Merge remote-tracking branch 'origin/master' into session-query-search

# Conflicts: # .agents/notes/implemented/feature/2026-07-10-session-query-service.md # .agents/notes/implemented/feature/2026-07-10-sqlite-session-query-provider.md # .agents/notes/proposed/feature/2026-07-10-sqlite-session-query-provider.md # docs/architecture.md # docs/capability-seams.md # docs/config-catalog.md # docs/cordis-catalog/services.md # docs/core-data-structures/core.md # docs/core-data-structures/persistence.md # docs/core-data-structures/session-query.md # docs/module-graph.md # docs/rfc/INDEX.md # packages/README.md # packages/cordis/tool-cordis/src/api-catalog.ts # packages/hooks/hooks-claude/tests/coverage.spec.ts # packages/session-persistence/session-persistence-jsonl/src/index.ts # packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts # packages/session-persistence/session-persistence-sqlite/README.md # packages/session-persistence/session-persistence-sqlite/src/index.ts # packages/session-persistence/session-persistence-sqlite/src/schema.ts # packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts # packages/session-persistence/session-persistence/README.md # packages/session-persistence/session-persistence/package.json # packages/session-query/README.md # packages/session-query/session-query/README.md # packages/session-query/session-query/package.json # packages/session-query/session-query/src/config.ts # packages/session-query/session-query/src/index.ts # packages/session-query/session-query/src/types.ts # pnpm-lock.yaml # scripts/gen-doc-graphs.ts # scripts/type-equiv.manifest.json # tsconfig.host.json # tsconfig.json
2026-07-23 13:56:56 +08:00
parent e8abfd6482 0401fd52b9
commit 0a0f19cf57
2630 changed files with 198302 additions and 30288 deletions
--- a/packages/session-persistence/session-persistence-jsonl/src/index.ts
+++ b/packages/session-persistence/session-persistence-jsonl/src/index.ts
@@ -1,7 +1,8 @@
 /**
 * JSONL durable session-persistence backend. It stores a header and contiguous
 * events in one append-only file per session, and delegates orchestration to
- * {@link PersistenceCoordinator}.
+ * {@link PersistenceCoordinator}. Its side-effect-free locator returns the
+ * absolute per-session log target before materialization.
 * @module @deepseek-ai/dsh-session-persistence-jsonl
 */

@@ -12,14 +13,28 @@ import { dirname, resolve } from 'node:path'
 import { randomBytes } from 'node:crypto'
 import {
  SessionPersistence, SessionPersistenceRevision, PersistenceCoordinator,
-  type PersistenceBackend, type SessionPersistenceSnapshot, type StoredPrefix,
+  type PersistenceBackend, type SessionLocation, type SessionPersistenceSnapshot,
+  type StoredPrefix,
 } from '@deepseek-ai/dsh-session-persistence'
 import type { SessionEvent, SessionId, SessionHeader } from '@deepseek-ai/dsh-session'
 import {
-  encodeSegment, eventLine, logPath, parseHeaderMeta, scanLog, sessionDir, toHeaderLine,
+  encodeSegment, eventLines, logPath, logSuffix, parseHeaderMeta, scanLog, sessionDir, toHeaderLine,
+  type JsonlCompression,
 } from './format.ts'
+import { compressZstdFrame, decompressZstdFrame, scanZstdFrames } from './zstd.ts'
+import { ensureDurableDirectoryWin32, publishNewFileWin32 } from './win32.ts'

