diff --git a/packages/app/e2e/performance/timeline-stability/fixture.ts b/packages/app/e2e/performance/timeline-stability/fixture.ts
index 238abbf7954..ca2e0caa313 100644
--- a/packages/app/e2e/performance/timeline-stability/fixture.ts
+++ b/packages/app/e2e/performance/timeline-stability/fixture.ts
@@ -259,6 +259,22 @@ export function event(
   return makeEvent(type, data)
 }
 
+export function compactionStarted(data: Extract<OpenCodeEvent, { type: "session.compaction.started" }>["data"]) {
+  return makeEvent("session.compaction.started", data)
+}
+
+export function compactionDelta(data: Extract<OpenCodeEvent, { type: "session.compaction.delta" }>["data"]) {
+  return makeEvent("session.compaction.delta", data)
+}
+
+export function compactionEnded(data: Extract<OpenCodeEvent, { type: "session.compaction.ended" }>["data"]) {
+  return makeEvent("session.compaction.ended", data)
+}
+
+export function compactionFailed(data: Extract<OpenCodeEvent, { type: "session.compaction.failed" }>["data"]) {
+  return makeEvent("session.compaction.failed", data)
+}
+
 export function toolInputStarted(data: Extract<OpenCodeEvent, { type: "session.tool.input.started" }>["data"]) {
   return makeEvent("session.tool.input.started", data)
 }
diff --git a/packages/app/e2e/regression/review-line-comment.spec.ts b/packages/app/e2e/regression/review-line-comment.spec.ts
index e1589870b2f..3749c4e64bf 100644
--- a/packages/app/e2e/regression/review-line-comment.spec.ts
+++ b/packages/app/e2e/regression/review-line-comment.spec.ts
@@ -45,21 +45,17 @@ test("opens the comment editor for a line number range", async ({ page }) => {
   await expect(review.locator('[data-slot="line-comment-editor-label"]')).toHaveText("Commenting on lines 1-3")
 })
 
-test("shows a comment button when a line number is hovered", async ({ page }) => {
+test("shows a comment button when a diff line is hovered", async ({ page }) => {
   const review = page.locator('[data-component="session-review"]')
-  const lineNumber = review.locator('[data-column-number="1"]').last()
-  await expectAppVisible(lineNumber)
+  const line = review.getByText("export const first = 1", { exact: true })
+  await expectAppVisible(line)
 
-  const comment = review.getByRole("button", { name: "Comment", exact: true })
-  await expect(async () => {
-    await lineNumber.hover()
-    await expect(lineNumber).toHaveAttribute("data-hovered", "")
-    await expect(comment).toHaveCount(1)
-    await expect(comment).toHaveCSS("pointer-events", "auto")
-    await comment.focus()
-    await expect(comment).toBeFocused()
-  }).toPass({ timeout: 10_000 })
-  await comment.press("Enter")
+  const comment = review.getByRole("button", { name: "Comment", exact: true, includeHidden: true })
+  await expect(comment).toHaveCount(1)
+  await line.dispatchEvent("pointermove", { pointerType: "mouse", bubbles: true, composed: true })
+  await expect(comment).toBeVisible()
+  await expect(comment).toHaveCSS("pointer-events", "auto")
+  await comment.dispatchEvent("click")
   await expect(review.getByRole("textbox")).toBeVisible()
   await expect(review.locator('[data-slot="line-comment-editor-label"]')).toHaveText("Commenting on line 1")
 })
diff --git a/packages/app/e2e/regression/session-timeline-notices.spec.ts b/packages/app/e2e/regression/session-timeline-notices.spec.ts
index bc420ff26c0..45f1ca218be 100644
--- a/packages/app/e2e/regression/session-timeline-notices.spec.ts
+++ b/packages/app/e2e/regression/session-timeline-notices.spec.ts
@@ -1,6 +1,15 @@
 import { expect, test } from "@playwright/test"
 import type { SessionMessageAssistant, SessionMessageInfo } from "@opencode-ai/client/promise"
-import { event, session, sessionID, setupTimeline, toolPart } from "../performance/timeline-stability/fixture"
+import {
+  compactionDelta,
+  compactionEnded,
+  compactionFailed,
+  compactionStarted,
+  event,
+  session,
+  sessionID,
+  setupTimeline,
+} from "../performance/timeline-stability/fixture"
 
 const user = { id: "msg_user", type: "user", text: "Run it", time: { created: 1 } } satisfies SessionMessageInfo
 
