Support durable JSONL persistence on Windows

docs/rfc/INDEX.md

@@ -150,6 +150,7 @@ Generated by `pnpm run gen-rfc-index` from the RFC tree — never edit by hand;
 | [Prompt variables and tool-guidance ownership](implemented/architecture/2026-07-05-prompt-variables-and-tool-guidance-ownership.md) | 2026-07-05 |
 | [Every LLM request is reconstructable from the session log](implemented/architecture/2026-07-05-reconstructable-requests.md) | 2026-07-05 |
 | [Subagent provider-lifecycle events — `subagent/provider-added` / `subagent/provider-removed`](implemented/architecture/2026-07-05-subagent-provider-lifecycle-events.md) | 2026-07-05 |
+| [Windows-native durable JSONL publication](implemented/architecture/2026-07-05-windows-jsonl-durable-publish.md) | 2026-07-05 |
 | [A shared timeout/deadline primitive, with hard-kill left to each capability](implemented/architecture/2026-07-06-timeout-deadline-library.md) | 2026-07-06 |
 | [Tool result retention library](implemented/architecture/2026-07-06-tool-result-retention-library.md) | 2026-07-06 |
 | [Tool-call timeout policy as a plugin](implemented/architecture/2026-07-07-tool-call-timeout-policy.md) | 2026-07-07 |

docs/rfc/implemented/architecture/2026-07-05-windows-jsonl-durable-publish.md

@@ -0,0 +1,33 @@
+# RFC: Windows-native durable JSONL publication
+
+Status: implemented
+
+## Problem
+
+`dsh-session-persistence-jsonl` publishes a session log lazily on the first append. The POSIX protocol writes a temp file, fsyncs it, links it to the final name, fsyncs the parent directory, and then removes the temp link. The parent-directory fsync is part of the durability contract: a crash after the namespace change must not lose the committed final name while leaving callers believing the session log materialized.
+
+Windows has atomic namespace operations, but Node does not expose a POSIX-equivalent parent-directory fsync contract there. Treating Windows directory sync failures as success would silently weaken a durable backend. The Windows path therefore needs a different publication primitive rather than a conditional inside the POSIX `syncDir` helper.
+
+## Decision
+
+The JSONL backend forks inside `materialize()` before any namespace mutation. Shared code computes the session directory, final log path, and initial JSONL bytes; POSIX and Windows then run separate publication protocols.
+
+POSIX keeps the existing protocol: create the root and cwd bucket with parent directory fsyncs, write and fsync a temp file, publish with `link()` so an existing final log is never overwritten, fsync the bucket directory, then remove the redundant temp hard link.
+
+Windows creates missing directories through a durable staging publish: create a random sibling directory, then publish it to the final directory name with `MoveFileExW(..., MOVEFILE_WRITE_THROUGH)` without `MOVEFILE_REPLACE_EXISTING` or `MOVEFILE_COPY_ALLOWED`. File materialization writes and fsyncs the temp log, then publishes that temp file to the final path with the same write-through `MoveFileExW` call and no replacement. `koffi` is the minimal Win32 bridge for this API surface; its install script is allowed in `pnpm-workspace.yaml` because the package ships the native loader and prebuilt platform modules.
+
+## Alternatives considered
+
+**Ignore Windows directory-sync failures.** Rejected because it reports a first append as durable without forcing the published namespace entry to stable storage.
+
+**Use `CreateHardLinkW`.** Rejected because hard links are filesystem-dependent, do not publish directories, and expose no write-through option.
+
+**Use replacement or transactional APIs.** `ReplaceFileW` has replacement semantics that conflict with same-id collision rejection, and Transactional NTFS is not recommended for new application designs.
+
+## Consequences
+
+The backend keeps one external contract across platforms: first append either publishes a complete log at the final name or fails without overwriting an existing log. The platform split is an implementation detail; `SessionPersistence` APIs and on-disk JSONL format do not change.
+
+Windows tests exercise the real Win32 publish path on native Windows. Power-loss behavior remains an API-contract property rather than something unit tests can prove; the testable invariants are that directory fsync is not called on Windows materialization, final-path collisions fail, temp logs are fsync'd before publication, and the resulting log loads normally.
+
+Append and repair still use ordinary file-handle fsyncs on both platforms. A failed append closes its append-only handle, reopens the log read/write, truncates it to the pre-append size, and fsyncs the rollback because Windows rejects `ftruncate` on append-only handles.

packages/session-persistence/session-persistence-jsonl/README.md

@@ -23,7 +23,7 @@ The JSONL durable session-persistence backend — a concrete `SessionPersistence
 