-/** Plugin config: where the JSONL backend keeps its session logs (`root` is required — no default). */
+export type { JsonlCompression } from './format.ts'
+
+const DEFAULT_COMPRESSION: JsonlCompression = 'zstd'
+
+/** Loader schema for the JSONL artifact's physical encoding. */
+export const JsonlCompressionSchema: z<JsonlCompression> = z.union([
+  z.const('zstd'),
+  z.const('none'),
+]).default(DEFAULT_COMPRESSION)
+
+/** Plugin config: where the JSONL backend keeps its session logs, and the packed-row write switch. */
 export interface Config {
  /**
   * Root directory for all session files. Required (no default): a default of
@@ -27,6 +42,23 @@ export interface Config {
   * (bash calls, subprocesses). Sessions group under per-cwd subdirectories.
   */
  root: string
+  /**
+   * Write runs of consecutive `assistant/chunk` delta events as packed
+   * `text-chunks`/`reasoning-chunks`/`tool-call-chunks` rows (lossless,
+   * ~60% smaller logs measured on a real session). Off by default while
+   * snapshot fixtures stay in the one-event-per-line layout: recording with
+   * packing on rewrites every golden `session.jsonl`. READING packed rows is
+   * unconditional — a log's layout never depends on this switch.
+   */
+  packChunks?: boolean
+  /** Physical encoding; defaults to checksummed Zstandard frames. */
+  compression?: JsonlCompression
+}
+
+/** Opaque coordinator token for replacing bytes recovered from a torn frame. */
+interface JsonlTornMarker {
+  truncateTo: number
+  recoveredEvents: SessionEvent[]
 }

 /** Whether a filesystem error means absence; every non-ENOENT failure must surface. */
@@ -37,13 +69,16 @@ function isENOENT(error: unknown): boolean {
 /**
 * The JSONL persistence backend. Load as a plugin; it registers as
 * `ctx.sessionPersistence` and (via the coordinator) installs the write-path
- * listeners. Its torn-tail marker is the byte offset to truncate the log to.
+ * listeners. Its torn-tail marker carries the byte offset and any events
+ * recovered from an incomplete final Zstandard frame.
 */
-export class SessionPersistenceJsonl extends SessionPersistence implements PersistenceBackend<number> {
+export class SessionPersistenceJsonl extends SessionPersistence implements PersistenceBackend<JsonlTornMarker> {
  static inject = ['sessions']

  static Config: z<Config> = z.object({
    root: z.string().required(),
+    packChunks: z.boolean().default(false),
+    compression: JsonlCompressionSchema,
  })

  /**
@@ -54,13 +89,20 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
  override readonly name = 'session-persistence-jsonl'

  private root: string
-  private coordinator: PersistenceCoordinator<number>
+  private packChunks: boolean
+  private compression: JsonlCompression
+  private coordinator: PersistenceCoordinator<JsonlTornMarker>
+  private rootEncodingCheck: Promise<void> | undefined

  constructor(ctx: Context, public config: Config) {
    super(ctx)
    // Resolve once so later process.cwd() changes cannot split one backend across roots.
    this.root = resolve(config.root)
-    this.coordinator = new PersistenceCoordinator<number>(this.ctx, this)
+    // schemastery (static Config) applied the default before construction;
+    // the cast records that runtime fact for exactOptionalPropertyTypes.
+    this.packChunks = (config as Required<Config>).packChunks
+    this.compression = config.compression ?? DEFAULT_COMPRESSION
+    this.coordinator = new PersistenceCoordinator<JsonlTornMarker>(this.ctx, this)
  }

  // Each backend keeps the typed service surface beside its storage hooks;
@@ -68,6 +110,11 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
  /* jscpd:ignore-start */
  // --- SessionPersistence service surface (delegated to the coordinator) ---

+  /** Resolve the absolute target path without touching the filesystem. */
+  locate(meta: SessionHeader): SessionLocation {
+    return { kind: 'jsonl', path: logPath(this.root, meta.cwd, meta.id, this.compression) }
+  }
+
  create(meta: SessionHeader): Promise<void> {
    return this.coordinator.create(meta)
  }
@@ -87,7 +134,8 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
  // --- PersistenceBackend hooks (the file-bytes storage primitives) ---

