feat(acl): server endpoints + client + UI for circle membership

Round-trip out a long-standing hole in the ACL feature: until
this commit a circle on Yavsc was an empty named bucket. You
could create 'Famille' and grant it on a post, but the circle
carried no members, so 'Famille' authorised no one. The MVC
admin controller (Yavsc.Org.Controllers.CircleMembersController)
existed but had no REST counterpart, so PostIt — which only
talks to the Yavsc.Blogs API — had no way to manage membership
at all.

This commit closes that gap end-to-end:

Server (Yavsc.Blogs)
- GET    /api/circle/{id}/members           list members
- POST   /api/circle/{id}/members           add a user (body { userId })
- DELETE /api/circle/{id}/members/{userId}  remove a user
  All three are scoped to caller == circle.OwnerId; non-owned
  circles return 404 (not 403) to avoid leaking existence, in
  line with the rest of the controller.
- Two new DTOs (CircleMemberDto, AddCircleMemberDto) for the
  wire shapes. CircleMemberDto mirrors UserSearchResultDto
  minus Email — membership UI doesn't need contact details.

Tests (Yavsc.Blogs.Tests)
- CircleMembersApiTests: 5 [Fact] covering empty list,
  add+get, duplicate add → 409, remove, and cross-owner 404.
  Test users (alice, bob) are seeded directly through the
  in-memory DbContext — the Blogs fixture doesn't stand up
  UserManager<ApplicationUser>.

Client (Yavsc.Api.Client)
- CircleMemberDto + 3 methods on CircleApiClient:
  GetMembersAsync, AddMemberAsync, RemoveMemberAsync.
  All match the server's contract: 404 flattens to null,
  409 surfaces as an exception (callers can dedupe beforehand
  if they want idempotent behaviour).

UI (PostIt)
- CirclesPageViewModel gains a Members ObservableCollection
  that auto-loads on SelectedCircle change (via the partial
  setter generated by [ObservableProperty]). Commands:
  LoadMembersAsync, OpenAddMember (raises an event the view
  subscribes to), OnAddMemberConfirmedAsync (called by the
  view when the dialog confirms a selection), RemoveMemberAsync.
  409 (already a member) is detected from the exception
  message and surfaced as a friendly status rather than an
  error — a likely race when the same user gets added twice
  through two UI paths.

- CirclesPage layout is now two-pane (circles + editor on the
  left, members of the selected circle on the right). The
  member pane has an 'Ajouter un membre' button that opens
  AddCircleMemberDialog. Code-behind wires the dialog's
  Confirmed event back into the VM via an async lambda
  wrapper (EventHandler<T> wants void, the VM method is
  async Task).

- AddCircleMemberDialog is a ContentPage (light modal, same
  pattern as PostAclDialog). Its ViewModel consumes
  IUserDirectory — the abstraction introduced by 04a31709
  to fix the 'user search should not be IContactService'
  confusion. The dialog raises Confirmed with the picked
  UserSummary; the host (CirclesPage) is responsible for
  calling CircleApiClient.AddMemberAsync.

Out of scope (tracked in MEMORY.md, 2026-08-18):
- i18n: all visible text still hard-coded French.
- XAML accessibility audit of pre-existing pages.
- Avalonia.Headless UI tests of the new navigation flow.

Tests: 51/51 PostIt.Tests green, 20/20 Yavsc.Blogs.Tests
green (was 15; +5 for CircleMembersApiTests), 44/44
Yavsc.Org.Tests green (no regression).