 ## Durability and crash semantics
 
-- **Lazy materialization.** `create(meta)` writes nothing; on the first `append`, the backend writes and `fsync`s a temporary file, publishes it without overwrite via a hard link, then `fsync`s the directory. A created-but-never-appended session leaves nothing on disk and is absent from `list`.
+- **Lazy materialization.** `create(meta)` writes nothing; the `.jsonl` (header + first batch) is written atomically on the first `append`: POSIX uses temp-write + file `fsync` + `link` + parent-directory `fsync`; Windows uses temp-write + file `fsync` + `MoveFileExW(..., MOVEFILE_WRITE_THROUGH)` and creates missing directories through the same write-through publish pattern. A created-but-never-appended session leaves nothing on disk and is absent from `list`.
 - **Append-only.** Committed events (at or below a flushed `turn/end`) are never rewritten. Subsequent appends are line appends at EOF + `fsync`.
 - **Crash recovery — preserve valid tail work.** `load` keeps the contiguous valid prefix of an interrupted final turn. It truncates from the first unparsable or sequence-gapped uncommitted record, then appends the synthetic tool, step, and turn closers required by the shared [persistence contract](../../../docs/rfc/implemented/architecture/2026-06-14-session-persistence.md); the same defect at or before the last committed `turn/end` rejects.
 - **Contiguous-seq.** `append` rejects a batch whose first `seq` does not continue the stored log, and rejects non-JSON-serializable `event.data` naming the offending event type.
@@ -45,4 +45,4 @@ The plugin buffers frozen session events and drains them on flush or disposal. A
 - **Only the current `SESSION_FORMAT_VERSION` (v0) loads** — the on-disk format is pre-release/unstable: a breaking format change is absorbed at v0 and non-current logs are rejected; there is no migration.
 - **Nothing deletes session files** — logs accumulate under `root` until removed externally (the seam has no deletion surface).
 - **Single-process assumption** — per-session serialization and the write cursor live in this process; two processes appending to the same `root` are not coordinated.
-- **Initial materialization requires hard-link support** — first append uses `link()` so same-id races fail instead of overwriting a committed log; a filesystem that cannot create hard links cannot host this backend.
+- **POSIX materialization requires hard-link support** — its first append uses `link()` so same-id races fail instead of overwriting a committed log; Windows uses write-through rename without replacement.

packages/session-persistence/session-persistence-jsonl/package.json

@@ -27,6 +27,7 @@
     "cordis": "^4.0.0-rc.7"
   },
   "dependencies": {
+    "koffi": "^3.1.0",
     "schemastery": "^3.18.0"
   },
   "devDependencies": {

packages/session-persistence/session-persistence-jsonl/src/index.ts

@@ -19,6 +19,7 @@ import type { SessionEvent, SessionId, SessionHeader } from '@deepseek-ai/dsh-se
 import {
   encodeSegment, eventLine, logPath, parseHeaderMeta, scanLog, sessionDir, toHeaderLine,
 } from './format.ts'
+import { ensureDurableDirectoryWin32, publishNewFileWin32 } from './win32.ts'
 
 /** Plugin config: where the JSONL backend keeps its session logs (`root` is required — no default). */
 export interface Config {
@@ -160,33 +161,35 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
 
   // --- materialization / append / repair (file mechanics) ---
 
-  /** Atomically write the header line + first batch (temp-write, fsync, collision-safe hard-link publish). */
+  /** Atomically write the header line + first batch (temp-write, fsync, publish). */
   private async materialize(meta: SessionHeader, events: readonly SessionEvent[]): Promise<void> {
     const dir = sessionDir(this.root, meta.cwd)
-    await mkdir(this.root, { recursive: true, mode: 0o700 })
-    await this.syncDir(dirname(this.root))
-    await mkdir(dir, { recursive: true, mode: 0o700 })
-    await this.syncDir(this.root)
     const finalPath = logPath(this.root, meta.cwd, meta.id)
-    // Materialization is the first write; an existing log is an id collision.
-    /* v8 ignore next 3 -- createCore guards collisions before materialize; this is a TOCTOU backstop */
-    if (await this.exists(finalPath)) {
-      throw new Error(`refusing to materialize "${meta.id}": a log already exists on disk (load/resume it instead)`)
+    const content = this.initialLogContent(meta, events)
+    /* v8 ignore next -- native Windows coverage exercises this platform dispatch; Linux covers the POSIX peer */
+    if (process.platform === 'win32') {
+      await this.materializeWin32(dir, finalPath, meta.id, content)
+    } else {
+      await this.materializePosix(dir, finalPath, meta.id, content)
     }
+  }
+
+  private initialLogContent(meta: SessionHeader, events: readonly SessionEvent[]): string {
     const header = JSON.stringify(toHeaderLine(meta))
     const body = events.map(eventLine).join('\n')
-    const content = header + '\n' + body + '\n'
+    return header + '\n' + body + '\n'
+  }
 
