diff --git a/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.i18n.yaml b/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.i18n.yaml
index 0c8a3f2781..e24e2894a5 100644
--- a/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.i18n.yaml
+++ b/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write .agents/notes/implemented/feature/2026-08-10-web-session-log-export.md
-2026-08-10-web-session-log-export.md: 427b6478ac44fb28030aa932630f276de7bb2edc
-2026-08-10-web-session-log-export.zh.md: 63b9804a54cda7eea4ff793d78a925fe296d06cb
+2026-08-10-web-session-log-export.md: 8fa62b877df1be55de2c373d4281672881dc2b9d
+2026-08-10-web-session-log-export.zh.md: 3040dda992492187245bfe92d29bc0812ef01ef2
diff --git a/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.md b/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.md
index 427b6478ac..8fa62b877d 100644
--- a/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.md
+++ b/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.md
@@ -10,10 +10,10 @@ The Trajectory view had no way to hand a debugging artifact to a human: the raw
 
 ## Decision
 
-- **The export is a host-only download, not an RPC**: `GET /api/session.export?sessionId=…&includeDescendants=true` streams one ZIP attachment. Every file is a session's **stored artifact text verbatim**: `readRaw` on the persistence service reads the backend's own durable bytes (the JSONL backend decodes its physical zstd frames, or returns plaintext) — never a reconstruction from parsed events, so packed-chunk rows, key order, and line breaks survive byte-for-byte — under its original base name (`session.jsonl` at the root, `subagents/<id>/session.jsonl` for descendants). Compression runs on the host with fflate's streaming `Zip`/`ZipDeflate` API, each entry deflated in bounded chunks as it is produced, so the response is chunked as it is generated and the host never holds the whole archive in one buffer (at most one descendant's artifact text beyond the preloaded root), 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). No manifest is written — every file is byte-identical to the durable artifact and self-describing through its own header line.
-- **Error vocabulary is HTTP-native**: missing services → 500, missing root session → 404 (both decided before any byte streams), a descendant without a stored artifact → the stream errors (fail-loud, never silent under-export). The carrier (`toFetchHandler`) already applies the `/api` trust fence; the GET branch sits beside the existing SSE GET routes, and `ApiProxy.downloads.sessionLog` (host-only, no wire envelope, absent from `IApiClient`) implements it.
-- **The UI just downloads**: the 导出 button fetches the endpoint and saves the response; the `session.log` RPC that an earlier iteration shipped was removed — the download endpoint is its only consumer, and the repo rule is no public interface without a current owner. The client bundle no longer carries fflate (the earlier browser-entry-alias pitfall is moot).
-- The 导出 button lives in the Trajectory toolbar; the plugin exposes `exportLog` through the view's inject face (components never touch ctx) and resolves the view tab label through the locale service (`轨迹` in Chinese, `Trajectory` in English). In-flight state disables the button; a failure surfaces in a visible alert bar under the toolbar.
+- **The export is a host-only download, not an RPC**: `GET /api/session.export?sessionId=…&includeDescendants=true` streams one ZIP attachment. Every file is a session's **stored artifact text verbatim**: `readRaw` on the persistence service reads the backend's own durable bytes (the JSONL backend decodes its physical zstd frames, or returns plaintext) — never a reconstruction from parsed events, so packed-chunk rows, key order, and line breaks survive byte-for-byte — under its original base name (`session.jsonl` at the root, `subagents/<id>/session.jsonl` for descendants). Compression runs on the host with fflate's streaming `Zip`/`ZipDeflate` API at validated `sessionExportCompressionLevel` 0–9 (default 6), letting deployments trade CPU and latency against archive size; each entry is deflated in bounded chunks as it is produced, so the response is chunked as it is generated and the host never holds the whole archive in one buffer (at most one descendant's artifact text beyond the preloaded root). At the 64 KiB response byte high-water mark, production waits for consumer pull to restore capacity; fflate's synchronous callback can add at most one bounded input push beyond that queue bound. No manifest is written — every file is byte-identical to the durable artifact and self-describing through its own header line.
+- **Error vocabulary is HTTP-native**: missing services → 500, a backend without per-session raw artifacts → 501, missing root session → 404 (all decided before any byte streams), and a descendant without a stored artifact → the stream errors (fail-loud, never silent under-export). Request abort remains cancellation instead of being rewritten as 500; request and response-consumer cancellation converge on the producer signal, which reaches lineage, persistence, and attachment reads and terminates the active compressor. The carrier (`toFetchHandler`) already applies the `/api` trust fence; the GET branch sits beside the existing SSE GET routes, and `ApiProxy.downloads.sessionLog` (host-only, no wire envelope, absent from `IApiClient`) implements it.
+- **The UI just downloads**: the 导出 button hands the endpoint directly to the browser's native download manager, so JavaScript neither fetches nor buffers the ZIP; the `session.log` RPC that an earlier iteration shipped was removed — the download endpoint is its only consumer, and the repo rule is no public interface without a current owner. The client bundle carries no archive implementation.
+- The 导出 button lives in the Trajectory toolbar; the plugin exposes `exportLog` through the view's inject face (components never touch ctx) and resolves the view tab label through the locale service (`轨迹` in Chinese, `Trajectory` in English). In-flight state disables the button during the handoff; a synchronous browser-handoff failure surfaces in a visible alert bar, while HTTP delivery is owned and reported by the browser.
 
 ## Alternatives considered
 
@@ -24,7 +24,7 @@ The Trajectory view had no way to hand a debugging artifact to a human: the raw
 
 ## Consequences
 
-- Export fidelity: every exported file is byte-identical to the backend's durable artifact as of the read moment (a live session may append after the read; the export reflects the durable state at read time). The archive name is `dsh-session-<sanitized-id>.zip` and archive paths sanitize ids before they can shape entries.
-- `readRaw` joins the persistence service as a concrete default (`undefined` for backends without a per-session artifact, e.g. SQLite) with a JSONL-backend override that owns the compression decode. `ApiProxy.downloads.sessionLog` adds one host-only member to the contract plus a host-side query schema and a GET branch in the fetch handler — no RPC map row, envelope schema, or client `IApiClient` surface.
-- Fixture mode (no host) answers 404 for the export, so the button's error bar explains the gap instead of hanging; the navigation-panes golden snapshot includes the 导出 button.
+- Export fidelity: immediately before reading each live root or descendant, the exporter crosses the authoritative `SessionStore.flush` durability barrier; every exported file is byte-identical to that resulting durable artifact. A live session may append again after its read, so the archive is a per-session read-boundary snapshot rather than one atomic tree snapshot. The archive name is `dsh-session-<sanitized-id>.zip` and archive paths sanitize ids before they can shape entries.
+- `supportsRawArtifacts` explicitly separates backend capability from session absence: unsupported backends such as SQLite report `false` and the concrete `readRaw` default rejects, while the JSONL override reports `true`, owns physical decoding, and reserves `undefined` for an absent artifact. `ApiProxy.downloads.sessionLog` adds one host-only member to the contract plus a host-side query schema and a GET branch in the fetch handler — no RPC map row, envelope schema, or client `IApiClient` surface.
+- Fixture mode (no host) answers 404 for the export, which the browser reports as a failed download; the navigation-panes golden snapshot includes the 导出 button.
 - Deferred: transcript.md and a report/feedback bundle remain future work; the byte-faithful, manifest-free shape keeps the v2 bundle extension cheap.
diff --git a/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.zh.md b/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.zh.md
index 63b9804a54..3040dda992 100644
--- a/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.zh.md
+++ b/.agents/notes/implemented/feature/2026-08-10-web-session-log-export.zh.md
@@ -10,10 +10,10 @@ Trajectory 视图没有任何方式把调试工件交到人手里：原始会话
 
 ## 决策
 
-- **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 附件。每个文件都是会话**存储工件的逐字原文**：持久化服务新增的 `readRaw` 读取后端自己的持久化字节（jsonl 后端解码其物理 zstd 帧，或直接返回明文）——绝非从解析后事件重建，因此 chunk 打包、键序、换行全部逐字节保留——放在其原始基础文件名下（根为 `session.jsonl`，子代理为 `subagents/<id>/session.jsonl`）。压缩在宿主侧用 fflate 的流式 `Zip`/`ZipDeflate` API 完成，每个条目按有界分块边产出边压缩，响应随生成分块写出，宿主从不把整个归档放进单个缓冲区（除预载的根外，最多同时持有一条后代的工件文本），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）。不写清单——每个文件都与持久化工件逐字节一致，并通过自身 header 行自描述。
-- **错误词汇是 HTTP 原生的**：服务缺失 → 500，根会话缺失 → 404（两者都在任何字节流出前判定），后代缺少存储工件 → 流失败（fail-loud，绝不静默少导出）。载体（`toFetchHandler`）已对 `/api` 应用信任围栏；GET 分支与既有 SSE GET 路由并列，由 `ApiProxy.downloads.sessionLog`（host-only、无 wire 信封、不在 `IApiClient` 上）实现。
-- **UI 只负责下载**：「导出」按钮 fetch 该端点并保存响应；早先迭代发布的 `session.log` RPC 已删除——下载端点是它唯一的消费者，仓库规则是不留无当前所有者的公共接口。客户端 bundle 不再携带 fflate（早先的浏览器入口别名坑随之消失）。
-- 「导出」按钮位于 Trajectory 工具栏；插件通过视图的 inject face 暴露 `exportLog`（组件从不接触 ctx），并通过 locale 服务解析视图标签页标题（中文「轨迹」、英文 "Trajectory"）。进行中状态会禁用按钮；失败会在工具栏下方的可见警示条中显示。
+- **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 附件。每个文件都是会话**存储工件的逐字原文**：持久化服务新增的 `readRaw` 读取后端自己的持久化字节（jsonl 后端解码其物理 zstd 帧，或直接返回明文）——绝非从解析后事件重建，因此 chunk 打包、键序、换行全部逐字节保留——放在其原始基础文件名下（根为 `session.jsonl`，子代理为 `subagents/<id>/session.jsonl`）。压缩在宿主侧使用 fflate 流式 `Zip`/`ZipDeflate` API 和已验证的 `sessionExportCompressionLevel` 0–9（默认 6），使部署可以在 CPU／延迟与归档大小之间取舍；每个条目按有界分块边产出边压缩，响应随生成分块写出，宿主从不把整个归档放进单个缓冲区（除预载的根外，最多同时持有一条后代的工件文本）。到达 64 KiB 响应字节高水位后，生产会等待 Consumer pull 恢复容量；fflate 的同步回调最多只会在该队列界限外再增加一次有界输入 push。不写清单——每个文件都与持久化工件逐字节一致，并通过自身 header 行自描述。
+- **错误词汇是 HTTP 原生的**：服务缺失 → 500，后端不提供每会话原始工件 → 501，根会话缺失 → 404（三者都在任何字节流出前判定），后代缺少存储工件 → 流失败（fail-loud，绝不静默少导出）。请求中止会保持取消语义而不会改写成 500；请求取消与响应 Consumer 取消汇合到生产者 signal，该 signal 会传到血缘、持久化与附件读取，并终止活跃压缩器。载体（`toFetchHandler`）已对 `/api` 应用信任围栏；GET 分支与既有 SSE GET 路由并列，由 `ApiProxy.downloads.sessionLog`（host-only、无 wire 信封、不在 `IApiClient` 上）实现。
+- **UI 只负责下载**：「导出」按钮将端点直接交给浏览器原生下载管理器，因此 JavaScript 既不会 fetch 也不会缓冲 ZIP；早先迭代发布的 `session.log` RPC 已删除——下载端点是它唯一的消费者，仓库规则是不留无当前所有者的公共接口。客户端 bundle 不包含任何归档实现。
+- 「导出」按钮位于 Trajectory 工具栏；插件通过视图的 inject face 暴露 `exportLog`（组件从不接触 ctx），并通过 locale 服务解析视图标签页标题（中文「轨迹」、英文 "Trajectory"）。进行中状态会在交接期间禁用按钮；同步的浏览器交接失败会在可见警示条中显示，而 HTTP 交付由浏览器负责并报告。
 
 ## 考虑过的替代方案
 
@@ -24,7 +24,7 @@ Trajectory 视图没有任何方式把调试工件交到人手里：原始会话
 
 ## 后果
 
-- 导出保真度：每个导出文件都与读取时刻的后端持久化工件逐字节一致（活跃会话可能在读取后继续追加；导出反映的是读取时的持久化状态）。压缩包名为 `dsh-session-<sanitized-id>.zip`，归档路径在塑造条目前会先净化会话 id。
-- `readRaw` 以具体默认（无每会话工件的后端如 SQLite 返回 `undefined`）加入持久化服务，jsonl 后端覆写并自持压缩解码。`ApiProxy.downloads.sessionLog` 为契约新增一个 host-only 成员，外加宿主侧 query schema，并在 fetch handler 加一个 GET 分支——没有 RPC map 行、信封 schema 或客户端 `IApiClient` 面。
-- fixture 模式（无宿主）对导出应答 404，按钮的错误条会解释这个缺口而非挂起；navigation-panes golden 快照包含「导出」按钮。
+- 导出保真度：读取每个实时根会话或后代前，导出器会通过权威的 `SessionStore.flush` 持久性屏障；每个导出文件都与由此得到的持久化工件逐字节一致。实时会话可能在自身读取后再次追加，因此归档是按会话读取边界形成的快照，而不是整棵树的原子快照。压缩包名为 `dsh-session-<sanitized-id>.zip`，归档路径在塑造条目前会先净化会话 id。
+- `supportsRawArtifacts` 明确区分后端能力与会话缺失：SQLite 等不支持的后端报告 `false`，具体 `readRaw` 默认会拒绝；JSONL 覆写则报告 `true`、自持物理解码，并只用 `undefined` 表示工件缺失。`ApiProxy.downloads.sessionLog` 为契约新增一个 host-only 成员，外加宿主侧 query schema，并在 fetch handler 加一个 GET 分支——没有 RPC map 行、信封 schema 或客户端 `IApiClient` 面。
+- fixture 模式（无宿主）对导出应答 404，浏览器会将其报告为下载失败；navigation-panes golden 快照包含「导出」按钮。
 - 暂缓：transcript.md 以及 report/feedback 打包留待后续；逐字节忠实、无清单的形态让 v2 的打包扩展保持廉价。
diff --git a/docs/config-catalog.i18n.yaml b/docs/config-catalog.i18n.yaml
index 82ce668a90..d6d5779a66 100644
--- a/docs/config-catalog.i18n.yaml
+++ b/docs/config-catalog.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write docs/config-catalog.md
-config-catalog.md: 2ddfdd167d28cf818559f2a1ec1fc1d9b50fb434
-config-catalog.zh.md: be6b5e5ac35fb18333f7cbbf8b6d9413e4c9a330
+config-catalog.md: 6dc37b56d67ebc82005262614436308fd2fdf539
+config-catalog.zh.md: 7a93954432e3ce6602eac623d051cea567e79c1a
diff --git a/docs/config-catalog.md b/docs/config-catalog.md
index 2ddfdd167d..6dc37b56d6 100644
--- a/docs/config-catalog.md
+++ b/docs/config-catalog.md
@@ -647,7 +647,7 @@ Source: [`packages/hooks/hooks-codex/src/index.ts:44`](../packages/hooks/hooks-c
 Requires: `agentDefaultModel` · `agents` · `attachments` · `directoryPicker` · `llm` · `sessions` · `subagents` · `sessionQuery` · `tools` · `userInteraction` · `workspace`
 
 ```ts config-catalog
-/** Gateway plugin config for native Host integration. */
+/** Gateway plugin configuration. */
 export interface Config {
   /**
    * Whether this deployment can hand paths to a native desktop opener —
@@ -657,10 +657,16 @@ export interface Config {
    * container whose DISPLAY points nowhere a user can see.
    */
   nativeOpen?: boolean
+  /**
+   * DEFLATE level for every session-log ZIP entry: `0` stores without
+   * compression, `1` favors CPU/latency, and `9` favors archive size.
+   * @default 6
+   */
+  sessionExportCompressionLevel?: 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
 }
 ```
 
-Source: [`packages/host/apiproxy/src/index.ts:37`](../packages/host/apiproxy/src/index.ts)
+Source: [`packages/host/apiproxy/src/index.ts:41`](../packages/host/apiproxy/src/index.ts)
 