src/PostIt/PostIt/ViewModels/AddCircleMemberDialogViewModel.cs

@@ -0,0 +1,118 @@
+using System;
+using System.Collections.ObjectModel;
+using System.Threading;
+using System.Threading.Tasks;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using PostIt.Services;
+using Yavsc.Api.Client;
+
+namespace PostIt.ViewModels;
+
+/// <summary>
+/// View model for the "add a Yavsc user to a circle" modal.
+///
+/// <para>Resolves users through <see cref="IUserDirectory"/>
+/// (which delegates to <c>/api/user-search</c>); the caller
+/// (CirclesPage) decides whether to add the picked user to
+/// the circle by calling
+/// <see cref="AddCircleMemberDialogViewModel.AddCommand"/>
+/// (which is bound to the dialog's "Ajouter" button).</para>
+///
+/// <para>The dialog itself doesn't know the target
+/// <c>CircleId</c>: that's set by the caller via the
+/// constructor and the dialog only triggers
+/// <see cref="IUserDirectory.SearchAsync"/> against the
+/// <see cref="SearchQuery"/> string. The "Add" command
+/// returns the picked <see cref="UserSummary"/> via the
+/// <see cref="Confirmed"/> event, and the hosting
+/// <c>CirclesPage</c> then calls
+/// <see cref="CircleApiClient.AddMemberAsync"/>.</para>
+/// </summary>
+public partial class AddCircleMemberDialogViewModel : ViewModelBase
+{
+    private readonly IUserDirectory _directory;
+
+    [ObservableProperty]
+    public partial string SearchQuery { get; set; } = string.Empty;
+
+    [ObservableProperty]
+    public partial ObservableCollection<UserSummary> Results { get; set; } = new();
+
+    [ObservableProperty]
+    public partial UserSummary? Selected { get; set; }
+
+    [ObservableProperty]
+    public partial bool IsBusy { get; set; }
+
+    [ObservableProperty]
+    public partial string StatusMessage { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Raised when the user confirms a selection. The hosting
+    /// <c>CirclesPage</c> subscribes to this event and calls
+    /// <c>CircleApiClient.AddMemberAsync</c> with the target
+    /// circle id + the picked user's id. The dialog itself
+    /// does not know the circle id by design: separation of
+    /// concerns — the modal is a user picker, not a
+    /// "circle joiner" form.
+    /// </summary>
+    public event EventHandler<UserSummary>? Confirmed;
+
+    public AddCircleMemberDialogViewModel(IUserDirectory directory)
+    {
+        _directory = directory ?? throw new ArgumentNullException(nameof(directory));
+    }
+
+    public override bool CanNavigateNext { get => throw new NotImplementedException(); protected set => throw new NotImplementedException(); }
+    public override bool CanNavigatePrevious { get => throw new NotImplementedException(); protected set => throw new NotImplementedException(); }
+
+    /// <summary>
+    /// Search the directory for users matching the current
+    /// <see cref="SearchQuery"/>. Triggered explicitly via the
+    /// "Rechercher" button — no debouncing, so the caller
+    /// stays in control of how often the network is hit.
+    /// </summary>
+    [RelayCommand]
+    public async Task SearchAsync()
+    {
+        if (string.IsNullOrWhiteSpace(SearchQuery))
+        {
+            Results.Clear();
+            StatusMessage = "Tapez un nom ou un email";
+            return;
+        }
+
+        IsBusy = true;
+        try
+        {
+            var hits = await _directory.SearchAsync(SearchQuery, CancellationToken.None).ConfigureAwait(true);
+            Results = new ObservableCollection<UserSummary>(hits ?? Array.Empty<UserSummary>());
+            StatusMessage = $"{Results.Count} résultat(s)";
+        }
+        catch (Exception ex)
+        {
+            StatusMessage = $"Erreur: {ex.Message}";
+        }
+        finally
+        {
+            IsBusy = false;
+        }
+    }
+
+    /// <summary>
+    /// Raise <see cref="Confirmed"/> for the currently selected
+    /// user. No-op when no selection has been made — keeps the
+    /// UI from firing an event with a null payload.
+    /// </summary>
+    [RelayCommand]
+    public void Add()
+    {
+        if (Selected is null)
+        {
+            StatusMessage = "Sélectionnez un utilisateur";
+            return;
+        }
+        Confirmed?.Invoke(this, Selected);
+    }
+}

src/PostIt/PostIt/ViewModels/CirclesPageViewModel.cs

@@ -1,8 +1,10 @@
 using System;
 using System.Collections.ObjectModel;
+using System.Linq;
 using System.Threading.Tasks;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
+using PostIt.Services;
 using Yavsc.Api.Client;
 using Yavsc.Api.Client.Dtos;
 