-    const tmp = `${finalPath}.${randomBytes(6).toString('hex')}.tmp`
-    const handle = await open(tmp, 'wx', 0o600)
-    try {
-      await handle.writeFile(content)
-      await handle.sync()
-    } finally {
-      await handle.close()
-    }
-    // Publish with link()+unlink(): unlike rename(), link fails if another
-    // process materialized the same id first.
+  private async materializePosix(dir: string, finalPath: string, id: SessionId, content: string): Promise<void> {
+    await mkdir(this.root, { recursive: true, mode: 0o700 })
+    await this.syncDirPosix(dirname(this.root))
+    await mkdir(dir, { recursive: true, mode: 0o700 })
+    await this.syncDirPosix(this.root)
+    await this.rejectExistingLog(finalPath, id)
+    const tmp = await this.writeSyncedTempFile(finalPath, content)
+    // Publish via link()+unlink(), NOT rename(): link fails with EEXIST if the
+    // final path already exists, so two processes materializing the same id
+    // concurrently cannot clobber each other. rename() would silently overwrite.
     let linked = false
     try {
       await link(tmp, finalPath)
@@ -197,10 +200,13 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
       /* v8 ignore next -- link failure is the TOCTOU/IO race guarded above; not reachable in test */
       if (!linked) await rm(tmp, { force: true })
     }
-    // The published link becomes crash-durable only after its directory fsync.
-    await this.syncDir(dir)
-    // Best-effort temp cleanup: the log is already published and durable, so a failure to
-    // remove the (now-redundant) temp hard link must not reject the append.
+    // link() succeeded — the log is published. fsync the directory so the new
+    // entry survives a power loss: the new link is not crash-durable until the
+    // parent directory's metadata is synced.
+    await this.syncDirPosix(dir)
+    // Best-effort temp cleanup: the log is already published and durable, so a
+    // failure to remove the (now-redundant) temp hard link must NOT reject the
+    // append. Swallow only the rm failure; nothing else of consequence runs here.
     try {
       await rm(tmp, { force: true })
     } catch {
@@ -208,8 +214,47 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
     }
   }
 
-  /** fsync a directory so a just-created or published entry inside it is crash-durable. */
-  private async syncDir(dir: string): Promise<void> {
+  /* v8 ignore start -- native Windows coverage exercises this integration path */
+  private async materializeWin32(dir: string, finalPath: string, id: SessionId, content: string): Promise<void> {
+    await ensureDurableDirectoryWin32(this.root)
+    await ensureDurableDirectoryWin32(dir)
+    await this.rejectExistingLog(finalPath, id)
+    const tmp = await this.writeSyncedTempFile(finalPath, content)
+    try {
+      await publishNewFileWin32(tmp, finalPath)
+    } catch (error) {
+      await rm(tmp, { force: true })
+      throw error
+    }
+  }
+  /* v8 ignore stop */
+
+  private async rejectExistingLog(finalPath: string, id: SessionId): Promise<void> {
+    // Never publish over an existing committed log: materialize is the FIRST
+    // write of a session the backend believes is new. A file here means a
+    // different session shares this id on disk — reject loudly. (createCore
+    // already guards the create path, so this is unreachable-in-practice TOCTOU
+    // defense.)
+    /* v8 ignore next 3 -- createCore guards collisions before materialize; this is a TOCTOU backstop */
+    if (await this.exists(finalPath)) {
+      throw new Error(`refusing to materialize "${id}": a log already exists on disk (load/resume it instead)`)
+    }
+  }
+
+  private async writeSyncedTempFile(finalPath: string, content: string): Promise<string> {
+    const tmp = `${finalPath}.${randomBytes(6).toString('hex')}.tmp`
+    const handle = await open(tmp, 'wx', 0o600)
+    try {
+      await handle.writeFile(content)
+      await handle.sync()
+    } finally {
+      await handle.close()
+    }
+    return tmp
+  }
+
+  /** fsync a POSIX directory so a just-created/renamed entry is crash-durable. */
+  private async syncDirPosix(dir: string): Promise<void> {
     const handle = await open(dir, 'r')
     try {
       await handle.sync()
@@ -226,17 +271,37 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
   private async appendLines(meta: SessionHeader, events: readonly SessionEvent[]): Promise<void> {
     const path = logPath(this.root, meta.cwd, meta.id)
     const handle = await open(path, 'a')
+    let closed = false
+    const closeAppendHandle = async (): Promise<void> => {
+      if (closed) return
+      closed = true
+      await handle.close()
+    }
+
     try {
       const { size: before } = await handle.stat()
       try {
         await handle.writeFile(events.map(eventLine).join('\n') + '\n')
         await handle.sync()
       } catch (error) {
-        // Roll back whatever bytes landed so a retry starts from a clean EOF.
-        await handle.truncate(before)
-        await handle.sync()
+        try {
+          await closeAppendHandle()
+          await this.rollbackAppend(path, before)
+        } catch (rollbackError) {
+          throw new AggregateError([error, rollbackError], `failed to roll back append to "${path}"`)
+        }
         throw error
       }
+    } finally {
+      await closeAppendHandle()
+    }
+  }
+
+  private async rollbackAppend(path: string, size: number): Promise<void> {
+    const handle = await open(path, 'r+')
+    try {
+      await handle.truncate(size)
+      await handle.sync()
     } finally {
       await handle.close()
     }
@@ -322,9 +387,8 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
       await handle.close()
       return true
     } catch (error) {
-      // Only ENOENT means absent. A permission/I/O error must surface, not be
-      // collapsed to `false` — otherwise load() reports "not found" and collision
-      // checks proceed under a false absence assumption.
+      // Only ENOENT means absent. A permission/I/O error must surface rather
+      // than letting load or collision checks proceed under false absence.
       if (isENOENT(error)) return false
       throw error
     }

