Merge branch 'master' into feat/produced-files-folder

packages/host/apiproxy/README.md

@@ -28,6 +28,8 @@ Question responses are validated against their pending request before the first
 
 `session.history`'s tail page (`beforeSeq` absent) additionally carries an optional `projections` block — the watermark snapshot of every unit registered on `ctx.sessionProjections` (`@deepseek-ai/dsh-session-projection`), with `asOfSeq` = the last event seq the values reflect (`-1` on an empty log). The gateway also subscribes to the registry's change feed and mints a `session/projection` mux frame per changed unit (`{sessionId, key, value, seq}` — live push state, never logged; clients hold one generic per-session value store under higher-seq-wins). The carrier holds zero domain knowledge (each value passed its unit's own schema inside the registry; the wire schemas keep `values`/`value` wide); loadOlder pages never carry the block, and a composition without the registry serves histories without either surface.
 
+Session-log export is a host-only download surface, not an RPC: `GET /api/session.export?sessionId=…&includeDescendants=true` streams a ZIP whose files are each session's stored artifact text verbatim (the persistence backend's `readRaw` — exact durable bytes decoded from the physical encoding, never a reconstruction from parsed events), root under its original base name plus each subagent descendant under `subagents/<id>/`, and every image any included log references under `media/<attachmentId>.<ext>` (read and verified from the attachment store; a shared image appears once). Compression runs on the host with fflate's streaming Zip API, so the response is chunked as it is produced and the host never holds the whole archive in one buffer, and production yields whenever the response queue fills, so a slow consumer bounds the accumulation (fflate's callback is synchronous — the drain point is the only backpressure). It requires the persistence, session-query, and attachment services: a deployment without any answers 500, a missing root session 404, and a descendant without a stored artifact or a referenced image that cannot be read fails the stream (fail-loud, never silent under-export). The carrier mounts the endpoint; `ApiProxy.downloads.sessionLog` implements it.
+
 Session titles ride the generic projection pair like every other domain — the history-tail `projections` block plus `session/projection` frames under the `title` key. Titles do not join `session.list`; cold sessions remain metadata-only there until opening or resuming attaches their logs. `session.rename` accepts an explicit user title (resuming a cold session first), delegating to `ctx.sessionTitle.rename` — the accepted `session/title` event pins the title against automatic regeneration — and returns the normalized title plus its event seq so a client settles its `title` projection cell ahead of the push frame; a title that normalizes to empty returns `title-invalid`.
 
 `session.fork` maps an optional event anchor to the first `turn/end` at or after it, letting a message action include that message's whole turn. An omitted or past-end anchor selects the last completed turn; an in-log anchor whose turn remains open returns `fork-unavailable` rather than clipping backward. The published child inherits the source's seeded history, cwd, latest logged `ModelSelection`, and lineage before joining the source Workspace. If Workspace attachment fails, `workspace-attach-failed` carries the already-published child id so clients can reconcile it. The [SessionStore fork decision](../../../.agents/notes/implemented/feature/2026-06-30-session-store-fork-api.md) records why the anchor maps to that `turn/end`.

packages/host/apiproxy/README.zh.md

@@ -28,6 +28,8 @@ Settings 分节中的 `reasoningEffort` 在 agent-default-model 插件配置中
 
 `session.history` 的尾页（不带 `beforeSeq`）额外携带一个可选的 `projections` 块——`ctx.sessionProjections`（`@deepseek-ai/dsh-session-projection`）上每个已注册单元的水位线快照，`asOfSeq` = 这些值共同反映到的最后一个事件 seq（空日志为 `-1`）。网关还订阅注册表的变更流，为每个状态发生变化的单元生成一个 `session/projection` mux 帧（`{sessionId, key, value, seq}`——实时推送状态，绝不入日志；客户端按 seq 高者胜维护一个按会话的通用值仓）。载体不持有任何领域知识（每个值在注册表内部已过其单元自己的 schema；协议 schema 对 `values`/`value` 保持宽松）；loadOlder 页永不携带该块，未装注册表的组合则两个面都不提供。
 
+会话日志导出是宿主侧的下载面，不是 RPC：`GET /api/session.export?sessionId=…&includeDescendants=true` 流式返回一个 ZIP，其中每个文件都是会话存储工件的逐字原文（持久化后端的 `readRaw`——按物理编码解码的确切持久化字节，绝非从解析后事件重建），根会话放在其原始基础文件名下，每个子代理后代放在 `subagents/<id>/` 下，每个被任何包含的日志引用的图片放在 `media/<attachmentId>.<ext>` 下（从附件存储读取并校验；共享图片只出现一次）。压缩在宿主侧用 fflate 的流式 Zip API 完成，响应边生成边分块写出，宿主从不把整个归档放进单个缓冲区，且每当响应队列填满时生产会让出，慢消费者因此只产生有界的积压（fflate 的回调是同步的——让出点是唯一的背压手段）。它要求同时挂载持久化、session-query 与附件服务：任一缺失应答 500，根会话缺失应答 404，后代缺少存储工件或引用的图片无法读取则整个流失败（fail-loud，绝不静默少导出）。端点由传输层挂载，`ApiProxy.downloads.sessionLog` 实现它。
+
 会话标题与其他所有领域一样搭乘这对通用投影机制——历史尾页的 `projections` 块外加 `title` 键下的 `session/projection` 帧。标题不会加入 `session.list`；冷会话在其中仍只有元数据，直到打开或恢复操作附加其日志。`session.rename` 接受用户显式标题（冷会话先恢复），委托给 `ctx.sessionTitle.rename`——被接受的 `session/title` 事件将标题钉住、不再被自动生成覆盖——并返回规范化后的标题及其事件 seq，让 client 在推送帧到达前就结算自己的 `title` 投影格；规范化后为空的标题返回 `title-invalid`。
 
 `session.fork` 将可选事件锚点映射到该锚点处或其后的首个 `turn/end`，使消息操作可包含该消息所在的完整轮次。锚点省略或超过末尾时，选择最后一个已完成轮次；若锚点已在日志中，而其所在轮次仍开放，则返回 `fork-unavailable`，不会向较早位置裁剪。发布后的子会话会先继承源会话的种子历史、cwd、日志中最新的 `ModelSelection` 及谱系，再加入源 Workspace。如果附加到 Workspace 失败，`workspace-attach-failed` 会携带已发布的子会话 id，供客户端对账。[SessionStore fork 决策](../../../.agents/notes/implemented/feature/2026-06-30-session-store-fork-api.md)记录了为何锚点要映射到该 `turn/end`。

packages/host/apiproxy/package.json

@@ -71,6 +71,7 @@
     "@deepseek-ai/dsh-user-interaction": "workspace:^",
     "@deepseek-ai/dsh-workspace": "workspace:^",
     "@deepseek-ai/schemastery": "workspace:^",
+    "fflate": "^0.8.2",
     "zod": "^4.4.3"
   },
   "peerDependencies": {

