Add /accounts/:address/balance derived endpoint

[Miracle656]

Background

Wraith already stores every token transfer in Postgres. From this data, a derived balance per token can be computed without any live Stellar RPC call. A GET /accounts/:address/balance endpoint would give developers a fast cached balance view — useful for dashboards and analytics tools.

What to build

A new endpoint that computes per-token balance for an address by summing incoming transfers and subtracting outgoing ones.

Key files

• src/routes/accounts.ts — create this route file
• src/server.ts — register the new route
• prisma/schema.prisma — TokenTransfer model (from/to/amount/contract)

Suggested execution

git checkout -b feat/accounts-balance-endpoint

1. Create src/routes/accounts.ts
2. SQL aggregation: sum amount where to = address, minus sum where from = address, grouped by contractId
3. Return JSON: { balances: [{ token: "C...", balance: "12.50" }] }
4. Add a note in the response that this is a derived balance — may not include pre-indexer history
5. Register at GET /accounts/:address/balance

Example commit message:
feat(api): add /accounts/:address/balance derived balance endpoint

Acceptance criteria

• Returns per-token derived balance from indexed transfers
• Response includes derived_from_ledger field
• Returns empty balances array (not 404) for unknown addresses
• At least one test case

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Drips Wave · Complexity: Medium · 150 points
Comment below to request assignment. PR must include Closes #[this issue].

[K1NGD4VID]

@K1NGD4VID has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hi!
Please, assign me this issue. I’ve worked on similar derived balance and aggregation endpoints before, so I can implement the route, handle efficient SQL grouping, and return accurate per-token balances with proper tests. ETA: 3–4 hours

ℹ️ Repo Maintainers: To accept this application, review their application or assign @K1NGD4VID to this issue.

[drips-wave]

Congratulations, @K1NGD4VID! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

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[drips-wave]

This issue has been marked as completed by a Drips Wave moderator for @K1NGD4VID as part of the Stellar Wave Program's 4th Wave 🥳

Moderator's reason: [Auto-assessed] The PR successfully implements the requested /accounts/:address/balance endpoint using the specified SQL aggregation logic. It has been open for over 48 hours without maintainer objections and includes comprehensive test coverage and additional infrastructure like token metadata caching and Prometheus metrics.

😎 @K1NGD4VID: You earned 150 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here.

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ℹ️ Note: This issue was marked complete via moderation. Points were issued even though the GitHub issue remains open.