packages/session-persistence/session-persistence-jsonl/src/win32.ts

@@ -0,0 +1,150 @@
+/**
+ * Windows durable namespace helpers for the JSONL backend.
+ *
+ * POSIX publishes a newly-created log by creating a directory entry and then
+ * fsyncing the parent directory. Windows does not expose that parent-directory
+ * fsync contract through Node, so the Windows path uses the native durable
+ * namespace primitive instead: create a staging object in the target directory
+ * and publish it with `MoveFileExW(..., MOVEFILE_WRITE_THROUGH)` without
+ * replacement or cross-volume copy fallback.
+ *
+ * @module dsh-session-persistence-jsonl/win32
+ */
+
+import { mkdtemp, rm, stat } from 'node:fs/promises'
+import { basename, join, parse, resolve, toNamespacedPath } from 'node:path'
+
+type MoveFileExW = (existing: string, replacement: string, flags: number) => boolean
+type GetLastError = () => number
+
+interface Win32Bindings {
+  moveFileExW: MoveFileExW
+  getLastError: GetLastError
+}
+
+interface Win32ErrnoException extends NodeJS.ErrnoException {
+  win32Code: number
+  dest: string
+}
+
+const MOVEFILE_WRITE_THROUGH = 0x00000008
+const ERROR_FILE_NOT_FOUND = 2
+const ERROR_PATH_NOT_FOUND = 3
+const ERROR_ACCESS_DENIED = 5
+const ERROR_NOT_SAME_DEVICE = 17
+const ERROR_FILE_EXISTS = 80
+const ERROR_INVALID_NAME = 123
+const ERROR_ALREADY_EXISTS = 183
+
+let bindings: Win32Bindings | undefined
+
+/** Load the small Win32 surface lazily so non-Windows processes never load Koffi. */
+async function win32(): Promise<Win32Bindings> {
+  if (bindings !== undefined) return bindings
+  const koffi = (await import('koffi')).default
+  const kernel32 = koffi.load('kernel32.dll')
+  bindings = {
+    moveFileExW: kernel32.func('__stdcall', 'MoveFileExW', 'bool', ['str16', 'str16', 'uint']) as MoveFileExW,
+    getLastError: kernel32.func('__stdcall', 'GetLastError', 'uint', []) as GetLastError,
+  }
+  return bindings
+}
+
+function errnoCode(win32Code: number): string {
+  switch (win32Code) {
+    case ERROR_FILE_NOT_FOUND:
+    case ERROR_PATH_NOT_FOUND:
+      return 'ENOENT'
+    case ERROR_ACCESS_DENIED:
+      return 'EACCES'
+    case ERROR_NOT_SAME_DEVICE:
+      return 'EXDEV'
+    case ERROR_FILE_EXISTS:
+    case ERROR_ALREADY_EXISTS:
+      return 'EEXIST'
+    case ERROR_INVALID_NAME:
+      return 'EINVAL'
+    default:
+      return 'EIO'
+  }
+}
+
+function win32Error(syscall: string, win32Code: number, path: string, dest: string): Win32ErrnoException {
+  const code = errnoCode(win32Code)
+  const error = new Error(`${syscall} ${code} (Win32 ${win32Code}): ${path} -> ${dest}`) as Win32ErrnoException
+  error.code = code
+  error.errno = win32Code
+  error.syscall = syscall
+  error.path = path
+  error.dest = dest
+  error.win32Code = win32Code
+  return error
+}
+
+function isENOENT(error: unknown): boolean {
+  return (error as NodeJS.ErrnoException | null)?.code === 'ENOENT'
+}
+
+function isEEXIST(error: unknown): boolean {
+  return (error as NodeJS.ErrnoException | null)?.code === 'EEXIST'
+}
+
+async function assertDirectory(path: string): Promise<boolean> {
+  try {
+    const info = await stat(path)
+    if (info.isDirectory()) return true
+    const error = new Error(`path exists but is not a directory: ${path}`) as NodeJS.ErrnoException
+    error.code = 'ENOTDIR'
+    error.path = path
+    throw error
+  } catch (error) {
+    if (isENOENT(error)) return false
+    throw error
+  }
+}
+
+/**
+ * Publish `existing` at `replacement` with Windows write-through rename
+ * semantics. The destination must not already exist; the move must stay within
+ * the volume (no copy fallback flag is set).
+ * @param existing - the synced staging path to move.
+ * @param replacement - the final path, which must not already exist.
+ */
+export async function publishNewFileWin32(existing: string, replacement: string): Promise<void> {
+  const api = await win32()
+  const ok = api.moveFileExW(toNamespacedPath(existing), toNamespacedPath(replacement), MOVEFILE_WRITE_THROUGH)
+  if (!ok) throw win32Error('MoveFileExW', api.getLastError(), existing, replacement)
+}
+
+/**
+ * Create `target` and its missing ancestors with durable Windows namespace
+ * publication. Each missing directory is first created as a random staging
+ * sibling, then moved to its final name with `MOVEFILE_WRITE_THROUGH`; races
+ * with another creator are accepted only after verifying the winner is a
+ * directory.
+ * @param target - the absolute directory path to create durably when absent.
+ */
+export async function ensureDurableDirectoryWin32(target: string): Promise<void> {
+  const absolute = resolve(target)
+  const root = parse(absolute).root
+  await assertDirectory(root)
+
+  const segments = absolute.slice(root.length).split(/[\\/]+/).filter(part => part.length > 0)
+  let current = root
+  for (const segment of segments) {
+    const next = join(current, segment)
+    if (!await assertDirectory(next)) await createLeafDirectoryWin32(current, next)
+    current = next
+  }
+}
+
+async function createLeafDirectoryWin32(parent: string, target: string): Promise<void> {
+  const staging = await mkdtemp(join(parent, `.dsh-mkdir-${basename(target)}-`))
+  try {
+    await publishNewFileWin32(staging, target)
+  } catch (error) {
+    await rm(staging, { recursive: true, force: true })
+    if (isEEXIST(error) && await assertDirectory(target)) return
+    throw error
+  }
+}

packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts

@@ -336,6 +336,45 @@ describe('SessionPersistenceJsonl: durability and crash semantics', () => {
     expect(loaded.events.map(e => e.seq)).toEqual([0, 1, 2, 3, 4, 5, 6, 7])
   })
 
+  it('reports both the append failure and a failed rollback', async () => {
+    const m = meta('rollback-failure')
+    await ctx.sessionPersistence.create(m)
+    await ctx.sessionPersistence.append(m.id, oneTurnLog())
+
+    const path = logPath(root, undefined, m.id)
+    const handle = await (await import('node:fs/promises')).open(path, 'r')
+    const proto = Object.getPrototypeOf(handle) as { sync: () => Promise<void> }
+    await handle.close()
+    const realSync = proto.sync
+    let failed = false
+    const syncSpy = vi.spyOn(proto, 'sync').mockImplementation(async function (this: unknown) {
+      if (!failed) { failed = true; throw new Error('simulated append fsync failure') }
+      return realSync.call(this)
+    })
+    const backend = ctx.sessionPersistence as unknown as {
+      rollbackAppend: (path: string, size: number) => Promise<void>
+    }
+    const realRollback = backend.rollbackAppend.bind(backend)
+    backend.rollbackAppend = () => Promise.reject(new Error('simulated rollback failure'))
+
+    try {
+      await ctx.sessionPersistence.append(m.id, [
+        { type: 'turn/start', seq: 6, time: 9, data: { turn: 2, trigger: { kind: 'message', source: { kind: 'user' } } } },
+      ] as SessionEvent[])
+      throw new Error('expected append to reject')
+    } catch (error) {
+      expect(error).toBeInstanceOf(AggregateError)
+      const aggregate = error as AggregateError
+      expect(aggregate.message).toContain(`failed to roll back append to "${path}"`)
+      expect(aggregate.errors).toHaveLength(2)
+      expect(aggregate.errors[0]).toMatchObject({ message: 'simulated append fsync failure' })
+      expect(aggregate.errors[1]).toMatchObject({ message: 'simulated rollback failure' })
+    } finally {
+      backend.rollbackAppend = realRollback
+      syncSpy.mockRestore()
+    }
+  })
+
   it('load returns a meta copy: mutating it does not corrupt backend pathing', async () => {
     const m = meta('meta-copy', '/proj')
     await ctx.sessionPersistence.create(m)

