API completeness validation

Ensure APIs are complete by validating that all necessary cases are handled, all required arguments are properly validated, and response structures are consistent across similar operations.

Key areas to check:

1. Switch statement completeness: When adding new enum values or operation types, ensure all switch statements that handle them include the new cases
2. Argument validation coverage: Test all invalid argument combinations, not just the happy path scenarios
3. Response structure consistency: Maintain consistent field presence across similar API responses (e.g., if one response has top-level error codes, related responses should too)
4. Parameter naming consistency: Follow established naming conventions from KIPs and existing APIs

Example from the discussions:

// Incomplete - missing new RPC cases
case UPDATE_VOTER:
    handledSuccessfully = handleUpdateVoterResponse(response, currentTimeMs);
    break;
// Need to add:
case ADD_RAFT_VOTER:
    handledSuccessfully = handleAddVoterResponse(response, currentTimeMs);
    break;
case REMOVE_RAFT_VOTER:
    handledSuccessfully = handleRemoveVoterResponse(response, currentTimeMs);
    break;

This prevents runtime failures from unhandled cases and ensures consistent developer experience across the API surface.