No automated contract test between this API and the Globe-Wallet/mobile clients

[ndii-dev]

Three other repos (Globe-Wallet, mobile) are described in this README as consumers of this API, but there's no contract/integration test anywhere confirming their expected request/response shapes actually match what this service returns (especially now that /wallet/send responses would need to reflect any future changes like fee-bump or structured error codes from other issues here). Set up cross-repo contract testing.

Definition of done:

• Machine-checkable contract (e.g. generated from the OpenAPI spec once it exists) that consumer repos can validate against
• CI in this repo fails if a response shape changes in a way that would break the documented contract
• At minimum, the /wallet/send and /account/:publicKey/balances shapes (the two most directly consumed) are covered first

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Before opening a PR for this issue, read CONTRIBUTING.md.

This is not a starter-issue. The Definition of done above is the full
acceptance criteria, not a subset to sample from — a PR that addresses part
of it is an unfinished issue, not a smaller one. Your PR must include, in
the PR description itself:

• Root cause / design-decision rationale in your own words — not a restatement of this issue
• Every Definition of done bullet above addressed explicitly, with a one-line note on how
• Evidence the code actually runs: pasted test/build output, a screen recording or before/after screenshots for UI changes, or real (non-mocked) logs for network/contract-facing work
• New or updated tests included and shown passing (paste the output)
• Any adjacent/related behavior this issue calls out re-verified, not assumed unaffected

PRs missing these will be sent back before review, not reviewed and rejected — please do this up front.

[heymide]

I'm interested in contributing to this issue because maintaining a stable API contract is critical when multiple applications depend on the same service.

My approach is to establish a machine-verifiable API contract based on the project's OpenAPI specification (or generate one if appropriate) and introduce contract tests for the most critical endpoints, starting with /wallet/send and /account/:publicKey/balances. This will ensure response structures remain consistent across consumer applications such as Globe-Wallet and Mobile.

I'll integrate the contract validation into CI so breaking API changes are detected automatically before they are merged. In addition, I'll include comprehensive contract tests, verify adjacent response behavior, and provide the required test/build output and implementation rationale in the PR to satisfy the project's contribution guidelines.

I have experience building TypeScript APIs, designing contract-driven integrations, and implementing automated testing pipelines, and I'm confident I can deliver a robust solution that improves compatibility and prevents regressions across dependent repositories.