diff --git a/src/services/compact/compact.test.ts b/src/services/compact/compact.test.ts
index 8c9d1faeb..ae62be186 100644
--- a/src/services/compact/compact.test.ts
+++ b/src/services/compact/compact.test.ts
@@ -45,6 +45,9 @@ const _realDiskOutputModule = await import(
 const _realMessagesModule = await import(
   `../../utils/messages.js?real=${Date.now()}-${Math.random()}`
 )
+const _realSystemFactoriesModule = await import(
+  `../../utils/messages/systemFactories.js?real=${Date.now()}-${Math.random()}`
+)
 const _realSlowOperationsModule = await import(
   `../../utils/slowOperations.js?real=${Date.now()}-${Math.random()}`
 )
@@ -663,6 +666,9 @@ afterAll(async () => {
     MAX_TASK_OUTPUT_BYTES_DISPLAY: _realDiskOutputModule.MAX_TASK_OUTPUT_BYTES_DISPLAY,
   }))
   mock.module('../../utils/messages.js', () => ({ ..._realMessagesModule }))
+  mock.module('../../utils/messages/systemFactories.js', () => ({
+    ..._realSystemFactoriesModule,
+  }))
   mock.module('../../utils/slowOperations.js', () => ({
     ..._realSlowOperationsModule,
   }))
diff --git a/src/utils/messages.ts b/src/utils/messages.ts
index f49f184c6..c476930df 100644
--- a/src/utils/messages.ts
+++ b/src/utils/messages.ts
@@ -4246,328 +4246,25 @@ function createToolUseMessage(
   })
 }
 
-export function createSystemMessage(
-  content: string,
-  level: SystemMessageLevel,
-  toolUseID?: string,
-  preventContinuation?: boolean,
-): SystemInformationalMessage {
-  return {
-    type: 'system',
-    subtype: 'informational',
-    content,
-    isMeta: false,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    toolUseID,
-    level,
-    ...(preventContinuation && { preventContinuation }),
-  }
-}
-
-export function createPermissionRetryMessage(
-  commands: string[],
-): SystemPermissionRetryMessage {
-  return {
-    type: 'system',
-    subtype: 'permission_retry',
-    content: `Allowed ${commands.join(', ')}`,
-    commands,
-    level: 'info',
-    isMeta: false,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-  }
-}
-
-export function createBridgeStatusMessage(
-  url: string,
-  upgradeNudge?: string,
-): SystemBridgeStatusMessage {
-  return {
-    type: 'system',
-    subtype: 'bridge_status',
-    content: `/remote-control is active. Code in CLI or at ${url}`,
-    url,
-    upgradeNudge,
-    isMeta: false,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-  }
-}
-
-export function createScheduledTaskFireMessage(
-  content: string,
-): SystemScheduledTaskFireMessage {
-  return {
-    type: 'system',
-    subtype: 'scheduled_task_fire',
-    content,
-    isMeta: false,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-  }
-}
-
-export function createStopHookSummaryMessage(
-  hookCount: number,
-  hookInfos: StopHookInfo[],
-  hookErrors: string[],
-  preventedContinuation: boolean,
-  stopReason: string | undefined,
-  hasOutput: boolean,
-  level: SystemMessageLevel,
-  toolUseID?: string,
-  hookLabel?: string,
-  totalDurationMs?: number,
-): SystemStopHookSummaryMessage {
-  return {
-    type: 'system',
-    subtype: 'stop_hook_summary',
-    hookCount,
-    hookInfos,
-    hookErrors,
-    preventedContinuation,
-    stopReason,
-    hasOutput,
-    level,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    toolUseID,
-    hookLabel,
-    totalDurationMs,
-  }
-}
-
-export function createTurnDurationMessage(
-  durationMs: number,
-  budget?: { tokens: number; limit: number; nudges: number },
-  messageCount?: number,
-): SystemTurnDurationMessage {
-  return {
-    type: 'system',
-    subtype: 'turn_duration',
-    durationMs,
-    budgetTokens: budget?.tokens,
-    budgetLimit: budget?.limit,
-    budgetNudges: budget?.nudges,
-    messageCount,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    isMeta: false,
-  }
-}
-
-export function createAwaySummaryMessage(
-  content: string,
-): SystemAwaySummaryMessage {
-  return {
-    type: 'system',
-    subtype: 'away_summary',
-    content,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    isMeta: false,
-  }
-}
-
-export function createMemorySavedMessage(
-  writtenPaths: string[],
-): SystemMemorySavedMessage {
-  return {
-    type: 'system',
-    subtype: 'memory_saved',
