feat(web): 添加 embedded session runtime 并默认启用 || feat(web): Add embedded session runtime and enable it by default

[luzhongqiu]

概要

• 为 kimi web 增加进程内的 embedded runtime，同时保留现有的 subprocess runtime
• 将 Web runtime 的默认值切换为 embedded，并保留 KIMI_WEB_RUNTIME=process 作为回退开关
• 保持当前 Web API、WebSocket 协议和前端行为不变
• 将 session 工作目录从进程级 cwd 改为 session-local kaos 状态，避免 embedded 模式下的多 session 串扰

背景

#1641 讨论了 kimi web 是否还需要维持“每个 session 一个 worker 子进程”的模式。由于底层 CLI 已经可以作为 Python async 代码在进程内运行，因此这个 PR 尝试以最小改动验证 embedded 方案是否可行。

这次改动的目标是：

• 不改现有 API 和前端契约
• 在现有 subprocess 实现旁边新增 embedded 实现
• 通过 runtime 选择开关完成切换，而不是重写整个 Web 层

改动内容

• 新增 EmbeddedSessionProcess 和 EmbeddedWireWorker，用于进程内执行 session
• 保留原有 SessionProcess 作为 subprocess 实现，并在 KimiCLIRunner 中按配置选择 runtime
• 复用现有 wire 协议和 websocket 广播链路，前端无需迁移
• 将 kimi web 的默认 runtime 切换为 embedded
• 新增 ScopedLocalKaos，将 cwd 从进程级状态改为 session-local 状态
• 保持 ACP 的相对路径行为：ACP session 使用 session-scoped kaos fallback，而不是依赖全局 chdir

兼容性

这次改动有意保持现有 Web 接口契约不变：

• 不修改前端
• 不修改 web/api/* 路由
• 不修改 WebSocket 协议

如果需要回退到原有子进程模式，仍然可以通过：

KIMI_WEB_RUNTIME=process kimi web

测试

• uv run ruff check src/kimi_cli/web/app.py src/kimi_cli/web/runner/process.py src/kimi_cli/web/runner/embedded_process.py src/kimi_cli/web/runner/embedded_worker.py tests/web/test_runner.py
• uv run pytest tests/web/test_runner.py tests/vis/test_app.py
• uv run pytest packages/kaos/tests/test_local_kaos.py
• uv run pytest tests/acp/test_kaos.py tests/acp/test_session_notifications.py tests/acp/test_protocol_v1.py
• uv run pyright packages/kaos/src packages/kaos/tests src/kimi_cli/acp/server.py tests/acp/test_kaos.py

Refs #1641

---

Summary

• Add an in-process embedded runtime for kimi web while retaining the existing subprocess runtime
• Switch the default value of Web runtime to embedded and keep KIMI_WEB_RUNTIME=process as fallback switch
• Keep current Web API, WebSocket protocol and front-end behavior unchanged
• Change the session working directory from process-level cwd to session-local kaos state to avoid multi-session crosstalk in embedded mode

Background

#1641 discussed whether kimi web still needs to maintain the "one worker child process per session" mode. Since the underlying CLI can already run in-process as Python async code, this PR attempts to verify whether the embedded solution is feasible with minimal changes.

The goals of this change are:

• No changes to existing API and front-end contracts
• Add embedded implementation next to existing subprocess implementation
• Switching is done via a runtime selector instead of rewriting the entire web layer

Change content

• Added EmbeddedSessionProcess and EmbeddedWireWorker for in-process session execution
• Retain the original SessionProcess as subprocess implementation, and select the runtime according to configuration in KimiCLIRunner
• Reuse existing wire protocol and websocket broadcast link, no need to migrate the front end
• Switch the default runtime of kimi web to embedded
• Added ScopedLocalKaos to change cwd from process-level state to session-local state
• Maintain ACP's relative path behavior: ACP sessions use session-scoped kaos fallback instead of relying on global chdir

Compatibility

This change intentionally leaves the existing web interface contract unchanged:

• No modifications to the frontend
• Do not modify web/api/* routes
• Does not modify the WebSocket protocol

If you need to return to the original sub-process mode, you can still pass:

KIMI_WEB_RUNTIME=process kimi web

Test

• uv run ruff check src/kimi_cli/web/app.py src/kimi_cli/web/runner/process.py src/kimi_cli/web/runner/embedded_process.py src/kimi_cli/web/runner/embedded_worker.py tests/web/test_runner.py
• uv run pytest tests/web/test_runner.py tests/vis/test_app.py
• uv run pytest packages/kaos/tests/test_local_kaos.py
• uv run pytest tests/acp/test_kaos.py tests/acp/test_session_notifications.py tests/acp/test_protocol_v1.py
• uv run pyright packages/kaos/src packages/kaos/tests src/kimi_cli/acp/server.py tests/acp/test_kaos.py

Refs #1641

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