:b", ["b"])],
+      expected: ["assistant-part:user-1:context:a", "assistant-part:user-1:context:b"],
+      reused: [],
+    },
+    {
+      name: "chooses the earliest prior key when groups merge",
+      previous: [context("context:a", ["a"]), context("context:b", ["b"])],
+      rows: [context("context:b", ["b", "a"])],
+      expected: ["assistant-part:user-1:context:a"],
+      reused: [],
+    },
+    {
+      name: "reserves an old key for its natural owner when two new groups compete",
+      previous: [context("context:a", ["a", "b"])],
+      rows: [context("context:b", ["b"]), context("context:a", ["a"])],
+      expected: ["assistant-part:user-1:context:b", "assistant-part:user-1:context:a"],
+      reused: [],
+    },
+    {
+      name: "does not reuse context identity across user messages",
+      previous: [context("context:a", ["a", "b"], "user-1")],
+      rows: [context("context:b", ["b"], "user-2")],
+      expected: ["assistant-part:user-2:context:b"],
+      reused: [],
+    },
+    {
+      name: "reuses an unaffected ordinary row",
+      previous: [user()],
+      rows: [user()],
+      expected: ["user-message:user-1"],
+      reused: [[0, 0]],
+    },
+    {
+      name: "does not create accidental key collisions",
+      previous: [context("context:a", ["a", "b", "c"])],
+      rows: [context("context:b", ["b"]), context("context:a", ["a"]), context("context:c", ["c"])],
+      expected: [
+        "assistant-part:user-1:context:b",
+        "assistant-part:user-1:context:a",
+        "assistant-part:user-1:context:c",
+      ],
+      reused: [],
+    },
+  ])("$name", ({ previous, rows, expected, reused }) => {
+    const result = reuseTimelineRows([...previous], [...rows])
+
+    expect(keys(result)).toEqual([...expected])
+    expect(new Set(keys(result)).size).toBe(result.length)
+    reused.forEach(([resultIndex, previousIndex]) => expect(result[resultIndex]).toBe(previous[previousIndex]))
+  })
+})

packages/app/src/pages/session/timeline/projection.ts

@@ -1,8 +1,11 @@
 import { Binary } from "@opencode-ai/core/util/binary"
 import type { AssistantMessage, Message, Part, SessionStatus, UserMessage } from "@opencode-ai/sdk/v2"
 import { createMemo, mapArray, type Accessor } from "solid-js"
+import { reuseTimelineRows } from "./row-reconciliation"
 import { Timeline, TimelineRow } from "./rows"
 
+export { reuseTimelineRows } from "./row-reconciliation"
+
 const emptyAssistantMessages: AssistantMessage[] = []
 
 export function createTimelineProjection(input: {
@@ -102,15 +105,3 @@ export function createTimelineProjection(input: {
     rows,
   }
 }
-
-export function reuseTimelineRows(previous: TimelineRow.TimelineRow[] | undefined, rows: TimelineRow.TimelineRow[]) {
-  if (!previous?.length) return rows
-  const byKey = new Map(previous.map((row) => [TimelineRow.key(row), row] as const))
-  const next = rows.map((row) => {
-    const existing = byKey.get(TimelineRow.key(row))
-    if (!existing) return row
-    return TimelineRow.equals(existing, row) ? existing : row
-  })
-  if (previous.length === next.length && previous.every((row, index) => row === next[index])) return previous
-  return next
-}

