fix(session): make transcript replacements crash-safe

src/entrypoints/sdk/sessions.ts

@@ -18,6 +18,7 @@ import {
   resolveSessionFilePath,
 } from '../../utils/sessionStoragePortable.js'
 import { readJSONLFile } from '../../utils/json.js'
+import { withTranscriptFileLock } from '../../utils/transcriptFileLock.js'
 import {
   assertValidSessionId,
   type JsonlEntry,
@@ -222,12 +223,10 @@ async function appendJsonlEntry(
   entry: Record<string, unknown>,
 ): Promise<void> {
   const line = JSON.stringify(entry) + '\n'
-  try {
+  await mkdir(dirname(filePath), { mode: 0o700, recursive: true })
+  await withTranscriptFileLock(filePath, async () => {
     await appendFile(filePath, line, { mode: 0o600 })
-  } catch {
-    await mkdir(dirname(filePath), { mode: 0o700, recursive: true })
-    await appendFile(filePath, line, { mode: 0o600 })
-  }
+  })
 }
 
 // ============================================================================

src/services/PromptSuggestion/speculation.ts

@@ -1,6 +1,6 @@
 import { randomUUID } from 'crypto'
 import { rm } from 'fs'
-import { appendFile, copyFile, mkdir } from 'fs/promises'
+import { copyFile, mkdir } from 'fs/promises'
 import { dirname, isAbsolute, join, relative } from 'path'
 import { getCwdState } from '../../bootstrap/state.js'
 import type { CompletionBoundary } from '../../state/AppStateStore.js'
@@ -45,8 +45,7 @@ import {
 } from '../../utils/messages.js'
 import { getClaudeTempDir } from '../../utils/permissions/filesystem.js'
 import { extractReadFilesFromMessages } from '../../utils/queryHelpers.js'
-import { getTranscriptPath } from '../../utils/sessionStorage.js'
-import { jsonStringify } from '../../utils/slowOperations.js'
+import { recordSpeculationAccept } from '../../utils/sessionStorage.js'
 import {
   type AnalyticsMetadata_I_VERIFIED_THIS_IS_NOT_CODE_OR_FILEPATHS,
   logEvent,
@@ -797,11 +796,9 @@ export async function acceptSpeculation(
       timestamp: new Date().toISOString(),
       timeSavedMs,
     }
-    void appendFile(getTranscriptPath(), jsonStringify(entry) + '\n', {
-      mode: 0o600,
-    }).catch(() => {
+    void recordSpeculationAccept(entry).catch(() => {
       logForDebugging(
-        '[Speculation] Failed to write speculation-accept to transcript',
+        '[Speculation] Failed to queue speculation-accept for transcript',
       )
     })
   }

