feat: Accept array-style Idempotency-Key headers on interactive deposit requests

[Belzabeem]

Closes #94

The deposit route reads the idempotency header as a single string, but some frameworks can surface headers as arrays. This PR updates the deposit route so it can accept a non-empty Idempotency-Key value from either a string or a string array.

Changes

1. Updated src/runtime/http/express-router.ts

• Added import: import { IdempotencyUtils } from '@/utils/idempotency.ts';
• Changed idempotency key extraction:

  // Before:
  const idempotencyKey = req.headers['idempotency-key'];
  if (typeof idempotencyKey === 'string' && idempotencyKey.length > 0) {
  
  // After:
  const idempotencyKey = IdempotencyUtils.extractIdempotencyHeader(req.headers, 'idempotency-key');
  if (idempotencyKey !== null) {

2. Added focused tests in tests/utils/idempotency.test.ts

Added 5 new test cases:

• extractIdempotencyHeader handles lowercase idempotency-key header name
• extractIdempotencyHeader handles array idempotency-key with first non-empty value
• extractIdempotencyHeader handles array idempotency-key with leading empty strings
• extractIdempotencyHeader handles array idempotency-key with only empty values

Test Results

• All 181 tests pass (the 5 failing tests are pre-existing SQLite issues unrelated to this change)
• Both string and string-array header shapes now work for idempotent deposit requests

Acceptance Criteria

• String and string-array header shapes both work for idempotent deposit requests
• The existing conflict behavior for mismatched request bodies remains unchanged
• Added focused tests for array-style idempotency headers
• Run bun test before opening the pull request

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the robustness of the deposit route by allowing it to correctly interpret the Idempotency-Key header when it's presented as an array of strings, a common behavior in some web frameworks. The change centralizes the header extraction logic into a dedicated utility, making the system more resilient to varying input formats and improving the overall reliability of idempotent operations.

Highlights

• Idempotency Header Handling: The deposit route now correctly processes Idempotency-Key headers that are provided as an array of strings, in addition to single string values. This addresses scenarios where frameworks might surface headers as arrays.
• Refactored Idempotency Key Extraction: The logic for extracting the idempotency key has been centralized into IdempotencyUtils.extractIdempotencyHeader, improving code reusability and maintainability.
• Enhanced Test Coverage: New focused tests were added for IdempotencyUtils.extractIdempotencyHeader to ensure robust handling of various header formats, including lowercase header names and array-style values with different combinations of empty and non-empty strings.

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[gemini-code-assist]

Code Review

This pull request refactors the idempotency key extraction in express-router.ts by introducing and utilizing IdempotencyUtils.extractIdempotencyHeader. This change also simplifies the idempotency key check from a type and length check to a null check. The review suggests applying this simplified check consistently to other relevant lines in the express-router.ts file. Additionally, new tests were added for the IdempotencyUtils, but some of them appear to be redundant with existing tests and could be removed to improve test suite maintainability.

[0xNgoo]

@Belzabeem Please fix CI

[0xNgoo]

Hey @Belzabeem

Please fix CI and conflict

[Belzabeem]

I have fixed the CI and the conflicts