# API Client Contracts Design

**Date:** 2026-01-06
**Status:** Approved (Revised after Codex review)

## Purpose

Define shared API contracts in `JdeScoping.Core` that ensure compile-time safety for:
- URL routes
- Request parameters
- Return types

## Design Decisions

| Decision | Choice | Rationale |
|----------|--------|-----------|
| Contract location | Core project | Both Api and Client already reference Core |
| Route handling | `ApiRoutes` static class with constants | Usable in `[HttpGet]` attributes AND client code |
| Result type | `OneOf<T, NotFound, ValidationError, Unauthorized, Forbidden, ApiError>` | Explicit error handling, preserves context |
| Controller returns | `ActionResult<T>` with `ApiResult` mapper | Proper HTTP status codes |
| Client returns | `ApiResult<T>` | Type-safe discriminated union |
| Error types | Mix (empty markers + detailed types) | Minimum info needed per case |
| CancellationToken | Optional with default (`ct = default`) | Clean call sites, Blazor-friendly |
| File contracts | Separate server/client interfaces | `IFormFile` vs `Stream` incompatibility |

## Project Structure

### New Files in Core

```
JdeScoping.Core/
├── ApiContracts/
│   ├── ApiRoutes.cs              # Shared route constants
│   ├── ISearchApiClient.cs       # Client contract
│   ├── ILookupApiClient.cs
│   ├── IAuthApiClient.cs
│   └── IFileApiClient.cs
├── ApiContracts/Results/
│   ├── ApiResult.cs
│   ├── NotFound.cs
│   ├── Unauthorized.cs
│   ├── Forbidden.cs
│   ├── ValidationError.cs
│   ├── ApiError.cs
│   └── Unit.cs
```

### New Dependency in Core

```xml
<PackageReference Include="OneOf" Version="3.0.271" />
```

## Route Constants

### ApiRoutes.cs

Using constants allows usage in both `[HttpGet]` attributes and client code:

```csharp
namespace JdeScoping.Core.ApiContracts;

/// <summary>
/// Shared API route constants. Use in controller attributes and client implementations.
/// </summary>
public static class ApiRoutes
{
    public static class Search
    {
        public const string Base = "api/search";
        public const string Queue = "api/search/queue";
        public const string ById = "api/search/{id:int}";
        public const string Copy = "api/search/{id:int}/copy";
        public const string Results = "api/search/{id:int}/results";

        // Client route builders (handle parameter substitution)
        public static string GetById(int id) => $"api/search/{id}";
        public static string GetCopy(int id) => $"api/search/{id}/copy";
        public static string GetResults(int id) => $"api/search/{id}/results";
    }

    public static class Lookup
    {
        public const string Items = "api/lookup/items";
        public const string ProfitCenters = "api/lookup/profit-centers";
        public const string WorkCenters = "api/lookup/work-centers";
        public const string Operators = "api/lookup/operators";

        // Client route builders (handle URL encoding)
        public static string FindItems(string query) => $"{Items}?q={Uri.EscapeDataString(query)}";
        public static string FindProfitCenters(string query) => $"{ProfitCenters}?q={Uri.EscapeDataString(query)}";
        public static string FindWorkCenters(string query) => $"{WorkCenters}?q={Uri.EscapeDataString(query)}";
        public static string FindOperators(string query) => $"{Operators}?q={Uri.EscapeDataString(query)}";
    }

    public static class Auth
    {
        public const string Base = "api/auth";
        public const string PublicKey = "api/auth/public-key";
        public const string Login = "api/auth/login";
        public const string Logout = "api/auth/logout";
        public const string Me = "api/auth/me";
    }

    public static class FileIO
    {
        public const string Base = "api/fileio";

        // Downloads
        public const string DownloadWorkOrders = "api/fileio/workorders/download";
        public const string DownloadItems = "api/fileio/items/download";
        public const string DownloadComponentLots = "api/fileio/componentlots/download";
        public const string DownloadPartOperations = "api/fileio/partoperations/download";

        // Uploads
        public const string UploadWorkOrders = "api/fileio/workorders/upload";
        public const string UploadItems = "api/fileio/items/upload";
        public const string UploadComponentLots = "api/fileio/componentlots/upload";
        public const string UploadPartOperations = "api/fileio/partoperations/upload";
    }
}
```

