diff --git a/config/scripts/native-chat-compaction-pagination.test.mjs b/config/scripts/native-chat-compaction-pagination.test.mjs
new file mode 100644
index 000000000000..0dd584138125
--- /dev/null
+++ b/config/scripts/native-chat-compaction-pagination.test.mjs
@@ -0,0 +1,172 @@
+import { readFile } from 'node:fs/promises'
+import { expect, it } from 'vitest'
+import { readAgentSessionHistory } from '../../src/main/native-chat/agent-session-wire/agent-session-history-page.ts'
+import { projectStructuredAgentSessionMessages } from '../../src/renderer/src/components/native-chat/structured-agent-session-message-projection.ts'
+import { nativeChatTurnMembership } from '../../src/shared/native-chat-turn-membership.ts'
+import { nativeChatRowsInDrawOrder } from '../../src/shared/native-chat-turn-grouping.ts'
+import { selectNativeChatTurnStatuses } from '../../src/shared/native-chat-turn-status.ts'
+import { selectStructuredAgentSettledTurns } from '../../src/shared/structured-agent-session-turn-timing.ts'
+import { buildNativeChatTranscriptSlots } from '../../src/renderer/src/components/native-chat/native-chat-transcript-slots.ts'
+
+async function snapshotWithLaterHistory() {
+  const captured = JSON.parse(
+    await readFile(
+      new URL('../../src/main/acp/fixtures/omp-v17-compact-skip.render.jsonl', import.meta.url),
+      'utf8'
+    )
+  )
+  const items = [...captured.items]
+  // Later turns are constructed test history; the skipped outcome is captured.
+  for (let n = 0; n < 66; n++) {
+    const sequence = 24 + n * 3
+    const startedAt = 1791468228000 + n * 1000
+    const userItemId = `later-user-${n}`
+    const turnItemId = `later-turn-${n}`
+    items.push(
+      {
+        itemId: userItemId,
+        revision: 1,
+        sequence,
+        observedAt: startedAt,
+        turnScope: { kind: 'thread' },
+        body: {
+          kind: 'message',
+          role: 'user',
+          blocks: [{ type: 'text', text: `later request ${n}` }]
+        }
+      },
+      {
+        itemId: turnItemId,
+        revision: 2,
+        sequence: sequence + 1,
+        observedAt: startedAt,
+        turnScope: { kind: 'thread' },
+        body: {
+          kind: 'turn',
+          turnId: turnItemId,
+          state: 'completed',
+          outcome: 'success',
+          userItemId,
+          requestedAt: startedAt,
+          startedAt,
+          completedAt: startedAt + 7
+        }
+      },
+      {
+        itemId: `later-answer-${n}`,
+        revision: 1,
+        sequence: sequence + 2,
+        observedAt: startedAt + 7,
+        turnScope: { kind: 'turn', turnItemId },
+        body: {
+          kind: 'message',
+          role: 'assistant',
+          blocks: [{ type: 'text', text: `later answer ${n}` }]
+        }
+      }
+    )
+  }
+  return {
+    sessionId: 'session-1',
+    cursor: { epoch: 'epoch-1', sequence: 221 },
+    items,
+    submissions: captured.submissions
+  }
+}
+
+function slotsFor(page) {
+  const messages = projectStructuredAgentSessionMessages(page.items, [], page.submissions)
+  const membership = nativeChatTurnMembership(messages, page)
+  const turnStatuses = selectNativeChatTurnStatuses(
+    {},
+    {
+      activeTurnKey: membership.liveTurnKey ?? '',
+      isWorking: false,
+      thinking: false,
+      settledByTurn: selectStructuredAgentSettledTurns(page.items, page.submissions)
+    }
+  )
+  return buildNativeChatTranscriptSlots({
+    messages: nativeChatRowsInDrawOrder(messages, membership.drawOrder),
+    turnKeys: nativeChatRowsInDrawOrder(membership.turnKeys, membership.drawOrder),
+    liveTurnKey: membership.liveTurnKey,
+    receipts: new Map(),
+    turnStatuses,
+    turnDiffs: new Map(),
+    expandedTurnKeys: new Set(),
+    isWorking: false,
+    lifecycleWorking: false
+  })
+}
+
+it('keeps the captured skip visible when the actual 200-item history tail omits only its opener', async () => {
+  const snapshot = await snapshotWithLaterHistory()
+  const result = readAgentSessionHistory(
+    { snapshot: () => snapshot },
+    { sessionId: 'session-1', direction: 'tail', limit: 200 },
+    snapshot
+  )
+  expect(result.ok).toBe(true)
+  const page = result.page
+  expect(page.items).toHaveLength(200)
+  expect(page.items[0].itemId).toBe('orca:command-turn%3Acompact-1')
+  expect(page.items[1].body.text).toBe('Nothing to compact (session too small)')
+  expect(page.submissions).toEqual([])
+  const slot = slotsFor(page).find(
+    (slot) =>
+      slot.kind === 'message' &&
+      slot.message.blocks.some(
+        (block) => block.type === 'text' && block.text === 'Nothing to compact (session too small)'
+      )
+  )
+  expect(slot).toMatchObject({ drawsMessage: true, folded: false })
+})
+
+it('restores the captured skip after the real older-page read loads its opener', async () => {
+  const snapshot = await snapshotWithLaterHistory()
+  const tail = readAgentSessionHistory(
+    { snapshot: () => snapshot },
+    { sessionId: 'session-1', direction: 'tail', limit: 200 },
+    snapshot
+  ).page
+  const older = readAgentSessionHistory(
+    { snapshot: () => snapshot },
+    { sessionId: 'session-1', direction: 'before', cursor: tail.window.nextCursor, limit: 200 },
+    snapshot
+  ).page
+  expect(older.items.map((item) => item.itemId)).toEqual(['orca:compact-1'])
+  const slots = slotsFor({
+    ...tail,
+    items: [...older.items, ...tail.items],
+    submissions: older.submissions
+  })
+  const slot = slots.find(
+    (slot) =>
+      slot.kind === 'message' &&
+      slot.message.blocks.some(
+        (block) => block.type === 'text' && block.text === 'Nothing to compact (session too small)'
+      )
+  )
+  expect(slot).toMatchObject({ drawsMessage: true, folded: false })
+})
+
+it('continues folding an ordinary warning at the same real history boundary', async () => {
+  const snapshot = await snapshotWithLaterHistory()
+  snapshot.items = snapshot.items.map((item) =>
+    item.body.kind === 'status' ? { ...item, itemId: 'orca:ordinary-warning' } : item
+  )
+  const result = readAgentSessionHistory(
+    { snapshot: () => snapshot },
+    { sessionId: 'session-1', direction: 'tail', limit: 200 },
+    snapshot
+  )
+  expect(result.ok).toBe(true)
+  const slot = slotsFor(result.page).find(
+    (slot) =>
+      slot.kind === 'message' &&
+      slot.message.blocks.some(
+        (block) => block.type === 'text' && block.text === 'Nothing to compact (session too small)'
+      )
+  )
+  expect(slot).toMatchObject({ drawsMessage: false, folded: true })
+})
diff --git a/src/main/acp/acp-compaction-journal-fixture.test.ts b/src/main/acp/acp-compaction-journal-fixture.test.ts
new file mode 100644
index 000000000000..21f7896afdd3
--- /dev/null
+++ b/src/main/acp/acp-compaction-journal-fixture.test.ts
@@ -0,0 +1,33 @@
+import { readFile } from 'node:fs/promises'
+import { expect, it } from 'vitest'
+import {
+  applyJournalRow,
+  createJournalReducerState,
+  renderJournalState
+} from '../native-chat/agent-session-journal/journal-reducer'
+import { parseJournalRow } from '../native-chat/agent-session-journal/journal-row-schema'
+
+async function capturedCompaction() {
+  const text = await readFile(
+    new URL('./fixtures/omp-v17-compact-skip.journal.jsonl', import.meta.url),
+    'utf8'
+  )
+  const state = createJournalReducerState('session-1', 'epoch-1')
+  for (const line of text.trim().split('\n')) {
+    const parsed = parseJournalRow(line)
+    expect(parsed.ok).toBe(true)
+    if (!parsed.ok) {
+      throw new Error('Unreadable captured journal row')
+    }
+    applyJournalRow(state, parsed.row)
+  }
+  return renderJournalState(state)
+}
+
+it('replays the captured OMP skip into the renderer fixture without changing its outcome', async () => {
+  const journal = await capturedCompaction()
+  const expected: unknown = JSON.parse(
+    await readFile(new URL('./fixtures/omp-v17-compact-skip.render.jsonl', import.meta.url), 'utf8')
+  )
+  expect({ items: journal.items, submissions: journal.submissions }).toEqual(expected)
+})
diff --git a/src/main/acp/acp-compaction-turn.ts b/src/main/acp/acp-compaction-turn.ts
new file mode 100644
index 000000000000..00a9db6ec417
--- /dev/null
+++ b/src/main/acp/acp-compaction-turn.ts
@@ -0,0 +1,134 @@
+// A `/compact` Orca sends as a prompt, run as the command turn the host opened. What the agent
+// writes meanwhile is the command's output, read for how it went and never drawn; its answer ends
+// the turn with one result row, as Claude's and Codex's compactions end.
+
+import { agentSessionFailureFact, providerDiagnostic } from '../../shared/agent-session-failure'
+import { agentSessionFailureWords } from '../../shared/agent-session-failure-words'
+import { AGENT_SESSION_COMPACTION_SKIPPED_PRESENTATION } from '../../shared/agent-session-compaction'
+import type { ProviderTimelineEvent } from '../native-chat/agent-session-timeline/provider-timeline-event'
+import { structuredCompactionOutcome } from '../native-chat/agent-session-wire/structured-conversation-command-outcome'
+import type { AcpDialect } from './acp-dialects/acp-dialect'
+import type { ContentBlock, SessionUpdate } from './generated/acp-protocol.generated'
+
+/** The prompt every compacting ACP agent takes as its own compaction command. */
+export const ACP_COMPACT_PROMPT: readonly ContentBlock[] = [{ type: 'text', text: '/compact' }]
+
+/** What a running compaction has said so far. */
+export type AcpCompaction = { reply: string; failureDetail?: string }
+
+/** The parts of a dialect's frame a running compaction reads. */
+export type AcpCompactionFrame = {
+  failureDetail?: string
+  end?: { durationMs?: number; failureDetail?: string }
+}
+
+/** Reads the running compaction's reply text; true for an update that is its output. */
+export function readAcpCompactionUpdate(compaction: AcpCompaction, update: SessionUpdate): boolean {
+  if (update.sessionUpdate === 'agent_message_chunk') {
+    if (update.content.type === 'text') {
+      compaction.reply += update.content.text
+    }
+    return true
+  }
+  return update.sessionUpdate === 'agent_thought_chunk'
+}
+
+/** Folds a frame of the running compaction into it: its words and end are read for the result its
+ *  answer writes. True for a frame that is the compaction's own, which draws nothing. */
+export function absorbAcpCompactionFrame(
+  prompt: { compaction?: AcpCompaction; durationMs?: number },
+  extension: AcpCompactionFrame | undefined,
+  update: SessionUpdate | undefined
+): boolean {
+  const { compaction } = prompt
+  if (!compaction) {
+    return false
+  }
+  if (extension?.failureDetail) {
+    compaction.failureDetail = extension.failureDetail
+  }
+  const end = extension?.end
+  if (end) {
+    prompt.durationMs = end.durationMs
+    if (end.failureDetail) {
+      compaction.failureDetail = end.failureDetail
+    }
+    return true
+  }
+  return update !== undefined && readAcpCompactionUpdate(compaction, update)
+}
+
+/** The compaction's result row and its turn's end, from the agent's answer. */
+export function acpCompactionEnd(input: {
+  compaction: AcpCompaction
+  turn: string
+  thread: string
+  stopReason: string
+  at: number
+  durationMs?: number
+  /** Words the answer itself carried, for one that failed. */
+  failureDetail?: string
+  /** The answer said the agent is not signed in. */
+  notSignedIn?: boolean
+  dialect: AcpDialect
+  agentName?: string
+}): ProviderTimelineEvent[] {
+  const { compaction, turn, stopReason } = input
+  // The host's command turn is the assembler's open turn, which no provider key names.
+  const join = { thread: input.thread }
+  const end = (outcome: 'success' | 'failure' | 'cancellation'): ProviderTimelineEvent => ({
+    type: 'turn.end',
+    at: input.at,
+    state: outcome === 'cancellation' ? 'interrupted' : 'completed',
+    outcome,
+    ...(input.durationMs === undefined ? {} : { durationMs: input.durationMs })
+  })
+  const reply =
+    stopReason === 'end_turn' ? input.dialect.compactionReply?.(compaction.reply) : undefined
+  if (reply?.outcome === 'skipped') {
+    // Nothing to compact is no failure: the turn succeeds and says why nothing changed.
+    const text = providerDiagnostic(reply.detail, 'person')?.text ?? 'Nothing to compact'
+    return [
+      {
+        type: 'item.close',
+        item: `compaction:${turn}`,
+        body: {
+          kind: 'status',
+          tone: 'warning',
+          text,
+          presentation: AGENT_SESSION_COMPACTION_SKIPPED_PRESENTATION
+        },
+        join
+      },
+      end('success')
+    ]
+  }
+  const words = reply?.detail ?? input.failureDetail ?? compaction.failureDetail
+  const detail = words === undefined ? undefined : providerDiagnostic(words, 'person')
+  const verdict = structuredCompactionOutcome({
+    // An agent that ends `/compact` normally compacted, unless its reply says otherwise.
+    compacted: stopReason === 'end_turn' && reply === undefined,
+    interruptRequested: stopReason === 'cancelled',
+    failed: detail ? { detail } : {}
+  })
+  if (verdict.outcome === 'cancellation') {
+    return [end('cancellation')]
+  }
+  // The same fact a signed-out send records, so its guidance shows and the child is replaced.
+  const failure =
+    verdict.failure && input.notSignedIn
+      ? agentSessionFailureFact('notSignedIn', detail ? { detail } : {})
+      : verdict.failure
+  const body =
+    verdict.outcome === 'success' || !failure
+      ? { kind: 'status' as const, text: 'Context compacted', presentation: 'compaction' as const }
+      : {
+          kind: 'status' as const,
+          ...agentSessionFailureWords(failure, {
+            surface: 'row',
+            ...(input.agentName === undefined ? {} : { agentName: input.agentName })
+          }),
+          tone: 'error' as const
+        }
+  return [{ type: 'item.close', item: `compaction:${turn}`, body, join }, end(verdict.outcome)]
+}
diff --git a/src/main/acp/acp-dialects/acp-dialect.ts b/src/main/acp/acp-dialects/acp-dialect.ts
index 47fba1f0f86d..2657f10d1b08 100644
--- a/src/main/acp/acp-dialects/acp-dialect.ts
+++ b/src/main/acp/acp-dialects/acp-dialect.ts
@@ -59,6 +59,9 @@ export type AcpDialectNotification =
       subagents?: AcpSubagentUpdate[]
     }
 