  /** Read a stored prefix by id across all cwd buckets when cwd is unknown. */
-  async loadStored(id: SessionId): Promise<StoredPrefix<number> | undefined> {
+  async loadStored(id: SessionId): Promise<StoredPrefix<JsonlTornMarker> | undefined> {
+    await this.ensureRootEncoding()
    const file = await this.findLog(id)
    if (file === undefined) return undefined
    return this.readPrefix(file.path)
@@ -97,28 +145,85 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
   * Read a stored prefix within one cwd for HMR adoption. `undefined` names the
   * no-cwd bucket rather than an unknown cwd, so this never scans other buckets.
   */
-  async loadLive(id: SessionId, cwd: string | undefined): Promise<StoredPrefix<number> | undefined> {
-    const path = logPath(this.root, cwd, id)
-    if (!await this.exists(path)) return undefined
+  async loadLive(id: SessionId, cwd: string | undefined): Promise<StoredPrefix<JsonlTornMarker> | undefined> {
+    await this.ensureRootEncoding()
+    const path = logPath(this.root, cwd, id, this.compression)
+    if (!await this.exists(path)) {
+      await this.rejectOppositeArtifact(cwd, id)
+      return undefined
+    }
    return this.readPrefix(path)
  }

  /**
-   * Read a stored prefix and convert torn-tail state to the byte offset the
-   * coordinator can round-trip without knowing the file format.
+   * Read a stored prefix and convert torn-tail state to the opaque marker the
+   * coordinator can round-trip without knowing the physical encoding.
   */
-  private async readPrefix(path: string): Promise<StoredPrefix<number>> {
+  private async readPrefix(path: string): Promise<StoredPrefix<JsonlTornMarker>> {
    const buffer = await readFile(path)
+    if (this.compression === 'zstd') return this.readZstdPrefix(buffer)
    const { meta, events, committedBytes } = scanLog(buffer)
    return {
      meta,
      events,
-      ...committedBytes < buffer.byteLength ? { tornMarker: committedBytes } : {},
+      ...committedBytes < buffer.byteLength
+        ? { tornMarker: { truncateTo: committedBytes, recoveredEvents: [] } }
+        : {},
+    }
+  }
+
+  /** Decode complete frames and retain complete JSONL records from a torn final frame. */
+  private async readZstdPrefix(buffer: Buffer): Promise<StoredPrefix<JsonlTornMarker>> {
+    const { frames, tornStart } = scanZstdFrames(buffer)
+    if (frames.length === 0) throw new Error('empty or header-less Zstandard session log')
+
+    const plaintextFrames: Buffer[] = []
+    for (const frame of frames) {
+      try {
+        plaintextFrames.push(await decompressZstdFrame(buffer.subarray(frame.start, frame.end)))
+      } catch (error) {
+        throw new Error(`corrupt Zstandard session log: frame at byte ${frame.start} failed validation`, { cause: error })
+      }
+    }
+
+    const headerFrame = plaintextFrames[0]
+    if (headerFrame === undefined || headerFrame.length === 0 || headerFrame.indexOf(0x0A) !== headerFrame.length - 1) {
+      throw new Error('corrupt Zstandard session log: first frame is not exactly one header line')
+    }
+    const completePlaintext = Buffer.concat(plaintextFrames)
+    const completePrefix = scanLog(completePlaintext)
+    if (completePrefix.committedBytes !== completePlaintext.length) {
+      throw new Error('corrupt Zstandard session log: complete frame contains a torn JSONL record')
+    }
+    if (tornStart === undefined) {
+      return { meta: completePrefix.meta, events: completePrefix.events }
+    }
+
+    let recoveredPlaintext: Buffer = Buffer.alloc(0)
+    try {
+      recoveredPlaintext = await decompressZstdFrame(buffer.subarray(tornStart))
+    } catch {
+      // A structurally incomplete final frame may end before Node's decoder can
+      // emit any plaintext; the complete prior frames remain recoverable.
+    }
+    const recoveredPrefix = scanLog(Buffer.concat([completePlaintext, recoveredPlaintext]))
+    /* v8 ignore next 3 -- appending plaintext cannot shorten the already-scanned complete prefix */
+    if (recoveredPrefix.events.length < completePrefix.events.length) {
+      throw new Error('corrupt Zstandard session log: recovered prefix does not extend complete frames')
+    }
+    return {
+      meta: recoveredPrefix.meta,
+      events: recoveredPrefix.events,
+      tornMarker: {
+        truncateTo: tornStart,
+        recoveredEvents: recoveredPrefix.events.slice(completePrefix.events.length),
+      },
    }
  }