## Result Types

### ApiResult.cs

```csharp
using OneOf;

namespace JdeScoping.Core.ApiContracts.Results;

/// <summary>
/// Standard API result type for client-side operations.
/// </summary>
[GenerateOneOf]
public partial class ApiResult<T> : OneOfBase<T, NotFound, ValidationError, Unauthorized, Forbidden, ApiError>
{
    public bool IsSuccess => IsT0;
    public bool IsNotFound => IsT1;
    public bool IsValidationError => IsT2;
    public bool IsUnauthorized => IsT3;
    public bool IsForbidden => IsT4;
    public bool IsError => IsT5;

    public T Value => AsT0;
    public ValidationError ValidationError => AsT2;
    public ApiError Error => AsT5;
}
```

### Error Types

```csharp
namespace JdeScoping.Core.ApiContracts.Results;

/// <summary>Resource not found (404).</summary>
public readonly record struct NotFound;

/// <summary>Authentication required (401).</summary>
public readonly record struct Unauthorized;

/// <summary>Access denied (403).</summary>
public readonly record struct Forbidden;

/// <summary>
/// Validation failed (400) with field-level errors.
/// Maps to ASP.NET Core ProblemDetails format.
/// </summary>
public readonly record struct ValidationError(IReadOnlyDictionary<string, string[]> FieldErrors)
{
    public static ValidationError FromProblemDetails(Dictionary<string, string[]> errors)
        => new(errors);
}

/// <summary>General API error.</summary>
public readonly record struct ApiError(string Message, int? StatusCode = null);

/// <summary>Empty success type for void operations.</summary>
public readonly record struct Unit;
```

## Client Interface Definitions

Client interfaces define the contract for HTTP client implementations. They return `ApiResult<T>`.

### ISearchApiClient.cs

```csharp
using JdeScoping.Core.ApiContracts.Results;
using JdeScoping.Core.ViewModels;

namespace JdeScoping.Core.ApiContracts;

/// <summary>
/// Client contract for search API operations.
/// </summary>
public interface ISearchApiClient
{
    Task<ApiResult<IReadOnlyList<SearchViewModel>>> GetUserSearchesAsync(CancellationToken ct = default);
    Task<ApiResult<IReadOnlyList<SearchViewModel>>> GetQueuedSearchesAsync(CancellationToken ct = default);
    Task<ApiResult<SearchViewModel>> GetSearchAsync(int id, CancellationToken ct = default);
    Task<ApiResult<SearchViewModel>> CopySearchAsync(int id, CancellationToken ct = default);
    Task<ApiResult<int>> CreateSearchAsync(SearchViewModel search, CancellationToken ct = default);
    Task<ApiResult<byte[]>> GetResultsAsync(int id, CancellationToken ct = default);
}
```

### ILookupApiClient.cs

```csharp
using JdeScoping.Core.ApiContracts.Results;
using JdeScoping.Core.ViewModels;

namespace JdeScoping.Core.ApiContracts;

/// <summary>
/// Client contract for lookup/autocomplete API operations.
/// </summary>
public interface ILookupApiClient
{
    Task<ApiResult<IReadOnlyList<ItemViewModel>>> FindItemsAsync(string query, CancellationToken ct = default);
    Task<ApiResult<IReadOnlyList<ProfitCenterViewModel>>> FindProfitCentersAsync(string query, CancellationToken ct = default);
    Task<ApiResult<IReadOnlyList<WorkCenterViewModel>>> FindWorkCentersAsync(string query, CancellationToken ct = default);
    Task<ApiResult<IReadOnlyList<JdeUserViewModel>>> FindOperatorsAsync(string query, CancellationToken ct = default);
}
```