+/** How a `/compact` the agent ended normally went, read from its reply; absent compacted. */
+export type AcpCompactionReply = { outcome: 'skipped' | 'failed'; detail: string }
+
 /** Hooks interpret extensions; lifecycle and row identity stay shared. */
 export type AcpDialect = {
   subagentStop?: {
@@ -91,6 +94,8 @@ export type AcpDialect = {
   authenticationRequired?(error: AcpAgentError): boolean
   /** The row for a failed turn the provider gave no words for. */
   failedTurnText?(stopReason: string): string
+  /** An agent that ends a `/compact` it did not do as a normal turn says so in its reply. */
+  compactionReply?(text: string): AcpCompactionReply | undefined
 }
 
 export const GENERIC_ACP_DIALECT: AcpDialect = {}
diff --git a/src/main/acp/acp-dialects/omp-dialect.ts b/src/main/acp/acp-dialects/omp-dialect.ts
index d09c455a7292..d696ee98f730 100644
--- a/src/main/acp/acp-dialects/omp-dialect.ts
+++ b/src/main/acp/acp-dialects/omp-dialect.ts
@@ -1,6 +1,6 @@
 import { z } from 'zod'
 import type { ToolCallContent, ToolCallUpdate } from '../generated/acp-protocol.generated'
-import type { AcpDialect } from './acp-dialect'
+import type { AcpCompactionReply, AcpDialect } from './acp-dialect'
 
 // OMP sends a tool's result as `rawOutput: {content: [{type: 'text', text}], details}`, with a
 // command's non-zero exit at `details.exitCode`, and repeats the text as content behind a
@@ -94,8 +94,24 @@ function normalizeToolUpdate(update: ToolCallUpdate): ToolCallUpdate {
   }
 }
 
+// OMP ends a `/compact` it could not do as a normal turn whose reply says `Compaction failed`;
+// "Nothing to compact" and "Already compacted" are its no-ops (its RPC errors say the same).
+const COMPACTION_FAILED = /\bcompaction failed\b/i
+const COMPACTION_NOOP = /\b(?:nothing to compact|already compacted)\b/i
+
+function compactionReply(text: string): AcpCompactionReply | undefined {
+  const reply = text.trim()
+  if (!COMPACTION_FAILED.test(reply)) {
+    return undefined
+  }
+  return COMPACTION_NOOP.test(reply)
+    ? { outcome: 'skipped', detail: reply.replace(/^compaction failed:\s*/i, '') }
+    : { outcome: 'failed', detail: reply }
+}
+
 export const OMP_ACP_DIALECT: AcpDialect = {
   normalizeToolUpdate,
+  compactionReply,
   authenticationRequired: (error) => {
     const details = promptErrorDataSchema.safeParse(error.data).data?.details
     return (
diff --git a/src/main/acp/acp-launch-specs.ts b/src/main/acp/acp-launch-specs.ts
index 2cceeb216d64..4bab75d6de0f 100644
--- a/src/main/acp/acp-launch-specs.ts
+++ b/src/main/acp/acp-launch-specs.ts
@@ -85,6 +85,8 @@ export type AcpLaunchSpec = {
   installDirectories(input: { env: Readonly<Record<string, string>>; homePath: string }): string[]
   /** Images go to the agent when it also advertises them; off sends text prompts only. */
   imagePrompts?: true
+  /** The agent compacts its conversation when sent `/compact` as a prompt; off hides `/compact`. */
+  compaction?: true
   /** The agent's own store of a session's user messages, read for restart recovery only. */
   readStoredUserMessages?: AcpStoredUserMessagesReader
   modelDiscovery: AcpModelDiscovery
@@ -121,7 +123,8 @@ const GROK_LAUNCH_SPEC: AcpLaunchSpec = {
     read: readGrokModelCatalog,
     listingNamesConfiguredModel: false
   },
-  visualsSkill: loadGrokVisualsSkill
+  visualsSkill: loadGrokVisualsSkill,
+  compaction: true
 }
 
 // `opencode acp` on 1.x serves in-process; on 2.x it starts a private `opencode serve --stdio` child
@@ -158,7 +161,8 @@ const OPENCODE_LAUNCH_SPEC: AcpLaunchSpec = {
     // The listing marks no default; a chat started with no pick names it.
     listingNamesConfiguredModel: false
   },
-  visualsSkill: loadOpenCodeVisualsSkill
+  visualsSkill: loadOpenCodeVisualsSkill,
+  compaction: true
 }
 