  /** Durably append a batch, lazily materializing the file when not yet present. */
  async appendBatch(meta: SessionHeader, events: readonly SessionEvent[], isMaterialized: boolean): Promise<void> {
+    await this.ensureRootEncoding()
    if (isMaterialized) {
      await this.appendLines(meta, events)
    } else {
@@ -127,13 +232,18 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
  }

  /**
-   * Make a crash repair durable: truncate the torn tail to `tornMarker` bytes (if
-   * any), then append the synthetic `closers` (if any). Two fsync'd steps — the
-   * seam does not require this to be atomic.
+   * Make a crash repair durable: truncate a torn tail, restore complete events
+   * decoded from it, then append synthetic closers. Two fsync'd steps — the seam
+   * does not require this to be atomic.
   */
-  async commitRepair(meta: SessionHeader, tornMarker: number | undefined, closers: readonly SessionEvent[]): Promise<void> {
-    if (tornMarker !== undefined) await this.repair(meta, tornMarker)
-    if (closers.length > 0) await this.appendLines(meta, closers)
+  async commitRepair(
+    meta: SessionHeader,
+    tornMarker: JsonlTornMarker | undefined,
+    closers: readonly SessionEvent[],
+  ): Promise<void> {
+    if (tornMarker !== undefined) await this.repair(meta, tornMarker.truncateTo)
+    const repairedEvents = [...(tornMarker?.recoveredEvents ?? []), ...closers]
+    if (repairedEvents.length > 0) await this.appendLines(meta, repairedEvents)
  }

  /** List all stored sessions' metadata (header line only — no full-log parse). */
@@ -165,12 +275,15 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
  }

  private async listArtifacts(): Promise<Array<{ header: SessionHeader; path: string }>> {
+    await this.ensureRootEncoding()
    const artifacts: Array<{ header: SessionHeader; path: string }> = []
    for (const dir of await this.listCwdDirs()) {
-      for (const name of await this.listJsonl(dir)) {
+      for (const name of await this.listArtifactNames(dir)) {
        const path = `${dir}/${name}`
        // Read only headers so listing scales with session count, not log size.
-        const first = await this.readFirstLine(path)
+        const first = this.compression === 'zstd'
+          ? await this.readFirstZstdLine(path)
+          : await this.readFirstLine(path)
        if (first === undefined) continue // empty/half-written file
        const meta = parseHeaderMeta(first)
        if (meta === undefined) continue // not a session header
@@ -182,33 +295,36 @@ 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 finalPath = logPath(this.root, meta.cwd, meta.id, this.compression)
+    await this.rejectOppositeArtifact(meta.cwd, meta.id)
+    const content = await this.encodeMaterialization(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)
    }
-    const header = JSON.stringify(toHeaderLine(meta))
-    const body = events.map(eventLine).join('\n')
-    const content = 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.
+  /* v8 ignore start -- Windows uses the Win32 durable-publish path; POSIX coverage exercises this peer. */
+  private async materializePosix(
+    dir: string,
+    finalPath: string,
+    id: SessionId,
+    content: Buffer | 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)
@@ -219,19 +335,84 @@ 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 {
      /* v8 ignore next -- redundant temp link; publish already durable, rm failure is an unreachable IO edge */
    }
  }
+  /* v8 ignore stop */