 ## `@deepseek-ai/dsh-host-directory-picker-browse`
 
diff --git a/docs/config-catalog.zh.md b/docs/config-catalog.zh.md
index be6b5e5ac3..7a93954432 100644
--- a/docs/config-catalog.zh.md
+++ b/docs/config-catalog.zh.md
@@ -649,7 +649,7 @@ export interface Config {
 需要：`agentDefaultModel` · `agents` · `attachments` · `directoryPicker` · `llm` · `sessions` · `subagents` · `sessionQuery` · `tools` · `userInteraction` · `workspace`
 
 ```ts config-catalog
-/** Gateway plugin config for native Host integration. */
+/** Gateway plugin configuration. */
 export interface Config {
   /**
    * Whether this deployment can hand paths to a native desktop opener —
@@ -659,10 +659,16 @@ export interface Config {
    * container whose DISPLAY points nowhere a user can see.
    */
   nativeOpen?: boolean
+  /**
+   * DEFLATE level for every session-log ZIP entry: `0` stores without
+   * compression, `1` favors CPU/latency, and `9` favors archive size.
+   * @default 6
+   */
+  sessionExportCompressionLevel?: 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
 }
 ```
 
-来源：[`packages/host/apiproxy/src/index.ts:37`](../packages/host/apiproxy/src/index.ts)
+来源：[`packages/host/apiproxy/src/index.ts:41`](../packages/host/apiproxy/src/index.ts)
 
 ## `@deepseek-ai/dsh-host-directory-picker-browse`
 
diff --git a/docs/subsystems/attachment.i18n.yaml b/docs/subsystems/attachment.i18n.yaml
index d53f337679..330f2db253 100644
--- a/docs/subsystems/attachment.i18n.yaml
+++ b/docs/subsystems/attachment.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write docs/subsystems/attachment.md
-attachment.md: bfc1a54107c75b442f6b5b61fb705852ab4213db
-attachment.zh.md: 4da600390ea111e9b2f640c51ab786ca0505db6e
+attachment.md: ff7f14ceae8d4f8055d5cfd4367373729dc5ecbc
+attachment.zh.md: d7a9527788588d5504fdeffd8ae7849b0f8b1378
diff --git a/docs/subsystems/attachment.md b/docs/subsystems/attachment.md
index bfc1a54107..ff7f14ceae 100644
--- a/docs/subsystems/attachment.md
+++ b/docs/subsystems/attachment.md
@@ -104,9 +104,11 @@ abstract saveImage(input: SaveImageAttachment): Promise<ImageAttachmentRef>
 /**
  * Read one image and verify that bytes still match the recorded reference.
  * @param ref - durable reference from the session log.
+ * @param signal - optional cancellation for backend read and verification work.
  * @returns the verified bytes and canonical reference.
+ * @throws the signal reason when aborted, or a storage error when verification fails.
  */
-abstract readImage(ref: ImageAttachmentRef): Promise<StoredImageAttachment>
+abstract readImage(ref: ImageAttachmentRef, signal?: AbortSignal): Promise<StoredImageAttachment>
 ```
 
 Source: [`packages/attachment/attachment/src/index.ts:29`](../../packages/attachment/attachment/src/index.ts)
diff --git a/docs/subsystems/attachment.zh.md b/docs/subsystems/attachment.zh.md
index 4da600390e..d7a9527788 100644
--- a/docs/subsystems/attachment.zh.md
+++ b/docs/subsystems/attachment.zh.md
@@ -104,9 +104,11 @@ abstract saveImage(input: SaveImageAttachment): Promise<ImageAttachmentRef>
 /**
  * Read one image and verify that bytes still match the recorded reference.
  * @param ref - durable reference from the session log.
+ * @param signal - optional cancellation for backend read and verification work.
  * @returns the verified bytes and canonical reference.
+ * @throws the signal reason when aborted, or a storage error when verification fails.
  */
-abstract readImage(ref: ImageAttachmentRef): Promise<StoredImageAttachment>
+abstract readImage(ref: ImageAttachmentRef, signal?: AbortSignal): Promise<StoredImageAttachment>
 ```
 
 Source: [`packages/attachment/attachment/src/index.ts:29`](../../packages/attachment/attachment/src/index.ts)
diff --git a/docs/subsystems/persistence.i18n.yaml b/docs/subsystems/persistence.i18n.yaml
index 888c2666ba..03460eae89 100644
--- a/docs/subsystems/persistence.i18n.yaml
+++ b/docs/subsystems/persistence.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write docs/subsystems/persistence.md
-persistence.md: 792d50c52ecb2255dee429098d2ef00744479292
-persistence.zh.md: 6e1f29ee6dfc12193e7e5e4e79b4bfc5f751410f
+persistence.md: fde8348d64a200eda5133abf66deedee6be09857
+persistence.zh.md: 7a334501ee7fcbefda9d1381dfe41a79679d33b3
diff --git a/docs/subsystems/persistence.md b/docs/subsystems/persistence.md
index 792d50c52e..fde8348d64 100644
--- a/docs/subsystems/persistence.md
+++ b/docs/subsystems/persistence.md
@@ -124,7 +124,7 @@ Replay/fork is therefore `ctx.sessions.create(id, { seed: seedEvents })`; resumi
 
 ## `SessionRawArtifact` — verbatim stored artifact text
 
-A backend's own artifact text for one session, byte-identical to what it durably wrote (decoded from its physical encoding). `readRaw` returns it without reconstructing from parsed events, so backend-specific serialization (chunk packing, key order, line breaks) survives; backends without a per-session artifact, such as SQLite, inherit the `undefined` default.
+A backend's own artifact text for one session, byte-identical to what it durably wrote (decoded from its physical encoding). `readRaw` returns it without reconstructing from parsed events, so backend-specific serialization (chunk packing, key order, line breaks) survives. Consumers first test `supportsRawArtifacts`: `false` means the backend does not provide this capability (for example SQLite), while `readRaw(...) === undefined` means a supported backend has no materialized artifact for that session.
 
 ```ts type-equiv
 /** A backend's own raw artifact text for one session, verbatim. */
@@ -262,13 +262,15 @@ abstract locate(meta: SessionHeader): SessionLocation | undefined
  * bytes the backend wrote (decoded from its physical encoding, e.g. a
  * decompressed JSONL). The returned `content` is the raw text, not a
  * reconstruction from parsed events, so it preserves backend-specific
- * serialization (chunk packing, key order, line breaks). Backends without a
- * per-session artifact (SQLite) inherit the `undefined` default.
+ * serialization (chunk packing, key order, line breaks). Callers first test
+ * {@link supportsRawArtifacts}; `undefined` then means only that the requested
+ * session has no materialized artifact.
  * @param _id - the persisted session to read (unused by the default: no
  * per-session artifact).
  * @param signal - optional cancellation for backend read work.
  * @returns the raw artifact plus its parsed header, or `undefined` when the
- * session is absent or the backend owns no per-session artifact.
+ * session is absent.
+ * @throws when this backend does not expose per-session raw artifacts.
  */
 readRaw(_id: SessionId, signal?: AbortSignal): Promise<SessionRawArtifact | undefined>
 
diff --git a/docs/subsystems/persistence.zh.md b/docs/subsystems/persistence.zh.md
index 6e1f29ee6d..7a334501ee 100644
--- a/docs/subsystems/persistence.zh.md
+++ b/docs/subsystems/persistence.zh.md
@@ -124,7 +124,7 @@ interface CreateSessionOptions {
 
 ## `SessionRawArtifact`——逐字存储工件文本
 
-后端为单个会话自持的工件文本，与其持久化写入的字节逐字一致（按物理编码解码）。`readRaw` 返回它而不从解析后事件重建，因此后端特定的序列化（chunk 打包、键序、换行）得以保留；没有每会话工件的后端（如 SQLite）继承 `undefined` 默认。
+后端为单个会话自持的工件文本，与其持久化写入的字节逐字一致（按物理编码解码）。`readRaw` 返回它而不从解析后事件重建，因此后端特定的序列化（chunk 打包、键序、换行）得以保留。Consumer 须先检查 `supportsRawArtifacts`：`false` 表示后端不提供此能力（如 SQLite），而 `readRaw(...) === undefined` 表示受支持的后端没有该会话的已实体化工件。
 
 ```ts type-equiv
 /** A backend's own raw artifact text for one session, verbatim. */
@@ -262,13 +262,15 @@ abstract locate(meta: SessionHeader): SessionLocation | undefined
  * bytes the backend wrote (decoded from its physical encoding, e.g. a
  * decompressed JSONL). The returned `content` is the raw text, not a
  * reconstruction from parsed events, so it preserves backend-specific
- * serialization (chunk packing, key order, line breaks). Backends without a
- * per-session artifact (SQLite) inherit the `undefined` default.
+ * serialization (chunk packing, key order, line breaks). Callers first test
+ * {@link supportsRawArtifacts}; `undefined` then means only that the requested
+ * session has no materialized artifact.
  * @param _id - the persisted session to read (unused by the default: no
  * per-session artifact).
  * @param signal - optional cancellation for backend read work.
  * @returns the raw artifact plus its parsed header, or `undefined` when the
- * session is absent or the backend owns no per-session artifact.
+ * session is absent.
+ * @throws when this backend does not expose per-session raw artifacts.
  */
 readRaw(_id: SessionId, signal?: AbortSignal): Promise<SessionRawArtifact | undefined>
 
diff --git a/packages/attachment/attachment-local/README.i18n.yaml b/packages/attachment/attachment-local/README.i18n.yaml
index daa65c2d38..d875ce6519 100644
--- a/packages/attachment/attachment-local/README.i18n.yaml
+++ b/packages/attachment/attachment-local/README.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/attachment/attachment-local/README.md
-README.md: 80001b29b392fe1c8b663f46d47f1ec0726e6d0f
-README.zh.md: c3b95ace06b9f5ada156f20f33a1740a235400aa
+README.md: ba0b9efb2cf51bfef671020bed4a2c16f6ee0119
+README.zh.md: 8e2474357a0dbb5e8834a3b25de7a977827a29e3
diff --git a/packages/attachment/attachment-local/README.md b/packages/attachment/attachment-local/README.md
index 80001b29b3..ba0b9efb2c 100644
--- a/packages/attachment/attachment-local/README.md
+++ b/packages/attachment/attachment-local/README.md
@@ -4,7 +4,7 @@ English | [中文](README.zh.md)
 
 The private local implementation of [`@deepseek-ai/dsh-attachment`](../attachment). Objects land at `<DSH_HOME>/attachments/v1/objects/<sha256-prefix>/<sha256>` and are addressed by an opaque `sha256:` id. Each process proves a home durable once by syncing every ancestor entry to the filesystem root, so a directory another process created but has not yet synced is never mistaken for a safe boundary. Writes then use a private staging directory, owner-only files, a synced temporary file, an atomic exclusive hard-link publish, and directory syncs on the publication path (POSIX; Windows relies on filesystem metadata journaling) so the reported reference survives a crash. Write admission and reads fully decode the raster before accepting its format and dimensions; reads also re-check the digest and logged metadata. Byte and pixel limits are write-time admission policy, so a later policy reduction does not make already-admitted history unreadable.
 
-`DSH_HOME` resolves through the shared path policy: explicit config, `$DSH_HOME`, then `~/.dsh`. Session logs contain only the reference and verified metadata, never this host path.
+`DSH_HOME` resolves through the shared path policy: explicit config, `$DSH_HOME`, then `~/.dsh`. Session logs contain only the reference and verified metadata, never this host path. `readImage` forwards optional cancellation into the filesystem read, observes it around verification, and preserves it instead of wrapping it as `ATTACHMENT_READ_FAILED`.
 
 ## Model Experience
 
diff --git a/packages/attachment/attachment-local/README.zh.md b/packages/attachment/attachment-local/README.zh.md
index c3b95ace06..8e2474357a 100644
--- a/packages/attachment/attachment-local/README.zh.md
+++ b/packages/attachment/attachment-local/README.zh.md
@@ -4,7 +4,7 @@
 
 这是 [`@deepseek-ai/dsh-attachment`](../attachment) 的私有本地实现。对象存放在 `<DSH_HOME>/attachments/v1/objects/<sha256-prefix>/<sha256>`，并通过不透明的 `sha256:` 标识符寻址。每个进程都会通过将每个祖先目录项逐级同步到文件系统根目录，为某个 home 一次性证明其持久性，因此绝不会把另一个进程已经创建但尚未同步的目录误认为安全边界。随后，写入过程使用私有暂存目录、仅所有者可访问的文件、经过同步的临时文件、原子且排他的硬链接发布，并对发布路径执行目录同步（适用于 POSIX；Windows 依赖文件系统元数据日志），确保已报告的引用能够在崩溃后继续存在。写入准入与读取都会完整解码光栅图片，之后才接受其格式和尺寸；读取还会重新校验摘要和已记录的元数据。字节和像素限制属于写入时的准入策略，因此后续收紧限制不会导致已经接纳的历史记录变得不可读。
 
-`DSH_HOME` 按共享路径策略解析：显式配置、`$DSH_HOME`，最后是 `~/.dsh`。会话日志只包含引用和经过校验的元数据，绝不包含这个宿主路径。
+`DSH_HOME` 按共享路径策略解析：显式配置、`$DSH_HOME`，最后是 `~/.dsh`。会话日志只包含引用和经过校验的元数据，绝不包含这个宿主路径。`readImage` 会把可选取消信号传入文件系统读取、在校验前后观察该信号，并保留取消语义，而不会将其包装成 `ATTACHMENT_READ_FAILED`。
 
 ## 模型体验
 
diff --git a/packages/attachment/attachment-local/src/index.ts b/packages/attachment/attachment-local/src/index.ts
index 3d67041ea4..ceb46f415d 100644
--- a/packages/attachment/attachment-local/src/index.ts
+++ b/packages/attachment/attachment-local/src/index.ts
@@ -68,8 +68,8 @@ export class LocalAttachmentStore extends AttachmentStore {
     return saveImageFile(this.root, input, this.imageLimits)
   }
 
-  async readImage(ref: ImageAttachmentRef): Promise<StoredImageAttachment> {
-    return readImageFile(this.root, ref)
+  async readImage(ref: ImageAttachmentRef, signal?: AbortSignal): Promise<StoredImageAttachment> {
+    return readImageFile(this.root, ref, signal)
   }
 }
 
diff --git a/packages/attachment/attachment-local/src/store.ts b/packages/attachment/attachment-local/src/store.ts
index d77f2be375..8e4e83c1c9 100644
--- a/packages/attachment/attachment-local/src/store.ts
+++ b/packages/attachment/attachment-local/src/store.ts
@@ -197,22 +197,32 @@ export async function saveImageFile(root: string, input: SaveImageAttachment, li
  * Read and verify one content-addressed image.
  * @param root - absolute `DSH_HOME/attachments/v1` root.
  * @param ref - reference recorded in the session log.
+ * @param signal - optional cancellation for filesystem and verification work.
  * @returns verified bytes and reference.
+ * @throws the signal reason when aborted, or an AttachmentError when verification fails.
  */
-export async function readImageFile(root: string, ref: ImageAttachmentRef): Promise<StoredImageAttachment> {
+export async function readImageFile(
+  root: string,
+  ref: ImageAttachmentRef,
+  signal?: AbortSignal,
+): Promise<StoredImageAttachment> {
+  signal?.throwIfAborted()
   const sha256 = ensureReference(ref)
   let data: Uint8Array
   try {
-    data = new Uint8Array(await readFile(objectPath(root, sha256)))
+    data = new Uint8Array(await readFile(objectPath(root, sha256), { signal }))
   } catch (error) {
+    signal?.throwIfAborted()
     if (error instanceof Error && 'code' in error && error.code === 'ENOENT') throw new AttachmentError('Attachment object is missing.', 'ATTACHMENT_NOT_FOUND')
     throw new AttachmentError('Unable to read image attachment.', 'ATTACHMENT_READ_FAILED', { cause: error })
   }
+  signal?.throwIfAborted()
   if (digest(data) !== sha256) throw new AttachmentError('Stored attachment failed integrity verification.', 'ATTACHMENT_CORRUPT')
   // The digest proves these are the exact bytes admission fully decoded, so
   // the read path only re-derives the header fields (no raster decode, no
   // per-request pixel amplification on history replay).
   const metadata = await probeImage(data)
+  signal?.throwIfAborted()
   if (metadata.mediaType !== ref.mediaType || data.byteLength !== ref.bytes
     || metadata.width !== ref.width || metadata.height !== ref.height) {
     throw new AttachmentError('Stored attachment metadata does not match its reference.', 'ATTACHMENT_CORRUPT')
diff --git a/packages/attachment/attachment-local/tests/store.spec.ts b/packages/attachment/attachment-local/tests/store.spec.ts
index bd2adb4c55..ec3551abb2 100644
--- a/packages/attachment/attachment-local/tests/store.spec.ts
+++ b/packages/attachment/attachment-local/tests/store.spec.ts
@@ -9,12 +9,23 @@ import sharp from 'sharp'
 import type { ImageAttachmentLimits } from '@deepseek-ai/dsh-attachment'
 import { readImageFile, saveImageFile } from '../src/store.ts'
 