 // OMP serves ACP through `omp acp`; its environment reaches it as the user set it.
@@ -184,7 +188,8 @@ const OMP_LAUNCH_SPEC: AcpLaunchSpec = {
     kind: 'unavailable',
     reason: 'omp has no session-free listing that matches what its chats offer'
   },
-  visualsSkill: loadOmpVisualsSkill
+  visualsSkill: loadOmpVisualsSkill,
+  compaction: true
 }
 
 export const ACP_LAUNCH_SPECS: readonly AcpLaunchSpec[] = [
diff --git a/src/main/acp/acp-prompt-turns.ts b/src/main/acp/acp-prompt-turns.ts
index 257ffc68523d..f40ec4eff17a 100644
--- a/src/main/acp/acp-prompt-turns.ts
+++ b/src/main/acp/acp-prompt-turns.ts
@@ -1,4 +1,12 @@
 import type { ProviderTimelineEvent } from '../native-chat/agent-session-timeline/provider-timeline-event'
+import {
+  absorbAcpCompactionFrame,
+  acpCompactionEnd,
+  type AcpCompaction,
+  type AcpCompactionFrame
+} from './acp-compaction-turn'
+import type { AcpDialect } from './acp-dialects/acp-dialect'
+import type { SessionUpdate } from './generated/acp-protocol.generated'
 
 export type AcpPromptTurn = {
   clientMessageId: string
@@ -6,6 +14,8 @@ export type AcpPromptTurn = {
   requestedAt: number
   opened: boolean
   durationMs?: number
+  /** A `/compact` running as the turn the host opened for it. */
+  compaction?: AcpCompaction
 }
 
 /** An injected identity is known before any provider output arrives. */
@@ -16,16 +26,70 @@ export class AcpPromptTurns {
 
   constructor(
     private readonly sessionId: string,
-    private readonly injected: boolean
+    private readonly dialect: AcpDialect,
+    private readonly agentName?: string
   ) {}
 
-  open(clientMessageId: string, at: number): { promptId: string; events: ProviderTimelineEvent[] } {
+  /** `compactionTurn` runs a `/compact` as the command turn the host already opened, which its
+   *  frames join and its answer ends. */
+  open(
+    clientMessageId: string,
+    at: number,
+    compactionTurn?: string
+  ): { promptId: string; events: ProviderTimelineEvent[] } {
     if (this.current) {
       throw new Error('ACP prompt overlaps a prompt or load')
     }
+    if (compactionTurn !== undefined) {
+      this.current = {
+        clientMessageId,
+        turn: compactionTurn,
+        requestedAt: at,
+        opened: true,
+        compaction: { reply: '' }
+      }
+      return { promptId: compactionTurn, events: [] }
+    }
     const turn = `prompt:${clientMessageId}`
     this.current = { clientMessageId, turn, requestedAt: at, opened: false }
-    return { promptId: turn, events: this.injected ? [] : this.start(turn, at) }
+    const injected = this.dialect.injectedPromptIdentity === true
+    return { promptId: turn, events: injected ? [] : this.start(turn, at) }
+  }
+
+  /** The running `/compact`, when `turn` is its turn. */
+  compacting(turn: string | undefined): AcpPromptTurn | undefined {
+    return turn !== undefined && this.current?.turn === turn && this.current.compaction
+      ? this.current
+      : undefined
+  }
+
+  /** True for a frame the running compaction `turn` read as its own. */
+  absorbCompaction(
+    turn: string | undefined,
+    extension: AcpCompactionFrame | undefined,
+    update: SessionUpdate | undefined
+  ): boolean {
+    const prompt = this.compacting(turn)
+    return prompt !== undefined && absorbAcpCompactionFrame(prompt, extension, update)
+  }
+
+  /** The running compaction's result row and end, when `turn` is its turn. */
+  endCompaction(
+    turn: string,
+    ending: { stopReason: string; at: number; failureDetail?: string; notSignedIn?: boolean }
+  ): ProviderTimelineEvent[] | undefined {
+    const prompt = this.compacting(turn)
+    if (!prompt?.compaction) {
+      return undefined
+    }
+    return acpCompactionEnd({
+      ...prompt,
+      ...ending,
+      compaction: prompt.compaction,
+      thread: this.sessionId,
+      dialect: this.dialect,
+      agentName: this.agentName
+    })
   }
 
   finish(): void {
diff --git a/src/main/acp/acp-session-update.ts b/src/main/acp/acp-session-update.ts
index 68429ea1356f..b9d45a7245b0 100644
--- a/src/main/acp/acp-session-update.ts
+++ b/src/main/acp/acp-session-update.ts
@@ -11,6 +11,16 @@ import type { AcpToolTimeline } from './acp-tool-timeline'
 import type { SessionNotification } from './generated/acp-protocol.generated'
 import { acpNamedTextKey } from './acp-turn-messages'
 