-    writtenPaths,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    isMeta: false,
-  }
-}
-
-export function createAgentsKilledMessage(): SystemAgentsKilledMessage {
-  return {
-    type: 'system',
-    subtype: 'agents_killed',
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    isMeta: false,
-  }
-}
-
-export function createApiMetricsMessage(metrics: {
-  ttftMs: number
-  otps: number
-  isP50?: boolean
-  hookDurationMs?: number
-  turnDurationMs?: number
-  toolDurationMs?: number
-  classifierDurationMs?: number
-  toolCount?: number
-  hookCount?: number
-  classifierCount?: number
-  configWriteCount?: number
-}): SystemApiMetricsMessage {
-  return {
-    type: 'system',
-    subtype: 'api_metrics',
-    ttftMs: metrics.ttftMs,
-    otps: metrics.otps,
-    isP50: metrics.isP50,
-    hookDurationMs: metrics.hookDurationMs,
-    turnDurationMs: metrics.turnDurationMs,
-    toolDurationMs: metrics.toolDurationMs,
-    classifierDurationMs: metrics.classifierDurationMs,
-    toolCount: metrics.toolCount,
-    hookCount: metrics.hookCount,
-    classifierCount: metrics.classifierCount,
-    configWriteCount: metrics.configWriteCount,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    isMeta: false,
-  }
-}
-
-export function createCommandInputMessage(
-  content: string,
-): SystemLocalCommandMessage {
-  return {
-    type: 'system',
-    subtype: 'local_command',
-    content,
-    level: 'info',
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    isMeta: false,
-  }
-}
-
-export function createCompactBoundaryMessage(
-  trigger: 'manual' | 'auto',
-  preTokens: number,
-  lastPreCompactMessageUuid?: UUID,
-  userContext?: string,
-  messagesSummarized?: number,
-): SystemCompactBoundaryMessage {
-  return {
-    type: 'system',
-    subtype: 'compact_boundary',
-    content: `Conversation compacted`,
-    isMeta: false,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    level: 'info',
-    compactMetadata: {
-      trigger,
-      preTokens,
-      userContext,
-      messagesSummarized,
-    },
-    ...(lastPreCompactMessageUuid && {
-      logicalParentUuid: lastPreCompactMessageUuid,
-    }),
-  }
-}
-
-export function createMicrocompactBoundaryMessage(
-  trigger: 'auto',
-  preTokens: number,
-  tokensSaved: number,
-  compactedToolIds: string[],
-  clearedAttachmentUUIDs: string[],
-): SystemMicrocompactBoundaryMessage {
-  logForDebugging(
-    `[microcompact] saved ~${formatTokens(tokensSaved)} tokens (cleared ${compactedToolIds.length} tool results)`,
-  )
-  return {
-    type: 'system',
-    subtype: 'microcompact_boundary',
-    content: 'Context microcompacted',
-    isMeta: false,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-    level: 'info',
-    microcompactMetadata: {
-      trigger,
-      preTokens,
-      tokensSaved,
-      compactedToolIds,
-      clearedAttachmentUUIDs,
-    },
-  }
-}
-
-export function createSystemAPIErrorMessage(
-  error: APIError,
-  retryInMs: number,
-  retryAttempt: number,
-  maxRetries: number,
-): SystemAPIErrorMessage {
-  return {
-    type: 'system',
-    subtype: 'api_error',
-    level: 'error',
-    cause: error.cause instanceof Error ? error.cause : undefined,
-    error,
-    retryInMs,
-    retryAttempt,
-    maxRetries,
-    timestamp: new Date().toISOString(),
-    uuid: randomUUID(),
-  }
-}
-
-/**
- * Checks if a message is a compact boundary marker
- */
-export function isCompactBoundaryMessage(
-  message: Message | NormalizedMessage,
-): message is SystemCompactBoundaryMessage {
-  return message?.type === 'system' && message.subtype === 'compact_boundary'
-}
-
-/**
- * Finds the index of the last compact boundary marker in the messages array
- * @returns The index of the last compact boundary, or -1 if none found
- */
-export function findLastCompactBoundaryIndex<
-  T extends Message | NormalizedMessage,
->(messages: T[]): number {
-  // Scan backwards to find the most recent compact boundary
-  for (let i = messages.length - 1; i >= 0; i--) {
-    const message = messages[i]
-    if (message && isCompactBoundaryMessage(message)) {
-      return i
-    }
-  }
-  return -1 // No boundary found
-}
-
-/**
- * Returns messages from the last compact boundary onward (including the boundary).
