docs(typescript6): note @typescript/old layout for path-based tooling

packages/typescript6/README.md

@@ -7,3 +7,39 @@ It also reexports the TypeScript 6 API, so you can import it in your code:
 ```ts
 import ts6 from "@typescript/typescript6";
 ```
+
+## Side-by-side with TypeScript 7
+
+TypeScript 7 does not yet ship a stable programmatic API. For tools that still need the TypeScript 6 JS API (for example typescript-eslint), install this package alongside TypeScript 7 via npm aliases. See [Running Side-by-Side with TypeScript 6.0](https://devblogs.microsoft.com/typescript/announcing-typescript-7-0/#running-side-by-side-with-typescript-6.0).
+
+Recommended layout:
+
+```json
+{
+  "devDependencies": {
+    "@typescript/native": "npm:typescript@^7.0.2",
+    "typescript": "npm:@typescript/typescript6@^6.0.2"
+  }
+}
+```
+
+## Package layout (`@typescript/old`)
+
+This package depends on [`@typescript/old`](https://www.npmjs.com/package/@typescript/old) (`npm:typescript@^6`), which contains the real TypeScript 6 API implementation.
+
+After install, `node_modules/typescript` (when aliased to this package) is a thin compatibility entrypoint. The large API bundle lives under:
+
+```text
+node_modules/@typescript/old/lib/typescript.js
+```
+
+If you use **path-based** ignores or excludes aimed at `node_modules/typescript/` (for example Jest `transformIgnorePatterns`, bundler excludes, or size checks), also cover `node_modules/@typescript/`. Otherwise tools may still process the ~8MB `@typescript/old` bundle.
+
+Example (Jest):
+
+```js
+transformIgnorePatterns: [
+  "/node_modules/typescript/",
+  "/node_modules/@typescript/",
+]
+```