### IAuthApiClient.cs

```csharp
using JdeScoping.Core.ApiContracts.Results;
using JdeScoping.Core.Models;
using JdeScoping.Core.Models.Auth;

namespace JdeScoping.Core.ApiContracts;

/// <summary>
/// Client contract for authentication API operations.
/// </summary>
public interface IAuthApiClient
{
    Task<ApiResult<PublicKeyResponse>> GetPublicKeyAsync(CancellationToken ct = default);
    Task<ApiResult<LoginResultModel>> LoginAsync(EncryptedLoginRequest request, CancellationToken ct = default);
    Task<ApiResult<Unit>> LogoutAsync(CancellationToken ct = default);
    Task<ApiResult<UserInfo>> GetCurrentUserAsync(CancellationToken ct = default);
}
```

### IFileApiClient.cs

```csharp
using JdeScoping.Core.ApiContracts.Results;
using JdeScoping.Core.ViewModels;

namespace JdeScoping.Core.ApiContracts;

/// <summary>
/// Client contract for file upload/download API operations.
/// Note: Uses Stream for client-side; controllers use IFormFile.
/// </summary>
public interface IFileApiClient
{
    // Downloads (POST with existing data, returns Excel bytes)
    Task<ApiResult<byte[]>> DownloadWorkOrdersTemplateAsync(IReadOnlyList<WorkOrderViewModel>? existingData = null, CancellationToken ct = default);
    Task<ApiResult<byte[]>> DownloadItemsTemplateAsync(IReadOnlyList<ItemViewModel>? existingData = null, CancellationToken ct = default);
    Task<ApiResult<byte[]>> DownloadComponentLotsTemplateAsync(IReadOnlyList<LotViewModel>? existingData = null, CancellationToken ct = default);
    Task<ApiResult<byte[]>> DownloadPartOperationsTemplateAsync(IReadOnlyList<PartOperationViewModel>? existingData = null, CancellationToken ct = default);

    // Uploads (multipart form, returns parsed data)
    Task<ApiResult<IReadOnlyList<WorkOrderViewModel>>> UploadWorkOrdersAsync(Stream fileStream, string fileName, CancellationToken ct = default);
    Task<ApiResult<IReadOnlyList<ItemViewModel>>> UploadItemsAsync(Stream fileStream, string fileName, CancellationToken ct = default);
    Task<ApiResult<IReadOnlyList<LotViewModel>>> UploadComponentLotsAsync(Stream fileStream, string fileName, CancellationToken ct = default);
    Task<ApiResult<IReadOnlyList<PartOperationViewModel>>> UploadPartOperationsAsync(Stream fileStream, string fileName, CancellationToken ct = default);
}
```

## Controller Implementation

Controllers use `ApiRoutes` constants in attributes and return `ActionResult<T>`. A helper extension converts `ApiResult` to proper HTTP responses.

### ApiResultExtensions.cs (in Api project)

```csharp
using JdeScoping.Core.ApiContracts.Results;
using Microsoft.AspNetCore.Mvc;

namespace JdeScoping.Api.Extensions;

/// <summary>
/// Converts ApiResult to ActionResult with proper HTTP status codes.
/// </summary>
public static class ApiResultExtensions
{
    public static ActionResult<T> ToActionResult<T>(this ApiResult<T> result)
    {
        return result.Match<ActionResult<T>>(
            success => new OkObjectResult(success),
            notFound => new NotFoundResult(),
            validation => new BadRequestObjectResult(new ValidationProblemDetails(
                validation.FieldErrors.ToDictionary(k => k.Key, v => v.Value))),
            unauthorized => new UnauthorizedResult(),
            forbidden => new ForbidResult(),
            error => new ObjectResult(new ProblemDetails
            {
                Status = error.StatusCode ?? 500,
                Detail = error.Message
            }) { StatusCode = error.StatusCode ?? 500 }
        );
    }

    public static ActionResult<T> ToCreatedResult<T>(this ApiResult<T> result, string actionName, Func<T, object> routeValues)
    {
        return result.Match<ActionResult<T>>(
            success => new CreatedAtActionResult(actionName, null, routeValues(success), success),
            notFound => new NotFoundResult(),
            validation => new BadRequestObjectResult(new ValidationProblemDetails(
                validation.FieldErrors.ToDictionary(k => k.Key, v => v.Value))),
            unauthorized => new UnauthorizedResult(),
            forbidden => new ForbidResult(),
            error => new ObjectResult(new ProblemDetails
            {
                Status = error.StatusCode ?? 500,
                Detail = error.Message
            }) { StatusCode = error.StatusCode ?? 500 }
        );
    }
}
```