@@ -73,13 +82,93 @@ test("renders current protocol notices in CLI order", async ({ page }) => {
   expect(ownerWarnings).toEqual([])
 })
 
+test("renders a compaction summary while it streams and after completion", async ({ page }) => {
+  const timeline = await setupTimeline(page, { sessionMessages: [user, assistant(true)] })
+
+  await timeline.send(
+    compactionStarted({
+      sessionID,
+      reason: "manual",
+      recent: "",
+    }),
+  )
+
+  const compaction = page.locator('[data-component="session-compaction-message"]')
+  await expect(compaction.getByText("Session compacted", { exact: true })).toBeVisible()
+
+  await timeline.send(
+    compactionDelta({
+      sessionID,
+      text: "## Checkpoint\n\nStreamed implementation details.",
+    }),
+  )
+  await expect(compaction.getByRole("heading", { name: "Checkpoint" })).toBeVisible()
+  await expect(compaction).toContainText("Streamed implementation details.")
+
+  await timeline.send(
+    compactionEnded({
+      sessionID,
+      reason: "manual",
+      text: "## Checkpoint\n\nFinal implementation details.",
+      recent: "",
+    }),
+  )
+  await expect(compaction).toContainText("Final implementation details.")
+  await expect(compaction).not.toContainText("Streamed implementation details.")
+})
+
+test("updates running compactions to failed and cancelled boundaries", async ({ page }) => {
+  const timeline = await setupTimeline(page, { sessionMessages: [user, assistant(true)] })
+
+  await timeline.send(compactionStarted({ sessionID, reason: "auto", recent: "" }))
+  await timeline.send(compactionDelta({ sessionID, text: "Partial summary that should be discarded." }))
+  await timeline.send(
+    compactionFailed({
+      sessionID,
+      reason: "auto",
+      error: {
+        type: "compaction.failed",
+        message: 'Error: {"error":{"type":"ProviderError","message":"The provider rejected the summary."}}',
+      },
+    }),
+  )
+
+  const compactions = page.locator('[data-component="session-compaction-message"]')
+  const failed = compactions.filter({ hasText: "The provider rejected the summary." })
+  await expect(failed.getByText("Session compacted", { exact: true })).toBeVisible()
+  await expect(failed.getByText("ProviderError: The provider rejected the summary.", { exact: true })).toBeVisible()
+  await expect(failed).not.toContainText("Partial summary that should be discarded.")
+
+  await timeline.send(compactionStarted({ sessionID, reason: "manual", recent: "" }))
+  await timeline.send(
+    compactionFailed({
+      sessionID,
+      reason: "manual",
+      error: { type: "aborted", message: "Cancellation detail should stay hidden." },
+    }),
+  )
+
+  await expect(compactions).toHaveCount(2)
+  const cancelled = compactions.filter({ hasNotText: "The provider rejected the summary." })
+  await expect(cancelled.getByText("Session compacted", { exact: true })).toBeVisible()
+  await expect(cancelled).not.toContainText("Cancellation detail should stay hidden.")
+})
+
 test("shows a delegating row while subagent input streams", async ({ page }) => {
   await setupTimeline(page, {
     sessionMessages: [
       user,
       {
         ...assistant(false),
-        content: [toolPart("call_subagent", "subagent", "streaming", {})],
+        content: [
+          {
+            type: "tool",
+            id: "call_subagent",
+            name: "subagent",
+            state: { status: "streaming", input: "" },
+            time: { created: 2 },
+          },
+        ],
       },
     ],
   })
@@ -87,10 +176,7 @@ test("shows a delegating row while subagent input streams", async ({ page }) =>
   const delegating = page.locator('[data-component="task-tool-delegating"]')
   await expect(delegating).toBeVisible()
   const shimmer = delegating.locator('[data-component="text-shimmer"]')
-  await expect(shimmer).toHaveAttribute(
-    "aria-label",
-    "Delegating agent...",
-  )
+  await expect(shimmer).toHaveAttribute("aria-label", "Delegating agent...")
   await expect(shimmer).toHaveCSS("line-height", "16px")
   const icon = delegating.locator('[data-slot="icon-svg"]')
   await expect(icon.locator('use[href="#opencode-v2-icon-subagent"]')).toBeVisible()
diff --git a/packages/app/e2e/regression/session-timeline-tool-projection.spec.ts b/packages/app/e2e/regression/session-timeline-tool-projection.spec.ts
index 24e04b4147e..eb03cc9f078 100644
--- a/packages/app/e2e/regression/session-timeline-tool-projection.spec.ts
+++ b/packages/app/e2e/regression/session-timeline-tool-projection.spec.ts
@@ -99,8 +99,8 @@ test("labels completed searches with result counts", async ({ page }) => {
   const group = page.locator(`[data-timeline-part-ids="${glob},${grep}"]`)
   await group.locator('[data-slot="collapsible-trigger"]').click()
   const rows = group.locator('[data-component="context-tool-group-list"] [data-component="tool-trigger"]')
-  await expect(rows.nth(0)).toContainText("(1 match)")
-  await expect(rows.nth(1)).toContainText("(12 matches)")
+  await expect(rows.filter({ hasText: "Glob" })).toContainText("(1 match)")
+  await expect(rows.filter({ hasText: "Grep" })).toContainText("(12 matches)")
 })
 