+/** Updates that open the turn they belong to. */
+export const ACP_SUBSTANTIVE_UPDATES = [
+  'user_message_chunk',
+  'agent_message_chunk',
+  'agent_thought_chunk',
+  'tool_call',
+  'tool_call_update',
+  'plan'
+]
+
 export function acpSessionUpdate(
   notification: SessionNotification,
   turn: string | undefined,
diff --git a/src/main/acp/acp-structured-agent-definitions.ts b/src/main/acp/acp-structured-agent-definitions.ts
index e42604f78a05..1bdf6cb08dd0 100644
--- a/src/main/acp/acp-structured-agent-definitions.ts
+++ b/src/main/acp/acp-structured-agent-definitions.ts
@@ -24,9 +24,9 @@ export function acpStructuredAgentDefinition(spec: AcpLaunchSpec): StructuredAge
     handleTransport: ACP_HANDLE_TRANSPORT,
     ...spec.account.pin,
     capabilities: {
-      // ACP has no stable rewind, compact or goal method; a command arrives through `/` instead.
+      // ACP has no stable rewind or goal method; a command arrives through `/` instead.
       rewind: false,
-      compact: false,
+      compact: spec.compaction === true,
       threadGoal: false,
       contextUsage: true,
       // An agent that does not also advertise images at its start has a message with one refused.
diff --git a/src/main/acp/acp-structured-compaction.test.ts b/src/main/acp/acp-structured-compaction.test.ts
new file mode 100644
index 000000000000..46a1802cdd44
--- /dev/null
+++ b/src/main/acp/acp-structured-compaction.test.ts
@@ -0,0 +1,345 @@
+import { afterEach, describe, expect, it } from 'vitest'
+import { agentJournalItemKey } from '../../shared/agent-session-journal-item-key'
+import { agentJournalTurnBody, readAgentJournalTurn } from '../../shared/agent-session-turn-record'
+import {
+  closeProviderTimelineRigs,
+  SESSION
+} from '../native-chat/agent-session-timeline/provider-timeline-assembler-test-support'
+import { structuredAgentSessionCommandTurn } from '../native-chat/agent-session-wire/structured-agent-session-command-turn'
+import type { StructuredAgentSessionCommandRun } from '../native-chat/agent-session-wire/structured-agent-session-adapter'
+import { StructuredAgentRegistry } from '../native-chat/agent-session-wire/structured-agent-registry'
+import { structuredAgentSessionChildReportedSignedOut } from '../native-chat/agent-session-wire/structured-agent-session-signed-out-child'
+import { ACP_LAUNCH_SPECS, acpLaunchSpecFor, type AcpLaunchSpec } from './acp-launch-specs'
+import { acpStructuredAgentDefinition } from './acp-structured-agent-definitions'
+import { GrokFixtureReplay } from './acp-structured-fixture-replay.test-support'
+import { readAcpFixture, type AcpFixtureFrame } from './acp-timeline-fixture.test-support'
+import {
+  GROK,
+  openAcpAdapterRig,
+  PROVIDER_SESSION,
+  waitFor,
+  type AcpAdapterRig
+} from './acp-structured-adapter.test-support'
+
+afterEach(async () => {
+  await closeProviderTimelineRigs()
+})
+
+const OPENCODE = acpLaunchSpecFor('opencode')!
+const OMP = acpLaunchSpecFor('omp')!
+
+function withoutCompaction(spec: AcpLaunchSpec): AcpLaunchSpec {
+  const { compaction: _compaction, ...rest } = spec
+  return rest
+}
+
+/** The command turn the host writes before it hands `/compact` over. */
+async function commandRun(rig: AcpAdapterRig): Promise<StructuredAgentSessionCommandRun> {
+  const turn = structuredAgentSessionCommandTurn('compact-1')
+  const running = agentJournalTurnBody({ turnId: turn.turnId, state: 'running', startedAt: 4_000 })
+  await rig.rig.journal.appendItem(turn.identity, running, {
+    fence: 1,
+    turnScope: { kind: 'thread' }
+  })
+  return { clientMessageId: 'compact-1', ...turn, running }
+}
+
+/** Starts the agent, sends `/compact`, and returns its prompt frame. */
+async function compact(spec: AcpLaunchSpec, frames?: AcpFixtureFrame[]) {
+  const rig = await openAcpAdapterRig({ spec })
+  await rig.acquire()
+  if (frames) {
+    new GrokFixtureReplay(frames).attach(rig.child().agent)
+  }
+  const command = await commandRun(rig)
+  expect(await rig.adapter.compact({ sessionId: SESSION, fence: 1, command })).toEqual({
+    state: 'accepted',
+    providerIdentity: null
+  })
+  return { rig, command, prompt: await rig.frame('session/prompt') }
+}
+
+function replyText(text: string, promptId?: string) {
+  return {
+    sessionId: PROVIDER_SESSION,
+    update: { sessionUpdate: 'agent_message_chunk', content: { type: 'text', text } },
+    ...(promptId ? { _meta: { promptId } } : {})
+  }
+}
+
+/** The command's turn once the agent's answer ended it, and the rows inside it. */
+async function ended(rig: AcpAdapterRig, command: StructuredAgentSessionCommandRun) {
+  return waitFor(async () => {
+    const rows = await rig.rig.rows()
+    const turn = readAgentJournalTurn(
+      rows.find((row) => row.itemId === agentJournalItemKey(command.identity))?.body
+    )
+    expect(turn?.state).not.toBe('running')
+    const inside = rows.filter(
+      (row) =>
+        row.turnScope?.kind === 'turn' &&
+        row.turnScope.turnItemId === agentJournalItemKey(command.identity)
+    )
+    return { turn, inside: inside.map((row) => row.body) }
+  })
+}
+
+describe('ACP compaction capability', () => {
+  it('offers /compact for Grok, OpenCode and OMP, and for no ACP agent without it', () => {
+    expect(
+      Object.fromEntries(
+        ACP_LAUNCH_SPECS.map((spec) => [
+          spec.agent,
+          acpStructuredAgentDefinition(spec).capabilities.compact
+        ])
+      )
+    ).toEqual({ grok: true, opencode: true, omp: true })
+    expect(acpStructuredAgentDefinition(withoutCompaction(GROK)).capabilities.compact).toBe(false)
+  })
+
+  it('registers each compacting agent with the adapter method its capability needs', async () => {
+    const rig = await openAcpAdapterRig()
+    expect(
+      () =>
+        new StructuredAgentRegistry(
+          ACP_LAUNCH_SPECS.map((spec) => ({
+            definition: acpStructuredAgentDefinition(spec),
+            adapter: rig.adapter
+          }))
+        )
+    ).not.toThrow()
+  })
+})
+
+describe('ACP compaction request', () => {
+  it("sends Grok `/compact` as a prompt under the command turn's id", async () => {
+    const { command, prompt } = await compact(GROK)
+    expect(prompt.params).toEqual({
+      sessionId: PROVIDER_SESSION,
+      prompt: [{ type: 'text', text: '/compact' }],
+      _meta: { promptId: command.turnId, requestId: command.turnId }
+    })
+  })
+
+  it.each([
+    ['OpenCode', OPENCODE],
+    ['OMP', OMP]
+  ])('sends %s `/compact` as a plain prompt', async (_name, spec) => {
+    const { prompt } = await compact(spec)
+    expect(prompt.params).toEqual({
+      sessionId: PROVIDER_SESSION,
+      prompt: [{ type: 'text', text: '/compact' }]
+    })
+  })
+})
+
+describe('ACP compaction settlement', () => {
+  it.each([
+    [
+      'omp-v17-compact-skip',
+      {
+        kind: 'status',
+        tone: 'warning',
+        text: 'Nothing to compact (session too small)',
+        presentation: 'compaction-skipped'
+      }
+    ],
+    [
+      'omp-v17-compact-tiny-skip',
+      {
+        kind: 'status',
+        tone: 'warning',
+        text: 'Nothing to compact (session too small)',
+        presentation: 'compaction-skipped'
+      }
+    ],
+    [
+      'omp-v17-compact-success',
+      { kind: 'status', text: 'Context compacted', presentation: 'compaction' }
+    ],
+    [
+      'omp-v18-compact-skip',
+      {
+        kind: 'status',
+        tone: 'warning',
+        text: 'Nothing to compact (session too small)',
+        presentation: 'compaction-skipped'
+      }
+    ],
+    [
+      'omp-v18-compact-tiny-skip',
+      {
+        kind: 'status',
+        tone: 'warning',
+        text: 'Nothing to compact (session too small)',
+        presentation: 'compaction-skipped'
+      }
+    ],
+    [
+      'omp-v18-compact-success',
+      { kind: 'status', text: 'Context compacted', presentation: 'compaction' }
+    ]
+  ])('replays captured %s under the host command turn', async (fixture, body) => {
+    const frames = await readAcpFixture(fixture)
+    const { rig, command } = await compact(OMP, frames)
+    const { turn, inside } = await ended(rig, command)
+    expect(turn).toMatchObject({ state: 'completed', outcome: 'success' })
+    expect(inside).toEqual([body])
+    expect((await rig.rig.rows()).some((row) => row.body.kind === 'message')).toBe(false)
+  })
+
+  it('ends a compaction the agent finished with one compacted row, drawing none of its words', async () => {
+    const { rig, command, prompt } = await compact(GROK)
+    const { agent } = rig.child()
+    agent.notify('session/update', replyText('Summarised 40 messages.', command.turnId))
+    agent.reply(prompt, { stopReason: 'end_turn' })
+    const { turn, inside } = await ended(rig, command)
+    expect(turn).toMatchObject({ turnId: command.turnId, state: 'completed', outcome: 'success' })
+    expect(inside).toEqual([
+      { kind: 'status', text: 'Context compacted', presentation: 'compaction' }
+    ])
+    expect((await rig.rig.rows()).some((row) => row.body.kind === 'message')).toBe(false)
+  })
+
+  it.each([
+    [
+      'Compaction failed: Nothing to compact (session too small)',
+      'Nothing to compact (session too small)'
+    ],
+    ['Compaction failed: Already compacted', 'Already compacted']
+  ])('reads OMP %j as skipped, not failed', async (reply, shown) => {
+    const { rig, command, prompt } = await compact(OMP)
+    const { agent } = rig.child()
+    agent.notify('session/update', replyText(reply))
+    agent.reply(prompt, { stopReason: 'end_turn' })
+    const { turn, inside } = await ended(rig, command)
+    expect(turn).toMatchObject({ state: 'completed', outcome: 'success' })
+    expect(inside).toEqual([
+      { kind: 'status', tone: 'warning', text: shown, presentation: 'compaction-skipped' }
+    ])
+  })
+
+  it('reads any other OMP compaction failure as failed, in its own words', async () => {
+    const { rig, command, prompt } = await compact(OMP)
+    const { agent } = rig.child()
+    agent.notify(
+      'session/update',
+      replyText('Compaction failed: summary model rejected the request')
+    )
+    agent.reply(prompt, { stopReason: 'end_turn' })
+    const { turn, inside } = await ended(rig, command)
+    expect(turn).toMatchObject({ state: 'completed', outcome: 'failure' })
+    expect(inside).toEqual([
+      expect.objectContaining({
+        kind: 'status',
+        tone: 'error',
+        failure: expect.objectContaining({
+          kind: 'compactionFailed',
+          detail: {
+            text: 'Compaction failed: summary model rejected the request',
+            audience: 'person'
+          }
+        })
+      })
+    ])
+  })
+
+  it('reads OMP failure words only from OMP', async () => {
+    const { rig, command, prompt } = await compact(OPENCODE)
+    const { agent } = rig.child()
+    agent.notify('session/update', replyText('Compaction failed: Nothing to compact'))
+    agent.reply(prompt, { stopReason: 'end_turn' })
+    const { turn, inside } = await ended(rig, command)
+    expect(turn).toMatchObject({ outcome: 'success' })
+    expect(inside).toEqual([
+      { kind: 'status', text: 'Context compacted', presentation: 'compaction' }
+    ])
+  })
+
+  it("fails a compaction the agent answered with an error, in the agent's words", async () => {
+    const { rig, command, prompt } = await compact(OPENCODE)
+    // -32000 means signed out to ACP; any other error code is the compaction's own failure.
+    rig.child().agent.fail(prompt, -32603, 'Summarization failed: 500')
+    const { turn, inside } = await ended(rig, command)
+    expect(turn).toMatchObject({ state: 'completed', outcome: 'failure' })
+    expect(inside).toEqual([
+      expect.objectContaining({
+        tone: 'error',
+        failure: expect.objectContaining({
+          kind: 'compactionFailed',
+          detail: { text: 'Summarization failed: 500', audience: 'person' }
+        })
+      })
+    ])
+  })
+
+  it.each([
+    { spec: OPENCODE, code: -32000, data: undefined },
+    { spec: OMP, code: -32603, data: { details: 'No model selected.\n\nUse /login to sign in.' } }
+  ])(
+    'says $spec.agent is not signed in, as a send does, so the next one starts a new agent',
+    async ({ spec, code, data }) => {
+      const { rig, command, prompt } = await compact(spec)
+      rig.child().agent.fail(prompt, code, 'Authentication required', data)
+      const { turn, inside } = await ended(rig, command)
+      expect(turn).toMatchObject({ state: 'completed', outcome: 'failure' })
+      expect(inside).toEqual([
+        expect.objectContaining({
+          tone: 'error',
+          failure: expect.objectContaining({ kind: 'notSignedIn' })
+        })
+      ])
+      expect(
+        structuredAgentSessionChildReportedSignedOut({
+          child: { generation: 'generation-1', fence: 1, phase: 'ready' },
+          journal: rig.rig.journal
+        })
+      ).toBe(true)
+    }
+  )
+
+  it('fails a compaction the agent ended with any other stop reason', async () => {
+    const { rig, command, prompt } = await compact(GROK)
+    rig.child().agent.reply(prompt, { stopReason: 'refusal' })
+    const { turn, inside } = await ended(rig, command)
+    expect(turn).toMatchObject({ state: 'completed', outcome: 'failure' })
+    expect(inside).toEqual([
+      expect.objectContaining({ failure: expect.objectContaining({ kind: 'compactionFailed' }) })
+    ])
+  })
+
+  it('ends a stopped compaction as cancelled, with no result row', async () => {
+    const { rig, command, prompt } = await compact(GROK)
+    const { agent } = rig.child()
+    agent.on('session/cancel', () => agent.reply(prompt, { stopReason: 'cancelled' }))
+    await expect(
+      rig.adapter.cancelTurn({
+        sessionId: SESSION,
+        fence: 1,
+        turnId: command.turnId,
+        resolveLiveTurnId: () => command.turnId
+      })
+    ).resolves.toEqual({ cancelled: true })
+    const { turn, inside } = await ended(rig, command)
+    expect(turn).toMatchObject({ state: 'interrupted', outcome: 'cancellation' })
+    expect(inside).toEqual([])
+  })
+
+  it('takes the next message as an ordinary turn once the compaction ended', async () => {
+    const { rig, command, prompt } = await compact(GROK)
+    rig.child().agent.reply(prompt, { stopReason: 'end_turn' })
+    await ended(rig, command)
+    expect(
+      await rig.adapter.dispatch({
+        sessionId: SESSION,
+        clientMessageId: 'send-2',
+        body: { kind: 'message', role: 'user', blocks: [{ type: 'text', text: 'next' }] },
+        fence: 1
+      })
+    ).toEqual({ state: 'admitted' })
+    expect((await rig.frame('session/prompt', 1)).params).toMatchObject({
+      prompt: [{ type: 'text', text: 'next' }],
+      _meta: { promptId: 'prompt:send-2' }
+    })
+  })
+})
diff --git a/src/main/acp/acp-structured-lane.ts b/src/main/acp/acp-structured-lane.ts
index 0fe2c6295f8b..6dac885d6ea0 100644
--- a/src/main/acp/acp-structured-lane.ts
+++ b/src/main/acp/acp-structured-lane.ts
@@ -10,6 +10,7 @@ import {
 import type { AcpTimelineEvent } from './acp-timeline-event'
 import { createLegacyProviderTimelineIdentityScheme } from '../native-chat/agent-session-timeline/provider-timeline-identity'
 import type { ProviderTimelineSink } from '../native-chat/agent-session-timeline/provider-timeline-plan'
+import type { StructuredAgentSessionCommandRun } from '../native-chat/agent-session-wire/structured-agent-session-adapter'
 import type { AcpDialect } from './acp-dialects/acp-dialect'
 import { AcpTimelineTranslator } from './acp-timeline-translator'
 import { acpSubagentChildWork, isAcpSubagentChildWorkEvent } from './acp-subagent-child-work'
@@ -80,6 +81,18 @@ export class AcpStructuredLane {
     return this.assembler.openTurnId
   }
 
