feat: preview Agent HTML in conversations and unblock long replies

Agent replies that produced HTML could only be read as source, so users had
to copy the markup into an external file to see the result. Completed Agent
and Subagent output now renders complete HTML documents, single-root HTML
replies, and `html` / `htm` code blocks as an isolated static preview in
place. Each preview keeps a persistent notice that scripts and network are
disabled and offers the same icon actions as Mermaid diagrams: a source
toggle and a full-screen preview. The new "render HTML in conversations"
switch under Platform Features / General is on by default, applies to the
open conversation immediately, and falls back to HTML source when disabled.
Previews cannot run scripts, reach the network, submit forms, open windows,
or load remote media; author stylesheets and inline styles are preserved so
the intended layout survives, and remote resource loading is refused by the
preview CSP instead.

Direct-model replies no longer fail once they grow large. The byte caps on
streaming responses, single stream blocks, non-streaming replies, model tool
arguments, tool request context, aggregate tool results, and accumulated
answer text are removed, so users stop seeing "模型接口流式响应超过安全限制"
on long answers. Response length is now governed by the request timeout,
cancellation, and context compression. Image generation responses keep their
decodable-image validation.

A message sent after a failed or interrupted run stayed in the pending queue
instead of running. The conversation is now released whenever a run reaches
any terminal state, not only when the renderer reports readiness again, and a
dispatched queue item whose run never starts releases its reservation and
returns to pending. Later messages dispatch without extra user action.

Release note: Agent 回复中的 HTML 现在可直接在会话内预览，支持查看源码和全屏预览，默认开启并可在“平台功能 / 通用设置”关闭；直连模型的长回复不再因大小限制中断；上一次运行失败或被中断后，新发送的消息会立即执行而不再排队等待。

docs/features/direct-model-agent/progress.md

@@ -6,8 +6,8 @@
 | --- | --- |
 | 文档类型 | 功能进度 |
 | 状态 | 已实施，本机验收完成 |
-| 版本 | 0.3 |
-| 日期 | 2026-09-03 |
+| 版本 | 0.4 |
+| 日期 | 2026-09-05 |
 | 关联入口 | [直连模型 Agent 能力](./README.md) |
 
 ## 当前结论
@@ -126,6 +126,18 @@
 - `npm run build`：Main、Preload、Renderer 和控制面安装器均成功构建。2026-09-02 按产品
   决策移除未对应实际性能问题的 Renderer bundle 基线门禁后复验通过。
 
+## 2026-09-05 移除直连模型响应字节上限
+
+- 直连模型不再对流式响应总量、单个流式块、非流式回复、模型工具参数、工具请求上下文、
+  聚合工具结果和累计回答长度设置字节上限；长回复和大工具结果由请求超时、取消和上下文
+  压缩控制。用户不再看到“模型接口流式响应超过安全限制”。
+- 图像生成响应仍按可解码图片大小校验，Provider 错误响应仍读取有界文本。
+- 回归测试改为验证超过旧上限的长流式回复可以完整返回，以及超过 1 MB 的图片工具结果会
+  进入下一轮模型请求。
+- `npx vitest run src/main/agent/model-runtime.test.ts`：`74 passed, 1 skipped`。
+- 全量 `npm test`：`3493 passed, 55 skipped`。
+- `npm run typecheck`、`npm run lint` 和 `npm run build`：通过。
+
 ## 进度维护要求
 
 - 只有真实生产路径完成并验证后才能勾选实施项。