-const fsControl = vi.hoisted(() => ({ syncedDirectories: [] as string[] }))
+const fsControl = vi.hoisted(() => ({
+  readSignals: [] as AbortSignal[],
+  syncedDirectories: [] as string[],
+}))
 
 vi.mock('node:fs/promises', async (importOriginal) => {
   const actual = await importOriginal<typeof import('node:fs/promises')>()
   return {
     ...actual,
+    readFile(...args: Parameters<typeof actual.readFile>): ReturnType<typeof actual.readFile> {
+      const options = args[1]
+      if (typeof options === 'object' && options !== null) {
+        const signal = (options as { signal?: AbortSignal }).signal
+        if (signal !== undefined) fsControl.readSignals.push(signal)
+      }
+      return actual.readFile(...args)
+    },
     async open(...args: Parameters<typeof actual.open>): ReturnType<typeof actual.open> {
       if (args[1] === constants.O_RDONLY) fsControl.syncedDirectories.push(String(args[0]))
       return actual.open(...args)
@@ -130,6 +141,20 @@ describe('local attachment store', () => {
     await expect(readImageFile(storageRoot, ref)).resolves.toEqual({ ref, data: PNG })
   })
 
+  it('forwards read cancellation to the filesystem and preserves its reason', async () => {
+    const storageRoot = await root()
+    const ref = await saveImageFile(storageRoot, { data: PNG, mediaType: 'image/png' }, LIMITS)
+    const controller = new AbortController()
+    fsControl.readSignals.length = 0
+
+    await expect(readImageFile(storageRoot, ref, controller.signal)).resolves.toEqual({ ref, data: PNG })
+    expect(fsControl.readSignals).toEqual([controller.signal])
+
+    const cancellation = new Error('attachment read cancelled')
+    controller.abort(cancellation)
+    await expect(readImageFile(storageRoot, ref, controller.signal)).rejects.toBe(cancellation)
+  })
+
   it('rejects malformed bytes, mismatched declarations, byte limits, and decoded-pixel limits', async () => {
     const storageRoot = await root()
     await expect(saveImageFile(storageRoot, {
diff --git a/packages/attachment/attachment/README.i18n.yaml b/packages/attachment/attachment/README.i18n.yaml
index c75c93eb1a..bebd5ee4e7 100644
--- a/packages/attachment/attachment/README.i18n.yaml
+++ b/packages/attachment/attachment/README.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/attachment/attachment/README.md
-README.md: 4f450316294e554396adb9a8454051a08d9befd3
-README.zh.md: fe51b0003cdf1659c7c56106b97c6f3139ebe890
+README.md: baeeca0cf939f1a3d4608769b362d532507b90f5
+README.zh.md: 238b90794c510e71fffe34d62b044a5c2ece8a6e
diff --git a/packages/attachment/attachment/README.md b/packages/attachment/attachment/README.md
index 4f45031629..baeeca0cf9 100644
--- a/packages/attachment/attachment/README.md
+++ b/packages/attachment/attachment/README.md
@@ -4,7 +4,7 @@ English | [中文](README.zh.md)
 
 The durable attachment seam. `ctx.attachments` validates and atomically commits immutable image bytes, then returns a serializable `ImageAttachmentRef`; consumers never persist browser paths, object URLs, provider URLs, or base64 in session events.
 
-Unsent composer images remain browser-owned temporary drafts. `validateImage` runs the same admission policy without persisting; batch writers validate every member first so a malformed member cannot strand earlier members as unreferenced objects. `saveImage` commits each accepted image before any model-visible session event is published, and `readImage` verifies the content-addressed object against its logged metadata.
+Unsent composer images remain browser-owned temporary drafts. `validateImage` runs the same admission policy without persisting; batch writers validate every member first so a malformed member cannot strand earlier members as unreferenced objects. `saveImage` commits each accepted image before any model-visible session event is published, and `readImage` verifies the content-addressed object against its logged metadata. Callers may cancel `readImage`; implementations observe cancellation around backend and verification work and preserve it instead of translating it into a storage failure.
 
 ## Model Experience
 
diff --git a/packages/attachment/attachment/README.zh.md b/packages/attachment/attachment/README.zh.md
index fe51b0003c..238b90794c 100644
--- a/packages/attachment/attachment/README.zh.md
+++ b/packages/attachment/attachment/README.zh.md
@@ -4,7 +4,7 @@
 
 持久附件服务边界。`ctx.attachments` 校验并以原子方式提交不可变图片字节，随后返回可序列化的 `ImageAttachmentRef`；消费方绝不会在会话事件中持久保存浏览器路径、对象 URL、提供方 URL 或 base64。
 
-未发送的输入区图片仍是由浏览器持有的临时草稿。`validateImage` 运行相同的准入策略，但不执行持久化；批量写入方会先校验每个成员，避免某个格式错误的成员使较早的成员成为无引用对象。`saveImage` 会在发布任何模型可见的会话事件前提交每张已接受的图片，`readImage` 则根据已记录的元数据校验内容寻址对象。
+未发送的输入区图片仍是由浏览器持有的临时草稿。`validateImage` 运行相同的准入策略，但不执行持久化；批量写入方会先校验每个成员，避免某个格式错误的成员使较早的成员成为无引用对象。`saveImage` 会在发布任何模型可见的会话事件前提交每张已接受的图片，`readImage` 则根据已记录的元数据校验内容寻址对象。调用方可以取消 `readImage`；实现会在后端读取与校验工作的边界观察取消，并保留取消语义，而不会将其转换为存储失败。
 
 ## 模型体验
 
diff --git a/packages/attachment/attachment/src/index.ts b/packages/attachment/attachment/src/index.ts
index d2dc2dbd86..1bfb1ea119 100644
--- a/packages/attachment/attachment/src/index.ts
+++ b/packages/attachment/attachment/src/index.ts
@@ -52,9 +52,11 @@ export abstract class AttachmentStore extends Service {
   /**
    * Read one image and verify that bytes still match the recorded reference.
    * @param ref - durable reference from the session log.
+   * @param signal - optional cancellation for backend read and verification work.
    * @returns the verified bytes and canonical reference.
+   * @throws the signal reason when aborted, or a storage error when verification fails.
    */
-  abstract readImage(ref: ImageAttachmentRef): Promise<StoredImageAttachment>
+  abstract readImage(ref: ImageAttachmentRef, signal?: AbortSignal): Promise<StoredImageAttachment>
 }
 
 export default AttachmentStore
diff --git a/packages/client/connection/src/client/fixture.ts b/packages/client/connection/src/client/fixture.ts
index 05706a3788..a26db9c473 100644
--- a/packages/client/connection/src/client/fixture.ts
+++ b/packages/client/connection/src/client/fixture.ts
@@ -2835,8 +2835,8 @@ function createFixtureWorld(options: FixtureOptions): FixtureWorld {
       return Promise.resolve({ accepted: true })
     },
     // Satisfies the ApiProxy contract type only: the browser export button
-    // fetches GET /api/session.export directly (window.fetch), so this stub is
-    // never reached through the fixture's dispatch.
+    // hands GET /api/session.export to the native download manager, so this
+    // stub is never reached through the fixture's dispatch.
     downloads: {
       sessionLog: () => Promise.resolve(new Response('fixture mode does not serve session export', { status: 404 })),
     },
diff --git a/packages/client/ui-trajectory/README.i18n.yaml b/packages/client/ui-trajectory/README.i18n.yaml
index baba46ae81..cad6321870 100644
--- a/packages/client/ui-trajectory/README.i18n.yaml
+++ b/packages/client/ui-trajectory/README.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/client/ui-trajectory/README.md
-README.md: e82b2cc9d4a65c3095aeee7002fb6c43a43b695d
-README.zh.md: a1ba62393c2aae3f6baa7c481dd80f04dbbb477d
+README.md: f4b3bd223c2872f0341d49bdaa102440d73b4f29
+README.zh.md: 9bcb3b6ad98d672cc524c168f2024be9ba56b577
diff --git a/packages/client/ui-trajectory/README.md b/packages/client/ui-trajectory/README.md
index e82b2cc9d4..f4b3bd223c 100644
--- a/packages/client/ui-trajectory/README.md
+++ b/packages/client/ui-trajectory/README.md
@@ -2,7 +2,7 @@
 
 English | [中文](README.zh.md)
 
-Trajectory renders a turn-aware event ledger with selectable User, Assistant, Tool, and nested Subtool records. Thick rules mark Turn boundaries, compact inline markers identify Steps, and the main ledger keeps only index, event, and content; selection opens a local inspector for token usage, duration, Input, Output, and Timing. Scrollable Summary regions keep their scrollbar thumbs transparent until the region is hovered or contains keyboard focus, without changing the reserved scroll geometry. A standalone compaction request appears chronologically in its own `Between turns` section, while a numbered compaction remains inside its owning turn. Long ledgers open at the current tail, load one older page when the user reaches the loaded range's top, and mount only the visible row window plus a small overscan; request-only separators share the next measurable virtual item, while semantic row keys and ARIA indexes survive prepends. Selection, timeline navigation, folding, search, and Request totals cover the currently loaded window. The ledger covers records with an explicit loading row until the initial tail is positioned and while an older page is pending. A fixed Overview above the ledger projects real record start/duration timing from left to right; when earlier records remain unloaded and the viewport includes the loaded domain's start, a neutral ellipsis control identifies the omitted prefix and loads one earlier page without assigning unknown history fabricated duration. Assistant spans divide recorded TTFT from decoding, and a 500 ms hover reveals exact clock and duration details. Dragging an interval focuses the ledger on every record active at any point in that inclusive range, while clearing the selection restores the full loaded ledger. Wheel gestures zoom the time domain. A right-button click clears the selected interval, while a right-button drag pans an already zoomed viewport without changing it. The initial view and streaming updates stay at the tail; scrolling upward suspends following so new records do not interrupt inspection of earlier rows. Content-only stream frames preserve virtual row keys and heights, reuse measurements, and do not issue repeated tail-scroll writes. The toolbar's Export button downloads the session log — the root plus every subagent descendant — as a ZIP streamed by the host (`GET /api/session.export`): every file is the session's stored artifact text verbatim (`session.jsonl` at the root, `subagents/<id>/session.jsonl` for descendants; no manifest, byte-identical to the backend's durable artifact), and every image any included log references sits under `media/<attachmentId>.<ext>`. Fixture mode (no host) answers 404 for the export. Completed replies retain assembled blocks, timing, and usage in Trajectory target State, while the shared Session window keeps the raw Events. Trajectory asks the conversation shell to float the composer over the full-height ledger, while its responsive vertical scrollers reserve the composer's live height so final rows remain reachable. Trajectory-owned Definitions assemble business records, including cancellation-frozen Assistant and Tool records, from the shared Session window, so Trajectory neither reads nor changes the Chat conversation snapshot. The package provides no service and declares no Context merge; it registers target-specific Event Definitions, a Trajectory view builder, and one tab in the conversation's `'conversation.view'` slot ring. Contract: api-contracts v3 §8.
+Trajectory renders a turn-aware event ledger with selectable User, Assistant, Tool, and nested Subtool records. Thick rules mark Turn boundaries, compact inline markers identify Steps, and the main ledger keeps only index, event, and content; selection opens a local inspector for token usage, duration, Input, Output, and Timing. Scrollable Summary regions keep their scrollbar thumbs transparent until the region is hovered or contains keyboard focus, without changing the reserved scroll geometry. A standalone compaction request appears chronologically in its own `Between turns` section, while a numbered compaction remains inside its owning turn. Long ledgers open at the current tail, load one older page when the user reaches the loaded range's top, and mount only the visible row window plus a small overscan; request-only separators share the next measurable virtual item, while semantic row keys and ARIA indexes survive prepends. Selection, timeline navigation, folding, search, and Request totals cover the currently loaded window. The ledger covers records with an explicit loading row until the initial tail is positioned and while an older page is pending. A fixed Overview above the ledger projects real record start/duration timing from left to right; when earlier records remain unloaded and the viewport includes the loaded domain's start, a neutral ellipsis control identifies the omitted prefix and loads one earlier page without assigning unknown history fabricated duration. Assistant spans divide recorded TTFT from decoding, and a 500 ms hover reveals exact clock and duration details. Dragging an interval focuses the ledger on every record active at any point in that inclusive range, while clearing the selection restores the full loaded ledger. Wheel gestures zoom the time domain. A right-button click clears the selected interval, while a right-button drag pans an already zoomed viewport without changing it. The initial view and streaming updates stay at the tail; scrolling upward suspends following so new records do not interrupt inspection of earlier rows. Content-only stream frames preserve virtual row keys and heights, reuse measurements, and do not issue repeated tail-scroll writes. The toolbar's Export button hands the session log — the root plus every subagent descendant — directly to the browser download manager as a ZIP streamed by the host (`GET /api/session.export`), so JavaScript never buffers the response: every file is the session's stored artifact text verbatim (`session.jsonl` at the root, `subagents/<id>/session.jsonl` for descendants; no manifest, byte-identical to the backend's durable artifact), and every image any included log references sits under `media/<attachmentId>.<ext>`. Fixture mode (no host) answers 404 for the export. Completed replies retain assembled blocks, timing, and usage in Trajectory target State, while the shared Session window keeps the raw Events. Trajectory asks the conversation shell to float the composer over the full-height ledger, while its responsive vertical scrollers reserve the composer's live height so final rows remain reachable. Trajectory-owned Definitions assemble business records, including cancellation-frozen Assistant and Tool records, from the shared Session window, so Trajectory neither reads nor changes the Chat conversation snapshot. The package provides no service and declares no Context merge; it registers target-specific Event Definitions, a Trajectory view builder, and one tab in the conversation's `'conversation.view'` slot ring. Contract: api-contracts v3 §8.
 