src/utils/atomicReplace.test.ts

@@ -0,0 +1,259 @@
+import { afterEach, beforeEach, expect, test } from 'bun:test'
+import {
+  chmod,
+  lstat,
+  mkdtemp,
+  readFile,
+  readlink,
+  readdir,
+  rm,
+  stat,
+  symlink,
+  writeFile,
+} from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { basename, join } from 'node:path'
+
+import {
+  type AtomicReplaceFaultStage,
+  replaceFileAtomic,
+  resetAtomicReplaceFaultInjectorForTesting,
+  setAtomicReplaceFaultInjectorForTesting,
+  setAtomicReplaceWriteLimitForTesting,
+} from './atomicReplace.js'
+import {
+  acquireSharedMutationLock,
+  releaseSharedMutationLock,
+} from '../test/sharedMutationLock.js'
+
+const tempDirs: string[] = []
+
+async function tempTarget(initial?: string): Promise<{
+  dir: string
+  target: string
+}> {
+  const dir = await mkdtemp(join(tmpdir(), 'openclaude-atomic-replace-'))
+  tempDirs.push(dir)
+  const target = join(dir, 'transcript.jsonl')
+  if (initial !== undefined) await writeFile(target, initial)
+  return { dir, target }
+}
+
+async function tempFiles(dir: string, target: string): Promise<string[]> {
+  const prefix = `.${basename(target)}.tmp-`
+  return (await readdir(dir)).filter(name => name.startsWith(prefix))
+}
+
+beforeEach(async () => {
+  await acquireSharedMutationLock('utils/atomicReplace.test.ts')
+})
+
+afterEach(async () => {
+  try {
+    resetAtomicReplaceFaultInjectorForTesting()
+    setAtomicReplaceWriteLimitForTesting(undefined)
+    await Promise.all(
+      tempDirs.splice(0).map(dir => rm(dir, { recursive: true, force: true })),
+    )
+  } finally {
+    releaseSharedMutationLock()
+  }
+})
+
+test('replaces from strings, bytes, and streamed chunks', async () => {
+  const { target } = await tempTarget('old')
+
+  await replaceFileAtomic(target, 'string')
+  expect(await readFile(target, 'utf8')).toBe('string')
+
+  await replaceFileAtomic(target, new TextEncoder().encode('bytes'))
+  expect(await readFile(target, 'utf8')).toBe('bytes')
+
+  async function* chunks() {
+    yield 'stream-'
+    yield new TextEncoder().encode('complete')
+  }
+  await replaceFileAtomic(target, chunks())
+  expect(await readFile(target, 'utf8')).toBe('stream-complete')
+})
+
+test('retries deterministic short low-level writes until the chunk is complete', async () => {
+  const { target } = await tempTarget('old-complete')
+  setAtomicReplaceWriteLimitForTesting(3)
+
+  await replaceFileAtomic(target, 'new-complete-transcript')
+
+  expect(await readFile(target, 'utf8')).toBe('new-complete-transcript')
+})
+
+test('a zero-progress low-level write preserves the original and cleans the temp', async () => {
+  const { dir, target } = await tempTarget('old-complete')
+  setAtomicReplaceWriteLimitForTesting(0)
+
+  await expect(replaceFileAtomic(target, 'new')).rejects.toThrow(
+    'Atomic replacement made no progress while writing',
+  )
+  expect(await readFile(target, 'utf8')).toBe('old-complete')
+  expect(await tempFiles(dir, target)).toEqual([])
+})
+
+test('preserves an existing restrictive mode and creates new files as 0600', async () => {
+  if (process.platform === 'win32') return
+
+  const existing = await tempTarget('old')
+  await chmod(existing.target, 0o640)
+  await replaceFileAtomic(existing.target, 'new')
+  expect((await stat(existing.target)).mode & 0o777).toBe(0o640)
+
+  const created = await tempTarget()
+  await replaceFileAtomic(created.target, 'new')
+  expect((await stat(created.target)).mode & 0o777).toBe(0o600)
+})
+
+test('an explicit mode overrides preservation for an existing target', async () => {
+  if (process.platform === 'win32') return
+
+  const existing = await tempTarget('old')
+  await chmod(existing.target, 0o640)
+
+  await replaceFileAtomic(existing.target, 'new', { mode: 0o600 })
+
+  expect((await stat(existing.target)).mode & 0o777).toBe(0o600)
+})
+
+test('preserveMode false applies the private default to an existing target', async () => {
+  if (process.platform === 'win32') return
+
+  const existing = await tempTarget('old')
+  await chmod(existing.target, 0o644)
+
+  await replaceFileAtomic(existing.target, 'new', { preserveMode: false })
+
+  expect((await stat(existing.target)).mode & 0o777).toBe(0o600)
+})
+
+test('full flush commits complete content', async () => {