- * If no boundary exists, returns all messages.
- *
- * Also filters snipped messages by default (when HISTORY_SNIP is enabled) —
- * the REPL keeps full history for UI scrollback, so model-facing paths need
- * both compact-slice AND snip-filter applied. Pass `{ includeSnipped: true }`
- * to opt out (e.g., REPL.tsx fullscreen compact handler which preserves
- * snipped messages in scrollback).
- *
- * Note: The boundary itself is a system message and will be filtered by normalizeMessagesForAPI.
- */
-export function getMessagesAfterCompactBoundary<
-  T extends Message | NormalizedMessage,
->(messages: T[], options?: { includeSnipped?: boolean }): T[] {
-  const boundaryIndex = findLastCompactBoundaryIndex(messages)
-  const sliced = boundaryIndex === -1 ? messages : messages.slice(boundaryIndex)
-  if (!options?.includeSnipped && feature('HISTORY_SNIP')) {
-    /* eslint-disable @typescript-eslint/no-require-imports */
-    const { projectSnippedView } =
-      require('../services/compact/snipProjection.js') as typeof import('../services/compact/snipProjection.js')
-    /* eslint-enable @typescript-eslint/no-require-imports */
-    return projectSnippedView(sliced as Message[]) as T[]
-  }
-  return sliced
-}
+export {
+  createAgentsKilledMessage,
+  createApiMetricsMessage,
+  createAwaySummaryMessage,
+  createBridgeStatusMessage,
+  createCommandInputMessage,
+  createCompactBoundaryMessage,
+  createMemorySavedMessage,
+  createMicrocompactBoundaryMessage,
+  createPermissionRetryMessage,
+  createScheduledTaskFireMessage,
+  createStopHookSummaryMessage,
+  createSystemAPIErrorMessage,
+  createSystemMessage,
+  createTurnDurationMessage,
+  findLastCompactBoundaryIndex,
+  getMessagesAfterCompactBoundary,
+  isCompactBoundaryMessage,
+} from "./messages/systemFactories.js"
 
 export function shouldShowUserMessage(
   message: NormalizedMessage,
diff --git a/src/utils/messages/systemFactories.test.ts b/src/utils/messages/systemFactories.test.ts
new file mode 100644
index 000000000..4a0b49cd4
--- /dev/null
+++ b/src/utils/messages/systemFactories.test.ts
@@ -0,0 +1,233 @@
+import { feature } from 'bun:bundle'
+import { expect, test } from 'bun:test'
+import {
+  createAgentsKilledMessage,
+  createApiMetricsMessage,
+  createAwaySummaryMessage,
+  createBridgeStatusMessage,
+  createCommandInputMessage,
+  createCompactBoundaryMessage,
+  createMemorySavedMessage,
+  createMicrocompactBoundaryMessage,
+  createPermissionRetryMessage,
+  createScheduledTaskFireMessage,
+  createStopHookSummaryMessage,
+  createSystemAPIErrorMessage,
+  createSystemMessage,
+  createTurnDurationMessage,
+  findLastCompactBoundaryIndex,
+  getMessagesAfterCompactBoundary,
+  isCompactBoundaryMessage,
+} from './systemFactories.js'
+import type { Message } from '../../types/message.js'
+
+test('createSystemMessage builds an informational system message', () => {
+  const message = createSystemMessage('ready', 'info', 'toolu_1', true)
+
+  expect(message).toMatchObject({
+    type: 'system',
+    subtype: 'informational',
+    content: 'ready',
+    level: 'info',
+    toolUseID: 'toolu_1',
+    preventContinuation: true,
+  })
+})
+
+test('system factory helpers build their expected message shapes', () => {
+  expect(createPermissionRetryMessage(['Bash(ls)', 'Read(*)'])).toMatchObject({
+    type: 'system',
+    subtype: 'permission_retry',
+    content: 'Allowed Bash(ls), Read(*)',
+    commands: ['Bash(ls)', 'Read(*)'],
+    level: 'info',
+    isMeta: false,
+  })
+  expect(createBridgeStatusMessage('https://remote.test', 'upgrade')).toMatchObject({
+    type: 'system',
