Callme Mobillity Ccar sales and rental platform in Spain

Performance Engineering & ROI Optimization: Retained by the client to optimize platform

performance driven by heavy ad-campaign traffic; integrated Upstash Redis for global caching,

implemented Lazy Loading, replaced heavy libraries with pure JavaScript to minimize bundle

size, and optimized assets to WebP, exceeding all target performance benchmarks and Core

Web Vitals.

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Concurrency & Race Condition Mitigation: Designed and engineered a state-driven booking

system for the rental vertical; pioneered a 7-minute server-side resource-locking

mechanism in the database to completely eliminate Race Conditions, preventing multiple

users from double-booking or purchasing the same vehicle simultaneously.

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Booking Funnel & Payment Automation: Architected a secure Booking Session pipeline that

tracks user steps to analyze drop-offs and friction points; integrated Stripe Webhooks to

seamlessly transition temporary sessions into real, immutable bookings upon successful

payment, preventing post-booking tampering.

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Infrastructure Recovery & Deliverability: Refactored legacy system modules to eliminate

critical bugs; resolved email delivery failures by implementing Zod for end-to-end type safety

between frontend and backend, and configured secure transactional mailing pipelines to

guarantee 100% email deliverability (preventing spam) for confirmations and password resets.

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Localization & Market Expansion (i18n): Implemented a production-ready i18n

multilingual architecture supporting English and Spanish, paired with dynamic rendering and

memoization (useMemo, useCallback) to deliver a localized, high-end 60fps user experience

tailored for the European market.