+  /** The host already opened this command's turn; the agent's frames and end join that turn. */
+  beginCommand(command: StructuredAgentSessionCommandRun): void {
+    if (this.failed || this.disposed || this.backlog.length > 0) {
+      throw new Error('ACP timeline has not drained for this command')
+    }
+    this.assembler.beginCommand(command)
+  }
+
+  forgetCommand(turnId: string): void {
+    this.assembler.forgetCommand(turnId)
+  }
+
   apply(events: readonly AcpTimelineEvent[]): void {
     if (this.failed || this.disposed) {
       return
diff --git a/src/main/acp/acp-structured-session-adapter.ts b/src/main/acp/acp-structured-session-adapter.ts
index a352c924e2cc..5decdb16c7d4 100644
--- a/src/main/acp/acp-structured-session-adapter.ts
+++ b/src/main/acp/acp-structured-session-adapter.ts
@@ -1,6 +1,6 @@
 // A structured chat over the Agent Client Protocol: one adapter per registered ACP agent, which
-// the router drives like the Claude and Codex lanes. Rewind, compaction and goals are absent, so
-// the chat hides them; everything else maps onto ACP methods.
+// the router drives like the Claude and Codex lanes. Rewind and goals are absent, so the chat hides
+// them; compaction is the agent's own `/compact` prompt, for an agent whose launch spec offers it.
 
 import { randomUUID } from 'node:crypto'
 import { agentSessionFailureFact } from '../../shared/agent-session-failure'
@@ -31,8 +31,7 @@ import {
   ProviderAcquisitionStarts,
   type ProviderStartAttempt
 } from '../provider-process/provider-acquisition-starts'
-import type { AcpStructuredConnection } from './acp-structured-connection'
-import { waitForAcpExit } from './acp-structured-connection'
+import { waitForAcpExit, type AcpStructuredConnection } from './acp-structured-connection'
 import { AcpConnectionClosedError } from './acp-errors'
 import { awaitAcpTurnEnd, interruptAcpTurn, windDownAcpTurn } from './acp-structured-stop'
 import { acpDispatchPrompt } from './acp-prompt-content'
@@ -172,6 +171,9 @@ export class AcpStructuredSessionAdapter implements StructuredAgentSessionAdapte
     return { state: 'admitted' }
   }
 
+  compact: NonNullable<StructuredAgentSessionAdapter['compact']> = async (input) =>
+    this.live(input.sessionId).turns.compact(input.command)
+
   cancelTurn: StructuredAgentSessionAdapter['cancelTurn'] = async (input) => {
     const session = this.live(input.sessionId)
     // The Stop ends the child unless it is declined here. Claude's rule: a Stop naming an ended turn
@@ -243,8 +245,7 @@ export class AcpStructuredSessionAdapter implements StructuredAgentSessionAdapte
 
   closeSession = (sessionId: string): Promise<boolean> => this.close(sessionId)
   disposeSession = (sessionId: string): Promise<boolean> => this.close(sessionId)
-  releaseAcquisition = (input: { sessionId: string }): Promise<boolean> =>
-    this.close(input.sessionId)
+  releaseAcquisition = (input: { sessionId: string }) => this.close(input.sessionId)
   /** After a sink failure: the exit is recovered as unexpected. */
   forceCloseSession = (sessionId: string): Promise<boolean> => this.stop(sessionId, false)
 
diff --git a/src/main/acp/acp-structured-turns.ts b/src/main/acp/acp-structured-turns.ts
index b3161cbe46ab..90e5d6b0c749 100644
--- a/src/main/acp/acp-structured-turns.ts
+++ b/src/main/acp/acp-structured-turns.ts
@@ -18,6 +18,11 @@ import {
   type AgentJournalDispatchRejection
 } from '../../shared/agent-session-failure-words'
 import type { AgentJournalItemIdentity } from '../../shared/agent-session-journal-types'
+import type {
+  AgentSessionCommandAdmission,
+  StructuredAgentSessionCommandRun
+} from '../native-chat/agent-session-wire/structured-agent-session-adapter'
+import { ACP_COMPACT_PROMPT } from './acp-compaction-turn'
 import { AcpAgentError, AcpConnectionClosedError } from './acp-errors'
 import type { AcpStructuredConnection } from './acp-structured-connection'
 import type { AcpStructuredLane } from './acp-structured-lane'
@@ -109,6 +114,35 @@ export class AcpStructuredTurns {
     this.start(send)
   }
 
+  /** A `/compact` in the command turn the host opened. The host settles its message, so nothing
+   *  here does; the answer ends the turn, or the child's end does. The prompt's write is the
+   *  receipt. */
+  async compact(command: StructuredAgentSessionCommandRun): Promise<AgentSessionCommandAdmission> {
+    if (this.active || this.ended) {
+      throw new Error(`${this.deps.agentName} is still working`)
+    }
+    const { lane } = this.deps
+    const send: Send = {
+      clientMessageId: command.clientMessageId,
+      prompt: [...ACP_COMPACT_PROMPT],
+      requestedAt: this.deps.now()
+    }
+    lane.beginCommand(command)
+    try {
+      const opened = lane.translator.openPrompt(
+        send.clientMessageId,
+        send.requestedAt,
+        command.turnId
+      )
+      this.active = send
+      this.run(send, opened.promptId)
+    } catch (error) {
+      lane.forgetCommand(command.turnId)
+      throw error
+    }
+    return { state: 'accepted', providerIdentity: null }
+  }
+
   /** The agent took the send: its turn's first event, or its answer, arrived. */
   accept(clientMessageId: string): void {
     if (this.unsettled.delete(clientMessageId)) {
@@ -147,10 +181,15 @@ export class AcpStructuredTurns {
     this.active = send
     const opened = lane.translator.openPrompt(send.clientMessageId, send.requestedAt)
     lane.apply(opened.events)
+    this.run(send, opened.promptId)
+  }
+
+  private run(send: Send, promptId: string): void {
+    const { lane } = this.deps
     // An agent whose dialect echoes this id on every event of the turn gets it, so its rows join the
     // turn Orca opened; no other agent is sent the extension.
     const meta = lane.translator.injectsPromptIdentity
-      ? { promptId: opened.promptId, requestId: opened.promptId }
+      ? { promptId, requestId: promptId }
       : undefined
     const answered = this.deps.connection.prompt(send.prompt, meta)
     if (this.steers.length > 0) {
diff --git a/src/main/acp/acp-timeline-translator.ts b/src/main/acp/acp-timeline-translator.ts
index b0f5e8804dc0..fbfdfba9dfb0 100644
--- a/src/main/acp/acp-timeline-translator.ts
+++ b/src/main/acp/acp-timeline-translator.ts
@@ -8,7 +8,7 @@ import { AcpAgentError } from './acp-errors'
 import { acpTurnEnd, AcpPromptTurns } from './acp-prompt-turns'
 import { readAcpSessionEvent, type AcpSessionEvent } from './acp-session-events'
 import { translateAcpRequest } from './acp-timeline-requests'
-import { acpSessionUpdate } from './acp-session-update'
+import { ACP_SUBSTANTIVE_UPDATES, acpSessionUpdate } from './acp-session-update'
 import { AcpSubagentTimeline } from './acp-subagent-timeline'
 import { AcpToolTimeline } from './acp-tool-timeline'
 import {
@@ -23,14 +23,6 @@ import type { NativeChatSubagentState } from '../../shared/native-chat-types'
 export { acpTurnEnd } from './acp-prompt-turns'
 
 const requestSessionSchema = z.object({ sessionId: z.string() })
-const SUBSTANTIVE_UPDATES = [
-  'user_message_chunk',
-  'agent_message_chunk',
-  'agent_thought_chunk',
-  'tool_call',
-  'tool_call_update',
-  'plan'
-]
 
 export type AcpTimelineTranslatorOptions = {
   sessionId: string
@@ -59,10 +51,7 @@ export class AcpTimelineTranslator {
     this.dialect = options.dialect ?? GENERIC_ACP_DIALECT
     this.failures = new AcpTurnFailures(options.sessionId, this.dialect, options.agentName)
     this.backgroundTasks = new AcpBackgroundTaskTimeline((callId) => this.tools.turn(callId))
-    this.prompts = new AcpPromptTurns(
-      options.sessionId,
-      this.dialect.injectedPromptIdentity === true
-    )
+    this.prompts = new AcpPromptTurns(options.sessionId, this.dialect, options.agentName)
   }
 
   dispose(): void {
@@ -74,15 +63,17 @@ export class AcpTimelineTranslator {
     return this.dialect.injectedPromptIdentity === true
   }
 