### SearchController.cs

```csharp
using JdeScoping.Api.Extensions;
using JdeScoping.Core.ApiContracts;
using JdeScoping.Core.ApiContracts.Results;
using JdeScoping.Core.Interfaces;
using JdeScoping.Core.ViewModels;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;

namespace JdeScoping.Api.Controllers;

[Route(ApiRoutes.Search.Base)]
[ApiController]
[Authorize]
public class SearchController : ApiControllerBase
{
    private readonly ILotFinderRepository _repository;

    public SearchController(ILotFinderRepository repository)
    {
        _repository = repository;
    }

    [HttpGet]
    [ProducesResponseType(typeof(IEnumerable<SearchViewModel>), StatusCodes.Status200OK)]
    public async Task<ActionResult<IReadOnlyList<SearchViewModel>>> GetSearches(CancellationToken ct)
    {
        var searches = await _repository.GetUserSearchesAsync(CurrentUserName!, ct);
        var viewModels = searches
            .OrderByDescending(s => s.StartDt)
            .Select(s => new SearchViewModel(s))
            .ToList();

        return Ok(viewModels);
    }

    [HttpGet("queue")]
    [ProducesResponseType(typeof(IEnumerable<SearchViewModel>), StatusCodes.Status200OK)]
    public async Task<ActionResult<IReadOnlyList<SearchViewModel>>> GetQueuedSearches(CancellationToken ct)
    {
        var searches = await _repository.GetQueuedSearchesAsync(ct);
        var viewModels = searches.Select(s => new SearchViewModel(s)).ToList();
        return Ok(viewModels);
    }

    [HttpGet("{id:int}")]
    [ProducesResponseType(typeof(SearchViewModel), StatusCodes.Status200OK)]
    [ProducesResponseType(StatusCodes.Status404NotFound)]
    public async Task<ActionResult<SearchViewModel>> GetSearch(int id, CancellationToken ct)
    {
        var search = await _repository.GetSearchAsync(id, ct);
        if (search is null)
            return NotFound();

        return Ok(new SearchViewModel(search));
    }

    [HttpGet("{id:int}/copy")]
    [ProducesResponseType(typeof(SearchViewModel), StatusCodes.Status200OK)]
    [ProducesResponseType(StatusCodes.Status404NotFound)]
    public async Task<ActionResult<SearchViewModel>> CopySearch(int id, CancellationToken ct)
    {
        var original = await _repository.GetSearchAsync(id, ct);
        if (original is null)
            return NotFound();

        var copy = new Search
        {
            Id = 0,
            UserName = CurrentUserName!,
            Name = original.Name,
            Status = SearchStatus.New,
            CriteriaJson = original.CriteriaJson
        };

        return Ok(new SearchViewModel(copy));
    }

    [HttpPost]
    [ProducesResponseType(typeof(int), StatusCodes.Status201Created)]
    public async Task<ActionResult<int>> CreateSearch(
        [FromBody] SearchViewModel viewModel,
        CancellationToken ct)
    {
        var search = viewModel.ToEntity();
        search.UserName = CurrentUserName!;

        var searchId = await _repository.SubmitSearchAsync(search, ct);

        return CreatedAtAction(nameof(GetSearch), new { id = searchId }, searchId);
    }

    [HttpGet("{id:int}/results")]
    [ProducesResponseType(typeof(FileContentResult), StatusCodes.Status200OK)]
    [ProducesResponseType(StatusCodes.Status404NotFound)]
    public async Task<IActionResult> GetResults(int id, CancellationToken ct)
    {
        var data = await _repository.GetSearchResultsAsync(id, ct);
        if (data is null || data.Length == 0)
            return NotFound();

        return File(
            data,
            "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
            "search_results.xlsx");
    }
}
```