@@ -11,13 +13,24 @@ namespace PostIt.ViewModels;
 /// <summary>
 /// View model for the "Mes cercles" page. CRUD on the caller's own
 /// circles (the server scopes every endpoint to the caller's uid
-/// since the BlogAcl fix on this branch).
+/// since the BlogAcl fix on this branch), plus membership
+/// management on the currently selected circle.
 ///
 /// <para>The view lists circles in <see cref="Circles"/>, supports
 /// create / edit via <see cref="DraftName"/>, and exposes
 /// per-item Delete and per-item edit commands. <see cref="IsBusy"/>
 /// drives a progress overlay during API calls; <see cref="StatusMessage"/>
 /// surfaces success / error feedback in the view footer.</para>
+///
+/// <para>When the user selects a circle in the list,
+/// <see cref="LoadMembersAsync"/> fetches its members into
+/// <see cref="Members"/>. The "Add a member" command
+/// (<see cref="OpenAddMemberAsync"/>) is a UI event the view
+/// raises to open <c>AddCircleMemberDialog</c>; the dialog
+/// raises a <c>Confirmed</c> event back, which the page's
+/// code-behind forwards here via
+/// <see cref="OnAddMemberConfirmedAsync"/>. The "remove"
+/// command is per-row and runs inline.</para>
 /// </summary>
 public partial class CirclesPageViewModel : ViewModelBase
 {
@@ -37,12 +50,26 @@ public partial class CirclesPageViewModel : ViewModelBase
     [ObservableProperty]
     public partial bool DraftPublic { get; set; }
 
+    /// <summary>Members of the currently selected circle. Empty
+    /// when no circle is selected or after a refresh that
+    /// produced an empty list. Updated by
+    /// <see cref="LoadMembersAsync"/>.</summary>
+    [ObservableProperty]
+    public partial ObservableCollection<CircleMemberDto> Members { get; set; } = new();
+
     [ObservableProperty]
     public partial bool IsBusy { get; set; }
 
     [ObservableProperty]
     public partial string StatusMessage { get; set; } = string.Empty;
 
+    /// <summary>
+    /// Raised when the user wants to add a member to the
+    /// currently selected circle. The view listens to this
+    /// event and opens <c>AddCircleMemberDialog</c>.
+    /// </summary>
+    public event EventHandler? AddMemberRequested;
+
     public CirclesPageViewModel(CircleApiClient client)
     {
         _client = client ?? throw new ArgumentNullException(nameof(client));
@@ -51,6 +78,24 @@ public partial class CirclesPageViewModel : ViewModelBase
     public override bool CanNavigateNext { get => throw new NotImplementedException(); protected set => throw new NotImplementedException(); }
     public override bool CanNavigatePrevious { get => throw new NotImplementedException(); protected set => throw new NotImplementedException(); }
 
+    /// <summary>
+    /// Partial property setter: when the selected circle
+    /// changes, refresh the members list. The setter is
+    /// invoked by the [ObservableProperty] source generator
+    /// for both user selections and programmatic resets.
+    /// </summary>
+    partial void OnSelectedCircleChanged(CircleDto? value)
+    {
+        Members = new ObservableCollection<CircleMemberDto>();
+        if (value is not null)
+        {
+            // Fire-and-forget: load members in the background.
+            // Errors are routed to StatusMessage inside
+            // LoadMembersAsync.
+            _ = LoadMembersAsync(value.Id);
+        }
+    }
+
     [RelayCommand]
     public async Task RefreshAsync()
     {
@@ -71,6 +116,33 @@ public partial class CirclesPageViewModel : ViewModelBase
         }
     }
 
