fix: preserve drafts, canvas edits, and remote Continue tools

Keep paragraph formatting and checklist todos when removing canvas pages,
and preserve accepted undo/redo history after oversized input is rejected.
Merge restored queued text into the latest conversation draft and retain
image delivery when OCR returns image references and generated warnings only.

Deliver session MCP servers to bridged remote Continue Execute while keeping
Ask read-only and preserving local model-profile isolation. Add regression
coverage and update feature documentation. Correct stale conversation-limit
and forced-color assertions and the measured Electron layout test deadline.

Validation: 4,826 tests passed, 67 skipped; full typecheck and lint passed.
Current-source Linux x64 Execute/Ask/Execute MCP delivery passed, using 10
real text-provider requests and no image-provider requests. Image generation
itself was not exercised. Staged whitespace checks passed before commit.

Release note: 修复恢复队列时覆盖新输入、画布删页丢失清单格式及超限输入清空撤销历史的问题；图片 OCR 无正文时保留原图发送方式，远程 Continue Execute 正确保留会话 MCP 工具。

docs/features/remote-host/technical-design.md

@@ -230,7 +230,13 @@ Composer Runtime 菜单显示 OpenCode、Continue 和管理入口，不显示直
 DeepSeek Harness。项目与历史会话保留 OC/CN 选择；不支持的旧 selection 恢复为项目
 默认值。Main 校验已安装 Runtime 身份与选择一致，按相应 CN/OC 模型 profile 建立模型桥。
 本机配置的 SKILL 包和 stdio MCP Server 不上传或分配给远程 Runtime；远程 ACP Session
-继续使用空 MCP Server 列表。Node.js、Python 等工具执行环境同样不修改或同步到 Host，
+仅接收当前请求由 Agent 管理的 HTTP MCP 能力（例如 Execute 图片工具），不继承本机原生
+MCP 配置。Continue helper 将 ACP Session 的服务器作为显式 `sessionMcpServers` 交给
+共享 `ContinueHostAdapter`，与模型桥配置一起生成最终配置；不先写入会被独立模型分支
+丢弃的原生配置。新建、加载和续接 Session 使用当前列表，空列表清除旧能力；Ask 在 helper
+和 adapter 两层均不注入这些 Execute 能力。本机独立模型 profile 仍不继承原生 MCP，
+既有知识库和自定义 MCP 的显式分配规则不变。
+Node.js、Python 等工具执行环境同样不修改或同步到 Host，
 完整边界见[工具执行环境](../local-tool-environment/README.md)。
 
 ### Ask