Bug: `Cannot read properties of undefined (reading '__CLIENT_INTERNALS_…')` on Vite + React 19

[dbuezas]

Environment

• agentation@3.0.2
• React 19.x, ReactDOM 19.x
• Vite (dev server, ESM)

Repro

1. Install agentation in a Vite + React 19 app
2. Render <Agentation endpoint="…" />
3. Click any element with the toolbar active

Error

Uncaught TypeError: Cannot read properties of undefined
  (reading '__CLIENT_INTERNALS_DO_NOT_USE_OR_WARN_USERS_THEY_CANNOT_UPGRADE')
  at getReactDispatcher (agentation.js:12205)
  at probeComponentSource (agentation.js:12273)
  at probeSourceWalk (agentation.js:12308)
  at getSourceLocation (agentation.js:12336)
  at detectSourceFile (agentation.js:13270)
  at HTMLDocument.handleClick (agentation.js:14458)

Root cause

src/utils/source-location.ts uses a default import:

import React from "react";

react does not have a default export — it's a namespace. Under tsup's CJS interop in your dev environment (and React 18's looser shape) the default-import shim makes this work. But under Vite's ESM resolution with React 19's exports map, the default import resolves to undefined, so React.__CLIENT_INTERNALS_… throws inside getReactDispatcher.

This is visible in the published bundle at dist/index.mjs line 7050:

// src/utils/source-location.ts
import React from "react";

Fix

Change the source to a namespace import:

import * as React from "react";

That keeps the React 18 / React 19 dual-shape guard inside getReactDispatcher working as intended (since the function already handles both __CLIENT_INTERNALS_… and __SECRET_INTERNALS_…).

Workaround for users on the current release

Apply a pnpm patch (or equivalent) editing dist/index.mjs line 7050 from import React from "react" to import * as React from "react".