feat(plugin-sdk): add TypeScript SDK for Infinite Canvas plugins with automatic JSX and build support

plugins/canvas/sdk/README.md

@@ -0,0 +1,77 @@
+# @infinite-canvas/plugin-sdk
+
+Infinite Canvas 画布节点插件的 **TypeScript SDK**。插件作者只写节点 UI 与逻辑,类型、JSX、运行时桥接、构建全部由 SDK 提供;产物仍是宿主加载器现有契约的 ESM(React external,宿主单例)。
+
+## 提供什么
+
+| 能力 | 说明 |
+| --- | --- |
+| **完整类型** | `CanvasPlugin` / `CanvasNodeDefinition` / `CanvasNodeContext` / `CanvasAgentOp` / `CanvasTheme` / `CanvasNodeData` … 全部有提示 |
+| `definePlugin(...)` | 给插件对象(或工厂)补全类型;对象形式无需再 `const { React } = runtime` |
+| automatic JSX | `jsxImportSource` 指向本包,TSX 自动转发到宿主 React,**不打包第二份 React** |
+| 类型化 hooks | `import { useState, useEffect, useMemo, useRef, ... }`,运行时转发宿主 React |
+| `buildPlugin(...)` | 统一 esbuild 构建,插件 `build.mjs` 只需一行 |
+
+## 最小插件
+
+```tsx
+// src/index.tsx
+import { definePlugin, useState } from "@infinite-canvas/plugin-sdk";
+import type { CanvasNodeContentProps } from "@infinite-canvas/plugin-sdk";
+
+function Content({ ctx }: CanvasNodeContentProps) {
+    const [n, setN] = useState(0);
+    return (
+        <button onMouseDown={(e) => e.stopPropagation()} onClick={() => setN((v) => v + 1)} style={{ color: ctx.theme.node.text }}>
+            {ctx.node.title}: {n}
+        </button>
+    );
+}
+
+export default definePlugin({
+    id: "my-plugin",
+    name: "我的插件",
+    version: "1.0.0",
+    nodes: [
+        {
+            type: "my-plugin:node",
+            title: "示例",
+            icon: "✨",
+            defaultSize: { width: 240, height: 160 },
+            Content,
+        },
+    ],
+});
+```
+
+```js
+// build.mjs
+import { buildPlugin } from "@infinite-canvas/plugin-sdk/build";
+await buildPlugin(import.meta.url);
+```
+
+`npm run build` 产出 `dist/<目录名>.js` 并同步到 `web/public/plugins/`。
+
+## 依赖接入
+
+插件 `package.json`:
+
+```json
+{
+    "type": "module",
+    "scripts": { "build": "node build.mjs", "dev": "node build.mjs --watch", "typecheck": "tsc --noEmit" },
+    "devDependencies": {
+        "@infinite-canvas/plugin-sdk": "file:../sdk",
+        "@types/react": "19.1.12",
+        "typescript": "^5"
+    }
+}
+```
+
+插件 `tsconfig.json` 关键项:`"jsx": "react-jsx"`、`"jsxImportSource": "@infinite-canvas/plugin-sdk"`、`"moduleResolution": "bundler"`。
+
+## 设计约束
+
+- **React 单例**:JSX 与 hooks 惰性读取 `globalThis.InfiniteCanvasRuntime.React`(宿主在加载插件前注入),react 全程 external,绝不打包第二份。
+- **重依赖**:three、marked 等在源码里 `await import("https://esm.sh/...")` 动态加载,esbuild 自动 external,不进 bundle。
+- **类型真源**:`src/types.ts` 是宿主 `web/src/types/canvas-plugin.ts` 公开契约的镜像;宿主契约变更时同步此处。