packages/host/apiproxy/src/api-proxy.ts

@@ -42,6 +42,13 @@ import type {
   QueuedInboxItem, SessionSummary, SettingsNamespaceView, SubagentAddress, TaskView, ToolEventView,
   WorkspaceId, WorkspaceView,
 } from './api/index.ts'
+import {
+  sessionLogExportDeps,
+  sessionLogZipFilename,
+  streamSessionLogZip,
+  type SessionLogExportReady,
+} from './session-export.ts'
+import type { SessionRawArtifact } from '@deepseek-ai/dsh-session-persistence'
 import {
   SESSION_SEARCH_RESULT_LIMIT,
   SESSION_SEARCH_SNIPPET_MAX_CODE_POINTS,
@@ -705,6 +712,16 @@ function historyPage(
  * registry). An absent registry means the deployment has no projection seam:
  * the whole block is absent and clients treat every key as capability-absent.
  */
+/**
+ * Which session a transcript read is served from. An attached session is the
+ * live object and keeps appending, so its events and projection baseline are
+ * read together in one synchronous step; a detached one is already a frozen
+ * inspection.
+ */
+type HistorySource =
+  | { readonly kind: 'attached'; readonly session: Session }
+  | { readonly kind: 'detached'; readonly header: SessionHeader; readonly events: SessionEvent[] }
+
 function projectionsFor(ctx: Context, session: Session): SessionProjectionsBlock | undefined {
   const registry = ctx.get('sessionProjections')
   if (registry === undefined) return undefined
@@ -1348,24 +1365,55 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
     return undefined
   }
 
-  /** Read one transcript cut and optional projection baseline without acquiring an Agent owner. */
-  async function historyStateFor(
-    sessionId: SessionId,
-    includeProjections: boolean,
-  ): Promise<{ header: SessionHeader; events: SessionEvent[]; projections?: SessionProjectionsBlock }> {
+  /**
+   * Resolve which session one transcript read is served from, without
+   * acquiring an Agent owner. This is the read's only asynchronous step
+   * besides ensuring the composition; {@link historyCutOf} takes the cut.
+   * @param sessionId - the transcript being read.
+   * @returns the attached session, or the inspected detached header and events.
+   * @throws {@link ApiRemoteSessionNotFound} when no project-backed session has that identity.
+   */
+  async function historySourceFor(sessionId: SessionId): Promise<HistorySource> {
     const attached = ctx.sessions.get(sessionId)
-    if (attached !== undefined) {
-      const events = [...attached.events]
-      const projections = includeProjections ? projectionsFor(ctx, attached) : undefined
-      return { header: attached.header, events, ...projections === undefined ? {} : { projections } }
-    }
+    if (attached !== undefined) return { kind: 'attached', session: attached }
     const inspected = await inspectServable(sessionId)
-    const projections = includeProjections ? detachedProjectionsFor(ctx, inspected.events) : undefined
-    return {
-      header: inspected.meta,
-      events: inspected.events,
-      ...projections === undefined ? {} : { projections },
+    return { kind: 'detached', header: inspected.meta, events: inspected.events }
+  }
+
+  /**
+   * The header and events {@link presenterScopeFor} reads to decide which
+   * composition a transcript ran under.
+   * @param source - the live or detached session this read is served from.
+   * @returns that session's creation header and its events.
+   */
+  function sourceSession(source: HistorySource): PresetBearingSession {
+    if (source.kind === 'detached') return { header: source.header, events: source.events }
+    return { header: source.session.header, events: source.session.events }
+  }
+
+  /**
+   * One transcript cut: the events and the projection baseline that describe
+   * the SAME log position.
+   *
+   * Synchronous, and the two reads sit next to each other, because an attached
+   * session keeps appending: an `await` between them would serve events cut at
+   * N beside a baseline folded to N+1, which is one response describing two
+   * moments. The caller does its awaiting before this call.
+   * @param source - the live or detached session this read is served from.
+   * @param includeProjections - whether the caller asked for the baseline (a tail page does).
+   * @returns the events and, when asked, the baseline for that same position.
+   */
+  function historyCutOf(
+    source: HistorySource,
+    includeProjections: boolean,
+  ): { events: SessionEvent[]; projections?: SessionProjectionsBlock } {
+    if (source.kind === 'detached') {
+      const projections = includeProjections ? detachedProjectionsFor(ctx, source.events) : undefined
+      return { events: source.events, ...projections === undefined ? {} : { projections } }
     }
+    const events = [...source.session.events]
+    const projections = includeProjections ? projectionsFor(ctx, source.session) : undefined
+    return { events, ...projections === undefined ? {} : { projections } }
   }
 
   /**
@@ -2025,9 +2073,22 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
 
       async history(request) {
         const { sessionId, beforeSeq, maxMessages } = request.payload
-        let state: { header: SessionHeader; events: SessionEvent[]; projections?: SessionProjectionsBlock }
         try {
-          state = await historyStateFor(sessionId, beforeSeq === undefined)
+          const source = await historySourceFor(sessionId)
+          // Both awaits happen BEFORE the cut. Ensuring the recorded
+          // composition's standing mount is what registers its projection
+          // units, so a first cold read would otherwise serve a baseline
+          // missing every preset-owned key; and an attached session keeps
+          // appending, so awaiting between the two reads would pair events cut
+          // at N with a baseline folded to N+1.
+          const scope = await presenterScopeFor(sessionId, sourceSession(source))
+          const cut = historyCutOf(source, beforeSeq === undefined)
+          const page = historyPage(ctx, cut.events, beforeSeq, maxMessages, scope)
+          return ok(request, {
+            events: page.events,
+            hasMore: page.hasMore,
+            ...cut.projections === undefined ? {} : { projections: cut.projections },
+          })
         } catch (error: unknown) {
           if (error instanceof SessionNotFound) {
             return err(request, { code: 'session-not-found', message: error.message, details: { sessionId } })
@@ -2038,12 +2099,6 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
             details: {},
           })
         }
-        const page = historyPage(ctx, state.events, beforeSeq, maxMessages, await presenterScopeFor(sessionId, state))
-        return ok(request, {
-          events: page.events,
-          hasMore: page.hasMore,
-          ...state.projections === undefined ? {} : { projections: state.projections },
-        })
       },
 
       async models(request) {
@@ -3423,6 +3478,46 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
       },
     },
 
+    downloads: {
+      async sessionLog(request, signal) {
+        // Clean error path first: missing services answer 500 and a missing
+        // root artifact 404 before any zip byte is produced. The root content
+        // read here is reused as the first zip entry, so nothing is read twice.
+        const deps = sessionLogExportDeps(ctx)
+        if (deps.sessionQuery === undefined || deps.sessionPersistence === undefined || deps.attachments === undefined) {
+          return new Response(
+            'session log export is unavailable: missing session-query, session-persistence, or attachments service',
+            { status: 500 },
+          )
+        }
+        const ready: SessionLogExportReady = {
+          sessionQuery: deps.sessionQuery,
+          sessionPersistence: deps.sessionPersistence,
+          attachments: deps.attachments,
+        }
+        let root: SessionRawArtifact | undefined
+        try {
+          root = await deps.sessionPersistence.readRaw(request.sessionId, signal)
+        } catch {
+          // Backend read failure: answer 500 without echoing the error, which
+          // may carry absolute host paths into the browser error bar.
+          return new Response('session log export failed to read the stored artifact', { status: 500 })
+        }
+        if (root === undefined) {
+          return new Response('session not found', { status: 404 })
+        }
+        return new Response(
+          streamSessionLogZip(ready, root, request.sessionId, request.includeDescendants === true, signal),
+          {
+            headers: {
+              'content-type': 'application/zip',
+              'content-disposition': `attachment; filename="${sessionLogZipFilename(request.sessionId)}"`,
+            },
+          },
+        )
+      },
+    },
+
     respond(message: ClientResponse): Promise<RpcReceipt> {
       // Route by the echoed rpcId (the wire correlation): approvals first,
       // then questions — the two registries share one id space of UUIDs.