+    /// <summary>
+    /// Load the members of one of the caller's circles. The
+    /// server scopes the endpoint with a 404 when the circle
+    /// doesn't belong to the caller (mirroring the rest of the
+    /// circle API); that case flattens to an empty list here.
+    /// </summary>
+    [RelayCommand]
+    public async Task LoadMembersAsync(long circleId)
+    {
+        IsBusy = true;
+        try
+        {
+            var list = await _client.GetMembersAsync(circleId);
+            Members = new ObservableCollection<CircleMemberDto>(list ?? new());
+            StatusMessage = $"{Members.Count} membre(s)";
+        }
+        catch (Exception ex)
+        {
+            StatusMessage = $"Erreur: {ex.Message}";
+            Members = new ObservableCollection<CircleMemberDto>();
+        }
+        finally
+        {
+            IsBusy = false;
+        }
+    }
+
     [RelayCommand]
     public void StartCreate()
     {
@@ -141,6 +213,12 @@ public partial class CirclesPageViewModel : ViewModelBase
         {
             await _client.DeleteCircleAsync(circle.Id);
             StatusMessage = $"Cercle « {circle.Name} » supprimé";
+            // If the deleted circle was the selected one,
+            // clear the selection so the Members view goes
+            // empty too (the partial setter on
+            // SelectedCircle will reset Members).
+            if (SelectedCircle?.Id == circle.Id)
+                SelectedCircle = null;
             await RefreshAsync();
         }
         catch (Exception ex)
@@ -152,4 +230,81 @@ public partial class CirclesPageViewModel : ViewModelBase
             IsBusy = false;
         }
     }
+
+    /// <summary>
+    /// Fire the <see cref="AddMemberRequested"/> event so
+    /// the view opens <c>AddCircleMemberDialog</c>. The view
+    /// forwards the dialog's <c>Confirmed</c> event back to
+    /// <see cref="OnAddMemberConfirmedAsync"/>.
+    /// </summary>
+    [RelayCommand]
+    public void OpenAddMember()
+    {
+        if (SelectedCircle is null)
+        {
+            StatusMessage = "Sélectionnez d'abord un cercle";
+            return;
+        }
+        AddMemberRequested?.Invoke(this, EventArgs.Empty);
+    }
+
+    /// <summary>
+    /// Called by the view when the dialog confirms a
+    /// selection. Adds the picked user to the currently
+    /// selected circle and refreshes the members list.
+    /// </summary>
+    public async Task OnAddMemberConfirmedAsync(object? sender, UserSummary picked)
+    {
+        if (SelectedCircle is null || picked is null) return;
+        IsBusy = true;
+        try
+        {
+            await _client.AddMemberAsync(SelectedCircle.Id, picked.Id);
+            StatusMessage = $"« {picked.DisplayName} » ajouté au cercle";
+            await LoadMembersAsync(SelectedCircle.Id);
+        }
+        catch (Exception ex)
+        {
+            // 409 (already a member) is a likely race — surface
+            // it as a friendly status, not an error. The
+            // server returns 409 for "already a member";
+            // YavscApiClient surfaces that as an exception
+            // today; future refactors could route 409 into a
+            // typed result, but for now the message string is
+            // distinctive enough.
+            var msg = ex.Message.Contains("409") || ex.Message.Contains("Conflict")
+                ? "Déjà membre du cercle"
+                : $"Erreur: {ex.Message}";
+            StatusMessage = msg;
+        }
+        finally
+        {
+            IsBusy = false;
+        }
+    }
+
+    /// <summary>
+    /// Per-row "remove" command. Updates the local
+    /// collection in place so the UI doesn't flash.
+    /// </summary>
+    [RelayCommand]
+    public async Task RemoveMemberAsync(CircleMemberDto? member)
+    {
+        if (member is null || SelectedCircle is null) return;
+        IsBusy = true;
+        try
+        {
+            await _client.RemoveMemberAsync(SelectedCircle.Id, member.Id);
+            Members.Remove(member);
+            StatusMessage = $"« {member.UserName} » retiré du cercle";
+        }
+        catch (Exception ex)
+        {
+            StatusMessage = $"Erreur: {ex.Message}";
+        }
+        finally
+        {
+            IsBusy = false;
+        }
+    }
 }

