@calcom/atoms crashes in Next.js App Router beyond version 2.6.0

[mogusbi-motech]

Issue Summary

@calcom/atoms@2.11.0 fails at runtime in a minimal Next.js App Router project when rendering the Booker atom from a client-only modal.

The same repro works on @calcom/atoms@2.6.0. The only intended difference between the working and failing branches is the package version and resulting lockfile changes.

Repro repo: https://github.com/mogusbi-motech/cal-com-atom-bundling-issue

Failing branch using @calcom/atoms@2.11.0:
https://github.com/mogusbi-motech/cal-com-atom-bundling-issue/tree/main

Working comparison branch using @calcom/atoms@2.6.0:
https://github.com/mogusbi-motech/cal-com-atom-bundling-issue/tree/working-2.6.0

The current failure appears to come from @calcom/atoms/dist/vendor/timezone-constants.js, which evaluates dayjs.tz.guess() before dayjs.tz is available.

Steps to Reproduce

1. Clone the repro:

   git clone https://github.com/mogusbi-motech/cal-com-atom-bundling-issue.git
   cd cal-com-atom-bundling-issue

2. Check out the failing branch:

   git checkout main

3. Install dependencies:

   pnpm install

4. Start the app:

   pnpm dev

5. Open the local Next.js URL.

6. Submit the form with valid Cal.com values:

   • Client ID
   • API URL, for example https://api.cal.com/v2
   • Username
   • Event slug

7. Click Open calendar modal.

For comparison, the same flow works on:

git checkout working-2.6.0
pnpm install
pnpm dev

Actual Results

• The calendar modal fails to load on @calcom/atoms@2.11.0.
• The browser shows:

Unhandled Runtime Error
TypeError: Cannot read properties of undefined (reading 'guess')

Call Stack
eval
node_modules/@calcom/atoms/dist/vendor/timezone-constants.js (4:21)

Before reaching this error, 2.11.0 also required adding Stripe packages because the top-level Atoms import pulls in payment modules:

Module not found: Can't resolve '@stripe/react-stripe-js'

Installing the Stripe dependencies resolves that module-resolution error, but the timezone runtime error remains.

Expected Results

• Importing and rendering CalProvider and Booker from @calcom/atoms should render the Booker atom successfully.
• Optional payment modules should not be required when the consuming app is not using payments.
• Package modules should not evaluate browser/runtime-sensitive values at module scope in a way that crashes before Booker renders.

Technical details

• Repro repo: https://github.com/mogusbi-motech/cal-com-atom-bundling-issue
• Failing branch: main
• Working branch: working-2.6.0
• Failing package version: @calcom/atoms@2.11.0
• Working package version: @calcom/atoms@2.6.0
• Next.js: 14.2.35
• React: 18.3.1
• Node.js: v24.14.1
• pnpm: 11.1.0

During incremental upgrade testing, these version ranges showed different failures:

Version range	Observation
2.6.0	Works.
2.7.0 to 2.8.2	Router/search-params runtime issue in the Booker path, with a failure like Cannot read properties of null (reading 'get').
2.8.3 to 2.8.9	Runtime failure from react-use/lib/usePrevious: TypeError: react_use_lib_usePrevious__WEBPACK_IMPORTED_MODULE_3__ is not a function.
2.9.0 to 2.11.0	Runtime failure from dist/vendor/timezone-constants.js: Cannot read properties of undefined (reading 'guess').

Evidence

The repro contains two branches that should make the difference easy to verify:

• main: fails with @calcom/atoms@2.11.0
• working-2.6.0: works with @calcom/atoms@2.6.0

The README contains the same reproduction notes:
https://github.com/mogusbi-motech/cal-com-atom-bundling-issue/blob/main/README.md