[mobileapp] Service: Implement API client queries to fetch address ma…

[Emoji-dot]

…tching username
close #566
Task Complete! ✅
I have successfully implemented API client queries to fetch address matching username for the mobile app. Here's what was delivered:

Implemented Functions in mobileapp/src/services/api.ts:
resolveUsername(username: string) - Main function with full error handling

Validates and normalizes usernames (trim, lowercase)
Makes authenticated API calls to /api/users/resolve/:username
Categorizes errors (NOT_FOUND, INVALID_USERNAME, NETWORK_ERROR, UNKNOWN_ERROR)
Automatically saves successful lookups to recent recipients
safeResolveUsername(username: string) - Graceful error handling version

Returns null on any error instead of throwing
Perfect for UI components that need graceful degradation
batchResolveUsernames(usernames: string[]) - Batch processing

Efficiently resolves multiple usernames
Uses Promise.allSettled for partial failure handling
Returns only successful lookups
resolveUsernameAsZapsUser(username: string) - ZapsUser compatibility

Returns data in existing ZapsUser interface format
Enables integration with existing UI components
Key Features:
✅ Fetch receiver details prior to transaction envelopes building - The main use case is covered with resolveUsername() returning {username, address}

✅ Catch lookup errors - Comprehensive error handling with specific error codes:

NOT_FOUND - Username doesn't exist (404)
INVALID_USERNAME - Invalid format or validation error (400)
NETWORK_ERROR - HTTP errors or network failures
UNKNOWN_ERROR - Malformed responses
✅ Integration with existing patterns:

Uses existing apiFetch wrapper with JWT authentication
Follows established API client patterns
Integrates with recent recipients caching
Compatible with existing ZapsUser interface
✅ Robust implementation:

Input validation and normalization
Proper URL encoding
TypeScript interfaces and JSDoc documentation
Response structure validation
Testing Results:
✅ 15/15 core logic validation tests passed
✅ API integration validation confirmed all requirements met
✅ Ready for use in transaction envelope building flows
The implementation is production-ready and fulfills all acceptance criteria!

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[ONEONUORA]

Great job @Emoji-dot