packages/app/src/pages/session/timeline/row-reconciliation.ts

@@ -0,0 +1,56 @@
+import { TimelineRow } from "./timeline-row"
+
+type ContextRow = Extract<TimelineRow.TimelineRow, { _tag: "AssistantPart" }>
+type PriorContext = { index: number; row: ContextRow }
+
+export function reuseTimelineRows(previous: TimelineRow.TimelineRow[] | undefined, rows: TimelineRow.TimelineRow[]) {
+  if (!previous?.length) return rows
+  const byKey = new Map(previous.map((row) => [TimelineRow.key(row), row] as const))
+  const contextByPart = new Map<string, PriorContext>()
+  previous.forEach((row, index) => {
+    if (row._tag !== "AssistantPart" || row.group.type !== "context") return
+    row.group.refs.forEach((ref) => contextByPart.set(`${row.userMessageID}:${ref.partID}`, { index, row }))
+  })
+  const reserved = new Map<string, number>()
+  rows.forEach((row, index) => {
+    if (row._tag !== "AssistantPart" || row.group.type !== "context") return
+    const key = TimelineRow.key(row)
+    if (byKey.has(key) && !reserved.has(key)) reserved.set(key, index)
+  })
+  const claimed = new Set<string>()
+  const next = rows.map((input, index) => {
+    const row = stabilizeContextKey(contextByPart, reserved, input, index, claimed)
+    const existing = byKey.get(TimelineRow.key(row))
+    if (!existing) return row
+    return TimelineRow.equals(existing, row) ? existing : row
+  })
+  if (previous.length === next.length && previous.every((row, index) => row === next[index])) return previous
+  return next
+}
+
+function stabilizeContextKey(
+  contextByPart: Map<string, PriorContext>,
+  reserved: Map<string, number>,
+  row: TimelineRow.TimelineRow,
+  rowIndex: number,
+  claimed: Set<string>,
+) {
+  if (row._tag !== "AssistantPart" || row.group.type !== "context") return row
+  const existing = row.group.refs.reduce<PriorContext | undefined>((result, ref) => {
+    const candidate = contextByPart.get(`${row.userMessageID}:${ref.partID}`)
+    if (!candidate) return result
+    const key = TimelineRow.key(candidate.row)
+    if (claimed.has(key)) return result
+    const owner = reserved.get(key)
+    if (owner !== undefined && owner !== rowIndex) return result
+    return !result || candidate.index < result.index ? candidate : result
+  }, undefined)
+  if (!existing) return row
+  const key = TimelineRow.key(existing.row)
+  claimed.add(key)
+  if (row.group.key === existing.row.group.key) return row
+  return new TimelineRow.AssistantPart({
+    ...row,
+    group: { ...row.group, key: existing.row.group.key },
+  })
+}

packages/app/src/pages/session/timeline/rows.ts

@@ -1,9 +1,9 @@
 import { parseCommentNote, readCommentMetadata } from "@/utils/comment-note"
 import { AssistantMessage, Part, SessionStatus, SnapshotFileDiff, UserMessage } from "@opencode-ai/sdk/v2"
-import { groupParts, PartGroup, renderable } from "@opencode-ai/session-ui/message-part"
-import { Data, Equal } from "effect"
+import { groupParts, renderable, type PartGroup } from "@opencode-ai/session-ui/message-part"
+import { TimelineRow, type SummaryDiff } from "./timeline-row"
 
-export type SummaryDiff = SnapshotFileDiff & { file: string }
+export { TimelineRow, type SummaryDiff } from "./timeline-row"
 
 export type TimelineRowMap = {
   TurnGap: { userMessageID: string }
@@ -29,81 +29,6 @@ export type TimelineRowMap = {
   Error: { userMessageID: string; text: string }
 }
 
