Maintaining 99% crash-free sessions at 20 million users, for Southeast Asia's largest fashion marketplace

The problem wasn't a broken product. It was a growth problem.

With 20 million users on iOS and Android, every release had to land at 99% crash-free. Falling below that in a competitive fashion marketplace meant user churn. In Southeast Asia's e-commerce market, loyalty is thin and the next app is one tap away.

The product roadmap wasn't waiting. The team needed a recommendation engine that could serve different results per vendor and per region. Their analytics setup couldn't surface event-level data fast enough to drive product decisions. They needed an influencer platform: onboarding flow, campaign management, and promo code tracking. And they needed to support multiple CMS systems simultaneously, with UI driven by the CMS response type.

Internal hiring couldn't keep pace. Onboarding a new mobile engineer takes months. Every month without the right people was a release cycle that slipped. In a market where a single bad release is front-page news, slipping wasn't an option.

Wednesday embedded 3-4 engineers directly into the marketplace's mobile team. Not a parallel track. The same review bar, the same release process, the same daily rhythm.

The first priority was the crash-free target. The team wrote exhaustive automated tests covering the full regression surface. Every release had to clear that gate before it moved.

Recommendation engine. The marketplace needed to serve different results per vendor and per region. The engine the squad built pulls from multiple underlying sources, controlled by feature flags. The product team can run regional experiments and vendor-specific configurations without touching the release cycle.

Analytics migration. The existing analytics setup couldn't surface event-level data at the speed the product team needed to act on. The squad migrated to Segment, building the new pipeline in parallel with the live system so no data was lost in transition. The product team gained real-time event analysis for the first time.

Influencer module. The marketplace's influencer program had no infrastructure. The squad built the onboarding flow, campaign management, and promo code tracking. Influencers got a self-serve path. The business got a trackable revenue channel.

Backend-driven authentication. Registration and login screens were static. The squad rebuilt them as configurable, server-driven pages. Product could iterate on the flows without a new release dependency.

CMS integration. The marketplace ran multiple CMS systems simultaneously. The squad built a dynamic UI layer that rendered the right component type based on the CMS response. No single CMS was coupled to the mobile layer.

Throughout, the standard held. Wednesday engineers followed the client's code review process, adopted their tools and workflow, and attended their daily syncs. The 99% crash-free rate didn't move.

Six platform improvements shipped. The crash rate held at 99% across every release.

The recommendation engine went live with feature flag control across all regions. The analytics migration gave the product team real-time event data for the first time, enabling faster feature prioritization. The influencer module launched a trackable revenue channel that didn't exist before. The backend-driven auth pages gave the product team full configuration control without a release dependency.

The engagement started in January 2021. It's still running.

For a marketplace at this scale, that longevity is the result. Three years of embedded mobile engineering while the product grew, the feature set expanded, and the user base continued to scale.