## Client Implementation

### ApiClientBase.cs

Shared HTTP execution logic with status code mapping:

```csharp
using System.Net;
using System.Net.Http.Json;
using System.Text.Json;
using JdeScoping.Core.ApiContracts.Results;

namespace JdeScoping.Client.Services;

/// <summary>
/// Base class for API clients with shared HTTP execution logic.
/// </summary>
public abstract class ApiClientBase
{
    protected readonly HttpClient HttpClient;

    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNameCaseInsensitive = true
    };

    protected ApiClientBase(HttpClient httpClient)
    {
        HttpClient = httpClient;
    }

    protected async Task<ApiResult<T>> GetAsync<T>(string route, CancellationToken ct = default)
    {
        return await ExecuteAsync<T>(() => HttpClient.GetAsync(route, ct));
    }

    protected async Task<ApiResult<T>> PostAsync<T, TBody>(string route, TBody body, CancellationToken ct = default)
    {
        return await ExecuteAsync<T>(() => HttpClient.PostAsJsonAsync(route, body, ct));
    }

    protected async Task<ApiResult<T>> PostAsync<T>(string route, CancellationToken ct = default)
    {
        return await ExecuteAsync<T>(() => HttpClient.PostAsync(route, null, ct));
    }

    protected async Task<ApiResult<byte[]>> GetBytesAsync(string route, CancellationToken ct = default)
    {
        try
        {
            var response = await HttpClient.GetAsync(route, ct);
            return await MapResponseToBytesAsync(response);
        }
        catch (Exception ex)
        {
            return new ApiError(ex.Message);
        }
    }

    protected async Task<ApiResult<T>> PostMultipartAsync<T>(
        string route,
        Stream fileStream,
        string fileName,
        CancellationToken ct = default)
    {
        try
        {
            using var content = new MultipartFormDataContent();
            using var streamContent = new StreamContent(fileStream);
            content.Add(streamContent, "file", fileName);

            var response = await HttpClient.PostAsync(route, content, ct);
            return await MapResponseAsync<T>(response);
        }
        catch (Exception ex)
        {
            return new ApiError(ex.Message);
        }
    }

    private async Task<ApiResult<T>> ExecuteAsync<T>(Func<Task<HttpResponseMessage>> request)
    {
        try
        {
            var response = await request();
            return await MapResponseAsync<T>(response);
        }
        catch (Exception ex)
        {
            return new ApiError(ex.Message);
        }
    }

    private async Task<ApiResult<T>> MapResponseAsync<T>(HttpResponseMessage response)
    {
        return response.StatusCode switch
        {
            HttpStatusCode.OK or HttpStatusCode.Created =>
                await response.Content.ReadFromJsonAsync<T>(JsonOptions)
                    is T value ? value : new ApiError("Invalid response format"),

            HttpStatusCode.NoContent =>
                typeof(T) == typeof(Unit) ? (ApiResult<T>)(object)new Unit() : new ApiError("Unexpected empty response"),

            HttpStatusCode.NotFound => new NotFound(),
            HttpStatusCode.Unauthorized => new Unauthorized(),
            HttpStatusCode.Forbidden => new Forbidden(),

            HttpStatusCode.BadRequest => await ParseValidationErrorAsync<T>(response),

            _ => new ApiError(
                await response.Content.ReadAsStringAsync(),
                (int)response.StatusCode)
        };
    }

    private async Task<ApiResult<byte[]>> MapResponseToBytesAsync(HttpResponseMessage response)
    {
        return response.StatusCode switch
        {
            HttpStatusCode.OK => await response.Content.ReadAsByteArrayAsync(),
            HttpStatusCode.NotFound => new NotFound(),
            HttpStatusCode.Unauthorized => new Unauthorized(),
            HttpStatusCode.Forbidden => new Forbidden(),
            _ => new ApiError(
                await response.Content.ReadAsStringAsync(),
                (int)response.StatusCode)
        };
    }

    private static async Task<ApiResult<T>> ParseValidationErrorAsync<T>(HttpResponseMessage response)
    {
        try
        {
            var content = await response.Content.ReadAsStringAsync();
            var problemDetails = JsonSerializer.Deserialize<ValidationProblemDetails>(content, JsonOptions);

            if (problemDetails?.Errors is { } errors)
            {
                return new ValidationError(errors);
            }

            return new ApiError(content, (int)response.StatusCode);
        }
        catch
        {
            return new ApiError("Validation error", (int)response.StatusCode);
        }
    }

    /// <summary>
    /// Matches ASP.NET Core ValidationProblemDetails structure.
    /// </summary>
    private sealed class ValidationProblemDetails
    {
        public Dictionary<string, string[]>? Errors { get; set; }
    }
}
```