 ## Model Experience
 
diff --git a/packages/client/ui-trajectory/README.zh.md b/packages/client/ui-trajectory/README.zh.md
index a1ba62393c..9bcb3b6ad9 100644
--- a/packages/client/ui-trajectory/README.zh.md
+++ b/packages/client/ui-trajectory/README.zh.md
@@ -2,7 +2,7 @@
 
 [English](README.md) | 中文
 
-Trajectory 渲染按轮次组织的事件记录表，其中可选择用户、助手、工具和嵌套子工具记录。较粗的分割线标示轮次边界，紧凑的行内标记标识步骤，主记录表仅保留索引、事件和内容；选择记录则会打开局部检查器，查看 token 用量、耗时、输入、输出和计时。可滚动的概述区域默认保持滚动条滑块透明，直到鼠标悬停该区域或其中包含键盘焦点时才显示，同时不改变滚动条预留的几何空间。独立运行的压缩（compaction）请求会按时间顺序显示在自己的 `Between turns` 区段中，而带编号的压缩仍位于其所属轮次内。长记录表打开时定位于当前尾部，用户到达已加载范围顶部时加载一页更早的历史，并且只挂载可见行窗口和少量额外缓冲行；仅含请求的分隔行并入下一个具备可测高度的虚拟项，语义行键和 ARIA 索引在向前补页后保持不变。选择、时间线导航、折叠、搜索和请求汇总只覆盖当前已加载的窗口。初始尾部完成定位前以及更早页面仍在等待时，记录表会用明确的加载行遮住真实记录。固定在记录表上方的 Overview 区域从左到右投影记录的真实开始时间与耗时；仍有更早记录未加载且 viewport 包含已加载时间域起点时，中性的省略号控件会标识被省略的前缀，并可加载一页更早历史，而不会为未知部分虚构耗时。助手时间条会区分记录到的 TTFT 与解码时间，悬停 500 ms 后可查看精确时刻和耗时详情。拖选一个区间会将记录表聚焦到活动区间与该闭区间有重叠的所有记录，清除选择则恢复完整的已加载记录表。滚轮手势用于缩放时间域。右键单击会清除所选区间；在已放大的 viewport 上按住右键拖动则只会平移视图，不会改变该区间。初始视图和流式更新都会停留在尾部；向上滚动会暂停跟随，因此新记录不会打断对旧记录的检查。仅含内容更新的流式帧会保持虚拟行的键和高度不变、复用测量结果，并且不会重复写入末尾滚动位置。工具栏的 “Export” 按钮会将会话日志——根会话及其全部子代理——下载为宿主流式返回的 ZIP（`GET /api/session.export`）：每个文件都是会话存储工件的逐字原文（根为 `session.jsonl`，子代理为 `subagents/<id>/session.jsonl`；无清单，与后端持久化工件逐字节一致），每个被包含日志引用的图片则放在 `media/<attachmentId>.<ext>` 下。fixture 模式（无宿主）对导出应答 404。已完成的回复会在 Trajectory target State 中保留组装后的 blocks、计时与用量，共享 Session 窗口则保留原始 Event。Trajectory 要求会话壳将 composer 作为浮层置于全高记录表上方；其响应式纵向滚动容器会预留 composer 的实时高度，确保仍可滚动到最后几行。Trajectory 自有的 Definition 从共享 Session 窗口组装业务记录，其中包括因取消而冻结的助手和工具记录，因此 Trajectory 既不读取也不改变 Chat 会话快照。该包不提供 service，也不声明 Context 合并；它会注册 target 专属 Event Definition、Trajectory view builder，以及会话 `'conversation.view'` slot 环中的一个视图标签页。约定：api-contracts v3 §8。
+Trajectory 渲染按轮次组织的事件记录表，其中可选择用户、助手、工具和嵌套子工具记录。较粗的分割线标示轮次边界，紧凑的行内标记标识步骤，主记录表仅保留索引、事件和内容；选择记录则会打开局部检查器，查看 token 用量、耗时、输入、输出和计时。可滚动的概述区域默认保持滚动条滑块透明，直到鼠标悬停该区域或其中包含键盘焦点时才显示，同时不改变滚动条预留的几何空间。独立运行的压缩（compaction）请求会按时间顺序显示在自己的 `Between turns` 区段中，而带编号的压缩仍位于其所属轮次内。长记录表打开时定位于当前尾部，用户到达已加载范围顶部时加载一页更早的历史，并且只挂载可见行窗口和少量额外缓冲行；仅含请求的分隔行并入下一个具备可测高度的虚拟项，语义行键和 ARIA 索引在向前补页后保持不变。选择、时间线导航、折叠、搜索和请求汇总只覆盖当前已加载的窗口。初始尾部完成定位前以及更早页面仍在等待时，记录表会用明确的加载行遮住真实记录。固定在记录表上方的 Overview 区域从左到右投影记录的真实开始时间与耗时；仍有更早记录未加载且 viewport 包含已加载时间域起点时，中性的省略号控件会标识被省略的前缀，并可加载一页更早历史，而不会为未知部分虚构耗时。助手时间条会区分记录到的 TTFT 与解码时间，悬停 500 ms 后可查看精确时刻和耗时详情。拖选一个区间会将记录表聚焦到活动区间与该闭区间有重叠的所有记录，清除选择则恢复完整的已加载记录表。滚轮手势用于缩放时间域。右键单击会清除所选区间；在已放大的 viewport 上按住右键拖动则只会平移视图，不会改变该区间。初始视图和流式更新都会停留在尾部；向上滚动会暂停跟随，因此新记录不会打断对旧记录的检查。仅含内容更新的流式帧会保持虚拟行的键和高度不变、复用测量结果，并且不会重复写入末尾滚动位置。工具栏的 “Export” 按钮会将会话日志——根会话及其全部子代理——作为宿主流式返回的 ZIP（`GET /api/session.export`）直接交给浏览器下载管理器，因此 JavaScript 不会缓冲响应：每个文件都是会话存储工件的逐字原文（根为 `session.jsonl`，子代理为 `subagents/<id>/session.jsonl`；无清单，与后端持久化工件逐字节一致），每个被包含日志引用的图片则放在 `media/<attachmentId>.<ext>` 下。fixture 模式（无宿主）对导出应答 404。已完成的回复会在 Trajectory target State 中保留组装后的 blocks、计时与用量，共享 Session 窗口则保留原始 Event。Trajectory 要求会话壳将 composer 作为浮层置于全高记录表上方；其响应式纵向滚动容器会预留 composer 的实时高度，确保仍可滚动到最后几行。Trajectory 自有的 Definition 从共享 Session 窗口组装业务记录，其中包括因取消而冻结的助手和工具记录，因此 Trajectory 既不读取也不改变 Chat 会话快照。该包不提供 service，也不声明 Context 合并；它会注册 target 专属 Event Definition、Trajectory view builder，以及会话 `'conversation.view'` slot 环中的一个视图标签页。约定：api-contracts v3 §8。
 
 ## 模型体验
 
diff --git a/packages/client/ui-trajectory/src/client/export-log.ts b/packages/client/ui-trajectory/src/client/export-log.ts
index 3a25794d4d..32a0aec0f1 100644
--- a/packages/client/ui-trajectory/src/client/export-log.ts
+++ b/packages/client/ui-trajectory/src/client/export-log.ts
@@ -1,7 +1,8 @@
 /**
- * Session log export: browser download of the host-streamed ZIP. The archive
- * itself is produced and streamed by the host (GET /api/session.export); this
- * module only derives the download filename and triggers the browser save.
+ * Session log export delivery. The host streams the archive from
+ * `GET /api/session.export`; this module owns the browser-native download
+ * handoff so the browser can stream the response directly to its download
+ * manager instead of buffering the ZIP in JavaScript.
  * @module
  */
 
@@ -27,16 +28,18 @@ export function sessionLogZipFilename(sessionId: string): string {
 }
 
 /**
- * Trigger a browser download of a blob response.
- * @param blob - the response body to save (passed straight through, no copy).
- * @param filename - the download filename.
+ * Hand one host-streamed session archive to the browser download manager.
+ * The operation resolves after dispatching the native download; HTTP delivery
+ * continues outside JavaScript and is reported by the browser itself.
+ * @param sessionId - the root session id to export with all descendants.
+ * @returns a promise that rejects if the browser handoff itself fails.
  */
-export function downloadBlob(blob: Blob, filename: string): void {
-  const url = URL.createObjectURL(blob)
-  const anchor = document.createElement('a')
-  anchor.href = url
-  anchor.download = filename
-  anchor.click()
-  // Revoke one tick later: some browsers read the blob URL after click().
-  setTimeout(() => { URL.revokeObjectURL(url) }, 0)
+export function downloadSessionLog(sessionId: string): Promise<void> {
+  return Promise.resolve().then(() => {
+    const query = new URLSearchParams({ sessionId, includeDescendants: 'true' })
+    const anchor = document.createElement('a')
+    anchor.href = `/api/session.export?${query.toString()}`
+    anchor.download = sessionLogZipFilename(sessionId)
+    anchor.click()
+  })
 }
diff --git a/packages/client/ui-trajectory/src/client/index.ts b/packages/client/ui-trajectory/src/client/index.ts
index 8337e060c9..c8325f6442 100644
--- a/packages/client/ui-trajectory/src/client/index.ts
+++ b/packages/client/ui-trajectory/src/client/index.ts
@@ -10,7 +10,7 @@ import type {} from '@deepseek-ai/dsh-client-locale/client'
 // owning package) must be in the program for the register calls to type.
 import type {} from '@deepseek-ai/dsh-client-ui-conversation/client'
 import { createTrajectoryDurationStore } from './duration-store.ts'
-import { downloadBlob, sessionLogZipFilename } from './export-log.ts'
+import { downloadSessionLog } from './export-log.ts'
 import { en, NS, zh } from './locales.ts'
 import { registerTrajectoryAssistantDefinition } from './trajectory-assistant-definition.ts'
 import { registerTrajectoryCompactionDefinitions } from './trajectory-compaction-definition.ts'
@@ -60,23 +60,7 @@ export function apply(ctx: Context): void {
           return session.getSnapshot().views.get('trajectory') !== before
         },
         setActualDuration: (value) => { duration.set(value) },
-        exportLog: async () => {
-          // The host streams the ZIP (root + descendant artifacts verbatim)
-          // from GET /api/session.export; the browser downloads the response.
-          // A null origin (no-location Node contexts) falls back like the
-          // carrier's resolveBase so the URL stays valid.
-          const loc = (globalThis as { location?: { origin?: string } }).location
-          const origin = loc?.origin !== undefined && loc.origin !== 'null' ? loc.origin : 'http://dsh.internal'
-          const url = new URL('/api/session.export', origin)
-          url.searchParams.set('sessionId', sessionId)
-          url.searchParams.set('includeDescendants', 'true')
-          const response = await fetch(url)
-          if (!response.ok) {
-            const detail = await response.text().catch(() => '')
-            throw new Error(`Export failed: HTTP ${response.status}${detail === '' ? '' : ` ${detail}`}`)
-          }
-          downloadBlob(await response.blob(), sessionLogZipFilename(sessionId))
-        },
+        exportLog: () => downloadSessionLog(sessionId),
       }
     },
   }, TrajectoryView))
diff --git a/packages/client/ui-trajectory/tests/export-log.spec.ts b/packages/client/ui-trajectory/tests/export-log.spec.ts
index ba7f739573..6ff7d1ddbf 100644
--- a/packages/client/ui-trajectory/tests/export-log.spec.ts
+++ b/packages/client/ui-trajectory/tests/export-log.spec.ts
@@ -1,12 +1,15 @@
-// @vitest-environment node
+// @vitest-environment jsdom
 /**
- * Session-log export filename derivation. The archive itself is produced and
- * streamed by the host (GET /api/session.export); this package only derives
- * the download filename and triggers the browser save.
+ * Session-log export browser delivery: safe filename derivation and a native
+ * download handoff that leaves the streamed response outside JavaScript.
  */
 
-import { describe, expect, it } from 'vitest'
-import { sessionLogZipFilename } from '../src/client/export-log.ts'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { downloadSessionLog, sessionLogZipFilename } from '../src/client/export-log.ts'
+
+afterEach(() => {
+  vi.restoreAllMocks()
+})
 
 describe('sessionLogZipFilename', () => {
   it('keeps safe session ids verbatim', () => {
@@ -22,3 +25,27 @@ describe('sessionLogZipFilename', () => {
     expect(sessionLogZipFilename('..')).toBe('dsh-session-__.zip')
   })
 })
+
+describe('downloadSessionLog', () => {
+  it('hands the descendant-inclusive endpoint directly to the browser', async () => {
+    const click = vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {})
+
+    await downloadSessionLog('session/with spaces')
+
+    expect(click).toHaveBeenCalledOnce()
+    const anchor = click.mock.contexts[0] as HTMLAnchorElement
+    const url = new URL(anchor.href)
+    expect(url.pathname).toBe('/api/session.export')
+    expect(url.searchParams.get('sessionId')).toBe('session/with spaces')
+    expect(url.searchParams.get('includeDescendants')).toBe('true')
+    expect(anchor.download).toBe('dsh-session-session_with_spaces.zip')
+  })
+
+  it('rejects when the browser download handoff fails', async () => {
+    vi.spyOn(HTMLAnchorElement.prototype, 'click').mockImplementation(() => {
+      throw new Error('download denied')
+    })
+
+    await expect(downloadSessionLog('session-root')).rejects.toThrow('download denied')
+  })
+})
diff --git a/packages/client/ui-trajectory/tests/views.spec.tsx b/packages/client/ui-trajectory/tests/views.spec.tsx
index d95d70168b..ceacfdaf09 100644
--- a/packages/client/ui-trajectory/tests/views.spec.tsx
+++ b/packages/client/ui-trajectory/tests/views.spec.tsx
@@ -1141,39 +1141,26 @@ describe('timeline projection', () => {
 describe('session log export', () => {
   afterEach(() => {
     vi.unstubAllGlobals()
-    Reflect.deleteProperty(URL, 'createObjectURL')
     Reflect.deleteProperty(HTMLAnchorElement.prototype, 'click')
   })
 
   it('downloads the host-streamed ZIP with descendants on click', async () => {
-    // exportLog always fetches a URL instance, so the mock's shape stays narrow.
-    const fetchMock = vi.fn(async (input: URL) => {
-      expect(input.pathname).toBe('/api/session.export')
-      expect(input.searchParams.get('sessionId')).toBe(SID)
-      expect(input.searchParams.get('includeDescendants')).toBe('true')
-      return new Response('zip-bytes')
-    })
-    vi.stubGlobal('fetch', fetchMock)
-    const createObjectURL = vi.fn(() => 'blob:export')
-    URL.createObjectURL = createObjectURL
     const clickAnchor = vi.fn()
     HTMLAnchorElement.prototype.click = clickAnchor
     const b = await bench(historySnapshot(NODES))
     mount(b.slots)
     fireEvent.click(screen.getByRole('tab', { name: 'Trajectory' }))
     fireEvent.click(screen.getByRole('button', { name: 'Export session log' }))
-    await vi.waitFor(() => {
-      expect(fetchMock).toHaveBeenCalledOnce()
-    })
-    // The blob download lands a few microtasks after the fetch settles.
-    await vi.waitFor(() => {
-      expect(createObjectURL).toHaveBeenCalled()
-    })
-    expect(clickAnchor).toHaveBeenCalled()
+    await vi.waitFor(() => { expect(clickAnchor).toHaveBeenCalledOnce() })
+    const anchor = clickAnchor.mock.contexts[0] as HTMLAnchorElement
+    const url = new URL(anchor.href)
+    expect(url.pathname).toBe('/api/session.export')
+    expect(url.searchParams.get('sessionId')).toBe(SID)
+    expect(url.searchParams.get('includeDescendants')).toBe('true')
   })
 
-  it('surfaces the download failure in the visible alert bar', async () => {
-    vi.stubGlobal('fetch', vi.fn(async () => new Response('boom', { status: 404 })))
+  it('surfaces a browser handoff failure in the visible alert bar', async () => {
+    HTMLAnchorElement.prototype.click = vi.fn(() => { throw new Error('download denied') })
     const b = await bench(historySnapshot(NODES))
     mount(b.slots)
     fireEvent.click(screen.getByRole('tab', { name: 'Trajectory' }))
@@ -1181,7 +1168,7 @@ describe('session log export', () => {
     await vi.waitFor(() => {
       const alert = screen.queryByRole('alert')
       expect(alert).not.toBeNull()
-      expect(alert!.textContent).toContain('HTTP 404')
+      expect(alert!.textContent).toContain('download denied')
     })
   })
 })
diff --git a/packages/feedback/message-feedback/tests/helpers.ts b/packages/feedback/message-feedback/tests/helpers.ts
index 1305387d68..f902ba38d7 100644
--- a/packages/feedback/message-feedback/tests/helpers.ts
+++ b/packages/feedback/message-feedback/tests/helpers.ts
@@ -109,6 +109,8 @@ export function messageFixture(
 
 /** Minimal controllable persistence provider for service-level tests. */
 class TestPersistence extends SessionPersistence {
+  override readonly supportsRawArtifacts = false
+
   static inject = ['sessions']
 
   readonly durable = new Map<SessionId, SessionInspection>()
diff --git a/packages/host/apiproxy/README.i18n.yaml b/packages/host/apiproxy/README.i18n.yaml
index 72568f241d..e020c6f93f 100644
--- a/packages/host/apiproxy/README.i18n.yaml
+++ b/packages/host/apiproxy/README.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/host/apiproxy/README.md
-README.md: 5fe19af8069766c56f8926ccef88dc1d9fb3c950
-README.zh.md: bdb26a63832c1461b4e56798e64c1253a916118d
+README.md: 2101c785a613477c04ecbfec6a39a0f403af40ef
+README.zh.md: 3ba37967ff88ca89911017945aeed857e4b4ff19
diff --git a/packages/host/apiproxy/README.md b/packages/host/apiproxy/README.md
index 5fe19af806..2101c785a6 100644
--- a/packages/host/apiproxy/README.md
+++ b/packages/host/apiproxy/README.md
@@ -2,7 +2,7 @@
 
 English | [中文](README.zh.md)
 
-The API gateway shared by every client consists of the TypeScript API contract (`src/api/`, zero Node dependencies, importable from the browser), the fetch carrier pair (`src/fetch/`: `toFetchHandler` on the host side, `AbstractApiClient` plus platform subclasses on the client side), and the host-side implementation (`src/api-proxy.ts`: `createApiProxy` plus the default-exported `ApiProxyService` gateway plugin — config `{nativeOpen?}`, provides `ctx.apiProxy`). This package registers no routes; carriers such as HTTP wrap `ctx.apiProxy` themselves. The shipped Web composition lives in [`packages/bundle/web-app/cordis.patch.yml`](../../bundle/web-app/cordis.patch.yml), while its default Agent model selection belongs to [`@deepseek-ai/dsh-agent-default-model`](../../core/agent-default-model/README.md) in the base bundle.
+The API gateway shared by every client consists of the TypeScript API contract (`src/api/`, zero Node dependencies, importable from the browser), the fetch carrier pair (`src/fetch/`: `toFetchHandler` on the host side, `AbstractApiClient` plus platform subclasses on the client side), and the host-side implementation (`src/api-proxy.ts`: `createApiProxy` plus the default-exported `ApiProxyService` gateway plugin — config `{nativeOpen?, sessionExportCompressionLevel?}`, provides `ctx.apiProxy`). This package registers no routes; carriers such as HTTP wrap `ctx.apiProxy` themselves. The shipped Web composition lives in [`packages/bundle/web-app/cordis.patch.yml`](../../bundle/web-app/cordis.patch.yml), while its default Agent model selection belongs to [`@deepseek-ai/dsh-agent-default-model`](../../core/agent-default-model/README.md) in the base bundle.
 