+    subtype: 'bridge_status',
+    content: '/remote-control is active. Code in CLI or at https://remote.test',
+    url: 'https://remote.test',
+    upgradeNudge: 'upgrade',
+  })
+  expect(createScheduledTaskFireMessage('run task')).toMatchObject({
+    type: 'system',
+    subtype: 'scheduled_task_fire',
+    content: 'run task',
+    isMeta: false,
+  })
+  expect(
+    createStopHookSummaryMessage(
+      2,
+      [{ hookName: 'stop', command: 'echo ok', matcher: undefined }],
+      ['failed'],
+      true,
+      'stop_sequence',
+      true,
+      'warning',
+      'toolu_stop',
+      'Stop',
+      123,
+    ),
+  ).toMatchObject({
+    type: 'system',
+    subtype: 'stop_hook_summary',
+    hookCount: 2,
+    hookErrors: ['failed'],
+    preventedContinuation: true,
+    stopReason: 'stop_sequence',
+    hasOutput: true,
+    level: 'warning',
+    toolUseID: 'toolu_stop',
+    hookLabel: 'Stop',
+    totalDurationMs: 123,
+  })
+  expect(
+    createTurnDurationMessage(
+      250,
+      { tokens: 10, limit: 100, nudges: 1 },
+      4,
+    ),
+  ).toMatchObject({
+    type: 'system',
+    subtype: 'turn_duration',
+    durationMs: 250,
+    budgetTokens: 10,
+    budgetLimit: 100,
+    budgetNudges: 1,
+    messageCount: 4,
+    isMeta: false,
+  })
+  expect(createAwaySummaryMessage('away')).toMatchObject({
+    type: 'system',
+    subtype: 'away_summary',
+    content: 'away',
+    isMeta: false,
+  })
+  expect(createMemorySavedMessage(['/tmp/memory.md'])).toMatchObject({
+    type: 'system',
+    subtype: 'memory_saved',
+    writtenPaths: ['/tmp/memory.md'],
+    isMeta: false,
+  })
+  expect(createAgentsKilledMessage()).toMatchObject({
+    type: 'system',
+    subtype: 'agents_killed',
+    isMeta: false,
+  })
+  expect(
+    createApiMetricsMessage({
+      ttftMs: 12,
+      otps: 34,
+      isP50: true,
+      hookDurationMs: 5,
+      turnDurationMs: 6,
+      toolDurationMs: 7,
+      classifierDurationMs: 8,
+      toolCount: 2,
+      hookCount: 3,
+      classifierCount: 1,
+      configWriteCount: 4,
+    }),
+  ).toMatchObject({
+    type: 'system',
+    subtype: 'api_metrics',
+    ttftMs: 12,
+    otps: 34,
+    isP50: true,
+    hookDurationMs: 5,
+    turnDurationMs: 6,
+    toolDurationMs: 7,
+    classifierDurationMs: 8,
+    toolCount: 2,
+    hookCount: 3,
+    classifierCount: 1,
+    configWriteCount: 4,
+    isMeta: false,
+  })
+  expect(createCommandInputMessage('<command-name>test</command-name>')).toMatchObject({
+    type: 'system',
+    subtype: 'local_command',
+    content: '<command-name>test</command-name>',
+    level: 'info',
+    isMeta: false,
+  })
+})
+
+test('microcompact and API error factories preserve branch-specific fields', () => {
+  const microcompact = createMicrocompactBoundaryMessage(
+    'auto',
+    1000,
+    250,
+    ['toolu_1'],
+    ['attachment_1'],
+  )
+  expect(microcompact).toMatchObject({
+    type: 'system',
+    subtype: 'microcompact_boundary',
+    content: 'Context microcompacted',
+    level: 'info',
+    isMeta: false,
+    microcompactMetadata: {
+      trigger: 'auto',
+      preTokens: 1000,
+      tokensSaved: 250,
+      compactedToolIds: ['toolu_1'],
+      clearedAttachmentUUIDs: ['attachment_1'],
+    },
+  })
+
+  const cause = new Error('network down')
+  const errorWithCause = { message: 'api failed', cause } as any
+  expect(createSystemAPIErrorMessage(errorWithCause, 100, 2, 5)).toMatchObject({
+    type: 'system',
+    subtype: 'api_error',
+    level: 'error',
+    error: errorWithCause,
+    cause,
+    retryInMs: 100,
+    retryAttempt: 2,