packages/host/apiproxy/src/api/downloads.schema.ts

@@ -0,0 +1,26 @@
+/**
+ * downloads domain zod schemas. The GET download surface has no wire
+ * envelope: the request arrives as query parameters (all strings), so its
+ * request schema parses the raw query-parameter object into the method's
+ * exact request shape. SessionId brand cast point: sessionIdSchema, and only
+ * there (hosted in sessions.schema like every other cast).
+ */
+
+import { z } from 'zod'
+import type { DownloadsApi } from './downloads.ts'
+import { sessionIdSchema } from './sessions.schema.ts'
+
+/**
+ * session.export query params → the sessionLog request. `includeDescendants`
+ * accepts exactly `true`/`false`/absent; any other value is rejected (400) so
+ * a misspelled flag cannot silently under-export.
+ */
+export const sessionLogQuerySchema = z
+  .object({
+    sessionId: sessionIdSchema,
+    includeDescendants: z.union([z.literal('true'), z.literal('false')]).optional(),
+  })
+  .transform(query => ({
+    sessionId: query.sessionId,
+    ...(query.includeDescendants === 'true' ? { includeDescendants: true } : {}),
+  })) satisfies z.ZodType<Parameters<DownloadsApi['sessionLog']>[0]>

packages/host/apiproxy/src/api/downloads.ts

@@ -0,0 +1,25 @@
+/**
+ * downloads domain contract: host-only download surfaces — the GET-download
+ * channel family, the mirror of the SSE-stream `events` domain. No wire
+ * envelope: the carrier's GET routes answer these directly, and the browser
+ * `IApiClient` never exposes them.
+ */
+
+import type { SessionId } from '@deepseek-ai/dsh-session/types'
+
+/** Host-only download surfaces (no wire envelope; absent from IApiClient). */
+export interface DownloadsApi {
+  /**
+   * Stream one session-log ZIP — the root artifact verbatim plus each subagent
+   * descendant's — as an attachment response. The carrier's GET route answers
+   * this directly; the browser never calls it.
+   * @param request - the root session id and whether to include descendants.
+   * @param signal - cancellation for the underlying reads.
+   * @returns the ZIP attachment response; missing services answer 500 and a
+   * missing root session 404 before any byte is produced.
+   */
+  sessionLog(
+    request: { sessionId: SessionId; includeDescendants?: boolean },
+    signal: AbortSignal,
+  ): Promise<Response>
+}

packages/host/apiproxy/src/api/index.ts

@@ -16,9 +16,10 @@ import type { GoalsApi } from './goals.ts'
 import type { SettingsApi } from './settings.ts'
 import type { CredentialsApi } from './credentials.ts'
 import type { LlmApi } from './llm.ts'
+import type { DownloadsApi } from './downloads.ts'
 import type { ClientResponse, RpcReceipt } from './rpc.ts'
 
-/** Root interface of the unified API surface. New client-request domain = one new file pair + one field here + one map row. */
+/** Root interface of the unified API. New client-request domain = one new file pair + one field here + one map row. */
 export interface ApiProxy {
   sessions: SessionsApi
   subagents: SubagentsApi
@@ -32,6 +33,8 @@ export interface ApiProxy {
   settings: SettingsApi
   credentials: CredentialsApi
   llm: LlmApi
+  /** Host-only download surfaces (GET, no wire envelope); absent from IApiClient. */
+  downloads: DownloadsApi
   /** Response entry for server-requests (client-response, echoing their rpcId); not a domain method (four-quadrant model). */
   respond(message: ClientResponse): Promise<RpcReceipt>
 }
@@ -39,9 +42,8 @@ export interface ApiProxy {
 // ---- Domain interfaces and payload entities ----
 export type {
   HistoryEntry, ModelCatalogFailure, ModelCatalogModel, ModelProviderGroup, ModelReasoning,
-  ModelReasoningEffort, ModelSelection, PromptContentPart, QueueAction, SessionModels, SessionProjectionsBlock,
-  SessionSearchItem,
-  SessionsApi, SessionSummary,
+  ModelReasoningEffort, ModelSelection, PromptContentPart, QueueAction, SessionModels,
+  SessionProjectionsBlock, SessionSearchItem, SessionsApi, SessionSummary,
 } from './sessions.ts'
 export type { DirectoryEntry, DirectoryListing, HostApi } from './host.ts'
 export type {
@@ -58,6 +60,7 @@ export type { GoalsApi, GoalId, GoalRef } from './goals.ts'
 export type { SettingsApi, SettingsNamespaceView, SettingsPathOpView, SettingsSecretView } from './settings.ts'
 export type { CredentialsApi, CredentialView } from './credentials.ts'
 export type { ConfigurableProviderView, DiscoveredModelView, LlmApi } from './llm.ts'
+export type { DownloadsApi } from './downloads.ts'
 export type { ApprovalResponsePayload } from './approvals.ts'
 
 export type { QuestionResponsePayload } from './questions.ts'

packages/host/apiproxy/src/api/rpc.ts

@@ -116,7 +116,7 @@ export type RpcResult<T> = { ok: true; value: T } | { ok: false; error: RpcError
 
 /**
  * Fold a transport exception into the RpcResult error branch (unified error
- * surface; 'internal' as the catch-all code). Lives with RpcResult so every
+ * API; 'internal' as the catch-all code). Lives with RpcResult so every
  * carrier consumer folds the same way.
  * @param error - the thrown value from the carrier.
  * @returns the error branch of an RpcResult.

packages/host/apiproxy/src/api/sessions.schema.ts

@@ -1,7 +1,7 @@
 /**
  * sessions domain zod schemas (names derived from map keys: sessionListRequestSchema /
  * sessionListValueSchema). SessionEvent passthrough = strict envelope (type/seq/time) + wide
- * data: the merge-extensible event surface keeps an unknown-type branch at the union level,
+ * data: the merge-extensible event API keeps an unknown-type branch at the union level,
  * with no field-level passthrough. SessionId brand cast point: sessionIdSchema, and only there.
  */
 

packages/host/apiproxy/src/fetch/client.ts

@@ -411,7 +411,7 @@ export abstract class AbstractApiClient implements IApiClient {
     }
   }
 