-  /** 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: Buffer | 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 "${id}": a log already exists on disk (load/resume it instead)`)
+    }
+  }
+
+  private async writeSyncedTempFile(finalPath: string, content: Buffer | string): Promise<string> {
+    const tmp = `${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
+  }
+
+  /** Encode the header and first batch without combining their frame boundaries. */
+  private async encodeMaterialization(meta: SessionHeader, events: readonly SessionEvent[]): Promise<Buffer | string> {
+    const header = JSON.stringify(toHeaderLine(meta)) + '\n'
+    const body = eventLines(events, this.packChunks) + '\n'
+    if (this.compression === 'none') return header + body
+    const headerFrame = await compressZstdFrame(header)
+    const eventFrame = await compressZstdFrame(body)
+    return Buffer.concat([headerFrame, eventFrame])
+  }
+
+  /** Encode one durable append batch in the configured physical representation. */
+  private async encodeEventBatch(events: readonly SessionEvent[]): Promise<Buffer | string> {
+    const body = eventLines(events, this.packChunks) + '\n'
+    return this.compression === 'zstd' ? compressZstdFrame(body) : body
+  }
+
+  /** fsync a POSIX directory so a just-created/renamed entry is crash-durable. */
+  /* v8 ignore start -- Windows uses write-through namespace operations; POSIX coverage exercises directory fsync. */
+  private async syncDirPosix(dir: string): Promise<void> {
    const handle = await open(dir, 'r')
    try {
      await handle.sync()
@@ -239,6 +420,7 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
      await handle.close()
    }
  }
+  /* v8 ignore stop */

  /**
   * Append and fsync event lines. On a partial write or sync failure, restore the
@@ -246,19 +428,40 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
   * batch; leaving partial bytes would create duplicate sequence numbers.
   */
  private async appendLines(meta: SessionHeader, events: readonly SessionEvent[]): Promise<void> {
-    const path = logPath(this.root, meta.cwd, meta.id)
+    const content = await this.encodeEventBatch(events)
+    const path = logPath(this.root, meta.cwd, meta.id, this.compression)
    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.writeFile(content)
        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()
    }
@@ -266,7 +469,7 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi

  /** Truncate the log file to `offset` bytes and fsync (discard the crash tail). */
  private async repair(meta: SessionHeader, offset: number): Promise<void> {
-    const path = logPath(this.root, meta.cwd, meta.id)
+    const path = logPath(this.root, meta.cwd, meta.id, this.compression)
    await truncate(path, offset)
    const handle = await open(path, 'r+')
    try {
@@ -304,17 +507,47 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
    }
  }

+  /** Read and validate only the independently compressed header frame. */
+  private async readFirstZstdLine(path: string): Promise<string | undefined> {
+    const handle = await open(path, 'r')
+    try {
+      let content = Buffer.alloc(0)
+      const chunk = Buffer.alloc(8192)
+      for (;;) {
+        const { bytesRead } = await handle.read(chunk, 0, chunk.length, null)
+        if (bytesRead === 0) return undefined
+        content = Buffer.concat([content, chunk.subarray(0, bytesRead)])
+        const first = scanZstdFrames(content, 1).frames[0]
+        if (first === undefined) continue
+        let plaintext: Buffer
+        try {
+          plaintext = await decompressZstdFrame(content.subarray(first.start, first.end))
+        } catch (error) {
+          throw new Error('corrupt Zstandard session log: header frame failed validation', { cause: error })
+        }
+        if (plaintext.length === 0 || plaintext.indexOf(0x0A) !== plaintext.length - 1) {
+          throw new Error('corrupt Zstandard session log: first frame is not exactly one header line')
+        }
+        return plaintext.subarray(0, -1).toString('utf8')
+      }
+    } finally {
+      await handle.close()
+    }
+  }
+
  /**
   * Find a session by id across cwd buckets for resume. Cwd-scoped HMR adoption
   * bypasses this scan so a no-cwd session cannot claim another bucket.
   */
  private async findLog(id: SessionId): Promise<{ path: string; cwd: string | undefined } | undefined> {
-    const target = encodeSegment(id) + '.jsonl'
+    const target = encodeSegment(id) + logSuffix(this.compression)
    for (const dir of await this.listCwdDirs()) {
      const path = `${dir}/${target}`
+      const opposite = `${dir}/${encodeSegment(id)}${logSuffix(this.oppositeCompression())}`
+      if (await this.exists(opposite)) throw this.encodingMismatch(opposite)
      if (await this.exists(path)) {
        // Recover the cwd from the header so the caller has the session's bucket.
-        const { meta } = scanLog(await readFile(path))
+        const { meta } = await this.readPrefix(path)
        return { path, cwd: meta.cwd }
      }
    }
@@ -333,9 +566,45 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
    }
  }