-  /** The host injects promptId as session/prompt._meta.promptId (and requestId). */
+  /** The host injects promptId as session/prompt._meta.promptId (and requestId). A `/compact` runs
+   *  as `compactionTurn`, the command turn the host opened. */
   openPrompt(
     clientMessageId: string,
-    at: number
+    at: number,
+    compactionTurn?: string
   ): { promptId: string; events: ProviderTimelineEvent[] } {
     if (this.loading) {
       throw new Error('ACP prompt overlaps a prompt or load')
     }
-    return this.prompts.open(clientMessageId, at)
+    return this.prompts.open(clientMessageId, at, compactionTurn)
   }
 
   promptResult(
@@ -207,13 +198,15 @@ export class AcpTimelineTranslator {
     }
     const providerTurn = extension?.turn
     const opens =
-      (update !== undefined && SUBSTANTIVE_UPDATES.includes(update.sessionUpdate)) ||
+      (update !== undefined && ACP_SUBSTANTIVE_UPDATES.includes(update.sessionUpdate)) ||
       extension?.end !== undefined ||
       extension?.started === true
     const offeredTurn =
       providerTurn ?? (this.prompts.current?.opened ? this.prompts.current.turn : this.activeTurn)
     const owner = update ? this.messages.owner(offeredTurn, update) : { turn: offeredTurn }
-    const turn = owner.turn
+    // A running compaction's turn is the host's, open in the assembler under no provider key, so
+    // its frames name none; its words and end are read for the result its answer writes.
+    const turn = this.prompts.compacting(owner.turn) ? undefined : owner.turn
     if (
       owner.settled &&
       (update?.sessionUpdate === 'agent_message_chunk' ||
@@ -245,6 +238,9 @@ export class AcpTimelineTranslator {
     if (extension?.usage) {
       events.push(...this.context.update(extension.usage, join))
     }
+    if (this.prompts.absorbCompaction(owner.turn, extension, update)) {
+      return events
+    }
     if (extension?.failureDetail && turn) {
       events.push(...this.failures.row(turn, extension.failureDetail))
     }
@@ -303,8 +299,11 @@ export class AcpTimelineTranslator {
     failureDetail: string | undefined,
     notSignedIn = false
   ): ProviderTimelineEvent[] {
-    const events = this.failures.ended(turn, stopReason, failureDetail, notSignedIn)
-    events.push(acpTurnEnd(turn, stopReason, at, durationMs))
+    const ending = { stopReason, at, failureDetail, notSignedIn }
+    const events = this.prompts.endCompaction(turn, ending) ?? [
+      ...this.failures.ended(turn, stopReason, failureDetail, notSignedIn),
+      acpTurnEnd(turn, stopReason, at, durationMs)
+    ]
     this.end(turn)
     if (this.prompts.current?.turn === turn) {
       this.prompts.finish()
diff --git a/src/main/acp/fixtures/omp-v17-compact-skip.journal.jsonl b/src/main/acp/fixtures/omp-v17-compact-skip.journal.jsonl
new file mode 100644
index 000000000000..aa938253b767
--- /dev/null
+++ b/src/main/acp/fixtures/omp-v17-compact-skip.journal.jsonl
@@ -0,0 +1,6 @@
+{"kind":"submission","clientMessageId":"compact-1","payloadFingerprint":"e0d6ad4ed5f5d09f57245e1c1ab64f773c6614954d9cff1b699f26f575b5504b","providerHandle":{"kind":"opaque","agent":"omp","value":"session-1"},"body":{"kind":"message","role":"user","blocks":[{"type":"text","text":"/compact"}],"command":{"name":"compact"}},"v":2,"epoch":"epoch-1","seq":18,"fence":1,"ts":1791468227120,"handoverRecorded":true,"origin":"client","source":{"kind":"user"}}
+{"kind":"dispatch","clientMessageId":"compact-1","state":"pending","providerItemId":null,"reason":null,"v":2,"epoch":"epoch-1","seq":19,"fence":1,"ts":1791468227121,"turnScope":{"kind":"thread"}}
+{"kind":"item","itemId":"orca:command-turn%3Acompact-1","revision":1,"body":{"kind":"turn","turnId":"compact:compact-1","state":"running","userItemId":"orca:compact-1","requestedAt":1791468227121,"startedAt":1791468227121},"v":3,"epoch":"epoch-1","seq":20,"fence":1,"ts":1791468227121,"turnScope":{"kind":"thread"}}
+{"kind":"dispatch","clientMessageId":"compact-1","state":"accepted","providerItemId":null,"reason":null,"v":2,"epoch":"epoch-1","seq":21,"fence":1,"ts":1791468227122}
+{"kind":"item","itemId":"legacy:omp:runtime-session-1:item%3Ap%3Asession-1%3Asession-1%2Fcompaction%253Acompact%253Acompact-1","revision":1,"body":{"kind":"status","tone":"warning","text":"Nothing to compact (session too small)"},"v":2,"epoch":"epoch-1","seq":22,"fence":1,"ts":1791468227128,"turnScope":{"kind":"turn","turnItemId":"orca:command-turn%3Acompact-1"}}
+{"kind":"lifecycle-batch","settlementId":"provider-timeline:runtime-session-1:b803ea1c-38a0-4510-bc07-ab0012411cb5:5:turn-end","mutations":[{"kind":"item","itemId":"orca:command-turn%3Acompact-1","revision":2,"body":{"kind":"turn","turnId":"compact:compact-1","state":"completed","outcome":"success","userItemId":"orca:compact-1","startedAt":1791468227121,"requestedAt":1791468227121,"completedAt":1791468227128},"turnScope":{"kind":"thread"}}],"v":3,"epoch":"epoch-1","seq":23,"fence":1,"ts":1791468227129}
diff --git a/src/main/acp/fixtures/omp-v17-compact-skip.jsonl b/src/main/acp/fixtures/omp-v17-compact-skip.jsonl
new file mode 100644
index 000000000000..ece76036f010
--- /dev/null
+++ b/src/main/acp/fixtures/omp-v17-compact-skip.jsonl
@@ -0,0 +1,3 @@
+{"direction":"out","process":"p1","message":{"jsonrpc":"2.0","id":3,"method":"session/prompt","params":{"sessionId":"session-1","prompt":[{"type":"text","text":"/compact"}]}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"session-1","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"Compaction failed: Nothing to compact (session too small)"},"messageId":"message-1"}}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","id":3,"result":{"stopReason":"end_turn"}}}
diff --git a/src/main/acp/fixtures/omp-v17-compact-skip.render.jsonl b/src/main/acp/fixtures/omp-v17-compact-skip.render.jsonl
new file mode 100644
index 000000000000..780364187e59
--- /dev/null
+++ b/src/main/acp/fixtures/omp-v17-compact-skip.render.jsonl
@@ -0,0 +1 @@
+{"items":[{"itemId":"orca:compact-1","revision":0,"body":{"kind":"message","role":"user","blocks":[{"type":"text","text":"/compact"}],"command":{"name":"compact"}},"sequence":19,"observedAt":1791468227121,"turnScope":{"kind":"thread"}},{"itemId":"orca:command-turn%3Acompact-1","revision":2,"body":{"kind":"turn","turnId":"compact:compact-1","state":"completed","outcome":"success","userItemId":"orca:compact-1","startedAt":1791468227121,"requestedAt":1791468227121,"completedAt":1791468227128},"sequence":20,"observedAt":1791468227121,"turnScope":{"kind":"thread"}},{"itemId":"legacy:omp:runtime-session-1:item%3Ap%3Asession-1%3Asession-1%2Fcompaction%253Acompact%253Acompact-1","revision":1,"body":{"kind":"status","tone":"warning","text":"Nothing to compact (session too small)"},"sequence":22,"observedAt":1791468227128,"turnScope":{"kind":"turn","turnItemId":"orca:command-turn%3Acompact-1"}}],"submissions":[{"clientMessageId":"compact-1","fence":1,"payloadFingerprint":"e0d6ad4ed5f5d09f57245e1c1ab64f773c6614954d9cff1b699f26f575b5504b","dispatchState":"accepted","providerItemId":null,"reason":null,"submittedAt":1791468227120,"resolvedAt":1791468227122,"submittedSequence":18,"handoverRecorded":true,"acceptedSequence":18,"origin":"client","source":{"kind":"user"},"handedOverAt":1791468227121}]}
diff --git a/src/main/acp/fixtures/omp-v17-compact-success.jsonl b/src/main/acp/fixtures/omp-v17-compact-success.jsonl
new file mode 100644
index 000000000000..76607d8c831f
--- /dev/null
+++ b/src/main/acp/fixtures/omp-v17-compact-success.jsonl
@@ -0,0 +1,3 @@
+{"direction":"out","process":"p1","message":{"jsonrpc":"2.0","id":6,"method":"session/prompt","params":{"sessionId":"session-1","prompt":[{"type":"text","text":"/compact"}]}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"session-1","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"Compaction complete. Tokens: 32814 -> 33362 (saved -548)."},"messageId":"message-1"}}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","id":6,"result":{"stopReason":"end_turn"}}}
diff --git a/src/main/acp/fixtures/omp-v17-compact-tiny-skip.jsonl b/src/main/acp/fixtures/omp-v17-compact-tiny-skip.jsonl
new file mode 100644
index 000000000000..91aed2344724
--- /dev/null
+++ b/src/main/acp/fixtures/omp-v17-compact-tiny-skip.jsonl
@@ -0,0 +1,3 @@
+{"direction":"out","process":"p1","message":{"jsonrpc":"2.0","id":5,"method":"session/prompt","params":{"sessionId":"session-1","prompt":[{"type":"text","text":"/compact"}]}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"session-1","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"Compaction failed: Nothing to compact (session too small)"},"messageId":"message-1"}}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","id":5,"result":{"stopReason":"end_turn"}}}
diff --git a/src/main/acp/fixtures/omp-v18-compact-skip.jsonl b/src/main/acp/fixtures/omp-v18-compact-skip.jsonl
new file mode 100644
index 000000000000..ece76036f010
--- /dev/null
+++ b/src/main/acp/fixtures/omp-v18-compact-skip.jsonl
@@ -0,0 +1,3 @@
+{"direction":"out","process":"p1","message":{"jsonrpc":"2.0","id":3,"method":"session/prompt","params":{"sessionId":"session-1","prompt":[{"type":"text","text":"/compact"}]}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"session-1","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"Compaction failed: Nothing to compact (session too small)"},"messageId":"message-1"}}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","id":3,"result":{"stopReason":"end_turn"}}}
diff --git a/src/main/acp/fixtures/omp-v18-compact-success.jsonl b/src/main/acp/fixtures/omp-v18-compact-success.jsonl
new file mode 100644
index 000000000000..23acc2ecc655
--- /dev/null
+++ b/src/main/acp/fixtures/omp-v18-compact-success.jsonl
@@ -0,0 +1,3 @@
+{"direction":"out","process":"p1","message":{"jsonrpc":"2.0","id":6,"method":"session/prompt","params":{"sessionId":"session-1","prompt":[{"type":"text","text":"/compact"}]}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"session-1","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"Compaction complete. Tokens: 32639 -> 17109 (saved 15530)."},"messageId":"message-1"}}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","id":6,"result":{"stopReason":"end_turn"}}}
diff --git a/src/main/acp/fixtures/omp-v18-compact-tiny-skip.jsonl b/src/main/acp/fixtures/omp-v18-compact-tiny-skip.jsonl
new file mode 100644
index 000000000000..91aed2344724
--- /dev/null
+++ b/src/main/acp/fixtures/omp-v18-compact-tiny-skip.jsonl
@@ -0,0 +1,3 @@
+{"direction":"out","process":"p1","message":{"jsonrpc":"2.0","id":5,"method":"session/prompt","params":{"sessionId":"session-1","prompt":[{"type":"text","text":"/compact"}]}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"session-1","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"Compaction failed: Nothing to compact (session too small)"},"messageId":"message-1"}}}}
+{"direction":"in","process":"p1","message":{"jsonrpc":"2.0","id":5,"result":{"stopReason":"end_turn"}}}
diff --git a/src/main/native-chat/agent-session-timeline/provider-timeline-identity.ts b/src/main/native-chat/agent-session-timeline/provider-timeline-identity.ts
index f1c0038b4d86..4cacb3efe2f1 100644
--- a/src/main/native-chat/agent-session-timeline/provider-timeline-identity.ts
+++ b/src/main/native-chat/agent-session-timeline/provider-timeline-identity.ts
@@ -81,16 +81,7 @@ export function isProviderTimelineTurnInNamespace(turnId: string, namespace: str
   return turnId.startsWith(`p:${providerTimelineKeyPart(namespace)}:`)
 }
 