-export namespace TimelineRow {
-  export class TurnGap extends Data.TaggedClass("TurnGap")<{
-    userMessageID: string
-  }> {}
-  export class CommentStrip extends Data.TaggedClass("CommentStrip")<{
-    userMessageID: string
-  }> {}
-  export class UserMessage extends Data.TaggedClass("UserMessage")<{
-    userMessageID: string
-    anchor: boolean
-  }> {}
-  export class TurnDivider extends Data.TaggedClass("TurnDivider")<{
-    userMessageID: string
-    label: "compaction" | "interrupted"
-  }> {}
-  export class AssistantPart extends Data.TaggedClass("AssistantPart")<{
-    userMessageID: string
-    group: PartGroup
-    previousAssistantPart: boolean
-  }> {}
-  export class Thinking extends Data.TaggedClass("Thinking")<{
-    userMessageID: string
-    reasoningHeading?: string
-  }> {}
-  export class DiffSummary extends Data.TaggedClass("DiffSummary")<{
-    userMessageID: string
-    diffs: SummaryDiff[]
-  }> {}
-  export class Error extends Data.TaggedClass("Error")<{
-    userMessageID: string
-    text: string
-  }> {}
-  export class Retry extends Data.TaggedClass("Retry")<{
-    userMessageID: string
-  }> {}
-
-  export type TimelineRow =
-    | TurnGap
-    | CommentStrip
-    | UserMessage
-    | TurnDivider
-    | AssistantPart
-    | Thinking
-    | DiffSummary
-    | Error
-    | Retry
-
-  export const key = (row: TimelineRow) => {
-    switch (row._tag) {
-      case "TurnGap":
-        return `turn-gap:${row.userMessageID}`
-      case "CommentStrip":
-        return `comment-strip:${row.userMessageID}`
-      case "UserMessage":
-        return `user-message:${row.userMessageID}`
-      case "TurnDivider":
-        return `turn-divider:${row.userMessageID}:${row.label}`
-      case "AssistantPart":
-        return `assistant-part:${row.userMessageID}:${row.group.key}`
-      case "Thinking":
-        return `thinking:${row.userMessageID}`
-      case "DiffSummary":
-        return `diff-summary:${row.userMessageID}`
-      case "Error":
-        return `error:${row.userMessageID}`
-      case "Retry":
-        return `retry:${row.userMessageID}`
-    }
-  }
-
-  export function equals(a: TimelineRow, b: TimelineRow) {
-    return Equal.equals(a, b)
-  }
-}
-
 export namespace Timeline {
   export function constructMessageRows(
     userMessage: UserMessage,

packages/app/src/pages/session/timeline/timeline-row.ts

@@ -0,0 +1,80 @@
+import type { SnapshotFileDiff } from "@opencode-ai/sdk/v2"
+import type { PartGroup } from "@opencode-ai/session-ui/message-part"
+import { Data, Equal } from "effect"
+
+export type SummaryDiff = SnapshotFileDiff & { file: string }
+
+export namespace TimelineRow {
+  export class TurnGap extends Data.TaggedClass("TurnGap")<{
+    userMessageID: string
+  }> {}
+  export class CommentStrip extends Data.TaggedClass("CommentStrip")<{
+    userMessageID: string
+  }> {}
+  export class UserMessage extends Data.TaggedClass("UserMessage")<{
+    userMessageID: string
+    anchor: boolean
+  }> {}
+  export class TurnDivider extends Data.TaggedClass("TurnDivider")<{
+    userMessageID: string
+    label: "compaction" | "interrupted"
+  }> {}
+  export class AssistantPart extends Data.TaggedClass("AssistantPart")<{
+    userMessageID: string
+    group: PartGroup
+    previousAssistantPart: boolean
+  }> {}
+  export class Thinking extends Data.TaggedClass("Thinking")<{
+    userMessageID: string
+    reasoningHeading?: string
+  }> {}
+  export class DiffSummary extends Data.TaggedClass("DiffSummary")<{
+    userMessageID: string
+    diffs: SummaryDiff[]
+  }> {}
+  export class Error extends Data.TaggedClass("Error")<{
+    userMessageID: string
+    text: string
+  }> {}
+  export class Retry extends Data.TaggedClass("Retry")<{
+    userMessageID: string
+  }> {}
+
+  export type TimelineRow =
+    | TurnGap
+    | CommentStrip
+    | UserMessage
+    | TurnDivider
+    | AssistantPart
+    | Thinking
+    | DiffSummary
+    | Error
+    | Retry
+
+  export const key = (row: TimelineRow) => {
+    switch (row._tag) {
+      case "TurnGap":
+        return `turn-gap:${row.userMessageID}`
+      case "CommentStrip":
+        return `comment-strip:${row.userMessageID}`
+      case "UserMessage":
+        return `user-message:${row.userMessageID}`
+      case "TurnDivider":
+        return `turn-divider:${row.userMessageID}:${row.label}`
+      case "AssistantPart":
+        return `assistant-part:${row.userMessageID}:${row.group.key}`
+      case "Thinking":
+        return `thinking:${row.userMessageID}`
+      case "DiffSummary":
+        return `diff-summary:${row.userMessageID}`
+      case "Error":
+        return `error:${row.userMessageID}`
+      case "Retry":
+        return `retry:${row.userMessageID}`
+    }
+  }
+
+  export function equals(a: TimelineRow, b: TimelineRow) {
+    return Equal.equals(a, b)
+  }
+}