I've noticed this bug after merging the following PR: TanStack/query#5597

When bundle: true is set, index.js (ESM) file looks like this:

import "./chunk-55J6XMHW.js";
import {
  QueriesObserver
} from "./chunk-FVYPMHO2.js";
import {
  QueryClient
} from "./chunk-6F4EPMPD.js";
import {
  QueryCache
} from "./chunk-5EQKN4WB.js";
import "./chunk-CSKZ3U2N.js";
...

When bundle: false is set, index.js (ESM) file looks like this:

import { CancelledError } from "./retryer";
import { QueryCache } from "./queryCache";
import { QueryClient } from "./queryClient";
import { QueryObserver } from "./queryObserver";
import { QueriesObserver } from "./queriesObserver";
import { InfiniteQueryObserver } from "./infiniteQueryObserver";
...

I expected that tsup would also add the required .mjs (or .js when "type": "module" is set) to relative imports within the project, like rollup did. This causes import errors when imported in ESM projects (e.g. Vite). For now, I've added https://github.com/favware/esbuild-plugin-file-path-extensions, but this seems to force override some tsup settings.