-  // ---- IApiClient surface (arrow properties so destructured/passed references stay bound) ----
+  // ---- IApiClient API (arrow properties so destructured/passed references stay bound) ----
 
   readonly sessions: IApiClient['sessions'] = {
     list: (payload, signal) => this.callUnary('session.list', payload, signal),

packages/host/apiproxy/src/fetch/handler.ts

@@ -9,6 +9,7 @@
 import { randomUUID } from 'node:crypto'
 import type { z } from 'zod'
 import type { ApiProxy, MuxFrame, HostFrame } from '../api/index.ts'
+import { sessionLogQuerySchema } from '../api/downloads.schema.ts'
 import type { RequestPayload, ResponseValue, RpcMethodMap } from '../api/rpc-map.ts'
 import type { ClientRequest, RpcError, RpcRequest, RpcResponse, ServerRequest, ServerResponse } from '../api/rpc.ts'
 import { RpcId } from '../api/rpc.ts'
@@ -249,12 +250,23 @@ export function toFetchHandler(api: ApiProxy): { fetch: typeof fetch } {
       const url = new URL(req.url)
       const path = url.pathname
 
+      // No-envelope GET channel surface (SSE streams + host-only download):
+      // physical routes that answer directly, without a wire envelope.
       if (path === '/api/events.mux' && req.method === 'GET') {
         return sseResponse(api.events.mux({ rpcId: RpcId(randomUUID()), payload: {} }, req.signal))
       }
       if (path === '/api/events.host' && req.method === 'GET') {
         return sseResponse(api.events.host({ rpcId: RpcId(randomUUID()), payload: {} }, req.signal))
       }
+      if (path === '/api/session.export' && req.method === 'GET') {
+        // Query params are a different boundary from the POST envelope, but
+        // the request still casts its brands only through the domain schema.
+        const parsed = sessionLogQuerySchema.safeParse(Object.fromEntries(url.searchParams))
+        if (!parsed.success) {
+          return new Response('missing or invalid sessionId query parameter', { status: 400 })
+        }
+        return api.downloads.sessionLog(parsed.data, req.signal)
+      }
 
       if (req.method !== 'POST' || !path.startsWith('/api/')) {
         return new Response('not found', { status: 404 })

packages/host/apiproxy/src/index.ts

@@ -72,6 +72,7 @@ export class ApiProxyService extends Service implements ApiProxy {
   readonly credentials: ApiProxy['credentials']
   readonly llm: ApiProxy['llm']
   readonly events: ApiProxy['events']
+  readonly downloads: ApiProxy['downloads']
   readonly respond: ApiProxy['respond']
 
   constructor(ctx: Context, config: Config) {
@@ -94,6 +95,7 @@ export class ApiProxyService extends Service implements ApiProxy {
     this.credentials = api.credentials
     this.llm = api.llm
     this.events = api.events
+    this.downloads = api.downloads
     // createApiProxy returns closures (no `this` capture), so the bind is
     // behavior-neutral.
     this.respond = api.respond.bind(api)