+  const { target } = await tempTarget('old')
+
+  await replaceFileAtomic(target, 'new-complete', { flush: 'full' })
+
+  expect(await readFile(target, 'utf8')).toBe('new-complete')
+})
+
+test('writes through live and dangling relative symlinks without replacing them', async () => {
+  if (process.platform === 'win32') return
+
+  const live = await tempTarget()
+  const liveTarget = join(live.dir, 'live-target.jsonl')
+  await writeFile(liveTarget, 'old-live')
+  await symlink(basename(liveTarget), live.target)
+  await replaceFileAtomic(live.target, 'new-live')
+  expect((await lstat(live.target)).isSymbolicLink()).toBe(true)
+  expect(await readlink(live.target)).toBe(basename(liveTarget))
+  expect(await readFile(liveTarget, 'utf8')).toBe('new-live')
+
+  const dangling = await tempTarget()
+  const danglingTarget = join(dangling.dir, 'created-through-link.jsonl')
+  await symlink(basename(danglingTarget), dangling.target)
+  await replaceFileAtomic(dangling.target, 'new-dangling')
+  expect((await lstat(dangling.target)).isSymbolicLink()).toBe(true)
+  expect(await readFile(danglingTarget, 'utf8')).toBe('new-dangling')
+})
+
+test('an already-aborted replacement preserves the original', async () => {
+  const { target } = await tempTarget('old')
+  const controller = new AbortController()
+  controller.abort()
+
+  await expect(
+    replaceFileAtomic(target, 'new', { signal: controller.signal }),
+  ).rejects.toBeDefined()
+  expect(await readFile(target, 'utf8')).toBe('old')
+})
+
+const preRenameFaults: AtomicReplaceFaultStage[] = [
+  'temp-open',
+  'stream-write',
+  'data-flush',
+  'chmod',
+  'close',
+  'rename',
+]
+
+for (const faultStage of preRenameFaults) {
+  test(`${faultStage} failure preserves the original and cleans the temp`, async () => {
+    const { dir, target } = await tempTarget('old-complete')
+    setAtomicReplaceFaultInjectorForTesting(stage => {
+      if (stage === faultStage) throw new Error(`fault:${stage}`)
+    })
+
+    async function* replacement() {
+      yield 'partial-'
+      yield 'replacement'
+    }
+
+    await expect(replaceFileAtomic(target, replacement())).rejects.toThrow(
+      `fault:${faultStage}`,
+    )
+    expect(await readFile(target, 'utf8')).toBe('old-complete')
+    expect(await tempFiles(dir, target)).toEqual([])
+  })
+}
+
+test('cleanup failure does not mask the primary failure or modify the target', async () => {
+  const { dir, target } = await tempTarget('old')
+  setAtomicReplaceFaultInjectorForTesting(stage => {
+    if (stage === 'rename') throw new Error('primary rename fault')
+    if (stage === 'cleanup') throw new Error('cleanup fault')
+  })
+
+  await expect(replaceFileAtomic(target, 'new')).rejects.toThrow(
+    'primary rename fault',
+  )
+  expect(await readFile(target, 'utf8')).toBe('old')
+  expect((await tempFiles(dir, target)).length).toBe(1)
+})
+
+test('directory sync failure is post-commit and leaves the complete new file', async () => {
+  const { target } = await tempTarget('old')
+  setAtomicReplaceFaultInjectorForTesting(stage => {
+    if (stage === 'directory-sync') throw new Error('directory sync fault')
+  })
+
+  await replaceFileAtomic(target, 'new-complete')
+  expect(await readFile(target, 'utf8')).toBe('new-complete')
+})
+
+test('concurrent readers observe only complete old or complete new bytes', async () => {
+  const oldContent = 'old-complete-transcript'
+  const newContent = 'new-complete-transcript'
+  const { target } = await tempTarget(oldContent)
+
+  let release!: () => void
+  const gate = new Promise<void>(resolve => {
+    release = resolve
+  })
+  let firstWrite!: () => void
+  const wroteFirstChunk = new Promise<void>(resolve => {
+    firstWrite = resolve
+  })
+  let writes = 0
+  setAtomicReplaceFaultInjectorForTesting(stage => {
+    if (stage === 'stream-write' && writes++ === 0) firstWrite()
+  })
+
+  async function* slowReplacement() {
+    yield 'new-complete-'
+    await gate
+    yield 'transcript'
+  }
+
+  const replacing = replaceFileAtomic(target, slowReplacement())
+  await wroteFirstChunk
+  for (let i = 0; i < 25; i++) {
+    expect(await readFile(target, 'utf8')).toBe(oldContent)
+  }
+  release()
+  await replacing
+  expect(await readFile(target, 'utf8')).toBe(newContent)
+})