I already have a fully functional TravelNDC-compliant flight booking engine. The core modules for flight booking, fare-rule application, and the automated reservation emails to both the traveller and our admin mailbox must stay exactly as they are—no regressions. What I need now is an extension that lets users plan complex itineraries in one go. • Search: Accept up to six legs in a single request, surface layover options, and let travellers toggle flexible dates (±3 days) or lock in exact dates. • Filters: Add a class-of-service selector (Economy, Premium, Business, First) that threads all the way through to the NDC OrderCreate payload. • UI: Expand the current single-/round-trip form into a multi-city layout while preserving visual consistency and our existing validation. • Access Control: Admin, registered members, and even guest visitors should all enjoy the new workflow without separate log-ins or feature flags. • Emails & Records: When an itinerary is confirmed, the existing reservation email template should populate the multi-city segments and send as usual to the traveller and admin. Acceptance criteria 1. Search response times remain within 1.5 × the current single-trip SLA. 2. Fare rules still parse and display for every individual leg. 3. All new fields map cleanly to our current database schema and NDC messages. 4. End-to-end QA passes on desktop and mobile. Tech stack is PHP (Laravel) with a Vue front-end; please stay inside those frameworks. I’ll provide the repo, API keys, and current documentation as soon as we start.