src/PostIt/PostIt/Views/AddCircleMemberDialog.axaml

@@ -0,0 +1,57 @@
+<ContentPage
+        xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        x:Class="PostIt.Views.AddCircleMemberDialog"
+        xmlns:vm="using:PostIt.ViewModels"
+        xmlns:services="using:PostIt.Services"
+        x:DataType="vm:AddCircleMemberDialogViewModel"
+      >
+    <Grid RowDefinitions="Auto,Auto,*,Auto" Margin="12">
+
+        <!-- Search box + button -->
+        <Grid Grid.Row="0" ColumnDefinitions="*,Auto" Margin="0,0,0,8"
+              IsEnabled="{Binding !IsBusy}">
+            <TextBox Grid.Column="0"
+                     Text="{Binding SearchQuery, Mode=TwoWay}"
+                     PlaceholderText="Nom ou email d'un utilisateur Yavsc..."
+                     HorizontalAlignment="Stretch"/>
+            <Button Grid.Column="1" Content="Rechercher"
+                    Command="{Binding SearchCommand}"
+                    Margin="8,0,0,0"/>
+        </Grid>
+
+        <!-- Selection hint -->
+        <TextBlock Grid.Row="1"
+                   Text="Sélectionnez un résultat puis cliquez Ajouter."
+                   FontSize="11" Opacity="0.6"
+                   Margin="0,0,0,8"/>
+
+        <!-- Search results -->
+        <ListBox Grid.Row="2"
+                 ItemsSource="{Binding Results}"
+                 SelectedItem="{Binding Selected, Mode=TwoWay}">
+            <ListBox.ItemTemplate>
+                <DataTemplate x:DataType="services:UserSummary">
+                    <StackPanel Spacing="2">
+                        <TextBlock Text="{Binding DisplayName}"
+                                   FontWeight="Bold"/>
+                        <TextBlock Text="{Binding UserName}"
+                                   FontSize="11" Opacity="0.6"/>
+                    </StackPanel>
+                </DataTemplate>
+            </ListBox.ItemTemplate>
+        </ListBox>
+
+        <!-- Action buttons -->
+        <Grid Grid.Row="3" ColumnDefinitions="*,Auto,Auto" Margin="0,8,0,0">
+            <TextBlock Grid.Column="0" Text="{Binding StatusMessage}"
+                       VerticalAlignment="Center"/>
+            <Button Grid.Column="1" Content="Ajouter"
+                    Command="{Binding AddCommand}"
+                    IsEnabled="{Binding Selected, Converter={x:Static ObjectConverters.IsNotNull}}"
+                    Margin="0,0,8,0"/>
+            <Button Grid.Column="2" Content="Fermer"
+                    Click="OnCloseClicked"/>
+        </Grid>
+    </Grid>
+</ContentPage>

src/PostIt/PostIt/Views/AddCircleMemberDialog.axaml.cs

@@ -0,0 +1,54 @@
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+using Avalonia.Interactivity;
+using PostIt.Services;
+using PostIt.ViewModels;
+
+namespace PostIt.Views;
+
+/// <summary>
+/// Modal "add a member to a circle" page. Hosted by
+/// <c>CirclesPage</c>; the caller passes the resolved
+/// <see cref="IUserDirectory"/> via the constructor.
+///
+/// <para>The dialog raises <c>Confirmed</c> on its ViewModel
+/// when the user picks a result and clicks "Ajouter"; the
+/// hosting page subscribes to that event and calls
+/// <c>CircleApiClient.AddMemberAsync</c> with the target
+/// circle id. The dialog itself does not know the circle id
+/// by design.</para>
+/// </summary>
+public partial class AddCircleMemberDialog : ContentPage
+{
+    public AddCircleMemberDialog()
+    {
+        InitializeComponent();
+    }
+
+    public AddCircleMemberDialog(IUserDirectory directory)
+    {
+        InitializeComponent();
+        DataContext = new AddCircleMemberDialogViewModel(directory);
+    }
+
+    private void InitializeComponent()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+
+    /// <summary>
+    /// Subscribe a handler to be notified when the user
+    /// confirms a selection. Returns the underlying VM so
+    /// the caller can also drive further state (clear the
+    /// selection, close the dialog, refresh its own list).
+    /// </summary>
+    public AddCircleMemberDialogViewModel? ViewModel
+        => DataContext as AddCircleMemberDialogViewModel;
+
+    private void OnCloseClicked(object? sender, RoutedEventArgs e)
+    {
+        // Same light-modal pattern as PostAclDialog: rely on
+        // the system back gesture or the navigation host's
+        // "pop" — the ContentPage doesn't own the back stack.
+    }
+}

src/PostIt/PostIt/Views/CirclesPage.axaml

@@ -6,7 +6,7 @@
         xmlns:dtos="using:Yavsc.Api.Client.Dtos"
         x:DataType="vm:CirclesPageViewModel"
       >
-    <Grid RowDefinitions="Auto,*,Auto,Auto">
+    <Grid RowDefinitions="Auto,*,Auto">
 