packages/host/apiproxy/src/session-export.ts

@@ -0,0 +1,357 @@
+/**
+ * Host-side session-log download: streams one ZIP archive whose files are the
+ * sessions' stored artifact text verbatim plus every referenced media object.
+ * The root artifact sits under its original base name (`session.jsonl`); each
+ * subagent descendant under `subagents/<id>/<filename>`; each image referenced
+ * by any included log under `media/<attachmentId>.<ext>` (content-addressed,
+ * so one archive never duplicates a shared image). No manifest is written —
+ * every file is byte-identical to the backend's durable artifact or attachment
+ * store and self-describing through its own header line or media type.
+ * Compression runs on the host with fflate's streaming Zip API, so the archive
+ * bytes are produced incrementally and the host never holds the whole archive
+ * in one buffer; production yields to the consumer whenever the response queue
+ * fills past its high-water mark, so a slow consumer bounds the accumulation
+ * instead of piling up the whole archive (fflate's callback is synchronous —
+ * this drain point is the only backpressure available).
+ * @module
+ */
+
+import { Zip, ZipDeflate } from 'fflate'
+import type { Context } from '@deepseek-ai/cordis'
+import type { AttachmentStore, ImageAttachmentRef } from '@deepseek-ai/dsh-attachment'
+import type { SessionLineageNode, SessionQueryService } from '@deepseek-ai/dsh-session-query'
+import type { SessionId } from '@deepseek-ai/dsh-session'
+import type { SessionPersistence, SessionRawArtifact } from '@deepseek-ai/dsh-session-persistence'
+
+/** The services a session-log export needs (absent → the export is unavailable). */
+export interface SessionLogExportDeps {
+  readonly sessionQuery: SessionQueryService | undefined
+  readonly sessionPersistence: SessionPersistence | undefined
+  readonly attachments: AttachmentStore | undefined
+}
+
+/** The export services narrowed to the mounted ones streaming actually reads. */
+export interface SessionLogExportReady {
+  readonly sessionQuery: SessionQueryService
+  readonly sessionPersistence: SessionPersistence
+  readonly attachments: AttachmentStore
+}
+
+/**
+ * Resolve the persistence, session-query, and attachment services a log export needs.
+ * @param ctx - the composed host context.
+ * @returns the export services (absent when the deployment does not mount them).
+ */
+export function sessionLogExportDeps(ctx: Context): SessionLogExportDeps {
+  return {
+    sessionQuery: ctx.get('sessionQuery'),
+    sessionPersistence: ctx.get('sessionPersistence'),
+    attachments: ctx.get('attachments'),
+  }
+}
+
+/** One exported file: a stored artifact text or one referenced media object. */
+export type SessionLogZipEntry =
+  | { readonly path: string; readonly content: string }
+  | { readonly path: string; readonly data: Uint8Array }
+
+/** Zip extension for each accepted raster media type. */
+const MEDIA_TYPE_EXTENSIONS: Record<ImageAttachmentRef['mediaType'], string> = {
+  'image/png': 'png',
+  'image/jpeg': 'jpg',
+  'image/webp': 'webp',
+  'image/gif': 'gif',
+}
+
+/**
+ * The zip path for one media object: content-addressed by the opaque
+ * attachment id so shared images land once and the id in the log maps back to
+ * the archive entry without a manifest.
+ * @param ref - the durable reference from a session log.
+ * @returns the archive path.
+ */
+function mediaEntryPath(ref: ImageAttachmentRef): string {
+  return `media/${String(ref.attachmentId)}.${MEDIA_TYPE_EXTENSIONS[ref.mediaType]}`
+}
+
+/**
+ * Collect every image reference inside one content array, descending into
+ * nested tool results the way the live attachment route does.
+ * @param content - an event content array (or nested tool-result content).
+ * @param refs - the dedupe map being filled (keyed by attachment id).
+ */
+function collectImageRefs(content: unknown, refs: Map<string, ImageAttachmentRef>): void {
+  if (!Array.isArray(content)) return
+  const pending: unknown[] = []
+  for (const item of content) pending.push(item)
+  while (pending.length > 0) {
+    const value = pending.pop()
+    if (typeof value !== 'object' || value === null || Array.isArray(value)) continue
+    const block = value as { type?: unknown; attachment?: unknown; content?: unknown }
+    if (block.type === 'image' && typeof block.attachment === 'object' && block.attachment !== null) {
+      const ref = block.attachment as ImageAttachmentRef
+      refs.set(String(ref.attachmentId), ref)
+    }
+    if (Array.isArray(block.content)) {
+      for (const item of block.content) pending.push(item)
+    }
+  }
+}
+
+/**
+ * Collect every image reference one session event carries, across the same
+ * carriers the live attachment route scans (direct content, message content,
+ * inserted messages, and completed assistant chunk blocks).
+ * @param event - one parsed JSONL event object.
+ * @param refs - the dedupe map being filled (keyed by attachment id).
+ */
+function collectEventImageRefs(event: unknown, refs: Map<string, ImageAttachmentRef>): void {
+  const data = (event as { data?: unknown }).data
+  if (typeof data !== 'object' || data === null) return
+  const carrier = data as {
+    content?: unknown
+    message?: { content?: unknown }
+    inserted?: Array<{ content?: unknown }>
+    chunk?: { type?: unknown; block?: unknown }
+  }
+  collectImageRefs(carrier.content, refs)
+  if (carrier.message !== undefined) collectImageRefs(carrier.message.content, refs)
+  if (carrier.inserted !== undefined) {
+    for (const message of carrier.inserted) collectImageRefs(message.content, refs)
+  }
+  if (carrier.chunk?.type === 'block-end') collectImageRefs([carrier.chunk.block], refs)
+}
+
+/**
+ * Collect the distinct media references one stored artifact text names.
+ * Lines that fail to parse cannot reference media and are skipped (the
+ * artifact text itself is exported verbatim regardless).
+ * @param content - the stored artifact text.
+ * @returns the dedupe map keyed by attachment id.
+ */
+function imageRefsInArtifact(content: string): Map<string, ImageAttachmentRef> {
+  const refs = new Map<string, ImageAttachmentRef>()
+  for (const line of content.split('\n')) {
+    if (line === '') continue
+    let event: unknown
+    try {
+      event = JSON.parse(line)
+    } catch {
+      continue
+    }
+    collectEventImageRefs(event, refs)
+  }
+  return refs
+}
+
+/**
+ * One safe zip path segment from an untrusted session id. Session ids are
+ * host-controlled, but the brand allows any non-empty string, so `../`, dot
+ * segments, and separator characters are neutralized before they can shape
+ * archive entries. Distinct ids may collapse onto one segment (id collision
+ * is impossible for the host-minted UUIDs, so no uniqueness suffix is kept).
+ * @param id - the raw session id.
+ * @returns a filesystem-safe single path segment.
+ */
+function safeSessionIdSegment(id: string): string {
+  return id.replace(/[^A-Za-z0-9_-]/g, '_')
+}
+
+/**
+ * The export archive filename for one root session.
+ * @param sessionId - the root session id (sanitized to one safe path segment).
+ * @returns the attachment filename for the session's export archive.
+ */
+export function sessionLogZipFilename(sessionId: string): string {
+  return `dsh-session-${safeSessionIdSegment(sessionId)}.zip`
+}
+
+/**
+ * Yield the export entries in zip order: the preloaded root artifact first,
+ * then every subagent descendant in lineage order (each read from the
+ * persistence backend right before it is yielded and dropped after the
+ * consumer moves on), then every distinct media object referenced by any of
+ * the included logs (read and verified from the attachment store, one archive
+ * entry per attachment id). The host holds at most one descendant's artifact
+ * text and one media object at a time beyond the root.
+ * @param deps - the mounted export services (the caller answered 500 before this runs).
+ * @param root - the already-read root artifact (read by the caller so the
+ * missing-session path can answer cleanly before streaming starts).
+ * @param sessionId - the root session id.
+ * @param includeDescendants - whether to include every subagent descendant.
+ * @param signal - optional cancellation for read work.
+ * @returns the export entries in zip order.
+ */
+export async function* sessionLogZipEntries(
+  deps: SessionLogExportReady,
+  root: SessionRawArtifact,
+  sessionId: SessionId,
+  includeDescendants: boolean,
+  signal?: AbortSignal,
+): AsyncGenerator<SessionLogZipEntry> {
+  const media = new Map<string, ImageAttachmentRef>()
+  const rememberMedia = (content: string): void => {
+    for (const [id, ref] of imageRefsInArtifact(content)) media.set(id, ref)
+  }
+  rememberMedia(root.content)
+  yield { path: root.filename, content: root.content }
+  if (includeDescendants) {
+    const seen = new Set<SessionId>([sessionId])
+    const collect = async function* (
+      nodes: readonly SessionLineageNode[],
+    ): AsyncGenerator<SessionLogZipEntry> {
+      for (const node of nodes) {
+        signal?.throwIfAborted()
+        const id = node.session.header.id
+        if (seen.has(id)) continue
+        seen.add(id)
+        const raw = await deps.sessionPersistence.readRaw(id)
+        if (raw === undefined) {
+          throw new Error(`subagent "${id}" has no stored log artifact`)
+        }
+        rememberMedia(raw.content)
+        yield {
+          path: `subagents/${safeSessionIdSegment(id)}/${raw.filename}`,
+          content: raw.content,
+        }
+        yield* collect(node.descendants)
+      }
+    }
+    const lineage = await deps.sessionQuery.traceSession(sessionId)
+    yield* collect(lineage.descendants)
+  }
+  for (const ref of media.values()) {
+    signal?.throwIfAborted()
+    const stored = await deps.attachments.readImage(ref)
+    yield { path: mediaEntryPath(ref), data: stored.data }
+  }
+}
+
+/** How many code units of artifact text one zip push carries (bounded encode memory). */
+const PUSH_CHUNK_CODE_UNITS = 1 << 16
+
+/** How many bytes of media one zip push carries (bounded memory; images are already size-capped). */
+const PUSH_CHUNK_BYTES = 1 << 16
+
+/**
+ * Push one media object's bytes into a deflate stream in bounded chunks,
+ * yielding to a slow consumer between chunks like the artifact path does.
+ * @param deflate - the zip entry's deflate stream.
+ * @param data - the stored image bytes.
+ * @param signal - optional cancellation; throws when aborted.
+ */
+async function pushBinaryChunks(
+  deflate: ZipDeflate,
+  data: Uint8Array,
+  controller: ReadableStreamDefaultController<Uint8Array>,
+  signal?: AbortSignal,
+): Promise<void> {
+  let offset = 0
+  do {
+    signal?.throwIfAborted()
+    const end = Math.min(offset + PUSH_CHUNK_BYTES, data.byteLength)
+    const finalChunk = end >= data.byteLength
+    deflate.push(data.subarray(offset, end), finalChunk)
+    offset = end
+    /* v8 ignore next 2 -- only fires when a slow consumer leaves the queue over-full */
+    if (controller.desiredSize !== null && controller.desiredSize < 0) {
+      await new Promise(resolve => setTimeout(resolve, 0))
+    }
+  } while (offset < data.byteLength)
+}
+
+/**
+ * Push one artifact's text into a deflate stream in bounded chunks, never
+ * splitting a surrogate pair across a chunk boundary (a lone high surrogate
+ * re-encodes as U+FFFD and would silently corrupt the exported artifact).
+ * @param deflate - the zip entry's deflate stream.
+ * @param content - the artifact text verbatim.
+ * @param signal - optional cancellation; throws when aborted.
+ */
+async function pushArtifactChunks(
+  deflate: ZipDeflate,
+  content: string,
+  controller: ReadableStreamDefaultController<Uint8Array>,
+  signal?: AbortSignal,
+): Promise<void> {
+  const encoder = new TextEncoder()
+  let offset = 0
+  let finalChunk: boolean
+  do {
+    signal?.throwIfAborted()
+    let end = Math.min(offset + PUSH_CHUNK_CODE_UNITS, content.length)
+    if (end < content.length && end - offset > 1) {
+      // Back off one code unit when the boundary lands inside a surrogate
+      // pair: the pair then starts the next chunk whole.
+      const last = content.charCodeAt(end - 1)
+      if (last >= 0xd800 && last <= 0xdbff) end -= 1
+    }
+    finalChunk = end >= content.length
+    deflate.push(encoder.encode(content.slice(offset, end)), finalChunk)
+    offset = end
+    /* v8 ignore next 2 -- only fires when a slow consumer leaves the queue over-full */
+    if (controller.desiredSize !== null && controller.desiredSize < 0) {
+      await new Promise(resolve => setTimeout(resolve, 0))
+    }
+  } while (!finalChunk)
+}
+
+/**
+ * Stream one session-log ZIP as a WHATWG ReadableStream. The root artifact is
+ * read and validated by the caller before this is called (missing root or
+ * missing services answer cleanly before any byte is produced); each entry is
+ * then encoded and deflated in bounded chunks as it is produced, so the
+ * archive bytes arrive incrementally. A descendant that fails to read errors
+ * the stream (fail-loud, never silent under-export).
+ * @param deps - the mounted export services (the caller answered 500 before this runs).
+ * @param root - the already-read root artifact (first zip entry).
+ * @param sessionId - the root session id.
+ * @param includeDescendants - whether to include every subagent descendant.
+ * @param signal - optional cancellation for read work.
+ * @returns the zip byte stream.
+ */
+export function streamSessionLogZip(
+  deps: SessionLogExportReady,
+  root: SessionRawArtifact,
+  sessionId: SessionId,
+  includeDescendants: boolean,
+  signal?: AbortSignal,
+): ReadableStream<Uint8Array> {
+  return new ReadableStream<Uint8Array>({
+    start(controller) {
+      // fflate invokes the callback synchronously per compressed chunk, so a
+      // single push can enqueue ahead of a slow consumer; pushArtifactChunks
+      // yields between chunks once the queue is over-full, bounding the
+      // accumulation to the queue high-water mark plus one push.
+      const zip = new Zip((error, data, final) => {
+        /* v8 ignore next 3 -- fflate reports only internal zip failures, unreachable for valid inputs */
+        if (error) {
+          controller.error(error)
+          return
+        }
+        /* v8 ignore next -- fflate may emit empty chunks; not controllable from tests */
+        if (data.byteLength > 0) controller.enqueue(data)
+        if (final) controller.close()
+      })
+      void (async () => {
+        try {
+          for await (const entry of sessionLogZipEntries(deps, root, sessionId, includeDescendants, signal)) {
+            const deflate = new ZipDeflate(entry.path, { level: 6 })
+            zip.add(deflate)
+            if ('content' in entry) {
+              await pushArtifactChunks(deflate, entry.content, controller, signal)
+            } else {
+              await pushBinaryChunks(deflate, entry.data, controller, signal)
+            }
+          }
+          zip.end()
+        } catch (error) {
+          // A mid-stream failure (missing descendant, cancellation, read
+          // error) must fail the download rather than ship a truncated archive.
+          /* v8 ignore next -- typed backends reject with Error, and DOMException is one in Node */
+          controller.error(error instanceof Error ? error : new Error(String(error)))
+        }
+      })()
+    },
+  })
+}