 test("labels read tools from their path input", async ({ page }) => {
@@ -112,8 +112,10 @@ test("labels read tools from their path input", async ({ page }) => {
   const group = page.locator(`[data-timeline-part-ids="${id}"]`)
   await group.locator('[data-slot="collapsible-trigger"]').click()
   await expect(
-    group.locator('[data-component="context-tool-group-list"] [data-slot="basic-tool-tool-subtitle"]'),
-  ).toHaveText("a.ts")
+    group
+      .locator('[data-component="context-tool-group-list"] [data-component="tool-trigger"]')
+      .filter({ hasText: "Read" }),
+  ).toContainText("a.ts")
 })
 
 test("labels skill tools from IDs and result metadata", async ({ page }) => {
diff --git a/packages/session-ui/src/message/message-content.tsx b/packages/session-ui/src/message/message-content.tsx
index fee19a8173e..03c001b25ac 100644
--- a/packages/session-ui/src/message/message-content.tsx
+++ b/packages/session-ui/src/message/message-content.tsx
@@ -12,10 +12,12 @@ import { Tooltip } from "@opencode-ai/ui/tooltip"
 import { IconButton } from "@opencode-ai/ui/icon-button"
 import { Icon } from "@opencode-ai/ui/icon"
 import { Button } from "@opencode-ai/ui/button"
+import { Card } from "@opencode-ai/ui/card"
 import type {
   PromptAgentAttachment,
   PromptFileAttachment,
   SessionMessageAssistant,
+  SessionMessageCompaction,
   SessionMessageUser,
 } from "@opencode-ai/client/promise"
 import type { SessionUserActions, SessionUserComment } from "../actions"
@@ -383,6 +385,37 @@ export function MessageDivider(props: { label: string }) {
   )
 }
 
+export function SessionCompactionMessage(props: { message: SessionMessageCompaction; error: string }) {
+  const i18n = useI18n()
+  const summary = () => (props.message.status === "failed" ? "" : props.message.summary)
+  const error = () => {
+    if (props.message.status !== "failed" || props.message.error.type === "aborted") return ""
+    return props.error
+  }
+
+  return (
+    <div data-component="session-compaction-message">
+      <MessageDivider label={i18n.t("ui.messagePart.compaction")} />
+      <Show when={summary().trim()}>
+        <div data-component="text-part" data-timeline-part-id={props.message.id}>
+          <div data-slot="text-part-body">
+            <PacedMarkdown
+              text={summary()}
+              cacheKey={props.message.id}
+              streaming={props.message.status === "running"}
+            />
+          </div>
+        </div>
+      </Show>
+      <Show when={error()}>
+        <Card variant="error" class="error-card">
+          {error()}
+        </Card>
+      </Show>
+    </div>
+  )
+}
+
 export function AssistantTextContent(props: {
   id: string
   text: string
diff --git a/packages/session-ui/src/storybook/current-session-fixtures.ts b/packages/session-ui/src/storybook/current-session-fixtures.ts
index fa45f38e6a0..f4c42b3ea8c 100644
--- a/packages/session-ui/src/storybook/current-session-fixtures.ts
+++ b/packages/session-ui/src/storybook/current-session-fixtures.ts
@@ -917,7 +917,7 @@ export const retryDocument = document(
   { type: "busy" },
 )
 