 ## The shared Agent default (`agent-default-model` Settings section)
 
@@ -28,7 +28,7 @@ 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-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). Each live root or descendant crosses the authoritative `SessionStore.flush` durability barrier immediately before its raw artifact read; cold sessions have no in-memory work to flush. Compression runs on the host with fflate's streaming Zip API at validated `sessionExportCompressionLevel` 0–9 (default 6), so deployments can trade CPU and latency against archive size; the response is chunked as it is produced and the host never holds the whole archive in one buffer. Once the response queue reaches its 64 KiB byte high-water mark, production waits until consumer pull restores positive capacity; fflate's synchronous callback can overshoot that bound only by the output of one bounded input push. Request abort and response-body cancellation stop lineage and artifact work, terminate the active compressor, and propagate as cancellation rather than an HTTP 500. It requires the persistence, session-query, and attachment services: a deployment without any answers 500, a persistence backend without per-session raw artifacts answers 501, a missing root session answers 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`.
 
diff --git a/packages/host/apiproxy/README.zh.md b/packages/host/apiproxy/README.zh.md
index bdb26a6383..3ba37967ff 100644
--- a/packages/host/apiproxy/README.zh.md
+++ b/packages/host/apiproxy/README.zh.md
@@ -2,7 +2,7 @@
 
 [English](README.md) | 中文
 
-所有客户端共用的 API 网关由三部分组成：TypeScript API 约定（`src/api/`，不依赖 Node，可从浏览器导入）、fetch 载体对（`src/fetch/`：宿主侧的 `toFetchHandler`，以及客户端侧的 `AbstractApiClient` 与平台子类）和宿主侧实现（`src/api-proxy.ts`：`createApiProxy` 加上默认导出的 `ApiProxyService` 网关插件，其配置为 `{nativeOpen?}`，提供 `ctx.apiProxy`）。该包不注册任何路由；HTTP 等载体自行包装 `ctx.apiProxy`。随发行版交付的 Web 组合位于 [`packages/bundle/web-app/cordis.patch.yml`](../../bundle/web-app/cordis.patch.yml)，其默认 Agent（智能体）模型选择属于 base 组合包中的 [`@deepseek-ai/dsh-agent-default-model`](../../core/agent-default-model/README.md)。
+所有客户端共用的 API 网关由三部分组成：TypeScript API 约定（`src/api/`，不依赖 Node，可从浏览器导入）、fetch 载体对（`src/fetch/`：宿主侧的 `toFetchHandler`，以及客户端侧的 `AbstractApiClient` 与平台子类）和宿主侧实现（`src/api-proxy.ts`：`createApiProxy` 加上默认导出的 `ApiProxyService` 网关插件，其配置为 `{nativeOpen?, sessionExportCompressionLevel?}`，提供 `ctx.apiProxy`）。该包不注册任何路由；HTTP 等载体自行包装 `ctx.apiProxy`。随发行版交付的 Web 组合位于 [`packages/bundle/web-app/cordis.patch.yml`](../../bundle/web-app/cordis.patch.yml)，其默认 Agent（智能体）模型选择属于 base 组合包中的 [`@deepseek-ai/dsh-agent-default-model`](../../core/agent-default-model/README.md)。
 
 ## 共享 Agent 默认值（`agent-default-model` Settings 分节）
 
@@ -28,7 +28,7 @@ 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）。每个实时根会话或后代都会在读取原始工件前立即通过权威的 `SessionStore.flush` 持久性屏障；冷会话没有需要 flush 的内存工作。压缩在宿主侧使用 fflate 流式 Zip API 和已验证的 `sessionExportCompressionLevel` 0–9（默认 6），使部署可以在 CPU／延迟与归档大小之间取舍；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。响应队列达到 64 KiB 字节高水位后，生产会等待 Consumer pull 恢复正容量；fflate 的同步回调最多只会让该界限多出一次有界输入 push 的输出。请求中止或响应 body 取消会停止血缘与工件工作、终止活跃压缩器，并继续按取消传播，而不会变成 HTTP 500。它要求同时挂载持久化、session-query 与附件服务：任一缺失应答 500，持久化后端不提供每会话原始工件时应答 501，根会话缺失时应答 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`。
 
diff --git a/packages/host/apiproxy/src/api-proxy.ts b/packages/host/apiproxy/src/api-proxy.ts
index c4e0a16756..2474a05df0 100644
--- a/packages/host/apiproxy/src/api-proxy.ts
+++ b/packages/host/apiproxy/src/api-proxy.ts
@@ -43,10 +43,13 @@ import type {
   WorkspaceId, WorkspaceView,
 } from './api/index.ts'
 import {
+  DEFAULT_SESSION_LOG_COMPRESSION_LEVEL,
+  flushLiveSessionLog,
   sessionLogExportDeps,
   sessionLogZipFilename,
   streamSessionLogZip,
   type SessionLogExportReady,
+  type SessionLogCompressionLevel,
 } from './session-export.ts'
 import type { SessionRawArtifact } from '@deepseek-ai/dsh-session-persistence'
 import {
@@ -543,6 +546,8 @@ export interface ApiProxyDefaults {
   openPath?: (path: string, signal: AbortSignal) => Promise<void>
   /** Native text-editor handoff; injectable for settings-document tests. */
   openTextFile?: (path: string, signal: AbortSignal) => Promise<void>
+  /** Validated DEFLATE level for session-log ZIP entries; defaults to 6. */
+  sessionExportCompressionLevel?: SessionLogCompressionLevel
   /**
    * Whether handing a path to the native opener can work at all — the
    * `hasDocument` capability the preset roster reports, and the switch
@@ -988,6 +993,8 @@ function changedWorkspaceView(workspaceId: string, value: unknown): WorkspaceVie
  * @returns the ApiProxy implementation.
  */
 export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiProxy {
+  const sessionExportCompressionLevel = defaults.sessionExportCompressionLevel
+    ?? DEFAULT_SESSION_LOG_COMPRESSION_LEVEL
   /** The seed model each create/resume declares; re-read so it never goes stale. */
   const agentOptions = (): AgentOptions => {
     const { provider, model } = defaults.defaultModelSelection()
@@ -3489,24 +3496,41 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
             { status: 500 },
           )
         }
+        if (!deps.sessionPersistence.supportsRawArtifacts) {
+          return new Response(
+            'session log export is unavailable: the persistence backend does not expose per-session raw artifacts',
+            { status: 501 },
+          )
+        }
         const ready: SessionLogExportReady = {
           sessionQuery: deps.sessionQuery,
           sessionPersistence: deps.sessionPersistence,
           attachments: deps.attachments,
+          sessions: deps.sessions,
         }
         let root: SessionRawArtifact | undefined
         try {
+          await flushLiveSessionLog(deps, request.sessionId, signal)
           root = await deps.sessionPersistence.readRaw(request.sessionId, signal)
+          signal.throwIfAborted()
         } 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 })
+          signal.throwIfAborted()
+          // Root preparation 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 prepare 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),
+          streamSessionLogZip(
+            ready,
+            root,
+            request.sessionId,
+            request.includeDescendants === true,
+            sessionExportCompressionLevel,
+            signal,
+          ),
           {
             headers: {
               'content-type': 'application/zip',
diff --git a/packages/host/apiproxy/src/index.ts b/packages/host/apiproxy/src/index.ts
index 6bb062dcad..ca0cf0329b 100644
--- a/packages/host/apiproxy/src/index.ts
+++ b/packages/host/apiproxy/src/index.ts
@@ -17,6 +17,10 @@ import z from '@deepseek-ai/schemastery'
 import type {} from '@deepseek-ai/dsh-agent-default-model'
 import type { ApiProxy } from './api/index.ts'
 import { createApiProxy } from './api-proxy.ts'
+import {
+  DEFAULT_SESSION_LOG_COMPRESSION_LEVEL,
+  type SessionLogCompressionLevel,
+} from './session-export.ts'
 
 export type * from './api/index.ts'
 export { RpcId } from './api/rpc.ts'
@@ -33,7 +37,7 @@ declare module '@deepseek-ai/cordis' {
   }
 }
 
-/** Gateway plugin config for native Host integration. */
+/** Gateway plugin configuration. */
 export interface Config {
   /**
    * Whether this deployment can hand paths to a native desktop opener —
@@ -43,6 +47,12 @@ export interface Config {
    * container whose DISPLAY points nowhere a user can see.
    */
   nativeOpen?: boolean
+  /**
+   * DEFLATE level for every session-log ZIP entry: `0` stores without
+   * compression, `1` favors CPU/latency, and `9` favors archive size.
+   * @default 6
+   */
+  sessionExportCompressionLevel?: 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
 }
 
 /**
@@ -58,6 +68,8 @@ export class ApiProxyService extends Service implements ApiProxy {
 
   static Config: z<Config> = z.object({
     nativeOpen: z.boolean(),
+    sessionExportCompressionLevel: z.number().step(1).min(0).max(9)
+      .default(DEFAULT_SESSION_LOG_COMPRESSION_LEVEL) as z<SessionLogCompressionLevel>,
   })
 
   readonly sessions: ApiProxy['sessions']
@@ -82,6 +94,9 @@ export class ApiProxyService extends Service implements ApiProxy {
       saveDefaultModelSelection: selection => ctx.agentDefaultModel.saveSelection(selection),
       cwd: process.cwd(),
       ...config.nativeOpen === undefined ? {} : { canOpenPath: () => config.nativeOpen as boolean },
+      ...(config.sessionExportCompressionLevel === undefined
+        ? {}
+        : { sessionExportCompressionLevel: config.sessionExportCompressionLevel }),
     })
     this.sessions = api.sessions
     this.subagents = api.subagents
diff --git a/packages/host/apiproxy/src/session-export.ts b/packages/host/apiproxy/src/session-export.ts
index 73026be20a..c42c603e85 100644
--- a/packages/host/apiproxy/src/session-export.ts
+++ b/packages/host/apiproxy/src/session-export.ts
@@ -6,13 +6,16 @@
  * 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.
+ * store and self-describing through its own header line or media type. Before
+ * each live session's artifact read, the SessionStore flush barrier makes the
+ * current in-memory log durable; cold sessions need no barrier. Request abort
+ * and response-consumer cancellation share one producer signal and terminate
+ * the active compressor.
  * 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).
+ * in one buffer; production waits for consumer pull whenever the response queue
+ * reaches its byte high-water mark, so a slow consumer bounds accumulation to
+ * the fixed 64 KiB response queue plus one synchronous fflate push.
  * @module
  */
 
@@ -20,14 +23,21 @@ 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 { SessionId, SessionStore } 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). */
+/** Valid fflate DEFLATE levels accepted by session-log export. */
+export type SessionLogCompressionLevel = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
+
+/** Balanced default used when a direct createApiProxy caller omits deployment config. */
+export const DEFAULT_SESSION_LOG_COMPRESSION_LEVEL: SessionLogCompressionLevel = 6
+
+/** The services a session-log export needs (the live-session store is optional). */
 export interface SessionLogExportDeps {
   readonly sessionQuery: SessionQueryService | undefined
   readonly sessionPersistence: SessionPersistence | undefined
   readonly attachments: AttachmentStore | undefined
+  readonly sessions: SessionStore | undefined
 }
 
 /** The export services narrowed to the mounted ones streaming actually reads. */
@@ -35,6 +45,7 @@ export interface SessionLogExportReady {
   readonly sessionQuery: SessionQueryService
   readonly sessionPersistence: SessionPersistence
   readonly attachments: AttachmentStore
+  readonly sessions: SessionStore | undefined
 }
 
 /**
@@ -47,9 +58,32 @@ export function sessionLogExportDeps(ctx: Context): SessionLogExportDeps {
     sessionQuery: ctx.get('sessionQuery'),
     sessionPersistence: ctx.get('sessionPersistence'),
     attachments: ctx.get('attachments'),
+    sessions: ctx.get('sessions'),
   }
 }
 
+/**
+ * Flush one currently live session through the store's authoritative durability
+ * barrier immediately before its raw artifact is read. A cold or absent id has
+ * no in-memory work to flush.
+ * @param deps - export services, including the optional live-session store.
+ * @param id - the session whose artifact is about to be read.
+ * @param signal - optional cancellation observed around the flush barrier.
+ */
+export async function flushLiveSessionLog(
+  deps: Pick<SessionLogExportDeps, 'sessions'>,
+  id: SessionId,
+  signal?: AbortSignal,
+): Promise<void> {
+  signal?.throwIfAborted()
+  const sessions = deps.sessions
+  if (sessions === undefined) return
+  const session = sessions.get(id)
+  if (session === undefined) return
+  await sessions.flush(session)
+  signal?.throwIfAborted()
+}
+
 /** One exported file: a stored artifact text or one referenced media object. */
 export type SessionLogZipEntry =
   | { readonly path: string; readonly content: string }
@@ -168,9 +202,9 @@ export function sessionLogZipFilename(sessionId: string): string {
 
 /**
  * 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
+ * then every subagent descendant in lineage order (each flushed when live,
+ * 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.
@@ -179,7 +213,7 @@ export function sessionLogZipFilename(sessionId: string): string {
  * 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.
+ * @param signal - optional cancellation forwarded to lineage, persistence, and attachment reads.
  * @returns the export entries in zip order.
  */
 export async function* sessionLogZipEntries(
@@ -205,7 +239,9 @@ export async function* sessionLogZipEntries(
         const id = node.session.header.id
         if (seen.has(id)) continue
         seen.add(id)
-        const raw = await deps.sessionPersistence.readRaw(id)
+        await flushLiveSessionLog(deps, id, signal)
+        const raw = await deps.sessionPersistence.readRaw(id, signal)
+        signal?.throwIfAborted()
         if (raw === undefined) {
           throw new Error(`subagent "${id}" has no stored log artifact`)
         }
@@ -217,12 +253,14 @@ export async function* sessionLogZipEntries(
         yield* collect(node.descendants)
       }
     }
-    const lineage = await deps.sessionQuery.traceSession(sessionId)
+    const lineage = await deps.sessionQuery.traceSession(sessionId, signal)
+    signal?.throwIfAborted()
     yield* collect(lineage.descendants)
   }
   for (const ref of media.values()) {
     signal?.throwIfAborted()
-    const stored = await deps.attachments.readImage(ref)
+    const stored = await deps.attachments.readImage(ref, signal)
+    signal?.throwIfAborted()
     yield { path: mediaEntryPath(ref), data: stored.data }
   }
 }
@@ -233,30 +271,66 @@ 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
 