packages/host/apiproxy/tests/api-proxy-tasks.spec.ts

@@ -51,7 +51,7 @@ async function harness(withRegistry: boolean): Promise<{ ctx: Context; session:
   await ctx.plugin(AgentRegistry)
   if (withRegistry) {
     await ctx.plugin(LocalTaskService)
-    ctx.tasks.attachSurface('api-proxy-test')
+    ctx.tasks.attachController('api-proxy-test')
   }
   const session = ctx.sessions.create()
   const agent = {

packages/host/apiproxy/tests/client-handler.spec.ts

@@ -135,6 +135,7 @@ function scriptedApi(overrides: {
     },
     events: { mux: () => empty<MuxFrame>(), host: () => empty<HostFrame>(), ...overrides.events },
     respond: overrides.respond ?? (() => Promise.resolve({ accepted: false as const, reason: 'not-pending' as const })),
+    downloads: { sessionLog: async () => new Response('stub', { status: 404 }) },
   }
 }
 

packages/host/apiproxy/tests/fetch-carrier.spec.ts

@@ -306,6 +306,11 @@ function fakeApi(overrides: Partial<{ muxFrames: MuxFrame[]; hostFrames: HostFra
     async respond(message: ClientResponse): Promise<RpcReceipt> {
       return message.rpcId === 'known' ? { accepted: true } : { accepted: false, reason: 'not-pending' }
     },
+    downloads: {
+      async sessionLog() {
+        return new Response('stub', { status: 404 })
+      },
+    },
   }
 }
 