packages/session-persistence/session-persistence-jsonl/tests/win32.spec.ts

@@ -0,0 +1,168 @@
+/**
+ * Unit tests for the Windows durable namespace helper with a mocked kernel32
+ * binding. The real JSONL suite exercises the helper on native Windows; these
+ * tests keep the Win32 error mapping and race handling covered on every host.
+ */
+
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { existsSync, mkdirSync, readFileSync, renameSync, writeFileSync } from 'node:fs'
+import { mkdtemp, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+
+const MOVEFILE_WRITE_THROUGH = 0x00000008
+const ERROR_FILE_NOT_FOUND = 2
+const ERROR_PATH_NOT_FOUND = 3
+const ERROR_ACCESS_DENIED = 5
+const ERROR_NOT_SAME_DEVICE = 17
+const ERROR_FILE_EXISTS = 80
+const ERROR_INVALID_NAME = 123
+const ERROR_ALREADY_EXISTS = 183
+
+type MoveFileExW = (existing: string, replacement: string, flags: number, setLastError: (code: number) => void) => boolean
+
+const roots: string[] = []
+
+function stripNamespace(path: string): string {
+  if (path.startsWith('\\\\?\\UNC\\')) return `\\\\${path.slice('\\\\?\\UNC\\'.length)}`
+  if (path.startsWith('\\\\?\\')) return path.slice('\\\\?\\'.length)
+  return path
+}
+
+async function tempRoot(): Promise<string> {
+  const dir = await mkdtemp(join(tmpdir(), 'dsh-jsonl-win32-'))
+  roots.push(dir)
+  return dir
+}
+
+async function importWithMove(moveFileExW: MoveFileExW): Promise<typeof import('../src/win32.ts')> {
+  vi.resetModules()
+  vi.doMock('koffi', () => {
+    let lastError = 0
+    const setLastError = (code: number): void => { lastError = code }
+    const move: MoveFileExW = (existing, replacement, flags, setError) => {
+      const ok = moveFileExW(existing, replacement, flags, setError)
+      lastError = ok ? 0 : lastError
+      return ok
+    }
+    return {
+      default: {
+        load: () => ({
+          func: (_convention: string, name: string) => {
+            if (name === 'MoveFileExW') return (existing: string, replacement: string, flags: number) => {
+              const ok = move(existing, replacement, flags, setLastError)
+              return ok
+            }
+            return () => lastError
+          },
+        }),
+      },
+    }
+  })
+  return import('../src/win32.ts')
+}
+
+async function importWithError(code: number): Promise<typeof import('../src/win32.ts')> {
+  vi.resetModules()
+  vi.doMock('koffi', () => ({
+    default: {
+      load: () => ({
+        func: (_convention: string, name: string) => {
+          if (name === 'MoveFileExW') return () => false
+          return () => code
+        },
+      }),
+    },
+  }))
+  return import('../src/win32.ts')
+}
+
+async function importWithFilesystemMove(): Promise<typeof import('../src/win32.ts')> {
+  return importWithMove((existing, replacement, flags, setLastError) => {
+    expect(flags).toBe(MOVEFILE_WRITE_THROUGH)
+    const from = stripNamespace(existing)
+    const to = stripNamespace(replacement)
+    if (!existsSync(from)) { setLastError(ERROR_FILE_NOT_FOUND); return false }
+    if (existsSync(to)) { setLastError(ERROR_ALREADY_EXISTS); return false }
+    renameSync(from, to)
+    return true
+  })
+}
+
+afterEach(async () => {
+  vi.doUnmock('koffi')
+  vi.resetModules()
+  for (const root of roots.splice(0)) await rm(root, { recursive: true, force: true })
+})
+
+describe('Windows durable namespace helpers', () => {
+  it('publishes a new file with write-through MoveFileExW semantics', async () => {
+    const { publishNewFileWin32 } = await importWithFilesystemMove()
+    const root = await tempRoot()
+    const tmp = join(root, 'log.tmp')
+    const final = join(root, 'log.jsonl')
+    await writeFile(tmp, 'content')
+
+    await publishNewFileWin32(tmp, final)
+    expect(existsSync(tmp)).toBe(false)
+    expect(readFileSync(final, 'utf8')).toBe('content')
+  })
+
+  it('maps Win32 publish failures to Node-style errno codes', async () => {
+    const cases = [
+      [ERROR_FILE_NOT_FOUND, 'ENOENT'],
+      [ERROR_PATH_NOT_FOUND, 'ENOENT'],
+      [ERROR_ACCESS_DENIED, 'EACCES'],
+      [ERROR_NOT_SAME_DEVICE, 'EXDEV'],
+      [ERROR_FILE_EXISTS, 'EEXIST'],
+      [ERROR_ALREADY_EXISTS, 'EEXIST'],
+      [ERROR_INVALID_NAME, 'EINVAL'],
+      [9999, 'EIO'],
+    ] as const
+    for (const [win32Code, code] of cases) {
+      const { publishNewFileWin32 } = await importWithError(win32Code)
+      await expect(publishNewFileWin32('from', 'to')).rejects.toMatchObject({ code, win32Code, path: 'from', dest: 'to' })
+    }
+  })
+
+  it('creates missing directories through staging siblings and tolerates an already-created race', async () => {
+    const root = await tempRoot()
+    const raced = join(root, 'raced')
+    const { ensureDurableDirectoryWin32 } = await importWithMove((existing, replacement, flags, setLastError) => {
+      expect(flags).toBe(MOVEFILE_WRITE_THROUGH)
+      const from = stripNamespace(existing)
+      const to = stripNamespace(replacement)
+      if (to === raced) {
+        mkdirSync(to)
+        setLastError(ERROR_ALREADY_EXISTS)
+        return false
+      }
+      if (!existsSync(from)) { setLastError(ERROR_FILE_NOT_FOUND); return false }
+      if (existsSync(to)) { setLastError(ERROR_ALREADY_EXISTS); return false }
+      renameSync(from, to)
+      return true
+    })
+
+    await ensureDurableDirectoryWin32(join(root, 'a', 'b'))
+    expect(existsSync(join(root, 'a', 'b'))).toBe(true)
+    await ensureDurableDirectoryWin32(join(root, 'a', 'b'))
+    await ensureDurableDirectoryWin32(raced)
+    expect(existsSync(raced)).toBe(true)
+  })
+
+  it('surfaces directory publication failures other than an existing-target race', async () => {
+    const { ensureDurableDirectoryWin32 } = await importWithError(ERROR_ACCESS_DENIED)
+    const root = await tempRoot()
+
+    await expect(ensureDurableDirectoryWin32(join(root, 'denied'))).rejects.toMatchObject({ code: 'EACCES' })
+  })
+
+  it('rejects a non-directory component instead of treating it as missing', async () => {
+    const { ensureDurableDirectoryWin32 } = await importWithFilesystemMove()
+    const root = await tempRoot()
+    const blocked = join(root, 'blocked')
+    writeFileSync(blocked, 'x')
+
+    await expect(ensureDurableDirectoryWin32(join(blocked, 'child'))).rejects.toMatchObject({ code: 'ENOTDIR' })
+  })
+})

