feat: show cache hit rate in web session info

README.md

@@ -129,6 +129,8 @@ Playwright 不下载独立 Chromium。首次 `setup` 只缓存 MCP 的 Node.js
 
 MCP 服务器可通过 Web UI 左下角的 MCP 按钮可视化配置（写入 `data/agent/mcp.json`）：支持 stdio（命令 + 参数）与 HTTP（URL + 请求头 + OAuth/Bearer）两种传输、环境变量键值编辑、工作目录、生命周期与超时设置，另保留原始 JSON 编辑兜底。保存后重启 pi（或 /reload）生效。
 
+Web UI 右上角的会话信息栏会汇总 Token 使用情况；当模型返回缓存读写数据时，还会显示按 Token 加权计算的缓存命中率：`cacheRead / (input + cacheRead + cacheWrite)`，不计输出 Token。
+
 #### 记忆模式
 
 默认设置 `PI_MEMORY_NO_SEARCH=1` 和 `PI_MEMORY_QMD_UPDATE=off`。这不会削弱 Markdown 记忆、每日日志、scratchpad 或恢复记录，但会跳过 qmd 探测、安装提示和 `memory_search` 工具，因此全新安装不会自动下载 qmd 的本地模型。集成补丁会在 `setup` 以及每次启动前自动检查并重放，受管插件重装后无需手工修改。
@@ -324,6 +326,8 @@ Playwright never downloads a standalone Chromium in this project. Setup caches o
 
 MCP servers can be configured visually from the MCP button in the lower-left Web UI (writes `data/agent/mcp.json`): stdio (command + args) or HTTP (URL + headers + OAuth/Bearer) transport, environment-variable row editing, working directory, lifecycle and timeout options, plus raw JSON editing as a fallback. Changes take effect after restarting pi (or /reload).
 
+The Web UI session-info panel in the upper-right summarizes Token usage. When a model reports cache read/write data, it also shows the token-weighted cache hit rate: `cacheRead / (input + cacheRead + cacheWrite)`, excluding output Tokens.
+
 #### Memory modes
 
 The managed launcher defaults to `PI_MEMORY_NO_SEARCH=1` and `PI_MEMORY_QMD_UPDATE=off`. Markdown memory, daily logs, scratchpad, and recovery stay available, while qmd detection, its installation notice, and the `memory_search` tool are skipped. A deterministic integration patch is checked during setup and before every launch, so reinstalling managed packages needs no manual repair.