packages/host/apiproxy/tests/session-export.spec.ts

@@ -0,0 +1,377 @@
+/**
+ * session.export host path: the GET download endpoint streams a ZIP whose
+ * files are the stored artifacts verbatim (root + optional descendants), and
+ * the degenerate compositions fail loudly (missing services → 500, missing
+ * root → 404, missing descendant → errored stream).
+ */
+
+import { describe, expect, it } from 'vitest'
+import { Context } from '@deepseek-ai/cordis'
+import { unzipSync, strFromU8 } from 'fflate'
+import type { ImageAttachmentRef } from '@deepseek-ai/dsh-attachment'
+import UserInteractionService from '@deepseek-ai/dsh-user-interaction'
+import type { SessionHeader, SessionId } from '@deepseek-ai/dsh-session'
+import type { SessionLineageNode } from '@deepseek-ai/dsh-session-query'
+import type { SessionRawArtifact } from '@deepseek-ai/dsh-session-persistence'
+import { toFetchHandler } from '@deepseek-ai/dsh-host-apiproxy'
+import { createApiProxy } from '@deepseek-ai/dsh-host-apiproxy'
+
+const sid = (id: string): SessionId => id as SessionId
+
+function header(id: string, parentSession?: SessionId): SessionHeader {
+  return {
+    version: 0,
+    id: sid(id),
+    createdAt: 1000,
+    cwd: '/proj',
+    ...parentSession === undefined ? {} : { parentSession },
+    delegationDepth: parentSession === undefined ? 0 : 1,
+  }
+}
+
+function artifact(id: string, parentSession?: SessionId, content?: string): SessionRawArtifact {
+  return {
+    meta: header(id, parentSession),
+    filename: 'session.jsonl',
+    content: content ?? `{"type":"session","version":0,"id":"${id}","createdAt":1000}\n{"type":"turn/start","seq":0,"time":2000,"data":{"turn":1}}\n`,
+  }
+}
+
+function node(id: string, ...descendants: SessionLineageNode[]): SessionLineageNode {
+  return { session: { header: header(id, sid('session-root')), live: false, persisted: true }, descendants }
+}
+
+/** One durable image object served by the fake attachment store. */
+function storedImage(id: string, mediaType: ImageAttachmentRef['mediaType'] = 'image/png') {
+  return {
+    ref: { attachmentId: sid(id), mediaType, bytes: 4, width: 2, height: 2 } as unknown as ImageAttachmentRef,
+    data: new Uint8Array([1, 2, 3, 4]),
+  }
+}
+
+/** A user/message event line carrying one image reference. */
+function imageEventLine(id: string, mediaType: ImageAttachmentRef['mediaType'] = 'image/png'): string {
+  return `{"type":"user/message","seq":1,"time":1000,"data":{"content":[{"type":"image","attachment":{"attachmentId":"${id}","mediaType":"${mediaType}","bytes":4,"width":2,"height":2}}]}}`
+}
+
+async function buildApi(
+  artifacts: Record<string, SessionRawArtifact>,
+  descendants: SessionLineageNode[] = [],
+  services: {
+    query?: boolean
+    persistence?: boolean | 'throw'
+    attachments?: boolean | ((ref: ImageAttachmentRef) => Promise<ReturnType<typeof storedImage>>)
+  } = {},
+) {
+  const ctx = new Context()
+  await ctx.plugin(UserInteractionService)
+  const query = services.query ?? true
+  const persistence = services.persistence ?? true
+  if (query) {
+    ctx.provide('sessionQuery', {
+      traceSession: async () => ({
+        target: { header: header('session-root'), live: false, persisted: true },
+        ancestors: [],
+        complete: true,
+        root: { header: header('session-root'), live: false, persisted: true },
+        descendants,
+      }),
+    } as never)
+  }
+  if (persistence) {
+    ctx.provide('sessionPersistence', {
+      readRaw: async (id: SessionId) => {
+        if (persistence === 'throw') throw new Error('/host/private/session.jsonl')
+        return artifacts[id]
+      },
+    } as never)
+  }
+  if (services.attachments !== false) {
+    const readImage = typeof services.attachments === 'function'
+      ? services.attachments
+      : async (ref: ImageAttachmentRef) => storedImage(String(ref.attachmentId), ref.mediaType)
+    ctx.provide('attachments', {
+      imageLimits: {} as never,
+      validateImage: async () => {},
+      saveImage: async () => { throw new Error('export never saves images') },
+      readImage,
+    } as never)
+  }
+  return createApiProxy(ctx, {
+    defaultModelSelection: () => ({ provider: 'p', model: 'm' }),
+    cwd: '/tmp',
+  })
+}
+
+async function responseBytes(response: Response): Promise<Uint8Array> {
+  return new Uint8Array(await response.arrayBuffer())
+}
+
+describe('session.export download endpoint', () => {
+  it('streams a ZIP with the root artifact verbatim under its original filename', async () => {
+    const api = await buildApi({ 'session-root': artifact('session-root') })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(response.status).toBe(200)
+    expect(response.headers.get('content-type')).toBe('application/zip')
+    expect(response.headers.get('content-disposition')).toContain('dsh-session-session-root.zip')
+    const files = unzipSync(await responseBytes(response))
+    expect(Object.keys(files)).toEqual(['session.jsonl'])
+    expect(strFromU8(files['session.jsonl'] as Uint8Array)).toBe(artifact('session-root').content)
+  })
+
+  it('includes descendant artifacts under subagents/<id>/ when requested', async () => {
+    const api = await buildApi({
+      'session-root': artifact('session-root'),
+      'child-a': artifact('child-a', sid('session-root')),
+      'grandchild-a': artifact('grandchild-a', sid('child-a')),
+    }, [
+      node('child-a', node('grandchild-a')),
+    ])
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root&includeDescendants=true'),
+    )
+    expect(response.status).toBe(200)
+    const files = unzipSync(await responseBytes(response))
+    expect(Object.keys(files).sort()).toEqual([
+      'session.jsonl',
+      'subagents/child-a/session.jsonl',
+      'subagents/grandchild-a/session.jsonl',
+    ])
+    expect(strFromU8(files['subagents/child-a/session.jsonl'] as Uint8Array))
+      .toBe(artifact('child-a').content)
+  })
+
+  it('answers 404 for a missing root session', async () => {
+    const api = await buildApi({})
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(response.status).toBe(404)
+  })
+
+  it('answers 400 when the sessionId query parameter is absent', async () => {
+    const api = await buildApi({ 'session-root': artifact('session-root') })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?includeDescendants=true'),
+    )
+    expect(response.status).toBe(400)
+  })
+
+  it('answers 400 for an includeDescendants value other than true or false', async () => {
+    const api = await buildApi({ 'session-root': artifact('session-root') })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root&includeDescendants=1'),
+    )
+    expect(response.status).toBe(400)
+  })
+
+  it('answers 500 when the deployment mounts no persistence or session-query service', async () => {
+    const api = await buildApi({}, [], { query: false, persistence: false })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(response.status).toBe(500)
+    expect(await response.text()).toContain('session-query')
+  })
+
+  it('fails the whole export when a descendant has no stored artifact', async () => {
+    const api = await buildApi({
+      'session-root': artifact('session-root'),
+    }, [node('child-missing')])
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root&includeDescendants=true'),
+    )
+    expect(response.status).toBe(200)
+    // The stream errors before completing, so the body read rejects rather
+    // than returning a truncated-but-valid archive.
+    await expect(response.arrayBuffer()).rejects.toThrow()
+  })
+
+  it('keeps an astral character whole when its surrogate pair straddles a push boundary', async () => {
+    // The push loop slices by 2^16 code units and must back off one unit when
+    // the boundary lands inside a surrogate pair; otherwise the pair re-encodes
+    // as U+FFFD and the exported artifact is silently corrupted.
+    const root = { ...artifact('session-root'), content: `${'a'.repeat((1 << 16) - 1)}😀tail` }
