fix: address ds-review-bot v7 findings on the merged image-input head

- gate model selection on steering-placement image carriers from enqueue
  until their steering/message event publishes; release the gate when an
  admission ends idle without publication (both behaviorally asserted)
- reject session.updateQueue edits carrying non-text blocks at the RPC
  boundary (queue edits cannot bypass image admission)
- extend the durable-directory walk past a first-created DSH_HOME to the
  deepest pre-existing ancestor
- strip Windows-style separators from attachment display names on POSIX
- verify attachment reads with a header-only probe (digest already proves
  the bytes decoded fully at admission); document the read path
- make SessionInputShell.addImages refusal observable and keep workspace
  transfers/composer intake from leaking refused drafts
- own ONE recursive image walk (dsh-llm contentHasImage) across apiproxy,
  pi-ai, compact-basic, and the DeepSeek text-only assertion
- drop the redundant canonical-base64 regex and the no-op role read
- move AttachmentId/AttachmentError out of types.ts (brand.ts/error.ts);
  document why AttachmentError does not extend HarnessError
- document the hard attachments inject in both consumer READMEs

packages/client/connection/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/connection/README.md
-README.md: 6f4d8bf15fb581d184a1bb36c912a88a319adf26
-README.zh.md: 6ae5291aee8e7e12d78a9c06c2ed9a1432b4f2a0
+README.md: 4a4ce324a0482072164d3c4f6badd464bfacfc6f
+README.zh.md: 7fb421ae206563a625df5bd53fbcef1f585bd269

packages/client/connection/README.md

@@ -22,5 +22,6 @@ None; this package neither assembles nor sends a provider request.
 
 ## Known Limitations and Deferred Work
 
+- **`attachments` is a hard inject** — the route plugin (and `host-apiproxy`) will not mount until an attachment backend provides `ctx.attachments`, and a composition missing one stalls silently as a cordis inject gap rather than failing loud; text-only deployments therefore still carry the native `sharp` dependency through `attachment-local`. A capability-degraded (image-refusing) mount is deliberate deferred work.
 - **history's implicit resume is arguable** — opening history on an unattached session pulls an agent up host-side; the pure-persistence-read alternative is recorded in the rt-core reconciliation ledger, unchanged in P-I. This package's consumers see it as latency on first open.
 - **`ToolEventView`/`ToolCallView`/`ToolResultView` re-exports are scheduled for removal** — they fall when the toolview migration deletes the host `viewFor` line (presentation belongs to the client); the fixture keeps a local `viewFor` mirror until then.

packages/client/connection/README.zh.md

@@ -22,5 +22,6 @@ node 半侧在桥接前守卫 `/api` 下的每个请求（`src/api-request-trust
 
 ## 已知限制与暂缓事项
 
+- **`attachments` 是硬性注入依赖**：路由插件（以及 `host-apiproxy`）在附件后端提供 `ctx.attachments` 之前不会挂载；缺少后端的组合会以 cordis 注入缺口的形式静默停滞，而非响亮失败；因此纯文本部署也会经由 `attachment-local` 携带原生 `sharp` 依赖。降级为拒绝图片的挂载方式是有意延期的工作。
 - **history 的隐式恢复存在争议**：在未附加的会话上打开 history，会在主机侧拉起 agent；纯持久化读取的替代方案记录在 rt-core 协调账本中，P-I 不作改变。该包的消费方会在首次打开时感受到这段延迟。
 - **计划移除 `ToolEventView`／`ToolCallView`／`ToolResultView` 的重新导出**：当 toolview 迁移删除主机 `viewFor` 行时，它们会一并移除（呈现属于客户端）；在此之前，fixture 保留一份局部 `viewFor` 镜像。