+    maxRetries: 5,
+  })
+
+  const errorWithoutErrorCause = { message: 'api failed', cause: 'string cause' } as any
+  expect(
+    createSystemAPIErrorMessage(errorWithoutErrorCause, 200, 1, 3).cause,
+  ).toBeUndefined()
+})
+
+test('compact boundary helpers find and slice from the latest boundary', () => {
+  const first = createSystemMessage('old', 'info')
+  const boundary = createCompactBoundaryMessage('manual', 100)
+  const last = createSystemMessage('new', 'info')
+
+  expect(isCompactBoundaryMessage(boundary)).toBe(true)
+  expect(findLastCompactBoundaryIndex([first, boundary, last])).toBe(1)
+  expect(getMessagesAfterCompactBoundary([first, boundary, last])).toEqual([
+    boundary,
+    last,
+  ])
+})
+
+test('compact boundary slicing also applies snip projection when enabled', () => {
+  const removed = createSystemMessage('removed', 'info')
+  const kept = createSystemMessage('kept', 'info')
+  const snipBoundary = {
+    ...createSystemMessage('snipped', 'info'),
+    subtype: 'snip_boundary',
+    snipMetadata: { removedUuids: [removed.uuid] },
+  } as Message
+
+  const messages = [removed, snipBoundary, kept]
+  const result = getMessagesAfterCompactBoundary(messages)
+
+  if (feature('HISTORY_SNIP')) {
+    expect(result).toEqual([snipBoundary, kept])
+  } else {
+    expect(result).toEqual(messages)
+  }
+
+  expect(getMessagesAfterCompactBoundary(messages, { includeSnipped: true })).toEqual(
+    messages,
+  )
+})
diff --git a/src/utils/messages/systemFactories.ts b/src/utils/messages/systemFactories.ts
new file mode 100644
index 000000000..b60d00087
--- /dev/null
+++ b/src/utils/messages/systemFactories.ts
@@ -0,0 +1,329 @@
+import { feature } from "bun:bundle"
+import type { APIError } from "@anthropic-ai/sdk"
+import { randomUUID, type UUID } from "crypto"
+import type { Message, NormalizedMessage, StopHookInfo, SystemAgentsKilledMessage, SystemAPIErrorMessage, SystemApiMetricsMessage, SystemAwaySummaryMessage, SystemBridgeStatusMessage, SystemCompactBoundaryMessage, SystemInformationalMessage, SystemLocalCommandMessage, SystemMemorySavedMessage, SystemMicrocompactBoundaryMessage, SystemPermissionRetryMessage, SystemScheduledTaskFireMessage, SystemStopHookSummaryMessage, SystemTurnDurationMessage, SystemMessageLevel } from "../../types/message.js"
+import { formatTokens } from "../format.js"
+import { logForDebugging } from "../debug.js"
+
+export function createSystemMessage(
+  content: string,
+  level: SystemMessageLevel,
+  toolUseID?: string,
+  preventContinuation?: boolean,
+): SystemInformationalMessage {
+  return {
+    type: 'system',
+    subtype: 'informational',
+    content,
+    isMeta: false,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    toolUseID,
+    level,
+    ...(preventContinuation && { preventContinuation }),
+  }
+}
+
+export function createPermissionRetryMessage(
+  commands: string[],
+): SystemPermissionRetryMessage {
+  return {
+    type: 'system',
+    subtype: 'permission_retry',
+    content: `Allowed ${commands.join(', ')}`,
+    commands,
+    level: 'info',
+    isMeta: false,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+  }
+}
+
+export function createBridgeStatusMessage(
+  url: string,
+  upgradeNudge?: string,
+): SystemBridgeStatusMessage {
+  return {
+    type: 'system',
+    subtype: 'bridge_status',
+    content: `/remote-control is active. Code in CLI or at ${url}`,
+    url,
+    upgradeNudge,
+    isMeta: false,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+  }
+}
+
+export function createScheduledTaskFireMessage(
+  content: string,
+): SystemScheduledTaskFireMessage {