+/** Byte capacity retained by the response stream before ZIP production waits for pull. */
+const RESPONSE_HIGH_WATER_MARK_BYTES = 1 << 16
+
+/** One producer waiter released only when ReadableStream pull restores capacity. */
+class ResponseCapacityGate {
+  private releasePending: (() => void) | undefined
+
+  /**
+   * Wait until the response queue has positive byte capacity or cancellation wins.
+   * @param controller - response controller whose desired size owns capacity.
+   * @param signal - combined request/consumer cancellation.
+   */
+  async wait(
+    controller: ReadableStreamDefaultController<Uint8Array>,
+    signal: AbortSignal,
+  ): Promise<void> {
+    signal.throwIfAborted()
+    if (controller.desiredSize === null || controller.desiredSize > 0) return
+    await new Promise<void>((resolve) => {
+      const release = (): void => {
+        this.releasePending = undefined
+        signal.removeEventListener('abort', release)
+        resolve()
+      }
+      this.releasePending = release
+      signal.addEventListener('abort', release, { once: true })
+    })
+    signal.throwIfAborted()
+  }
+
+  /** Release the current producer waiter after a consumer pull. */
+  pulled(): void {
+    this.releasePending?.()
+  }
+}
+
 /**
  * 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.
+ * waiting for consumer capacity 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.
+ * @param controller - response queue controller.
+ * @param capacity - pull-driven response-capacity gate.
+ * @param signal - cancellation; throws when aborted.
  */
 async function pushBinaryChunks(
   deflate: ZipDeflate,
   data: Uint8Array,
   controller: ReadableStreamDefaultController<Uint8Array>,
-  signal?: AbortSignal,
+  capacity: ResponseCapacityGate,
+  signal: AbortSignal,
 ): Promise<void> {
   let offset = 0
   do {
-    signal?.throwIfAborted()
+    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))
-    }
+    await capacity.wait(controller, signal)
   } while (offset < data.byteLength)
 }
 
@@ -266,19 +340,22 @@ async function pushBinaryChunks(
  * 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.
+ * @param controller - response queue controller.
+ * @param capacity - pull-driven response-capacity gate.
+ * @param signal - cancellation; throws when aborted.
  */
 async function pushArtifactChunks(
   deflate: ZipDeflate,
   content: string,
   controller: ReadableStreamDefaultController<Uint8Array>,
-  signal?: AbortSignal,
+  capacity: ResponseCapacityGate,
+  signal: AbortSignal,
 ): Promise<void> {
   const encoder = new TextEncoder()
   let offset = 0
   let finalChunk: boolean
   do {
-    signal?.throwIfAborted()
+    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
@@ -289,10 +366,7 @@ async function pushArtifactChunks(
     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))
-    }
+    await capacity.wait(controller, signal)
   } while (!finalChunk)
 }
 
@@ -307,7 +381,8 @@ async function pushArtifactChunks(
  * @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.
+ * @param compressionLevel - validated fflate DEFLATE level for every ZIP entry.
+ * @param signal - request cancellation combined with response-consumer cancellation.
  * @returns the zip byte stream.
  */
 export function streamSessionLogZip(
@@ -315,15 +390,26 @@ export function streamSessionLogZip(
   root: SessionRawArtifact,
   sessionId: SessionId,
   includeDescendants: boolean,
-  signal?: AbortSignal,
+  compressionLevel: SessionLogCompressionLevel,
+  signal: AbortSignal,
 ): ReadableStream<Uint8Array> {
+  const consumerAbort = new AbortController()
+  const producerSignal = AbortSignal.any([signal, consumerAbort.signal])
+  let zip: Zip | undefined
+  let zipTerminated = false
+  const capacity = new ResponseCapacityGate()
+  const terminateZip = (): void => {
+    if (zip === undefined || zipTerminated) return
+    zipTerminated = true
+    zip.terminate()
+  }
   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) => {
+      // single push can enqueue ahead of a slow consumer; the capacity gate
+      // waits for pull between pushes once the byte queue is full, bounding
+      // accumulation to the queue high-water mark plus one synchronous push.
+      const archive = new Zip((error, data, final) => {
         /* v8 ignore next 3 -- fflate reports only internal zip failures, unreachable for valid inputs */
         if (error) {
           controller.error(error)
@@ -333,25 +419,39 @@ export function streamSessionLogZip(
         if (data.byteLength > 0) controller.enqueue(data)
         if (final) controller.close()
       })
+      zip = archive
       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)
+          for await (const entry of sessionLogZipEntries(deps, root, sessionId, includeDescendants, producerSignal)) {
+            const deflate = new ZipDeflate(entry.path, { level: compressionLevel })
+            archive.add(deflate)
             if ('content' in entry) {
-              await pushArtifactChunks(deflate, entry.content, controller, signal)
+              await pushArtifactChunks(deflate, entry.content, controller, capacity, producerSignal)
             } else {
-              await pushBinaryChunks(deflate, entry.data, controller, signal)
+              await pushBinaryChunks(deflate, entry.data, controller, capacity, producerSignal)
             }
           }
-          zip.end()
+          archive.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 */
+          terminateZip()
           controller.error(error instanceof Error ? error : new Error(String(error)))
         }
       })()
     },
+    pull() {
+      capacity.pulled()
+    },
+    cancel(reason) {
+      consumerAbort.abort(
+        reason instanceof Error ? reason : new Error('session log export stream cancelled'),
+      )
+      terminateZip()
+    },
+  }, {
+    highWaterMark: RESPONSE_HIGH_WATER_MARK_BYTES,
+    size: chunk => chunk.byteLength,
   })
 }
diff --git a/packages/host/apiproxy/tests/session-export.spec.ts b/packages/host/apiproxy/tests/session-export.spec.ts
index 923e70b380..a766c4b4eb 100644
--- a/packages/host/apiproxy/tests/session-export.spec.ts
+++ b/packages/host/apiproxy/tests/session-export.spec.ts
@@ -5,7 +5,8 @@
  * root → 404, missing descendant → errored stream).
  */
 
-import { describe, expect, it } from 'vitest'
+import { randomBytes } from 'node:crypto'
+import { describe, expect, it, vi } from 'vitest'
 import { Context } from '@deepseek-ai/cordis'
 import { unzipSync, strFromU8 } from 'fflate'
 import type { ImageAttachmentRef } from '@deepseek-ai/dsh-attachment'
@@ -13,8 +14,7 @@ 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'
+import ApiProxyService, { createApiProxy, toFetchHandler } from '@deepseek-ai/dsh-host-apiproxy'
 
 const sid = (id: string): SessionId => id as SessionId
 
@@ -59,8 +59,21 @@ async function buildApi(
   descendants: SessionLineageNode[] = [],
   services: {
     query?: boolean
-    persistence?: boolean | 'throw'
-    attachments?: boolean | ((ref: ImageAttachmentRef) => Promise<ReturnType<typeof storedImage>>)
+    persistence?: boolean | 'throw' | 'unsupported'
+    attachments?: boolean | ((ref: ImageAttachmentRef, signal?: AbortSignal) => Promise<ReturnType<typeof storedImage>>)
+    sessions?: {
+      get(id: SessionId): { readonly id: SessionId } | undefined
+      flush(session: { readonly id: SessionId }): Promise<boolean>
+    }
+    readRaw?: (id: SessionId, signal?: AbortSignal) => Promise<SessionRawArtifact | undefined>
+    traceSession?: (id: SessionId, signal?: AbortSignal) => Promise<{
+      target: { header: SessionHeader; live: boolean; persisted: boolean }
+      ancestors: readonly SessionLineageNode[]
+      complete: boolean
+      root: { header: SessionHeader; live: boolean; persisted: boolean }
+      descendants: readonly SessionLineageNode[]
+    }>
+    compressionLevel?: 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
   } = {},
 ) {
   const ctx = new Context()
@@ -69,21 +82,22 @@ async function buildApi(
   const persistence = services.persistence ?? true
   if (query) {
     ctx.provide('sessionQuery', {
-      traceSession: async () => ({
+      traceSession: services.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) => {
+      supportsRawArtifacts: persistence !== 'unsupported',
+      readRaw: services.readRaw ?? (async (id: SessionId) => {
         if (persistence === 'throw') throw new Error('/host/private/session.jsonl')
         return artifacts[id]
-      },
+      }),
     } as never)
   }
   if (services.attachments !== false) {
@@ -97,9 +111,13 @@ async function buildApi(
       readImage,
     } as never)
   }
+  if (services.sessions !== undefined) ctx.provide('sessions', services.sessions as never)
   return createApiProxy(ctx, {
     defaultModelSelection: () => ({ provider: 'p', model: 'm' }),
     cwd: '/tmp',
+    ...services.compressionLevel === undefined
+      ? {}
+      : { sessionExportCompressionLevel: services.compressionLevel },
   })
 }
 
@@ -107,6 +125,19 @@ async function responseBytes(response: Response): Promise<Uint8Array> {
   return new Uint8Array(await response.arrayBuffer())
 }
 
+describe('session export compression config', () => {
+  it('defaults to level 6 and rejects values outside the integer 0-9 range', () => {
+    expect(ApiProxyService.Config({})).toEqual({ sessionExportCompressionLevel: 6 })
+    expect(ApiProxyService.Config({ sessionExportCompressionLevel: 0 }))
+      .toEqual({ sessionExportCompressionLevel: 0 })
+    expect(ApiProxyService.Config({ sessionExportCompressionLevel: 9 }))
+      .toEqual({ sessionExportCompressionLevel: 9 })
+    for (const value of [-1, 10, 1.5]) {
+      expect(() => ApiProxyService.Config({ sessionExportCompressionLevel: value } as never)).toThrow()
+    }
+  })
+})
+
 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') })
@@ -121,6 +152,24 @@ describe('session.export download endpoint', () => {
     expect(strFromU8(files['session.jsonl'] as Uint8Array)).toBe(artifact('session-root').content)
   })
 
+  it('uses the resolved compression level for ZIP entries', async () => {
+    const root = artifact('session-root', undefined, 'compressible\n'.repeat(32 * 1024))
+    const storedApi = await buildApi({ 'session-root': root }, [], { compressionLevel: 0 })
+    const compressedApi = await buildApi({ 'session-root': root }, [], { compressionLevel: 9 })
+    const stored = await storedApi.downloads.sessionLog(
+      { sessionId: sid('session-root'), includeDescendants: false },
+      new AbortController().signal,
+    )
+    const compressed = await compressedApi.downloads.sessionLog(
+      { sessionId: sid('session-root'), includeDescendants: false },
+      new AbortController().signal,
+    )
+    const storedBytes = await responseBytes(stored)
+    const compressedBytes = await responseBytes(compressed)
+    expect(compressedBytes.byteLength).toBeLessThan(storedBytes.byteLength)
+    expect(strFromU8(unzipSync(compressedBytes)['session.jsonl'] as Uint8Array)).toBe(root.content)
+  })
+
   it('includes descendant artifacts under subagents/<id>/ when requested', async () => {
     const api = await buildApi({
       'session-root': artifact('session-root'),
@@ -143,6 +192,55 @@ describe('session.export download endpoint', () => {
       .toBe(artifact('child-a').content)
   })
 
+  it('flushes each live root and descendant immediately before reading its artifact', async () => {
+    const stored: Record<string, SessionRawArtifact> = {
+      'session-root': artifact('session-root', undefined, 'stale root'),
+      'child-a': artifact('child-a', sid('session-root'), 'stale child'),
+    }
+    const durable: Record<string, SessionRawArtifact> = {
+      'session-root': artifact('session-root', undefined, 'durable root'),
+      'child-a': artifact('child-a', sid('session-root'), 'durable child'),
+    }
+    const flushed: SessionId[] = []
+    const api = await buildApi(stored, [node('child-a')], {
+      sessions: {
+        get: id => durable[id] === undefined ? undefined : { id },
+        flush: async (session) => {
+          const artifactAfterFlush = durable[session.id]
+          if (artifactAfterFlush === undefined) throw new Error('unexpected session')
+          flushed.push(session.id)
+          stored[session.id] = artifactAfterFlush
+          return true
+        },
+      },
+    })
+    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(flushed).toEqual([sid('session-root'), sid('child-a')])
+    expect(strFromU8(files['session.jsonl'] as Uint8Array)).toBe('durable root')
+    expect(strFromU8(files['subagents/child-a/session.jsonl'] as Uint8Array)).toBe('durable child')
+  })
+
+  it('reads a cold artifact without asking the live-session store to flush', async () => {
+    const flush = vi.fn(async () => true)
+    const root = artifact('session-root')
+    const api = await buildApi({ 'session-root': root }, [], {
+      sessions: {
+        get: () => undefined,
+        flush,
+      },
+    })
+    const response = await api.downloads.sessionLog(
+      { sessionId: sid('session-root'), includeDescendants: false },
+      new AbortController().signal,
+    )
+    const files = unzipSync(await responseBytes(response))
+    expect(flush).not.toHaveBeenCalled()
+    expect(strFromU8(files['session.jsonl'] as Uint8Array)).toBe(root.content)
+  })
+
   it('answers 404 for a missing root session', async () => {
     const api = await buildApi({})
     const response = await toFetchHandler(api).fetch(
@@ -151,6 +249,15 @@ describe('session.export download endpoint', () => {
     expect(response.status).toBe(404)
   })
 
+  it('answers 501 when the persistence backend has no per-session raw artifacts', async () => {
+    const api = await buildApi({}, [], { persistence: 'unsupported' })
+    const response = await toFetchHandler(api).fetch(
+      new Request('http://host/api/session.export?sessionId=session-root'),
+    )
+    expect(response.status).toBe(501)
+    expect(await response.text()).toContain('does not expose per-session raw artifacts')
+  })
+
   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(
@@ -214,6 +321,37 @@ describe('session.export download endpoint', () => {
     expect(strFromU8(files['session.jsonl'] as Uint8Array)).toBe(root.content)
   })
 
+  it('waits for response pull capacity before reading the next archive entry', async () => {
+    const root = artifact('session-root', undefined, [
+      imageEventLine('after-root'),
+      randomBytes(512 * 1024).toString('base64'),
+    ].join('\n'))
+    let imageReads = 0
+    const api = await buildApi({ 'session-root': root }, [], {
+      attachments: async (ref) => {
+        imageReads += 1
+        return storedImage(String(ref.attachmentId), ref.mediaType)
+      },
+    })
+    vi.useFakeTimers()
+    let response: Response | undefined
+    try {
+      response = await toFetchHandler(api).fetch(
+        new Request('http://host/api/session.export?sessionId=session-root'),
+      )
+      // Exhausting timer turns must not advance a producer whose byte queue is
+      // full; only a consumer pull can release it.
+      await vi.runAllTimersAsync()
+      expect(imageReads).toBe(0)
+    } finally {
+      vi.useRealTimers()
+    }
+    if (response === undefined) throw new Error('missing export response')
+    const files = unzipSync(await responseBytes(response))
+    expect(imageReads).toBe(1)
+    expect(files['media/after-root.png']).toEqual(storedImage('after-root').data)
+  })
+
   it('exports an empty artifact as an empty zip entry', async () => {
     const root = { ...artifact('session-root'), content: '' }
     const api = await buildApi({ 'session-root': root })
@@ -254,10 +392,179 @@ describe('session.export download endpoint', () => {
     )
     expect(response.status).toBe(500)
     const body = await response.text()
-    expect(body).toBe('session log export failed to read the stored artifact')
+    expect(body).toBe('session log export failed to prepare the stored artifact')
     expect(body).not.toContain('/host/private/')
   })
 
