fix(api): avoid duplicate customer creation on lookup errors

[Adarsh9977]

What does this PR do?

• Fix createStripeCustomerId in API v2 so Stripe customer lookup failures no longer silently create duplicate customers.
• Only create a new Stripe customer when the email lookup succeeds and returns an empty list.
• Surface Stripe lookup/create failures as InternalServerErrorException instead of masking them with a fallback create.

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Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• [N/A] I have updated the developer docs if this PR makes changes that would require a documentation change. If N/A, write N/A here and check the checkbox.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

• Are there environment variables that should be set?
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[github-actions]

Welcome to Cal.diy, @Adarsh9977! Thanks for opening this pull request.

A few things to keep in mind:

• This is Cal.diy, not Cal.com. Cal.diy is a community-driven, fully open-source fork of Cal.com licensed under MIT. Your changes here will be part of Cal.diy — they will not be deployed to the Cal.com production app.
• Please review our Contributing Guidelines if you haven't already.
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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: a7f72191-7396-47ad-9145-970a394d3989

📥 Commits

Reviewing files that changed from the base of the PR and between 92ad7f5 and fb30c52.

📒 Files selected for processing (1)

• apps/api/v2/src/modules/stripe/stripe.service.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• apps/api/v2/src/modules/stripe/stripe.service.ts

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📝 Walkthrough

Walkthrough

createStripeCustomerId now validates that the first Stripe customer exists and has an identifier before reusing it. Otherwise, it creates a customer with an idempotency key based on the lowercased email. The error handler still throws InternalServerErrorException without binding an unused error variable.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the main change: preventing duplicate Stripe customer creation on lookup errors.
Description check	✅ Passed	The description is directly related to the Stripe customer lookup and fallback behavior changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@apps/api/v2/src/modules/stripe/stripe.service.ts`:
- Around line 245-250: Serialize the customers.list and stripe.customers.create
flow in the surrounding customer lookup method per user, or supply a stable
per-user idempotency key to creation, so concurrent requests cannot create
duplicate Stripe customers before stripeCustomerId is persisted. Preserve the
existing reuse of customersResponse.data[0].id and assignment of customerId for
both existing and newly created customers.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: a08def53-c924-465a-8321-c0dd70d21cfb

📥 Commits

Reviewing files that changed from the base of the PR and between f004349 and 92ad7f5.

📒 Files selected for processing (1)

• apps/api/v2/src/modules/stripe/stripe.service.ts