+  return {
+    type: 'system',
+    subtype: 'scheduled_task_fire',
+    content,
+    isMeta: false,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+  }
+}
+
+export function createStopHookSummaryMessage(
+  hookCount: number,
+  hookInfos: StopHookInfo[],
+  hookErrors: string[],
+  preventedContinuation: boolean,
+  stopReason: string | undefined,
+  hasOutput: boolean,
+  level: SystemMessageLevel,
+  toolUseID?: string,
+  hookLabel?: string,
+  totalDurationMs?: number,
+): SystemStopHookSummaryMessage {
+  return {
+    type: 'system',
+    subtype: 'stop_hook_summary',
+    hookCount,
+    hookInfos,
+    hookErrors,
+    preventedContinuation,
+    stopReason,
+    hasOutput,
+    level,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    toolUseID,
+    hookLabel,
+    totalDurationMs,
+  }
+}
+
+export function createTurnDurationMessage(
+  durationMs: number,
+  budget?: { tokens: number; limit: number; nudges: number },
+  messageCount?: number,
+): SystemTurnDurationMessage {
+  return {
+    type: 'system',
+    subtype: 'turn_duration',
+    durationMs,
+    budgetTokens: budget?.tokens,
+    budgetLimit: budget?.limit,
+    budgetNudges: budget?.nudges,
+    messageCount,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    isMeta: false,
+  }
+}
+
+export function createAwaySummaryMessage(
+  content: string,
+): SystemAwaySummaryMessage {
+  return {
+    type: 'system',
+    subtype: 'away_summary',
+    content,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    isMeta: false,
+  }
+}
+
+export function createMemorySavedMessage(
+  writtenPaths: string[],
+): SystemMemorySavedMessage {
+  return {
+    type: 'system',
+    subtype: 'memory_saved',
+    writtenPaths,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    isMeta: false,
+  }
+}
+
+export function createAgentsKilledMessage(): SystemAgentsKilledMessage {
+  return {
+    type: 'system',
+    subtype: 'agents_killed',
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    isMeta: false,
+  }
+}
+
+export function createApiMetricsMessage(metrics: {
+  ttftMs: number
+  otps: number
+  isP50?: boolean
+  hookDurationMs?: number
+  turnDurationMs?: number
+  toolDurationMs?: number
+  classifierDurationMs?: number
+  toolCount?: number
+  hookCount?: number
+  classifierCount?: number
+  configWriteCount?: number
+}): SystemApiMetricsMessage {
+  return {
+    type: 'system',
+    subtype: 'api_metrics',
+    ttftMs: metrics.ttftMs,
+    otps: metrics.otps,
+    isP50: metrics.isP50,
+    hookDurationMs: metrics.hookDurationMs,
+    turnDurationMs: metrics.turnDurationMs,
+    toolDurationMs: metrics.toolDurationMs,
+    classifierDurationMs: metrics.classifierDurationMs,
+    toolCount: metrics.toolCount,
+    hookCount: metrics.hookCount,
+    classifierCount: metrics.classifierCount,
+    configWriteCount: metrics.configWriteCount,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    isMeta: false,
+  }
+}
+
+export function createCommandInputMessage(
+  content: string,
+): SystemLocalCommandMessage {
+  return {
+    type: 'system',
+    subtype: 'local_command',
+    content,
+    level: 'info',
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    isMeta: false,
+  }
+}
+
+export function createCompactBoundaryMessage(
+  trigger: 'manual' | 'auto',
+  preTokens: number,
+  lastPreCompactMessageUuid?: UUID,
+  userContext?: string,
+  messagesSummarized?: number,
+): SystemCompactBoundaryMessage {
+  return {
+    type: 'system',
+    subtype: 'compact_boundary',
+    content: `Conversation compacted`,