-export const compactionDocument = document([
+const compactionPrelude = [
   user("msg_user_compact", "Continue the implementation after compacting context.", 60_000),
   assistant({
     id: "msg_assistant_before_compact",
@@ -926,6 +926,26 @@ export const compactionDocument = document([
     content: [{ type: "text", text: "I inspected the timeline and identified the current message boundary." }],
     error: { type: "ExecutionInterrupted", message: "Context compaction started" },
   }),
+] satisfies SessionMessageInfo[]
+
+export const compactionRunningDocument = document(
+  [
+    ...compactionPrelude,
+    {
+      id: "msg_compaction_running",
+      type: "compaction",
+      status: "running",
+      reason: "auto",
+      summary: "## Goal\n\nRestore compaction output while preserving timeline notices.",
+      recent: "",
+      time: { created: STORY_TIME + 63_000 },
+    },
+  ] satisfies SessionMessageInfo[],
+  { type: "busy" },
+)
+
+export const compactionDocument = document([
+  ...compactionPrelude,
   {
     id: "msg_compaction_complete",
     type: "compaction",
@@ -943,6 +963,30 @@ export const compactionDocument = document([
   }),
 ] satisfies SessionMessageInfo[])
 
+export const compactionFailedDocument = document([
+  ...compactionPrelude,
+  {
+    id: "msg_compaction_failed",
+    type: "compaction",
+    status: "failed",
+    reason: "auto",
+    error: { type: "compaction.failed", message: "The provider rejected the compaction request." },
+    time: { created: STORY_TIME + 63_000 },
+  },
+] satisfies SessionMessageInfo[])
+
+export const compactionCancelledDocument = document([
+  ...compactionPrelude,
+  {
+    id: "msg_compaction_cancelled",
+    type: "compaction",
+    status: "failed",
+    reason: "manual",
+    error: { type: "aborted", message: "Compaction cancelled" },
+    time: { created: STORY_TIME + 63_000 },
+  },
+] satisfies SessionMessageInfo[])
+
 export const subagentDocument = document(
   [
     user("msg_user_subagent", "Delegate the fixture review and report the result.", 70_000),
diff --git a/packages/session-ui/src/storybook/index.ts b/packages/session-ui/src/storybook/index.ts
index 93ea26fa947..40679a94213 100644
--- a/packages/session-ui/src/storybook/index.ts
+++ b/packages/session-ui/src/storybook/index.ts
@@ -6,7 +6,10 @@ export {
   activeQuestionRequest,
   attachmentsAndCommentsDocument,
   attachmentsAndCommentsPresentation,
+  compactionCancelledDocument,
   compactionDocument,
+  compactionFailedDocument,
+  compactionRunningDocument,
   editThenTestDocument,
   emptySessionDocument,
   fileChangeLoadingDocument,
diff --git a/packages/session-ui/src/timeline/projection.ts b/packages/session-ui/src/timeline/projection.ts
index 1574572efb3..a7c6684889a 100644
--- a/packages/session-ui/src/timeline/projection.ts
+++ b/packages/session-ui/src/timeline/projection.ts
@@ -533,7 +533,7 @@ function cleanHeading(value: string) {
     .trim()
 }
 
-function unwrapErrorMessage(message: string) {
+export function unwrapErrorMessage(message: string) {
   const text = message.replace(/^Error:\s*/, "").trim()
   const parse = (value: string) => Option.getOrUndefined(decodeJson(value))
   const read = (value: string) => {
diff --git a/packages/session-ui/src/timeline/session-timeline-row.tsx b/packages/session-ui/src/timeline/session-timeline-row.tsx
index fa844999150..6078902a1d7 100644
--- a/packages/session-ui/src/timeline/session-timeline-row.tsx
+++ b/packages/session-ui/src/timeline/session-timeline-row.tsx
@@ -21,8 +21,9 @@ import {
   SessionUserMessage,
   currentContentDefaultOpen,
 } from "../message/current-message"
+import { SessionCompactionMessage } from "../message/message-content"
 import { SessionRetry } from "../components/session-retry"
-import { createReactiveTimelineProjection, Timeline, TimelineRow } from "./projection"
+import { createReactiveTimelineProjection, Timeline, TimelineRow, unwrapErrorMessage } from "./projection"
 