-  private async listJsonl(dir: string): Promise<string[]> {
+  private async listArtifactNames(dir: string): Promise<string[]> {
    const entries = await readdir(dir)
-    return entries.filter(n => n.endsWith('.jsonl'))
+    const oppositeSuffix = logSuffix(this.oppositeCompression())
+    const incompatible = entries.find(name => name.endsWith(oppositeSuffix))
+    if (incompatible !== undefined) throw this.encodingMismatch(`${dir}/${incompatible}`)
+    const suffix = logSuffix(this.compression)
+    return entries.filter(name => name.endsWith(suffix))
+  }
+
+  /** Reject a root that already belongs to the other physical encoding. */
+  private ensureRootEncoding(): Promise<void> {
+    this.rootEncodingCheck ??= this.checkRootEncoding()
+    return this.rootEncodingCheck
+  }
+
+  private async checkRootEncoding(): Promise<void> {
+    const oppositeSuffix = logSuffix(this.oppositeCompression())
+    for (const dir of await this.listCwdDirs()) {
+      const entries = await readdir(dir)
+      const incompatible = entries.find(name => name.endsWith(oppositeSuffix))
+      if (incompatible !== undefined) throw this.encodingMismatch(`${dir}/${incompatible}`)
+    }
+  }
+
+  private async rejectOppositeArtifact(cwd: string | undefined, id: SessionId): Promise<void> {
+    const path = logPath(this.root, cwd, id, this.oppositeCompression())
+    if (await this.exists(path)) throw this.encodingMismatch(path)
+  }
+
+  private oppositeCompression(): JsonlCompression {
+    return this.compression === 'zstd' ? 'none' : 'zstd'
+  }
+
+  private encodingMismatch(path: string): Error {
+    return new Error(
+      `session artifact ${JSON.stringify(path)} uses ${logSuffix(this.oppositeCompression())}, `
+      + `but this backend is configured for compression ${JSON.stringify(this.compression)}; `
+      + 'use a separate root or select the matching compression mode',
+    )
  }

  private async exists(path: string): Promise<boolean> {
@@ -344,13 +613,36 @@ 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.
-      if (isENOENT(error)) return false
+      // Only ENOENT means absent. A permission/I/O error must surface rather
+      // than letting load or collision checks proceed under false absence.
+      // Windows reports ENOENT, not ENOTDIR, for `regular-file/child`; verify
+      // the immediate parent so a blocked cwd bucket remains a storage fault.
+      /* v8 ignore else -- Windows reports file-valued parents as ENOENT; POSIX covers direct ENOTDIR. */
+      if (isENOENT(error)) {
+        await this.assertLogParentAllowsAbsence(path)
+        return false
+      }
+      /* v8 ignore next -- Windows repairs ENOTDIR from ENOENT above; POSIX covers direct ENOTDIR. */
      throw error
    }
  }
+
+  /* v8 ignore start -- native Windows coverage exercises this repair; POSIX open reports ENOTDIR before this point. */
+  private async assertLogParentAllowsAbsence(path: string): Promise<void> {
+    try {
+      const parent = dirname(path)
+      const info = await stat(parent)
+      if (info.isDirectory()) return
+      const error = new Error(`ENOTDIR: parent path exists but is not a directory: ${parent}`) as NodeJS.ErrnoException
+      error.code = 'ENOTDIR'
+      error.path = parent
+      throw error
+    } catch (error) {
+      if (isENOENT(error)) return
+      throw error
+    }
+  }
+  /* v8 ignore stop */
 }

 export default SessionPersistenceJsonl