docs: document programmatic configuration loading

website/docs/en/guide/api-reference.mdx

@@ -11,6 +11,7 @@ Rstack CLI provides a unified configuration API and re-exports the public APIs o
 | Import path              | Contents                                          | Use case                                |
 | ------------------------ | ------------------------------------------------- | --------------------------------------- |
 | `rstack`                 | Rstack CLI configuration API                      | Register tool configurations            |
+| `rstack/config`          | Configuration loader and its types                | Load shared and project configurations  |
 | `rstack/app`             | Public APIs from `@rsbuild/core`                  | Build applications and extend Rsbuild   |
 | `rstack/lib`             | Public APIs from `@rslib/core`                    | Build libraries and extend Rslib        |
 | `rstack/test`            | Public APIs from `@rstest/core`                   | Write tests and configure test projects |
@@ -71,6 +72,36 @@ import { js, reactPlugin, ts } from 'rstack/lint';
 
 For details about the available presets and plugins, see [Rslint rules and presets](https://rslint.rs/config/rules-and-presets).
 
+## Loading configurations
+
+### `loadRstackConfig()` \{#loadrstackconfig}
+
+Use `loadRstackConfig()` from `rstack/config` to load Rstack configurations in your own code:
+
+```ts
+import { loadRstackConfig } from 'rstack/config';
+
+const { configs, filePath, dependencies } = await loadRstackConfig({
+  cwd: process.cwd(),
+  configFilePath: './rstack.config.ts',
+});
+```
+
+The function accepts these optional parameters:
+
+- `cwd`: the directory to search for a configuration file. Relative `configFilePath` values are also resolved from this directory. Defaults to the current working directory.
+- `configFilePath`: a relative or absolute path to the configuration file. If omitted, the loader uses the path specified by the CLI's `--config` option. If neither is set, it searches `cwd` for the [default file names](./configuration#configuration-file).
+
+The returned object has these fields:
+
+- `configs`: configuration objects or functions for each tool, including project settings and inherited [shared configurations](./configuration#shared-configurations).
+- `filePath`: the loaded configuration file's path, or `null` if no file was found.
+- `dependencies`: paths to configuration dependencies collected by the loader.
+
+`loadRstackConfig()` only loads configurations; it does not run tool configuration functions. Before running a tool, the caller must resolve its configuration and initialize it.
+
+`rstack/config` also exports the related types: `LoadRstackConfigOptions` for the parameters, `LoadedRstackConfig` for the return value, and `Configs` for the tool configurations.
+
 ## TypeScript types
 
 These type-only entry points add ambient declarations to a TypeScript project. Add only the entries your project needs to [`compilerOptions.types`](https://www.typescriptlang.org/tsconfig/#types) in `tsconfig.json`.

website/docs/zh/guide/api-reference.mdx

@@ -11,6 +11,7 @@ Rstack CLI 提供统一的配置 API，并通过专用子路径重导出 Rsbuild
 | 导入路径                 | 内容                                      | 使用场景                 |
 | ------------------------ | ----------------------------------------- | ------------------------ |
 | `rstack`                 | Rstack CLI 配置 API                       | 注册各项工具配置         |
+| `rstack/config`          | 配置加载器及其类型                        | 加载公共配置和项目配置   |
 | `rstack/app`             | `@rsbuild/core` 的公开 API                | 构建应用及扩展 Rsbuild   |
 | `rstack/lib`             | `@rslib/core` 的公开 API                  | 构建库及扩展 Rslib       |
 | `rstack/test`            | `@rstest/core` 的公开 API                 | 编写测试及配置测试项目   |
@@ -71,6 +72,36 @@ import { js, reactPlugin, ts } from 'rstack/lint';
 
 可用的预设和插件请参阅 [Rslint 规则和预设](https://rslint.rs/config/rules-and-presets)。
 
+## 加载配置 \{#loading-configurations}
+
+### `loadRstackConfig()` \{#loadrstackconfig}
+
+使用 `rstack/config` 导出的 `loadRstackConfig()`，可以在代码中加载 Rstack 配置：
+
+```ts
+import { loadRstackConfig } from 'rstack/config';
+
+const { configs, filePath, dependencies } = await loadRstackConfig({
+  cwd: process.cwd(),
+  configFilePath: './rstack.config.ts',
+});
+```
+
+支持以下可选参数：
+
+- `cwd`：查找配置文件的目录。`configFilePath` 为相对路径时，也以此目录为基准。默认为当前工作目录。
+- `configFilePath`：配置文件路径，可以是相对路径或绝对路径。省略时，优先使用 CLI 通过 `--config` 指定的路径；若也未指定，则在 `cwd` 中按[默认文件名](./configuration#configuration-file)查找配置。
+
+返回对象包含以下字段：
+
+- `configs`：各工具的配置对象或函数，包含项目配置及继承的[公共配置](./configuration#shared-configurations)。
+- `filePath`：加载的配置文件路径，未找到文件时为 `null`。
+- `dependencies`：加载器收集到的配置依赖路径列表。
+
+`loadRstackConfig()` 仅负责加载配置，不会执行工具配置函数。调用方仍需完成相应工具的配置解析和初始化，才能运行工具。
+
+`rstack/config` 还导出相关类型：`LoadRstackConfigOptions`（参数）、`LoadedRstackConfig`（返回值）和 `Configs`（工具配置）。
+
 ## TypeScript 类型 \{#typescript-types}
 
 以下纯类型入口用于为 TypeScript 项目补充环境类型声明。请仅将项目需要的入口添加到 `tsconfig.json` 的 [`compilerOptions.types`](https://www.typescriptlang.org/tsconfig/#types) 中。