-/** The spelled key of a provider-keyed item's record id, whichever session and thread wrote it;
- *  null for any other row. Compare it with `providerTimelineKeyPart(key)`. */
-export function spelledProviderTimelineItemKey(recordId: string): string | null {
-  if (!recordId.startsWith('item:p:')) {
-    return null
-  }
-  // Every part is URI-encoded, so `:` and `/` only ever separate parts.
-  const scoped = recordId.slice(recordId.lastIndexOf(':') + 1)
-  return scoped.slice(scoped.lastIndexOf('/') + 1)
-}
+export { spelledProviderTimelineItemKey } from '../../../shared/provider-timeline-item-key'
 
 /** The existing `legacy` arm. Turn rows keep the `turn-lifecycle:` record prefix the other lanes
  *  write; provider keys are spelled inside their namespace, and apart from minted ones. */
diff --git a/src/main/runtime/structured-agent-runtime-registrations-acp.test.ts b/src/main/runtime/structured-agent-runtime-registrations-acp.test.ts
index c3892d5e6556..809b99aaeea3 100644
--- a/src/main/runtime/structured-agent-runtime-registrations-acp.test.ts
+++ b/src/main/runtime/structured-agent-runtime-registrations-acp.test.ts
@@ -16,7 +16,7 @@ describe('ACP agents in the runtime registrations', () => {
       accountHomeVariable: 'GROK_HOME',
       capabilities: {
         rewind: false,
-        compact: false,
+        compact: true,
         threadGoal: false,
         contextUsage: true,
         imagePrompts: false,
diff --git a/src/renderer/src/components/native-chat/NativeChatNoticeRow.test.tsx b/src/renderer/src/components/native-chat/NativeChatNoticeRow.test.tsx
index d412b58f18a3..7e9a627101f7 100644
--- a/src/renderer/src/components/native-chat/NativeChatNoticeRow.test.tsx
+++ b/src/renderer/src/components/native-chat/NativeChatNoticeRow.test.tsx
@@ -18,6 +18,17 @@ afterEach(async () => {
   await i18n.changeLanguage('en')
 })
 