         <!-- Toolbar: refresh + new -->
         <StackPanel Grid.Row="0" Orientation="Horizontal" Spacing="8" Margin="12">
@@ -16,8 +16,15 @@
                     Command="{Binding StartCreateCommand}"/>
         </StackPanel>
 
-        <!-- List of circles -->
+        <!-- Two-pane body: circles (left) + members (right) -->
-        <ListBox Grid.Row="1" Margin="12,0,12,12"
+        <Grid Grid.Row="1" Margin="12,0,12,12"
+              ColumnDefinitions="*,16,*"
+              RowDefinitions="*,Auto">
+
+            <!-- Left column: list of circles + editor -->
+            <Grid Grid.Row="0" Grid.Column="0"
+                  RowDefinitions="*,Auto">
+                <ListBox Grid.Row="0"
                          ItemsSource="{Binding Circles}"
                          SelectedItem="{Binding SelectedCircle, Mode=TwoWay}">
                     <ListBox.ItemTemplate>
@@ -40,7 +47,7 @@
                 </ListBox>
 
                 <!-- Editor -->
-        <Grid Grid.Row="2" Margin="12" RowDefinitions="Auto,Auto,Auto"
+                <Grid Grid.Row="1" Margin="0,12,0,0" RowDefinitions="Auto,Auto,Auto"
                       ColumnDefinitions="Auto,*" IsEnabled="{Binding !IsBusy}">
                     <TextBlock Grid.Row="0" Grid.Column="0" Text="Nom :"
                                VerticalAlignment="Center" Margin="0,0,8,0"/>
@@ -53,9 +60,47 @@
                             Command="{Binding SaveCommand}"
                             HorizontalAlignment="Right" Margin="0,8,0,0"/>
                 </Grid>
+            </Grid>
+
+            <!-- Right column: members of the selected circle -->
+            <Grid Grid.Row="0" Grid.Column="2"
+                  RowDefinitions="Auto,*,Auto">
+                <StackPanel Grid.Row="0" Orientation="Horizontal" Spacing="8" Margin="0,0,0,8">
+                    <TextBlock Text="Membres"
+                               FontWeight="Bold"
+                               VerticalAlignment="Center"/>
+                    <Button Content="Ajouter un membre"
+                            Command="{Binding OpenAddMemberCommand}"/>
+                </StackPanel>
+                <ListBox Grid.Row="1"
+                         ItemsSource="{Binding Members}">
+                    <ListBox.ItemTemplate>
+                        <DataTemplate x:DataType="dtos:CircleMemberDto">
+                            <Grid ColumnDefinitions="*,Auto">
+                                <StackPanel Grid.Column="0" Spacing="2">
+                                    <TextBlock Text="{Binding FullName}"
+                                               FontWeight="Bold"/>
+                                    <TextBlock Text="{Binding UserName}"
+                                               FontSize="11" Opacity="0.6"/>
+                                </StackPanel>
+                                <Button Grid.Column="1" Content="Retirer"
+                                        Command="{Binding $parent[ContentPage].((vm:CirclesPageViewModel)DataContext).RemoveMemberCommand}"
+                                        CommandParameter="{Binding}"/>
+                            </Grid>
+                        </DataTemplate>
+                    </ListBox.ItemTemplate>
+                </ListBox>
+                <!-- Empty-state hint -->
+                <TextBlock Grid.Row="2"
+                           Text="Sélectionnez un cercle pour voir ses membres."
+                           IsVisible="{Binding SelectedCircle, Converter={x:Static ObjectConverters.IsNull}}"
+                           FontSize="11" Opacity="0.6"
+                           Margin="0,8,0,0"/>
+            </Grid>
+        </Grid>
 
         <!-- Status bar -->
-        <Grid Grid.Row="3" ColumnDefinitions="*,Auto" Margin="12,0,12,12">
+        <Grid Grid.Row="2" ColumnDefinitions="*,Auto" Margin="12,0,12,12">
             <TextBlock Grid.Column="0" Text="{Binding StatusMessage}"
                        VerticalAlignment="Center"/>
             <ProgressBar Grid.Column="1" IsIndeterminate="True"

src/PostIt/PostIt/Views/CirclesPage.axaml.cs

@@ -1,14 +1,55 @@
+using System;
+using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
+using Microsoft.Extensions.DependencyInjection;
+using PostIt.Services;
 using PostIt.ViewModels;
 