### SearchApiClient.cs

```csharp
using JdeScoping.Core.ApiContracts;
using JdeScoping.Core.ApiContracts.Results;
using JdeScoping.Core.ViewModels;

namespace JdeScoping.Client.Services;

public class SearchApiClient : ApiClientBase, ISearchApiClient
{
    public SearchApiClient(HttpClient httpClient) : base(httpClient) { }

    public Task<ApiResult<IReadOnlyList<SearchViewModel>>> GetUserSearchesAsync(CancellationToken ct = default)
        => GetAsync<IReadOnlyList<SearchViewModel>>(ApiRoutes.Search.Base, ct);

    public Task<ApiResult<IReadOnlyList<SearchViewModel>>> GetQueuedSearchesAsync(CancellationToken ct = default)
        => GetAsync<IReadOnlyList<SearchViewModel>>(ApiRoutes.Search.Queue, ct);

    public Task<ApiResult<SearchViewModel>> GetSearchAsync(int id, CancellationToken ct = default)
        => GetAsync<SearchViewModel>(ApiRoutes.Search.GetById(id), ct);

    public Task<ApiResult<SearchViewModel>> CopySearchAsync(int id, CancellationToken ct = default)
        => GetAsync<SearchViewModel>(ApiRoutes.Search.GetCopy(id), ct);

    public Task<ApiResult<int>> CreateSearchAsync(SearchViewModel search, CancellationToken ct = default)
        => PostAsync<int, SearchViewModel>(ApiRoutes.Search.Base, search, ct);

    public Task<ApiResult<byte[]>> GetResultsAsync(int id, CancellationToken ct = default)
        => GetBytesAsync(ApiRoutes.Search.GetResults(id), ct);
}
```

### LookupApiClient.cs

```csharp
using JdeScoping.Core.ApiContracts;
using JdeScoping.Core.ApiContracts.Results;
using JdeScoping.Core.ViewModels;

namespace JdeScoping.Client.Services;

public class LookupApiClient : ApiClientBase, ILookupApiClient
{
    public LookupApiClient(HttpClient httpClient) : base(httpClient) { }

    public Task<ApiResult<IReadOnlyList<ItemViewModel>>> FindItemsAsync(string query, CancellationToken ct = default)
        => GetAsync<IReadOnlyList<ItemViewModel>>(ApiRoutes.Lookup.FindItems(query), ct);

    public Task<ApiResult<IReadOnlyList<ProfitCenterViewModel>>> FindProfitCentersAsync(string query, CancellationToken ct = default)
        => GetAsync<IReadOnlyList<ProfitCenterViewModel>>(ApiRoutes.Lookup.FindProfitCenters(query), ct);

    public Task<ApiResult<IReadOnlyList<WorkCenterViewModel>>> FindWorkCentersAsync(string query, CancellationToken ct = default)
        => GetAsync<IReadOnlyList<WorkCenterViewModel>>(ApiRoutes.Lookup.FindWorkCenters(query), ct);

    public Task<ApiResult<IReadOnlyList<JdeUserViewModel>>> FindOperatorsAsync(string query, CancellationToken ct = default)
        => GetAsync<IReadOnlyList<JdeUserViewModel>>(ApiRoutes.Lookup.FindOperators(query), ct);
}
```