pnpm-lock.yaml

@@ -1259,6 +1259,9 @@ importers:
 
   packages/session-persistence/session-persistence-jsonl:
     dependencies:
+      koffi:
+        specifier: ^3.1.0
+        version: 3.1.1
       schemastery:
         specifier: ^3.18.0
         version: 3.18.0
@@ -3453,6 +3456,81 @@ packages:
   '@jridgewell/trace-mapping@0.3.31':
     resolution: {integrity: sha512-zzNR+SdQSDJzc8joaeP8QQoCQr8NuYx2dIIytl1QeBEZHJ9uW6hebsrYgbz8hJwUQao3TWCMtmfV8Nu1twOLAw==}
 
+  '@koromix/koffi-darwin-arm64@3.1.1':
+    resolution: {integrity: sha512-+Dl0zQDh1Wb55AWOn9hp7K30qgkODvrvN+ZNkFOh81Q0oFX/rpJQtocgjAuYk2zFAcajSeVDumkcHMPwnKSXzA==}
+    cpu: [arm64]
+    os: [darwin]
+
+  '@koromix/koffi-darwin-x64@3.1.1':
+    resolution: {integrity: sha512-cDFAKn1qdZBFLrp7dAc9QUDw3l4xAhTJbOdPWWb0LxssVicUdHcRCLZGrDsmPW2tpH6LGNNeLgqRpAoD2Mo8iA==}
+    cpu: [x64]
+    os: [darwin]
+
+  '@koromix/koffi-freebsd-arm64@3.1.1':
+    resolution: {integrity: sha512-zaP7FJISI/scQW9Wa5QicY3a09WmtKBWSbmC+5nfCqPzwWe7Hx2so74Er7mPsDfCiMMR0Ya+evKbJQDkfyXicg==}
+    cpu: [arm64]
+    os: [freebsd]
+
+  '@koromix/koffi-freebsd-ia32@3.1.1':
+    resolution: {integrity: sha512-7GejVb688TLM8rbjfc0oezJrATxZc0dn801xWEDJekN2DgmRXu7HquGqWQ6z3NeSq7ZxEggz4T3xtlbCysQapA==}
+    cpu: [ia32]
+    os: [freebsd]
+
+  '@koromix/koffi-freebsd-x64@3.1.1':
+    resolution: {integrity: sha512-XLiCFP9OFCyOoGTjAimtDKLhzhfo34WcP1ShVWxRzNCWDGjfz8BYjwd69cp/cDSUXZbxamqs4+/6vmkePq9wxA==}
+    cpu: [x64]
+    os: [freebsd]
+
+  '@koromix/koffi-linux-arm64@3.1.1':
+    resolution: {integrity: sha512-HA9xINK7G4dRAkpfnBWD9VfuyIBgW1SuK+KPHjksUwRMOnhgqP8J/JqgrAzdzcDiefGBkqEacIP776OUwz7knQ==}
+    cpu: [arm64]
+    os: [linux]
+
+  '@koromix/koffi-linux-ia32@3.1.1':
+    resolution: {integrity: sha512-jG7IFytmP8K5Qtbx0ro0ZeuX3JjSsLxmYhq+nmXDdrtOAlxIsWGynuiDLS6Jk3vOchVii2m6Y2f/L3GLG2fG5A==}
+    cpu: [ia32]
+    os: [linux]
+
+  '@koromix/koffi-linux-loong64@3.1.1':
+    resolution: {integrity: sha512-CIsT1cNnih8FuU52Me/IVlJBpH28SQfoDeYPctJswgJzaARktusF7m4MUbtR1PBDjuquCVM4/vFyNdOzfPonvA==}
+    cpu: [loong64]
+    os: [linux]
+
+  '@koromix/koffi-linux-riscv64@3.1.1':
+    resolution: {integrity: sha512-9D6RmqeKsSvs3U6jILJU9PcAjMwKKyn7yLxNBb5k6z9PCoUoGJ3/BrhXAX0qjrLLwEiIpP/hS/40RuXvH8Lc3Q==}
+    cpu: [riscv64]
+    os: [linux]
+
+  '@koromix/koffi-linux-x64@3.1.1':
+    resolution: {integrity: sha512-pyTcX5fePeYbt7TZAwRby69wdlRx3PT+g15ra5IYdat/Pgh3qAKEYeZ+uu7WpPGOy43p/oSRqqZoa2kORzozlA==}
+    cpu: [x64]
+    os: [linux]
+
+  '@koromix/koffi-openbsd-ia32@3.1.1':
+    resolution: {integrity: sha512-iPnPzvG2HOfdzaiG1drdkt86sAqmTPDv9mAf+5gL7mRzkeeQC88EVGboRy7eXwdXn7R+v0ntA3iQxdHrBn6yXw==}
+    cpu: [ia32]
+    os: [openbsd]
+
+  '@koromix/koffi-openbsd-x64@3.1.1':
+    resolution: {integrity: sha512-/Xqc3R0SVoMCYjMPZnJ9bULtRo364+dKmnQhfDrI83tSpxUHRw7HRNf12vBeL+hPgKxSBjtMpWfQ/ZIyVyLFag==}
+    cpu: [x64]
+    os: [openbsd]
+
+  '@koromix/koffi-win32-arm64@3.1.1':
+    resolution: {integrity: sha512-JhqHauEwQvdcWUERxrV5HH/DT9W7hY1A1eU6/o8tB+yck+D3kt5elpRDBt9KjpW6h+vHPy3V0sjDvO0CXyabTA==}
+    cpu: [arm64]
+    os: [win32]
+
+  '@koromix/koffi-win32-ia32@3.1.1':
+    resolution: {integrity: sha512-ZRuyYmlGS/rCc966qqs0qREXDW4FRdul7rDF1VgSWHbVmdc196PUgUT+blq/GjZgTwqzeEXtMRgM+cU8krHjvA==}
+    cpu: [ia32]
+    os: [win32]
+
+  '@koromix/koffi-win32-x64@3.1.1':
+    resolution: {integrity: sha512-KqHPmvj6QILhNyI/To8QSihHsijeVGIYYPBOUnXEpcnH2LuLbargY4Hd6dDeTN3Z90uUUxN+1FWz1UnhVzFOiA==}
+    cpu: [x64]
+    os: [win32]
+
   '@mermaid-js/parser@1.2.0':
     resolution: {integrity: sha512-oYPyv8A4As1yH5Bx+04iQEQxXuIQDe0GKCNSRgao6z8AM9jixXIfP0vsppRLvGf+nKIOb9/LdpWA4YuJiVvESA==}
 
