[Chore] Deduplicate route logic between api/v1 serverless functions and apps/api Fastify server

[collinsezedike]

Summary

api/v1/ (Vercel serverless functions) and apps/api/ (Fastify server) both implement the same set of routes (vaults, positions, tx/deposit, tx/withdraw, tx/add-trustline, tx/submit) as separate handler files. They share the underlying @meridian/shared and @meridian/stellar-sdk-helpers packages, but the routing, request parsing, and response shaping is written and maintained twice.

Motivation

Every endpoint change has to be made in two places by hand, and nothing in the type system enforces that they stay in sync. A behavior fix applied to one (for example the CORS/rate-limit middleware) is not automatically applied to the other unless someone remembers to port it. This is a correctness risk, not just duplicated effort: the two layers can silently drift.

Proposed Solution

Extract the shared per-route logic (validation, calling into the SDK helpers, error shaping) into framework-agnostic functions in packages/shared or a new package, and have both the Vercel handlers and the Fastify routes call the same functions, differing only in the thin adapter layer that maps their respective request/response objects to the shared signature.

Scope

Field	Value
Area	API
Protocol affected	None
Network	N/A
Breaking change?	No

Alternatives Considered

Leaving them separate and relying on code review to catch drift: this is the current state and has already produced inconsistencies between the two layers.

Acceptance Criteria

• Shared route logic lives in one place, called by both api/v1/ and apps/api/
• No behavior change for either API surface
• pnpm lint && pnpm typecheck && pnpm test pass with no regressions

[Ayinkx1]

Hi i would like to work on this issue please assign to me
I can do it perfectly