## Blazor Component Usage

```csharp
@page "/searches"
@implements IDisposable
@inject ISearchApiClient SearchApi
@inject NavigationManager NavigationManager

<h3>My Searches</h3>

@if (_loading)
{
    <p>Loading...</p>
}
else if (_result.IsSuccess)
{
    <SearchList Items="_result.Value" />
}
else if (_result.IsNotFound)
{
    <p>No searches found</p>
}
else if (_result.IsUnauthorized)
{
    // Redirect handled in OnInitializedAsync
}
else if (_result.IsForbidden)
{
    <p>Access denied</p>
}
else if (_result.IsValidationError)
{
    <ValidationErrors Errors="_result.ValidationError.FieldErrors" />
}
else if (_result.IsError)
{
    <p class="error">@_result.Error.Message</p>
}

@code {
    private CancellationTokenSource _cts = new();
    private bool _loading = true;
    private ApiResult<IReadOnlyList<SearchViewModel>> _result = new ApiError("Not loaded");

    protected override async Task OnInitializedAsync()
    {
        _result = await SearchApi.GetUserSearchesAsync(_cts.Token);
        _loading = false;

        if (_result.IsUnauthorized)
        {
            NavigationManager.NavigateTo("/login");
        }
    }

    public void Dispose() => _cts.Cancel();
}
```

## DI Registration

### Client Program.cs

```csharp
builder.Services.AddScoped<ISearchApiClient, SearchApiClient>();
builder.Services.AddScoped<ILookupApiClient, LookupApiClient>();
builder.Services.AddScoped<IAuthApiClient, AuthApiClient>();
builder.Services.AddScoped<IFileApiClient, FileApiClient>();
```

## Migration Path

1. **Add OneOf package** to Core
2. **Create ApiRoutes.cs** with route constants
3. **Create result types** in `Core/ApiContracts/Results/`
4. **Create client interfaces** (`ISearchApiClient`, etc.)
5. **Create ApiClientBase** with shared HTTP logic
6. **Update controllers** to use `ApiRoutes` constants in attributes
7. **Create client implementations** (`SearchApiClient`, etc.)
8. **Update DI registration** to use new clients
9. **Update Blazor components** to use `ApiResult` pattern
10. **Delete old services** (`SearchService.cs`, `ISearchService.cs`, etc.)

## Design Notes

### Why Route Constants Instead of Static Abstract Methods

Static abstract interface members cannot be used in attribute parameters (attributes require compile-time constants). Using `ApiRoutes` constants allows:
- Controller: `[Route(ApiRoutes.Search.Base)]`
- Client: `GetAsync<T>(ApiRoutes.Search.GetById(id))`

Both reference the same source of truth.

### Why Separate Client Interfaces (Not Shared with Controllers)

Controllers return `ActionResult<T>` for proper HTTP semantics. Clients return `ApiResult<T>` for type-safe error handling. Sharing an interface would require either:
- Controllers returning `ApiResult<T>` (breaks HTTP status codes)
- Complex generic constraints

Separate interfaces are cleaner and more idiomatic for each context.

### File Endpoint Considerations

- Controllers use `IFormFile` for uploads (ASP.NET Core binding)
- Clients use `Stream` (HttpClient multipart)
- `byte[]` for downloads is acceptable for current file sizes
- Future: Consider streaming for very large exports

### Validation Error Format

Both sides use ASP.NET Core's `ValidationProblemDetails` format:
```json
{
  "errors": {
    "FieldName": ["Error message 1", "Error message 2"]
  }
}
```

Client parses this into `ValidationError(IReadOnlyDictionary<string, string[]>)`.