@@ -5662,6 +5740,9 @@ packages:
     engines: {node: ^20.19.0 || >=22.12.0}
     hasBin: true
 
+  koffi@3.1.1:
+    resolution: {integrity: sha512-mRX6AMeeKCxSOeOopqAcLAl5jcNvge7NAG8l7rF/8gGJATI0tdHFYjteIdE0mGOtWdsrJOij+PjnP8Q9c1gwgA==}
+
   layout-base@1.0.2:
     resolution: {integrity: sha512-8h2oVEZNktL4BH2JCOI90iD1yXwL6iNW7KcCKT2QZgQJR2vbqDsldCTPRU9NifTCqHZci57XvQQ15YTu+sTYPg==}
 
@@ -7842,6 +7923,51 @@ snapshots:
       '@jridgewell/resolve-uri': 3.1.2
       '@jridgewell/sourcemap-codec': 1.5.5
 
+  '@koromix/koffi-darwin-arm64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-darwin-x64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-freebsd-arm64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-freebsd-ia32@3.1.1':
+    optional: true
+
+  '@koromix/koffi-freebsd-x64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-linux-arm64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-linux-ia32@3.1.1':
+    optional: true
+
+  '@koromix/koffi-linux-loong64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-linux-riscv64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-linux-x64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-openbsd-ia32@3.1.1':
+    optional: true
+
+  '@koromix/koffi-openbsd-x64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-win32-arm64@3.1.1':
+    optional: true
+
+  '@koromix/koffi-win32-ia32@3.1.1':
+    optional: true
+
+  '@koromix/koffi-win32-x64@3.1.1':
+    optional: true
+
   '@mermaid-js/parser@1.2.0':
     dependencies:
       '@chevrotain/types': 11.1.2
@@ -10072,6 +10198,24 @@ snapshots:
       yaml: 2.9.0
       zod: 4.4.3
 
+  koffi@3.1.1:
+    optionalDependencies:
+      '@koromix/koffi-darwin-arm64': 3.1.1
+      '@koromix/koffi-darwin-x64': 3.1.1
+      '@koromix/koffi-freebsd-arm64': 3.1.1
+      '@koromix/koffi-freebsd-ia32': 3.1.1
+      '@koromix/koffi-freebsd-x64': 3.1.1
+      '@koromix/koffi-linux-arm64': 3.1.1
+      '@koromix/koffi-linux-ia32': 3.1.1
+      '@koromix/koffi-linux-loong64': 3.1.1
+      '@koromix/koffi-linux-riscv64': 3.1.1
+      '@koromix/koffi-linux-x64': 3.1.1
+      '@koromix/koffi-openbsd-ia32': 3.1.1
+      '@koromix/koffi-openbsd-x64': 3.1.1
+      '@koromix/koffi-win32-arm64': 3.1.1
+      '@koromix/koffi-win32-ia32': 3.1.1
+      '@koromix/koffi-win32-x64': 3.1.1
+
   layout-base@1.0.2: {}
 
   layout-base@2.0.1: {}

pnpm-workspace.yaml

@@ -31,6 +31,8 @@ allowBuilds:
   '@google/genai': false
   protobufjs: false
   node-addon-require-builtin: false
+  # JSONL durability calls MoveFileExW with write-through publication on Windows.
+  koffi: true
 
 # The Landlock launcher family is our own sibling-repo release, consumed
 # fresh (hours old at each coordinated bump) — the release-age quarantine