+it('keeps a skipped compaction warning truthful instead of showing the success separator', () => {
+  renderStatus({
+    kind: 'status',
+    tone: 'warning',
+    text: 'Nothing to compact (session too small)',
+    presentation: 'compaction-skipped'
+  })
+  expect(screen.getByText('Nothing to compact (session too small)')).toBeInTheDocument()
+  expect(screen.queryByText('Context compacted')).toBeNull()
+})
+
 function orcaStopView(
   hostLabel: string | null,
   continueAvailable: boolean
diff --git a/src/renderer/src/components/native-chat/native-chat-compaction-visibility.test.ts b/src/renderer/src/components/native-chat/native-chat-compaction-visibility.test.ts
new file mode 100644
index 000000000000..14755413cc48
--- /dev/null
+++ b/src/renderer/src/components/native-chat/native-chat-compaction-visibility.test.ts
@@ -0,0 +1,146 @@
+import { readFile } from 'node:fs/promises'
+import { describe, expect, it } from 'vitest'
+import { nativeChatTurnMembership } from '../../../../shared/native-chat-turn-membership'
+import { selectNativeChatTurnStatuses } from '../../../../shared/native-chat-turn-status'
+import { selectStructuredAgentSettledTurns } from '../../../../shared/structured-agent-session-turn-timing'
+import { projectStructuredAgentSessionMessages } from './structured-agent-session-message-projection'
+import { buildNativeChatTranscriptSlots } from './native-chat-transcript-slots'
+import { z } from 'zod'
+import type {
+  AgentJournalRenderItem,
+  AgentJournalSubmission
+} from '../../../../shared/agent-session-journal-types'
+import { isAdmissibleAgentJournalRenderItem } from '../../../../shared/agent-session-journal-schemas'
+import { isAdmissibleAgentJournalSubmission } from '../../../../shared/agent-session-journal-submission-schema'
+
+type CapturedJournal = { items: AgentJournalRenderItem[]; submissions: AgentJournalSubmission[] }
+
+async function capturedCompaction(
+  transform: (journal: CapturedJournal) => CapturedJournal = (journal) => journal
+) {
+  const text = await readFile(
+    new URL('../../../../main/acp/fixtures/omp-v17-compact-skip.render.jsonl', import.meta.url),
+    'utf8'
+  )
+  const captured = z
+    .object({
+      items: z.array(z.custom<AgentJournalRenderItem>(isAdmissibleAgentJournalRenderItem)),
+      submissions: z.array(z.custom<AgentJournalSubmission>(isAdmissibleAgentJournalSubmission))
+    })
+    .parse(JSON.parse(text))
+  const journal = transform(captured)
+  const messages = projectStructuredAgentSessionMessages(journal.items, [], journal.submissions)
+  const membership = nativeChatTurnMembership(messages, journal)
+  const turnStatuses = selectNativeChatTurnStatuses(
+    {},
+    {
+      activeTurnKey: membership.liveTurnKey ?? '',
+      isWorking: false,
+      thinking: false,
+      settledByTurn: selectStructuredAgentSettledTurns(journal.items, journal.submissions)
+    }
+  )
+  return { messages, membership, turnStatuses }
+}
+
+function slotsFor({
+  messages,
+  membership,
+  turnStatuses
+}: Awaited<ReturnType<typeof capturedCompaction>>) {
+  return buildNativeChatTranscriptSlots({
+    messages,
+    ...membership,
+    receipts: new Map(),
+    turnStatuses,
+    turnDiffs: new Map(),
+    expandedTurnKeys: new Set(),
+    isWorking: false,
+    lifecycleWorking: false
+  })
+}
+
+describe('captured OMP compaction visibility', () => {
+  it('keeps the saved skipped outcome visible after the command settles and reloads', async () => {
+    const { messages, membership, turnStatuses } = await capturedCompaction()
+    const command = messages.find((message) => message.command?.name === 'compact')
+    const warning = messages.find((message) => message.role === 'system')
+    expect(command).toBeDefined()
+    expect(warning?.blocks).toEqual([
+      {
+        type: 'text',
+        tone: 'warning',
+        text: 'Nothing to compact (session too small)',
+        presentation: 'compaction-skipped'
+      }
+    ])
+    expect(membership.turnKeys).toEqual([command?.id, command?.id])
+    expect(turnStatuses.completedByTurn[command?.id ?? '']).toMatchObject({
+      workedSeconds: 0,
+      verdict: 'success'
+    })
+    const slots = slotsFor({ messages, membership, turnStatuses })
+    expect(
+      slots.find((slot) => slot.kind === 'message' && slot.message.id === warning?.id)
+    ).toMatchObject({ drawsMessage: true, folded: false, turnFolds: false })
+  })
+
+  it('keeps the saved warning visible when paging omits its command opener and submission', async () => {
+    const captured = await capturedCompaction((journal) => ({
+      items: journal.items.filter((item) => item.body.kind !== 'message'),
+      submissions: []
+    }))
+    expect(captured.messages.some((message) => message.command)).toBe(false)
+    expect(captured.membership.turnKeys).toEqual(['orca:command-turn%3Acompact-1'])
+    expect(slotsFor(captured)[0]).toMatchObject({
+      drawsMessage: true,
+      folded: false,
+      statusAbove: true,
+      turnFolds: false
+    })
+  })
+
+  it('keeps a newly marked outcome visible without an opener or a legacy identity', async () => {
+    const captured = await capturedCompaction((journal) => ({
+      items: journal.items
+        .filter((item) => item.body.kind !== 'message')
+        .map((item) =>
+          item.body.kind === 'status'
+            ? {
+                ...item,
+                itemId: 'orca:future-outcome',
+                body: { ...item.body, presentation: 'compaction-skipped' }
+              }
+            : item
+        ),
+      submissions: []
+    }))
+    expect(slotsFor(captured)[0]).toMatchObject({ drawsMessage: true, folded: false })
+  })
+
+  it.each([
+    'orca:ordinary-warning',
+    'legacy:grok:runtime-session-1:item%3Ap%3Asession-1%3Acompaction%253Acompact%253Acompact-1'
+  ])('continues folding an ordinary warning beside a compact command: %s', async (itemId) => {
+    const captured = await capturedCompaction((journal) => ({
+      ...journal,
+      items: journal.items.map((item) => (item.body.kind === 'status' ? { ...item, itemId } : item))
+    }))
+    const slots = slotsFor(captured)
+    expect(slots.map((slot) => slot.kind === 'message' && slot.message.role)).toEqual(['user'])
+    expect(slots[0]).toMatchObject({ turnFolds: true })
+  })
+
+  it('preserves an unknown presentation instead of reclassifying its warning', async () => {
+    const captured = await capturedCompaction((journal) => ({
+      ...journal,
+      items: journal.items.map((item) =>
+        item.body.kind === 'status'
+          ? { ...item, body: { ...item.body, presentation: 'future-presentation' } }
+          : item
+      )
+    }))
+    expect(captured.messages[1]?.blocks[0]).toMatchObject({ presentation: 'future-presentation' })
+    expect(slotsFor(captured)).toHaveLength(1)
+  })
+})
diff --git a/src/renderer/src/components/native-chat/native-chat-transcript-slots.ts b/src/renderer/src/components/native-chat/native-chat-transcript-slots.ts
index ebae5d79e213..2b4a748a79de 100644
--- a/src/renderer/src/components/native-chat/native-chat-transcript-slots.ts
+++ b/src/renderer/src/components/native-chat/native-chat-transcript-slots.ts
@@ -12,6 +12,7 @@ import type {
   AgentJournalSubmission
 } from '../../../../shared/agent-session-journal-types'
 import { AGENT_SESSION_ORCA_STOP_PRESENTATION } from '../../../../shared/agent-session-orca-stop'
+import { AGENT_SESSION_COMPACTION_SKIPPED_PRESENTATION } from '../../../../shared/agent-session-compaction'
 import {
   isBackgroundTaskBlock,
   isSubagentGroupBlock,
@@ -163,6 +164,7 @@ export function buildNativeChatTranscriptSlots(
       (block) =>
         block.type === 'text' &&
         (block.presentation === 'compaction' ||
+          block.presentation === AGENT_SESSION_COMPACTION_SKIPPED_PRESENTATION ||
           block.presentation === AGENT_SESSION_ORCA_STOP_PRESENTATION)
     )
   }))
diff --git a/src/shared/agent-session-compaction.ts b/src/shared/agent-session-compaction.ts
new file mode 100644
index 000000000000..2a33dd82bda5
--- /dev/null
+++ b/src/shared/agent-session-compaction.ts
@@ -0,0 +1,15 @@
+import { parseAgentJournalItemKey } from './agent-session-journal-item-key'
+import { spelledProviderTimelineItemKey } from './provider-timeline-item-key'
+
+export const AGENT_SESSION_COMPACTION_SKIPPED_PRESENTATION = 'compaction-skipped'
+
+/** Older OMP outcomes carried their meaning in the host's reserved item identity. */
+export function isAgentSessionLegacyCompactionResult(itemId: string): boolean {
+  const identity = parseAgentJournalItemKey(itemId)
+  return (
+    identity?.provider === 'legacy' &&
+    identity.agent === 'omp' &&
+    spelledProviderTimelineItemKey(identity.recordId)?.startsWith('compaction%3Acompact%3A') ===
+      true
+  )
+}
diff --git a/src/shared/agent-session-journal-schemas.test.ts b/src/shared/agent-session-journal-schemas.test.ts
index 6ff5e56e30c6..25e289f926e8 100644
--- a/src/shared/agent-session-journal-schemas.test.ts
+++ b/src/shared/agent-session-journal-schemas.test.ts
@@ -320,6 +320,7 @@ describe('optional notice metadata', () => {
   it.each([
     {},
     { presentation: 'compaction' },
+    { presentation: 'compaction-skipped', tone: 'warning' },
     { presentation: 'plan-document' },
     { tone: 'warning' },
     { tone: 'error' },
diff --git a/src/shared/provider-timeline-item-key.ts b/src/shared/provider-timeline-item-key.ts
new file mode 100644
index 000000000000..677ee9637766
--- /dev/null
+++ b/src/shared/provider-timeline-item-key.ts
@@ -0,0 +1,9 @@
+/** The encoded key inside a provider-keyed journal record, independent of session and thread. */
+export function spelledProviderTimelineItemKey(recordId: string): string | null {
+  if (!recordId.startsWith('item:p:')) {
+    return null
+  }
+  // Parts are URI-encoded; only separators retain literal colons and slashes.
+  const scoped = recordId.slice(recordId.lastIndexOf(':') + 1)
+  return scoped.slice(scoped.lastIndexOf('/') + 1)
+}
diff --git a/src/shared/structured-agent-session-projection.test.ts b/src/shared/structured-agent-session-projection.test.ts
index 0f56b920b32b..fdf7529ac627 100644
--- a/src/shared/structured-agent-session-projection.test.ts
+++ b/src/shared/structured-agent-session-projection.test.ts
@@ -555,6 +555,7 @@ describe('structured agent session status projection', () => {
 describe('notice projection for desktop and mobile consumers', () => {
   it.each([
     { presentation: 'compaction' },
+    { presentation: 'compaction-skipped', tone: 'warning' },
     { presentation: 'plan-document' },
     { tone: 'warning' },
     { tone: 'error' },
diff --git a/src/shared/structured-agent-session-projection.ts b/src/shared/structured-agent-session-projection.ts
index d5b08c833665..610b08e91670 100644
--- a/src/shared/structured-agent-session-projection.ts
+++ b/src/shared/structured-agent-session-projection.ts
@@ -134,7 +134,10 @@ function itemBlocks(item: AgentJournalRenderItem): {
   if (body.kind !== 'status' || body.turnLifecycle) {
     return null
   }
-  return { role: 'system', blocks: [structuredAgentSessionStatusBlock(body, item.turnScope)] }
+  return {
+    role: 'system',
+    blocks: [structuredAgentSessionStatusBlock(body, item.turnScope, item.itemId)]
+  }
 }
 
 function isAgentJournalMessageSendMode(value: string): value is AgentJournalMessageSendMode {
diff --git a/src/shared/structured-agent-session-status-block.ts b/src/shared/structured-agent-session-status-block.ts
index 222420d217f4..2febb6af6872 100644
--- a/src/shared/structured-agent-session-status-block.ts
+++ b/src/shared/structured-agent-session-status-block.ts
@@ -2,18 +2,28 @@ import { readWholeAgentSessionFailureFact } from './agent-session-failure'
 import type { AgentJournalStatusItem, AgentJournalTurnScope } from './agent-session-journal-types'
 import { readAgentSessionOrcaStop } from './agent-session-orca-stop'
 import type { NativeChatTextBlock } from './native-chat-types'
+import {
+  AGENT_SESSION_COMPACTION_SKIPPED_PRESENTATION,
+  isAgentSessionLegacyCompactionResult
+} from './agent-session-compaction'
 
 /** A status row as the line a chat paints: named fields only, so a host-only key never leaks. */
 export function structuredAgentSessionStatusBlock(
   body: AgentJournalStatusItem,
-  turnScope?: AgentJournalTurnScope
+  turnScope?: AgentJournalTurnScope,
+  itemId?: string
 ): NativeChatTextBlock {
   const failure = readWholeAgentSessionFailureFact(body.failure)
   const orcaStop = readAgentSessionOrcaStop(body.orcaStop)
+  const presentation =
+    body.presentation ??
+    (body.tone === 'warning' && itemId !== undefined && isAgentSessionLegacyCompactionResult(itemId)
+      ? AGENT_SESSION_COMPACTION_SKIPPED_PRESENTATION
+      : undefined)
   return {
     type: 'text',
     text: body.text,
-    ...(body.presentation !== undefined ? { presentation: body.presentation } : {}),
+    ...(presentation !== undefined ? { presentation } : {}),
     ...(body.contextClear !== undefined ? { contextClear: body.contextClear } : {}),
     ...(body.tone !== undefined ? { tone: body.tone } : {}),
     ...(body.providerFrame ? { providerFrame: body.providerFrame } : {}),