+  it('answers the private-error-safe 500 when the live root flush fails', async () => {
+    const api = await buildApi({ 'session-root': artifact('session-root') }, [], {
+      sessions: {
+        get: id => ({ id }),
+        flush: async () => { throw new Error('/host/private/flush-state') },
+      },
+    })
+    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 prepare the stored artifact')
+    expect(body).not.toContain('/host/private/')
+  })
+
+  it('forwards one request signal through root, lineage, and descendant reads', async () => {
+    const reads: Array<{ id: SessionId; signal: AbortSignal | undefined }> = []
+    const traces: AbortSignal[] = []
+    const api = await buildApi({}, [node('child-a')], {
+      readRaw: async (id, signal) => {
+        reads.push({ id, signal })
+        return id === sid('session-root')
+          ? artifact('session-root')
+          : artifact('child-a', sid('session-root'))
+      },
+      traceSession: async (_id, signal) => {
+        if (signal !== undefined) traces.push(signal)
+        return {
+          target: { header: header('session-root'), live: false, persisted: true },
+          ancestors: [],
+          complete: true,
+          root: { header: header('session-root'), live: false, persisted: true },
+          descendants: [node('child-a')],
+        }
+      },
+    })
+    const controller = new AbortController()
+    const response = await api.downloads.sessionLog(
+      { sessionId: sid('session-root'), includeDescendants: true },
+      controller.signal,
+    )
+    await response.arrayBuffer()
+    const producerSignal = traces[0]
+    if (producerSignal === undefined) throw new Error('missing lineage signal')
+    expect(reads[0]).toEqual({ id: sid('session-root'), signal: controller.signal })
+    expect(reads[1]).toEqual({ id: sid('child-a'), signal: producerSignal })
+    const cancellation = new Error('request cancelled after response')
+    controller.abort(cancellation)
+    expect(producerSignal.aborted).toBe(true)
+    expect(producerSignal.reason).toBe(cancellation)
+  })
+
+  it('preserves request cancellation instead of translating it to HTTP 500', async () => {
+    const api = await buildApi({ 'session-root': artifact('session-root') })
+    const controller = new AbortController()
+    const cancellation = new Error('request cancelled')
+    controller.abort(cancellation)
+    await expect(api.downloads.sessionLog(
+      { sessionId: sid('session-root'), includeDescendants: false },
+      controller.signal,
+    )).rejects.toBe(cancellation)
+  })
+
+  it('aborts descendant work and terminates ZIP production when its reader cancels', async () => {
+    let reportDescendantStarted!: (signal: AbortSignal) => void
+    const descendantStarted = new Promise<AbortSignal>((resolve) => {
+      reportDescendantStarted = resolve
+    })
+    const api = await buildApi({}, [node('child-a')], {
+      readRaw: async (id, signal) => {
+        if (id === sid('session-root')) return artifact('session-root')
+        if (signal === undefined) throw new Error('missing descendant signal')
+        reportDescendantStarted(signal)
+        return new Promise((_, reject) => {
+          signal.addEventListener('abort', () => {
+            reject(signal.reason as Error)
+          }, { once: true })
+        })
+      },
+    })
+    const response = await api.downloads.sessionLog(
+      { sessionId: sid('session-root'), includeDescendants: true },
+      new AbortController().signal,
+    )
+    const reader = response.body?.getReader()
+    if (reader === undefined) throw new Error('missing response body')
+    const descendantSignal = await descendantStarted
+    const cancellation = new Error('download consumer left')
+    await reader.cancel(cancellation)
+    expect(descendantSignal.aborted).toBe(true)
+    expect(descendantSignal.reason).toBe(cancellation)
+  })
+
+  it('aborts attachment reads when its reader cancels', async () => {
+    let reportAttachmentStarted!: (signal: AbortSignal) => void
+    const attachmentStarted = new Promise<AbortSignal>((resolve) => {
+      reportAttachmentStarted = resolve
+    })
+    const root = artifact('session-root', undefined, [
+      '{"type":"session","version":0,"id":"session-root","createdAt":1000}',
+      imageEventLine('slow-img'),
+    ].join('\n') + '\n')
+    const api = await buildApi({ 'session-root': root }, [], {
+      attachments: async (_ref, signal) => {
+        if (signal === undefined) throw new Error('missing attachment signal')
+        reportAttachmentStarted(signal)
+        return new Promise((_, reject) => {
+          signal.addEventListener('abort', () => {
+            reject(signal.reason as Error)
+          }, { once: true })
+        })
+      },
+    })
+    const response = await api.downloads.sessionLog(
+      { sessionId: sid('session-root'), includeDescendants: false },
+      new AbortController().signal,
+    )
+    const reader = response.body?.getReader()
+    if (reader === undefined) throw new Error('missing response body')
+    const attachmentSignal = await attachmentStarted
+    const cancellation = new Error('download consumer left during attachment read')
+    await reader.cancel(cancellation)
+    expect(attachmentSignal.aborted).toBe(true)
+    expect(attachmentSignal.reason).toBe(cancellation)
+  })
+
+  it('uses a stable Error reason when its reader cancels without one', async () => {
+    let reportDescendantStarted!: (signal: AbortSignal) => void
+    const descendantStarted = new Promise<AbortSignal>((resolve) => {
+      reportDescendantStarted = resolve
+    })
+    const api = await buildApi({}, [node('child-a')], {
+      readRaw: async (id, signal) => {
+        if (id === sid('session-root')) return artifact('session-root')
+        if (signal === undefined) throw new Error('missing descendant signal')
+        reportDescendantStarted(signal)
+        return new Promise((_, reject) => {
+          signal.addEventListener('abort', () => {
+            reject(signal.reason as Error)
+          }, { once: true })
+        })
+      },
+    })
+    const response = await api.downloads.sessionLog(
+      { sessionId: sid('session-root'), includeDescendants: true },
+      new AbortController().signal,
+    )
+    const reader = response.body?.getReader()
+    if (reader === undefined) throw new Error('missing response body')
+    const descendantSignal = await descendantStarted
+    await reader.cancel()
+    expect(descendantSignal.reason).toEqual(new Error('session log export stream cancelled'))
+  })
+
+  it('normalizes a non-Error descendant failure before erroring the stream', async () => {
+    const api = await buildApi({}, [node('child-a')], {
+      readRaw: async (id) => {
+        if (id === sid('session-root')) return artifact('session-root')
+        throw 'descendant read failed'
+      },
+    })
+    const response = await api.downloads.sessionLog(
+      { sessionId: sid('session-root'), includeDescendants: true },
+      new AbortController().signal,
+    )
+    await expect(response.arrayBuffer()).rejects.toEqual(new Error('descendant read failed'))
+  })
+
   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}',
diff --git a/packages/self-modification/tool-cordis/src/api-catalog.ts b/packages/self-modification/tool-cordis/src/api-catalog.ts
index cd96f0fcb6..94835f96b5 100644
--- a/packages/self-modification/tool-cordis/src/api-catalog.ts
+++ b/packages/self-modification/tool-cordis/src/api-catalog.ts
@@ -237,8 +237,8 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
         jsDoc: '/**\n * Validate and durably commit one image before its owning session event is appended.\n * @param input - encoded bytes, declared media type, and optional display name.\n * @returns a durable content-addressed reference.\n */',
       },
       {
-        signature: 'abstract readImage(ref: ImageAttachmentRef): Promise<StoredImageAttachment>',
-        jsDoc: '/**\n * Read one image and verify that bytes still match the recorded reference.\n * @param ref - durable reference from the session log.\n * @returns the verified bytes and canonical reference.\n */',
+        signature: 'abstract readImage(ref: ImageAttachmentRef, signal?: AbortSignal): Promise<StoredImageAttachment>',
+        jsDoc: '/**\n * Read one image and verify that bytes still match the recorded reference.\n * @param ref - durable reference from the session log.\n * @param signal - optional cancellation for backend read and verification work.\n * @returns the verified bytes and canonical reference.\n * @throws the signal reason when aborted, or a storage error when verification fails.\n */',
       },
     ],
   },
@@ -720,7 +720,7 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
       },
       {
         signature: 'readRaw(_id: SessionId, signal?: AbortSignal): Promise<SessionRawArtifact | undefined>',
-        jsDoc: '/**\n * Read a session\'s backend-owned artifact text verbatim — the exact durable\n * bytes the backend wrote (decoded from its physical encoding, e.g. a\n * decompressed JSONL). The returned `content` is the raw text, not a\n * reconstruction from parsed events, so it preserves backend-specific\n * serialization (chunk packing, key order, line breaks). Backends without a\n * per-session artifact (SQLite) inherit the `undefined` default.\n * @param _id - the persisted session to read (unused by the default: no\n * per-session artifact).\n * @param signal - optional cancellation for backend read work.\n * @returns the raw artifact plus its parsed header, or `undefined` when the\n * session is absent or the backend owns no per-session artifact.\n */',
+        jsDoc: '/**\n * Read a session\'s backend-owned artifact text verbatim — the exact durable\n * bytes the backend wrote (decoded from its physical encoding, e.g. a\n * decompressed JSONL). The returned `content` is the raw text, not a\n * reconstruction from parsed events, so it preserves backend-specific\n * serialization (chunk packing, key order, line breaks). Callers first test\n * {@link supportsRawArtifacts}; `undefined` then means only that the requested\n * session has no materialized artifact.\n * @param _id - the persisted session to read (unused by the default: no\n * per-session artifact).\n * @param signal - optional cancellation for backend read work.\n * @returns the raw artifact plus its parsed header, or `undefined` when the\n * session is absent.\n * @throws when this backend does not expose per-session raw artifacts.\n */',
       },
       {
         signature: 'abstract create(meta: SessionHeader): Promise<void>',
diff --git a/packages/session-query/session-query-sqlite/tests/sqlite.spec.ts b/packages/session-query/session-query-sqlite/tests/sqlite.spec.ts
index bbba91453d..4b27f056af 100644
--- a/packages/session-query/session-query-sqlite/tests/sqlite.spec.ts
+++ b/packages/session-query/session-query-sqlite/tests/sqlite.spec.ts
@@ -67,6 +67,8 @@ function replaceCursorOffset(
 }
 
 class TestPersistence extends SessionPersistence {
+  override readonly supportsRawArtifacts = false
+
   static entries = new Map<SessionIdType, { meta: SessionHeader; events: SessionEvent[] }>()
   static revisions = new Map<SessionIdType, number>()
   static nextRevision = 0
diff --git a/packages/session-query/session-query/tests/session-query.spec.ts b/packages/session-query/session-query/tests/session-query.spec.ts
index 5a4228329b..a61be6a7a0 100644
--- a/packages/session-query/session-query/tests/session-query.spec.ts
+++ b/packages/session-query/session-query/tests/session-query.spec.ts
@@ -29,6 +29,8 @@ function eventLog(text = 'hello'): SessionEvent[] {
 }
 
 class TestPersistence extends SessionPersistence {
+  override readonly supportsRawArtifacts = false
+
   static entries = new Map<SessionIdType, { meta: SessionHeader; events: SessionEvent[] }>()
   static listFailure: unknown
   static listOverride: ((signal?: AbortSignal) => Promise<SessionHeader[]>) | undefined
diff --git a/packages/session-query/session-query/tests/tracing.spec.ts b/packages/session-query/session-query/tests/tracing.spec.ts
index 8c9588be26..c9e9d2ad50 100644
--- a/packages/session-query/session-query/tests/tracing.spec.ts
+++ b/packages/session-query/session-query/tests/tracing.spec.ts
@@ -32,6 +32,8 @@ function appendEvent(seq: number, sources?: number[]): SessionEvent {
 }
 
 class TracePersistence extends SessionPersistence {
+  override readonly supportsRawArtifacts = false
+
   static entries = new Map<SessionIdType, { meta: SessionHeader; events: SessionEvent[] }>()
   static listCalls = 0
   static inspectCalls = 0
diff --git a/packages/session/session-checkpoint-policy/tests/session-checkpoint-policy.spec.ts b/packages/session/session-checkpoint-policy/tests/session-checkpoint-policy.spec.ts
index 6501941c77..2ed880e355 100644
--- a/packages/session/session-checkpoint-policy/tests/session-checkpoint-policy.spec.ts
+++ b/packages/session/session-checkpoint-policy/tests/session-checkpoint-policy.spec.ts
@@ -13,6 +13,8 @@ import * as checkpointPolicy from '../src/index.ts'
 const contexts: Context[] = []
 
 class TestPersistence extends SessionPersistence {
+  override readonly supportsRawArtifacts = false
+
   locate(_meta: SessionHeader): undefined { return undefined }
   create(_meta: SessionHeader): Promise<void> { return Promise.resolve() }
   append(_id: SessionId, _events: readonly SessionEvent[]): Promise<void> { return Promise.resolve() }
diff --git a/packages/session/session-persistence-jsonl/README.i18n.yaml b/packages/session/session-persistence-jsonl/README.i18n.yaml
index 333ef8ce62..4aefe2b524 100644
--- a/packages/session/session-persistence-jsonl/README.i18n.yaml
+++ b/packages/session/session-persistence-jsonl/README.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/session/session-persistence-jsonl/README.md
-README.md: e2416cd36e3fb1d8f93e921800f2247fe29f3b09
-README.zh.md: 4eb2d4f2bebf9ed17190ef3cb21a2bc3c8d9123b
+README.md: 4cff3215cdb083d2fdb7c4a8f1b60e8c4028ba84
+README.zh.md: 7e3ba5be4f2707ff6408d296ece1f43550d76286
diff --git a/packages/session/session-persistence-jsonl/README.md b/packages/session/session-persistence-jsonl/README.md
index e2416cd36e..4cff3215cd 100644
--- a/packages/session/session-persistence-jsonl/README.md
+++ b/packages/session/session-persistence-jsonl/README.md
@@ -42,7 +42,7 @@ A root belongs to one encoding. Startup discovery and targeted lookup reject the
 - **Bound storage identity.** Lookup requires one matching session directory across the readable project directories, then verifies that the header id equals the requested id and that the header's id/cwd derive the selected transcript path. Listing applies the same path check and rejects duplicate ids. Identity failures occur before repair or append.
 - **Lazy materialization.** `create(meta)` writes nothing; on the first `append`, the backend writes and `fsync`s the encoded header and first batch in a temporary file. POSIX publishes it without overwrite via a hard link and `fsync`s the parent directory. Windows publishes it without overwrite via `MoveFileExW(..., MOVEFILE_WRITE_THROUGH)` and creates missing directories through the same write-through pattern. A created-but-never-appended session leaves nothing on disk and is absent from `list`.
 - **Append-only.** Flushed events are never rewritten. Subsequent raw batches append lines; compressed batches append one frame. Both paths `fsync`, and a caught write or sync failure rolls the file back to its prior byte length.
-- **Crash recovery — preserve valid tail work.** `load` validates every complete compressed frame and scans their decompressed JSONL. If the last frame is structurally incomplete, the reader keeps its complete decoded records, truncates from that frame's start, and re-encodes those records with the synthetic tool, step, and turn closers required by the shared [persistence contract](../../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md). Raw mode truncates from its first incomplete line. A checksum/decompression failure in a complete frame, or a defect at or before the last committed `turn/end`, is corruption and rejects.
+- **Crash recovery — preserve valid tail work.** `load` validates every complete compressed frame and scans their decompressed JSONL. If the last frame is structurally incomplete, the reader keeps its complete decoded records, truncates from that frame's start, and re-encodes those records with the synthetic tool, step, and turn closers required by the shared [persistence contract](../../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md). Raw mode truncates from its first incomplete line. An existing compressed artifact with no complete header frame, a checksum/decompression failure in a complete frame, or a defect at or before the last committed `turn/end` is corruption and rejects.
 - **Non-mutating inspection.** `inspect()` returns an immutable balanced logical view and may synthesize recovery closers in memory, without truncating an incomplete tail or changing the lightweight revision.
 - **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.
 - **Lightweight revisions.** `listSnapshots(signal?)` identifies a log by its device, inode, size, and nanosecond timestamps, avoiding a full-log parse while changing after append, repair, replacement, or store changes. A full-prefix read requires the same identity before and after reading the bytes, and `readStoredRevision()` uses that identity to validate retained preparations without loading the log. Snapshot listing forwards the exact signal through artifact discovery and checks cancellation around every `stat`; because filesystem `stat` is not interruptible, cancellation waits for the active call to settle, then rejects without starting another.
diff --git a/packages/session/session-persistence-jsonl/README.zh.md b/packages/session/session-persistence-jsonl/README.zh.md
index 4eb2d4f2be..7e3ba5be4f 100644
--- a/packages/session/session-persistence-jsonl/README.zh.md
+++ b/packages/session/session-persistence-jsonl/README.zh.md
@@ -42,7 +42,7 @@ JSONL 持久会话存储后端：`SessionPersistence` 的一个具体实现（`d
 - **绑定存储身份。** 查找要求可读项目目录中只有一个匹配会话目录，然后验证 header id 等于请求 id，且 header id/cwd 派生所选 transcript 路径。列表应用同一路径检查，并拒绝重复 id。身份失败发生在修复或 append 前。
 - **延迟实体化。**`create(meta)` 不写入；第一次 `append` 将编码 header 和第一批写入临时文件并执行 `fsync`。POSIX 通过硬链接无覆盖发布，并对父目录 `fsync`。Windows 通过 `MoveFileExW(..., MOVEFILE_WRITE_THROUGH)` 无覆盖发布，并通过同一 write-through pattern 创建缺失目录。已创建但从未 append 的会话不留下磁盘内容，不在 `list` 中。
 - **仅追加。** 已 flush 事件绝不重写。后续原始批次 append 行；压缩批次 append 一个 frame。两条路径都执行 `fsync`，并在捕获到写入或同步失败时回滚到之前字节长度。
-- **崩溃恢复：保留有效尾部工作。**`load` 验证每个完整压缩 frame，并扫描解压 JSONL。最后 frame 结构不完整时，读取器保留其完整解码记录，从 frame 开头截断，并使用共享[持久化约定](../../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md) 需要的合成工具、步骤和轮次 closer 重新编码这些记录。原始 mode 从第一个不完整行截断。完整 frame 中的 checksum/解压失败，或位于最后已提交的 `turn/end` 处或之前的缺陷属于损坏，会被拒绝。
+- **崩溃恢复：保留有效尾部工作。**`load` 验证每个完整压缩 frame，并扫描解压 JSONL。最后 frame 结构不完整时，读取器保留其完整解码记录，从 frame 开头截断，并使用共享[持久化约定](../../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md) 需要的合成工具、步骤和轮次 closer 重新编码这些记录。原始 mode 从第一个不完整行截断。已经存在却没有完整 header frame 的压缩工件、完整 frame 中的 checksum/解压失败，或位于最后已提交的 `turn/end` 处或之前的缺陷都属于损坏，会被拒绝。
 - **非变更检查。**`inspect()` 返回不可变、平衡的逻辑视图，并可在内存中合成恢复 closer，但不会截断不完整尾部或更改轻量修订。
 - **连续 seq。**`append` 拒绝第一个 `seq` 不继续已存储日志的批次，并拒绝非 JSON 可序列化 `event.data`，同时命名违规事件类型。
 - **轻量修订。**`listSnapshots(signal?)` 使用 device、inode、size 和纳秒时间戳标识日志，避免解析完整日志；该标识会在 append、修复、替换或存储变更后改变。完整前缀读取要求读取字节前后的身份一致，`readStoredRevision()` 使用同一身份校验保留的 preparation，而不加载日志。快照列表通过产物发现转发精确信号，并在每个 `stat` 前后检查取消；由于文件系统 `stat` 不可中断，取消会等待活动调用完成，然后在不启动另一次调用的情况下拒绝。
diff --git a/packages/session/session-persistence-jsonl/src/index.ts b/packages/session/session-persistence-jsonl/src/index.ts
index 96ded55c73..9c0e418a2b 100644
--- a/packages/session/session-persistence-jsonl/src/index.ts
+++ b/packages/session/session-persistence-jsonl/src/index.ts
@@ -119,6 +119,8 @@ function isENOENT(error: unknown): boolean {
  * recovered from an incomplete final Zstandard frame.
  */
 export class SessionPersistenceJsonl extends SessionPersistence implements PersistenceBackend<JsonlTornMarker> {
+  override readonly supportsRawArtifacts = true
+
   static inject = ['sessions']
 