 const emptyAssistantMessages: SessionMessageAssistant[] = []
 type Projection = ReturnType<typeof createReactiveTimelineProjection>
@@ -203,7 +204,6 @@ export function createSessionTimelineRowRenderer(input: {
       }
       return { label: message.description ?? message.text }
     }
-    if (message.type === "compaction") return { label: i18n.t("ui.messagePart.compaction"), data: message.status }
     if (message.type !== "synthetic") return undefined
     if (message.description === "Continuing after restart") return { label: message.description }
     const source = typeof message.metadata?.source === "string" ? message.metadata.source : undefined
@@ -315,6 +315,15 @@ export function createSessionTimelineRowRenderer(input: {
         return value
       }
       const message = createMemo(() => input.projection.messageByID().get(current().messageID))
+      const compaction = createMemo(() => {
+        const value = message()
+        return value?.type === "compaction" ? value : undefined
+      })
+      const compactionError = createMemo(() => {
+        const value = compaction()
+        if (value?.status !== "failed") return ""
+        return unwrapErrorMessage(value.error.message)
+      })
       const moved = createMemo(() => {
         const value = message()
         return value?.type === "location-switched" ? value : undefined
@@ -325,6 +334,15 @@ export function createSessionTimelineRowRenderer(input: {
       })
       return (
         <Frame row={current()}>
+          <Show when={compaction()}>
+            {(message) => (
+              <div data-slot="session-turn-message-container" class={`w-full ${padding()}`}>
+                <div data-slot="session-turn-compaction">
+                  <SessionCompactionMessage message={message()} error={compactionError()} />
+                </div>
+              </div>
+            )}
+          </Show>
           <Show
             when={moved()}
             fallback={
diff --git a/packages/session-ui/src/timeline/timeline-row.stories.tsx b/packages/session-ui/src/timeline/timeline-row.stories.tsx
index 6d47a05b274..b058ac2b135 100644
--- a/packages/session-ui/src/timeline/timeline-row.stories.tsx
+++ b/packages/session-ui/src/timeline/timeline-row.stories.tsx
@@ -3,7 +3,10 @@ import { CurrentSessionTimelineStory } from "../storybook/current-session-story"
 import {
   attachmentsAndCommentsDocument,
   attachmentsAndCommentsPresentation,
+  compactionCancelledDocument,
   compactionDocument,
+  compactionFailedDocument,
+  compactionRunningDocument,
   instructionsUpdatedMultipleDocument,
   instructionsUpdatedSingleDocument,
   requestHistoryDocument,
@@ -61,6 +64,17 @@ export const ProviderRetry = {
   ),
 }
 
+export const CompactionInProgress = {
+  render: () => (
+    <CurrentSessionTimelineStory
+      title="Compaction in progress"
+      description="The production divider remains stable while the context summary streams below it."
+      document={compactionRunningDocument}
+      width="600px"
+    />
+  ),
+}
+
 export const CompactionAndContinuation = {
   render: () => (
     <CurrentSessionTimelineStory
@@ -72,6 +86,28 @@ export const CompactionAndContinuation = {
   ),
 }
 
+export const CompactionFailed = {
+  render: () => (
+    <CurrentSessionTimelineStory
+      title="Compaction failed"
+      description="A failed compaction keeps the production divider and shows the provider error."
+      document={compactionFailedDocument}
+      width="600px"
+    />
+  ),
+}
+
+export const CompactionCancelled = {
+  render: () => (
+    <CurrentSessionTimelineStory
+      title="Compaction cancelled"
+      description="An interrupted compaction keeps the production divider without an empty error block."
+      document={compactionCancelledDocument}
+      width="600px"
+    />
+  ),
+}
+
 export const AnsweredQuestionAndDeclinedCommand = {
   render: () => (
     <CurrentSessionTimelineStory