+    const api = await buildApi({ 'session-root': root })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    const files = unzipSync(await responseBytes(response))
+    expect(strFromU8(files['session.jsonl'] as Uint8Array)).toBe(root.content)
+  })
+
+  it('splits a long artifact on a plain code-unit boundary without backoff', async () => {
+    // A boundary that lands on a BMP character needs no surrogate backoff; the
+    // round trip must still be byte-identical across the multi-chunk push.
+    const root = { ...artifact('session-root'), content: 'z'.repeat((1 << 16) + 4096) }
+    const api = await buildApi({ 'session-root': root })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    const files = unzipSync(await responseBytes(response))
+    expect(strFromU8(files['session.jsonl'] as Uint8Array)).toBe(root.content)
+  })
+
+  it('exports an empty artifact as an empty zip entry', async () => {
+    const root = { ...artifact('session-root'), content: '' }
+    const api = await buildApi({ 'session-root': root })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    const files = unzipSync(await responseBytes(response))
+    expect(Object.keys(files)).toEqual(['session.jsonl'])
+    expect(strFromU8(files['session.jsonl'] as Uint8Array)).toBe('')
+  })
+
+  it('exports a shared lineage node once (seen-set dedup)', async () => {
+    const api = await buildApi({
+      'session-root': artifact('session-root'),
+      'child-a': artifact('child-a', sid('session-root')),
+      'child-b': artifact('child-b', sid('session-root')),
+      shared: artifact('shared', sid('child-a')),
+    }, [
+      node('child-a', node('shared')),
+      node('child-b', node('shared')),
+    ])
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root&includeDescendants=true'),
+    )
+    const files = unzipSync(await responseBytes(response))
+    expect(Object.keys(files).sort()).toEqual([
+      'session.jsonl',
+      'subagents/child-a/session.jsonl',
+      'subagents/child-b/session.jsonl',
+      'subagents/shared/session.jsonl',
+    ])
+  })
+
+  it('answers 500 without leaking the backend error when the root artifact read fails', async () => {
+    const api = await buildApi({}, [], { query: true, persistence: 'throw' })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(response.status).toBe(500)
+    const body = await response.text()
+    expect(body).toBe('session log export failed to read the stored artifact')
+    expect(body).not.toContain('/host/private/')
+  })
+
+  it('includes media objects referenced by the root log under media/<id>.<ext>', async () => {
+    const root = artifact('session-root', undefined, [
+      '{"type":"session","version":0,"id":"session-root","createdAt":1000}',
+      imageEventLine('img-1'),
+    ].join('\n') + '\n')
+    const api = await buildApi({ 'session-root': root })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(response.status).toBe(200)
+    const files = unzipSync(await responseBytes(response))
+    expect(Object.keys(files).sort()).toEqual(['media/img-1.png', 'session.jsonl'])
+    expect(files['media/img-1.png']).toEqual(storedImage('img-1').data)
+  })
+
+  it('collects media referenced from nested tool results', async () => {
+    const nested = '{"type":"assistant/message","seq":2,"time":2000,"data":{"content":[{"type":"tool-result","content":[{"type":"image","attachment":{"attachmentId":"nested-1","mediaType":"image/webp","bytes":4,"width":2,"height":2}}]}]}}'
+    const root = artifact('session-root', undefined, [
+      '{"type":"session","version":0,"id":"session-root","createdAt":1000}',
+      nested,
+    ].join('\n') + '\n')
+    const api = await buildApi({ 'session-root': root })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    const files = unzipSync(await responseBytes(response))
+    expect(Object.keys(files).sort()).toEqual(['media/nested-1.webp', 'session.jsonl'])
+  })
+
+  it('scans the wrapped, inserted, and chunk carriers plus non-object content items', async () => {
+    const block = (id: string, mediaType: string) =>
+      `{"type":"image","attachment":{"attachmentId":"${id}","mediaType":"${mediaType}","bytes":4,"width":2,"height":2}}`
+    const wrapped = `{"type":"assistant/message","seq":2,"time":2000,"data":{"message":{"role":"assistant","content":["noise",${block('wrapped-1', 'image/jpeg')}]}}}`
+    const inserted = `{"type":"context/inserted","seq":3,"time":3000,"data":{"inserted":[{"content":[${block('inserted-1', 'image/gif')}]}]}}`
+    const chunk = `{"type":"assistant/chunk","seq":4,"time":4000,"data":{"chunk":{"type":"block-end","block":${block('chunk-1', 'image/png')}}}}`
+    const root = artifact('session-root', undefined, [
+      '{"type":"session","version":0,"id":"session-root","createdAt":1000}',
+      wrapped,
+      inserted,
+      chunk,
+    ].join('\n') + '\n')
+    const api = await buildApi({ 'session-root': root })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    const files = unzipSync(await responseBytes(response))
+    expect(Object.keys(files).sort()).toEqual([
+      'media/chunk-1.png',
+      'media/inserted-1.gif',
+      'media/wrapped-1.jpg',
+      'session.jsonl',
+    ])
+  })
+
+  it('deduplicates one media object referenced by several included logs', async () => {
+    const line = imageEventLine('shared-img')
+    const root = artifact('session-root', undefined, [
+      '{"type":"session","version":0,"id":"session-root","createdAt":1000}',
+      line,
+    ].join('\n') + '\n')
+    const child = artifact('child-a', sid('session-root'), [
+      '{"type":"session","version":0,"id":"child-a","createdAt":1000}',
+      line,
+    ].join('\n') + '\n')
+    const api = await buildApi({ 'session-root': root, 'child-a': child }, [node('child-a')])
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root&includeDescendants=true'),
+    )
+    const files = unzipSync(await responseBytes(response))
+    expect(files['media/shared-img.png']).toEqual(storedImage('shared-img').data)
+    expect(Object.keys(files).filter(name => name.startsWith('media/'))).toEqual(['media/shared-img.png'])
+  })
+
+  it('includes descendant media only when descendants are requested', async () => {
+    const child = artifact('child-a', sid('session-root'), [
+      '{"type":"session","version":0,"id":"child-a","createdAt":1000}',
+      imageEventLine('child-img'),
+    ].join('\n') + '\n')
+    const api = await buildApi({ 'session-root': artifact('session-root'), 'child-a': child }, [node('child-a')])
+    const without = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(Object.keys(unzipSync(await responseBytes(without)))).toEqual(['session.jsonl'])
+    const withDescendants = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root&includeDescendants=true'),
+    )
+    expect(Object.keys(unzipSync(await responseBytes(withDescendants))).sort()).toEqual([
+      'media/child-img.png',
+      'session.jsonl',
+      'subagents/child-a/session.jsonl',
+    ])
+  })
+
+  it('fails the whole export when a referenced image cannot be read', async () => {
+    const root = artifact('session-root', undefined, [
+      '{"type":"session","version":0,"id":"session-root","createdAt":1000}',
+      imageEventLine('gone-img'),
+    ].join('\n') + '\n')
+    const api = await buildApi({ 'session-root': root }, [], {
+      attachments: async () => { throw new Error('attachment bytes missing') },
+    })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(response.status).toBe(200)
+    await expect(response.arrayBuffer()).rejects.toThrow('attachment bytes missing')
+  })
+
+  it('answers 500 when the deployment mounts no attachments service', async () => {
+    const api = await buildApi({ 'session-root': artifact('session-root') }, [], { attachments: false })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(response.status).toBe(500)
+    expect(await response.text()).toContain('attachments')
+  })
+})