   static Config: z<Config> = z.object({
@@ -257,7 +259,7 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
     let content: string
     if (this.compression === 'zstd') {
       const { frames } = scanZstdFrames(buffer)
-      if (frames.length === 0) return undefined
+      if (frames.length === 0) throw new Error('empty or header-less Zstandard session log')
       const decoder = createZstdFrameDecoder()
       const plaintexts: Buffer[] = []
       // The decoder yields views into a reused buffer; copy each frame's
diff --git a/packages/session/session-persistence-jsonl/tests/zstd.spec.ts b/packages/session/session-persistence-jsonl/tests/zstd.spec.ts
index 49d1182b44..0b7bb5d93d 100644
--- a/packages/session/session-persistence-jsonl/tests/zstd.spec.ts
+++ b/packages/session/session-persistence-jsonl/tests/zstd.spec.ts
@@ -377,16 +377,16 @@ describe('SessionPersistenceJsonl: default Zstandard encoding', () => {
     expect(scanned.events.map(event => event.type)).toEqual(oneTurnLog().map(event => event.type))
   })
 
-  it('readRaw is undefined for a zstd artifact that carries no frame', async () => {
+  it('readRaw rejects a present zstd artifact that carries no frame', async () => {
     const root = await freshRoot()
     const ctx = await mount(root)
     const header = meta('raw-zero-frame', '/work')
     await ctx.sessionPersistence.create(header)
     await ctx.sessionPersistence.append(header.id, oneTurnLog())
-    // Overwrite the physical artifact with a short buffer: frame scanning
-    // answers zero frames before any magic check, so readRaw reports no artifact.
+    // The path still exists, so zero frames is corruption rather than absence.
     await writeFile(logPath(root, '/work', header.id, 'zstd'), Buffer.alloc(0))
-    expect(await ctx.sessionPersistence.readRaw(header.id)).toBeUndefined()
+    await expect(ctx.sessionPersistence.readRaw(header.id))
+      .rejects.toThrow('empty or header-less Zstandard session log')
   })
 
   it('resolves the default when a programmatic wrapper bypasses Loader schema normalization', async () => {
diff --git a/packages/session/session-persistence-sqlite/src/index.ts b/packages/session/session-persistence-sqlite/src/index.ts
index fa78c32030..71fc34281c 100644
--- a/packages/session/session-persistence-sqlite/src/index.ts
+++ b/packages/session/session-persistence-sqlite/src/index.ts
@@ -97,6 +97,8 @@ export interface Config {
  * listeners. Its torn-tail marker is the seq to delete from.
  */
 export class SessionPersistenceSqlite extends SessionPersistence implements PersistenceBackend<number> {
+  override readonly supportsRawArtifacts = false
+
   static inject = ['sessions']
 
   static Config: z<Config> = z.object({
diff --git a/packages/session/session-persistence/README.i18n.yaml b/packages/session/session-persistence/README.i18n.yaml
index 8228e1bb92..b7a04de848 100644
--- a/packages/session/session-persistence/README.i18n.yaml
+++ b/packages/session/session-persistence/README.i18n.yaml
@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/session/session-persistence/README.md
-README.md: c6875dbcfecdfd6ba4eb46d75feca1fbc6fc956d
-README.zh.md: 2ef5e9a90f0323f8edf8fdc4f936c41ca7e08c70
+README.md: 6e1898f8a49e54f8fe90ff27cf8571c5959f27e9
+README.zh.md: 901c41b6894d86bdc4ffb345314a3dd506e4a770
diff --git a/packages/session/session-persistence/README.md b/packages/session/session-persistence/README.md
index c6875dbcfe..6e1898f8a4 100644
--- a/packages/session/session-persistence/README.md
+++ b/packages/session/session-persistence/README.md
@@ -11,6 +11,8 @@ The persisted unit IS the existing `SessionEvent` (event-sourced model — the l
 | Method | Contract |
 |---|---|
 | `locate(meta): SessionLocation \| undefined` | Resolve an absolute per-session artifact target without I/O or materialization. Backends without an independent local artifact return `undefined`. |
+| `supportsRawArtifacts: boolean` | State explicitly whether this backend exposes one verbatim artifact per session. Consumers check this capability before calling `readRaw`; `false` is not session absence. |
+| `readRaw(id, signal?): Promise<SessionRawArtifact \| undefined>` | Read a supported backend's own artifact text verbatim, decoded from its physical encoding but never reconstructed from events. `undefined` means only that the requested artifact is absent; an unsupported backend rejects. |
 | `create(meta): Promise<void>` | Register a new session's metadata. MAY defer the physical write until the first `append` (lazy materialization). |
 | `append(id, events): Promise<void>` | Durably persist a batch. Append-only; first event `seq` == stored next-seq after any repair; rejects non-JSON-serializable data naming the offending type. |
 | `prepare(id, signal?): Promise<SessionPreparation>` | Reserve the exact unpublished Session used by resume. A coordinator reuses an earlier inspection when available, commits pending recovery, and releases an unpublished reservation back to its bounded cache on disposal. |
diff --git a/packages/session/session-persistence/README.zh.md b/packages/session/session-persistence/README.zh.md
index 2ef5e9a90f..901c41b689 100644
--- a/packages/session/session-persistence/README.zh.md
+++ b/packages/session/session-persistence/README.zh.md
@@ -11,6 +11,8 @@
 | 方法 | 约定 |
 |---|---|
 | `locate(meta): SessionLocation \| undefined` | 在不执行 I/O 或实体化的情况下解析绝对的每会话产物目标。没有独立本地产物的后端返回 `undefined`。 |
+| `supportsRawArtifacts: boolean` | 明确说明该后端是否为每个会话暴露一份逐字工件。Consumer 在调用 `readRaw` 前检查此能力；`false` 并不表示会话缺失。 |
+| `readRaw(id, signal?): Promise<SessionRawArtifact \| undefined>` | 读取受支持后端自身的逐字工件文本；只解码物理编码，绝不从事件重建。`undefined` 仅表示所请求工件缺失；不支持的后端会拒绝。 |
 | `create(meta): Promise<void>` | 注册新会话元数据。可以将物理写入延迟到第一次 `append`（延迟实体化）。 |
 | `append(id, events): Promise<void>` | 持久保存一个批次。仅追加；任何修复后，第一个事件 `seq` == 已存储 next-seq；非 JSON 可序列化数据会被拒绝，并命名违规类型。 |
 | `prepare(id, signal?): Promise<SessionPreparation>` | 预留恢复所使用的那个未发布 Session。协调器会尽可能复用之前的检查结果、提交待处理恢复，并在 dispose 时将未发布 reservation 释放回有界缓存。 |
diff --git a/packages/session/session-persistence/src/index.ts b/packages/session/session-persistence/src/index.ts
index aa01f68f7a..d579dc46d9 100644
--- a/packages/session/session-persistence/src/index.ts
+++ b/packages/session/session-persistence/src/index.ts
@@ -95,24 +95,32 @@ export abstract class SessionPersistence extends Service {
    */
   abstract locate(meta: SessionHeader): SessionLocation | undefined
 
+  /**
+   * Whether this backend exposes one verbatim raw artifact per session.
+   * A backend that declares `true` must override {@link readRaw}.
+   */
+  abstract readonly supportsRawArtifacts: boolean
+
   /**
    * Read a session's backend-owned artifact text verbatim — the exact durable
    * bytes the backend wrote (decoded from its physical encoding, e.g. a
    * decompressed JSONL). The returned `content` is the raw text, not a
    * reconstruction from parsed events, so it preserves backend-specific
-   * serialization (chunk packing, key order, line breaks). Backends without a
-   * per-session artifact (SQLite) inherit the `undefined` default.
+   * serialization (chunk packing, key order, line breaks). Callers first test
+   * {@link supportsRawArtifacts}; `undefined` then means only that the requested
+   * session has no materialized artifact.
    * @param _id - the persisted session to read (unused by the default: no
    * per-session artifact).
    * @param signal - optional cancellation for backend read work.
    * @returns the raw artifact plus its parsed header, or `undefined` when the
-   * session is absent or the backend owns no per-session artifact.
+   * session is absent.
+   * @throws when this backend does not expose per-session raw artifacts.
    */
   readRaw(_id: SessionId, signal?: AbortSignal): Promise<SessionRawArtifact | undefined> {
     if (signal?.aborted === true) {
       return Promise.reject(signal.reason instanceof Error ? signal.reason : new Error('aborted'))
     }
-    return Promise.resolve(undefined)
+    return Promise.reject(new Error('this session persistence backend does not expose raw artifacts'))
   }
 
   /**
diff --git a/packages/session/session-persistence/tests/persistence.spec.ts b/packages/session/session-persistence/tests/persistence.spec.ts
index 5ea3d905e9..50ad798e04 100644
--- a/packages/session/session-persistence/tests/persistence.spec.ts
+++ b/packages/session/session-persistence/tests/persistence.spec.ts
@@ -68,6 +68,8 @@ interface CoordinatorInternals {
  * durable behavior is covered by the JSONL and SQLite backends.
  */
 class MemoryPersistence extends SessionPersistence implements PersistenceBackend<never> {
+  override readonly supportsRawArtifacts = false
+
   static inject = ['sessions']
 
   override readonly name = 'session-persistence-memory'
@@ -247,11 +249,14 @@ runPersistenceContract('memory', async () => {
 })
 
 describe('the inherited readRaw default', () => {
-  it('answers undefined and honors an aborted signal', async () => {
+  it('rejects unsupported reads distinctly from absence and honors an aborted signal', async () => {
     const ctx = new Context()
     await ctx.plugin(SessionStore)
     await ctx.plugin(MemoryPersistence)
-    expect(await ctx.sessionPersistence.readRaw(SessionId('any-session'))).toBeUndefined()
+    expect(ctx.sessionPersistence.supportsRawArtifacts).toBe(false)
+    await expect(
+      ctx.sessionPersistence.readRaw(SessionId('any-session')),
+    ).rejects.toThrow('does not expose raw artifacts')
     await expect(
       ctx.sessionPersistence.readRaw(SessionId('any-session'), AbortSignal.abort()),
     ).rejects.toThrow()
diff --git a/scripts/rescope-vendor.ts b/scripts/rescope-vendor.ts
index 45f936e58b..d6f84efd63 100644
--- a/scripts/rescope-vendor.ts
+++ b/scripts/rescope-vendor.ts
@@ -242,8 +242,8 @@ const EXACT_EDITS: readonly ExactEdit[] = [
   {
     id: 'vendor-readme-local-modification-log',
     file: 'vendor/README.md',
-    find: '\n18. **`cordis/package.json` publishes `src`**',
-    replace: '\n17. **`@deepseek-ai` rescope**: every vendored manifest `name`, every internal dependency entry among the vendored set, and every module specifier that reaches them use the scoped names in the manifest table\'s `npm name` column. Directory names, version numbers, and dependency ranges are unchanged, and no upstream runtime identifier is renamed — `Symbol.for(\'schemastery\')` and Schemastery\'s `vendor:` metadata field keep their upstream values. Re-apply with `pnpm run rescope-vendor --apply` after a sync; the table\'s two name columns are the mapping, restated for consumers in [docs/rescope.md](../docs/rescope.md).\n18. **`cordis/package.json` publishes `src`**',
+    find: '\n16. **`cordis/package.json` publishes `src`**',
+    replace: '\n16. **`cordis/package.json` publishes `src`**: added `src` to the `files` list, joining the other eight vendored packages. Cordis declares `"./src/*": "./src/*"` in its exports, so a tarball without `src` publishes an export map pointing at absent files; the release change judgement also reads `files` to decide whether a diff reaches the payload, and a package whose only published paths are build output has no tracked path to match.\n17. **`@deepseek-ai` rescope**: every vendored manifest `name`, every internal dependency entry among the vendored set, and every module specifier that reaches them use the scoped names in the manifest table\'s `npm name` column. Directory names, version numbers, and dependency ranges are unchanged, and no upstream runtime identifier is renamed — `Symbol.for(\'schemastery\')` and Schemastery\'s `vendor:` metadata field keep their upstream values. Re-apply with `pnpm run rescope-vendor --apply` after a sync; the table\'s two name columns are the mapping, restated for consumers in [docs/rescope.md](../docs/rescope.md).',
     expect: 1,
   },
   {