 namespace PostIt.Views;
 
 public partial class CirclesPage : ContentPage
 {
+    private CirclesPageViewModel? _vm;
+
     public CirclesPage()
     {
         InitializeComponent();
+        DataContextChanged += OnDataContextChanged;
+    }
+
+    private void OnDataContextChanged(object? sender, EventArgs e)
+    {
+        // Unsubscribe from the previous VM to avoid leaking
+        // handlers across navigation pushes / DataContext resets.
+        if (_vm is not null)
+            _vm.AddMemberRequested -= OnAddMemberRequested;
+
+        _vm = DataContext as CirclesPageViewModel;
+        if (_vm is not null)
+            _vm.AddMemberRequested += OnAddMemberRequested;
+    }
+
+    private void OnAddMemberRequested(object? sender, EventArgs e)
+    {
+        var app = Application.Current as App;
+        var services = app?.ServiceProvider;
+        if (services is null || _vm is null) return;
+
+        // Resolve the directory via DI. The dialog raises its
+        // own Confirmed event; the VM subscribes via the method
+        // below — we pass the VM in so the closure can call
+        // back into it without the dialog needing to know the
+        // type of its caller. EventHandler<UserSummary> wants a
+        // void return, so wrap the async VM method in a fire-
+        // and-forget helper.
+        var directory = services.GetRequiredService<IUserDirectory>();
+        var dialog = new AddCircleMemberDialog(directory);
+        dialog.ViewModel!.Confirmed += async (sender, picked) =>
+            await _vm.OnAddMemberConfirmedAsync(sender, picked);
+
+        if (this.VisualRoot is MainWindow window)
+            _ = window.NavRoot.PushAsync(dialog);
     }
 
     private void InitializeComponent()

src/Yavsc.Api.Client/CircleApiClient.cs

@@ -50,4 +50,36 @@ public sealed class CircleApiClient
 
     public Task DeleteCircleAsync(long id, CancellationToken ct = default)
         => _api.CallAsync(HttpMethod.Delete, $"{Path}/{id}", ct: ct);
+
+    /// <summary>
+    /// Returns the members of one of the caller's circles.
+    /// Returns null when the circle does not exist or is not
+    /// owned by the caller (the server scopes the endpoint
+    /// with a 404 in either case to avoid leaking existence
+    /// — this client flattens that into a null result).
+    /// </summary>
+    public Task<List<CircleMemberDto>?> GetMembersAsync(long id, CancellationToken ct = default)
+        => _api.CallAsync<List<CircleMemberDto>?>(HttpMethod.Get, $"{Path}/{id}/members", ct: ct);
+
+    /// <summary>
+    /// Adds a Yavsc user (resolved client-side via
+    /// <c>/api/user-search</c>) to one of the caller's
+    /// circles. Returns null when the circle does not exist
+    /// or is not owned by the caller, or when the target
+    /// user does not exist. Throws on 409 (already a
+    /// member) — callers that want idempotent behaviour
+    /// can swallow the exception or dedupe beforehand.
+    /// </summary>
+    public Task AddMemberAsync(long id, string userId, CancellationToken ct = default)
+        => _api.CallAsync(HttpMethod.Post, $"{Path}/{id}/members",
+            body: new { userId }, ct: ct);
+
+    /// <summary>
+    /// Removes a user from one of the caller's circles.
+    /// Returns null on success (the server returns 200 OK
+    /// with no body) or when the membership does not
+    /// exist — both treated as success by the caller.
+    /// </summary>
+    public Task RemoveMemberAsync(long id, string userId, CancellationToken ct = default)
+        => _api.CallAsync(HttpMethod.Delete, $"{Path}/{id}/members/{userId}", ct: ct);
 }