+    isMeta: false,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    level: 'info',
+    compactMetadata: {
+      trigger,
+      preTokens,
+      userContext,
+      messagesSummarized,
+    },
+    ...(lastPreCompactMessageUuid && {
+      logicalParentUuid: lastPreCompactMessageUuid,
+    }),
+  }
+}
+
+export function createMicrocompactBoundaryMessage(
+  trigger: 'auto',
+  preTokens: number,
+  tokensSaved: number,
+  compactedToolIds: string[],
+  clearedAttachmentUUIDs: string[],
+): SystemMicrocompactBoundaryMessage {
+  logForDebugging(
+    `[microcompact] saved ~${formatTokens(tokensSaved)} tokens (cleared ${compactedToolIds.length} tool results)`,
+  )
+  return {
+    type: 'system',
+    subtype: 'microcompact_boundary',
+    content: 'Context microcompacted',
+    isMeta: false,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+    level: 'info',
+    microcompactMetadata: {
+      trigger,
+      preTokens,
+      tokensSaved,
+      compactedToolIds,
+      clearedAttachmentUUIDs,
+    },
+  }
+}
+
+export function createSystemAPIErrorMessage(
+  error: APIError,
+  retryInMs: number,
+  retryAttempt: number,
+  maxRetries: number,
+): SystemAPIErrorMessage {
+  return {
+    type: 'system',
+    subtype: 'api_error',
+    level: 'error',
+    cause: error.cause instanceof Error ? error.cause : undefined,
+    error,
+    retryInMs,
+    retryAttempt,
+    maxRetries,
+    timestamp: new Date().toISOString(),
+    uuid: randomUUID(),
+  }
+}
+
+/**
+ * Checks if a message is a compact boundary marker
+ */
+export function isCompactBoundaryMessage(
+  message: Message | NormalizedMessage,
+): message is SystemCompactBoundaryMessage {
+  return message?.type === 'system' && message.subtype === 'compact_boundary'
+}
+
+/**
+ * Finds the index of the last compact boundary marker in the messages array
+ * @returns The index of the last compact boundary, or -1 if none found
+ */
+export function findLastCompactBoundaryIndex<
+  T extends Message | NormalizedMessage,
+>(messages: T[]): number {
+  // Scan backwards to find the most recent compact boundary
+  for (let i = messages.length - 1; i >= 0; i--) {
+    const message = messages[i]
+    if (message && isCompactBoundaryMessage(message)) {
+      return i
+    }
+  }
+  return -1 // No boundary found
+}
+
+/**
+ * Returns messages from the last compact boundary onward (including the boundary).
+ * If no boundary exists, returns all messages.
+ *
+ * Also filters snipped messages by default (when HISTORY_SNIP is enabled) —
+ * the REPL keeps full history for UI scrollback, so model-facing paths need
+ * both compact-slice AND snip-filter applied. Pass `{ includeSnipped: true }`
+ * to opt out (e.g., REPL.tsx fullscreen compact handler which preserves
+ * snipped messages in scrollback).
+ *
+ * Note: The boundary itself is a system message and will be filtered by normalizeMessagesForAPI.
+ */
+export function getMessagesAfterCompactBoundary<
+  T extends Message | NormalizedMessage,
+>(messages: T[], options?: { includeSnipped?: boolean }): T[] {
+  const boundaryIndex = findLastCompactBoundaryIndex(messages)
+  const sliced = boundaryIndex === -1 ? messages : messages.slice(boundaryIndex)
+  if (!options?.includeSnipped && feature('HISTORY_SNIP')) {
+    /* eslint-disable @typescript-eslint/no-require-imports */
+    const { projectSnippedView } =
+      require('../../services/compact/snipProjection.js') as typeof import('../../services/compact/snipProjection.js')
+    /* eslint-enable @typescript-eslint/no-require-imports */
+    return projectSnippedView(sliced as Message[]) as T[]
+  }
+  return sliced
+}