src/Yavsc.Api.Client/Dtos/CircleMemberDto.cs

@@ -0,0 +1,21 @@
+namespace Yavsc.Api.Client.Dtos;
+
+/// <summary>
+/// Wire format for <c>GET /api/circle/{id}/members</c>.
+///
+/// <para>Mirrors the server-side
+/// <c>Yavsc.Blogs.Controllers.CircleMemberDto</c>. Intentionally
+/// stops short of the Email field that
+/// <see cref="UserSearchResultDto"/> carries — the circle
+/// membership UI only needs a name and an avatar to render the
+/// list. If the future ACL UI wants contact details, it can
+/// fall back to <see cref="IYavscApiClient"/>'s other
+/// endpoints rather than widening this shape.</para>
+/// </summary>
+public sealed class CircleMemberDto
+{
+    public string Id { get; set; } = string.Empty;
+    public string UserName { get; set; } = string.Empty;
+    public string? FullName { get; set; }
+    public string? Avatar { get; set; }
+}

src/Yavsc.Blogs.Tests/CircleMembersApiTests.cs

@@ -0,0 +1,199 @@
+using System.Net;
+using System.Net.Http;
+using System.Net.Http.Json;
+using System.Text.Json;
+using Microsoft.Extensions.DependencyInjection;
+using Yavsc.Models;
+using Yavsc.Models.Relationship;
+using Yavsc.Tests.Shared;
+
+namespace Yavsc.Blogs.Tests;
+
+/// <summary>
+/// Behavioural tests for the circle-members endpoints on
+/// <c>CircleApiController</c>:
+/// <c>GET /api/circle/{id}/members</c>,
+/// <c>POST /api/circle/{id}/members</c>,
+/// <c>DELETE /api/circle/{id}/members/{userId}</c>.
+///
+/// <para>Same fixture as <see cref="BlogApiTests"/>:
+/// <see cref="BlogsWebServerFixture"/> provides an in-memory
+/// <c>ApplicationDbContext</c>, JWT bearer auth with HS256,
+/// and the production <c>BlogScope</c> policy. Tests use
+/// <c>TestTokenIssuer</c> to mint tokens whose <c>sub</c>
+/// claim identifies the caller.</para>
+///
+/// <para>Test users (<c>alice</c>, <c>bob</c>) are seeded
+/// directly via <see cref="ApplicationDbContext.Users"/>:
+/// the Blogs fixture doesn't stand up
+/// <c>UserManager&lt;ApplicationUser&gt;</c>, so we go
+/// through the DbContext the same way the production code
+/// would.</para>
+/// </summary>
+[Collection("JwtClaimMapping")]
+public sealed class CircleMembersApiTests : IClassFixture<BlogsWebServerFixture>
+{
+    private readonly BlogsWebServerFixture _fixture;
+
+    public CircleMembersApiTests(BlogsWebServerFixture fixture)
+    {
+        _fixture = fixture;
+    }
+
+    /// <summary>Reset the in-memory database and seed
+    /// <c>alice</c> + <c>bob</c>. <c>UseInMemoryDatabase</c>
+    /// shares its store across the fixture lifetime, so each
+    /// test starts from a clean slate.</summary>
+    private void ResetDatabaseWithUsers()
+    {
+        using var scope = _fixture.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>();
+        db.Database.EnsureDeleted();
+        db.Database.EnsureCreated();
+
+        db.Users.Add(new ApplicationUser
+        {
+            Id = "alice",
+            UserName = "alice",
+            Email = "alice@example.com",
+            EmailConfirmed = true,
+            FullName = "Alice Dupont",
+            Avatar = "/avatars/alice.png",
+        });
+        db.Users.Add(new ApplicationUser
+        {
+            Id = "bob",
+            UserName = "bob",
+            Email = "bob@example.com",
+            EmailConfirmed = true,
+            FullName = "Bob Martin",
+            Avatar = "/avatars/bob.png",
+        });
+        db.SaveChanges();
+    }
+
+    /// <summary>Create a circle owned by <paramref name="ownerId"/>
+    /// directly in the in-memory store and return its server-assigned
+    /// id. The tests below use this to bypass the controller's POST
+    /// (which is already covered by other tests on the branch);
+    /// the focus here is the members endpoints.</summary>
+    private long SeedCircle(string ownerId, string name)
+    {
+        using var scope = _fixture.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>();
+        var circle = new Circle { OwnerId = ownerId, Name = name };
+        db.Circle.Add(circle);
+        db.SaveChanges();
+        return circle.Id;
+    }
+
+    private string MembersUrl(long circleId)
+        => $"{_fixture.Addresses.First(a => a.StartsWith("https://"))}/api/circle/{circleId}/members";
+
+    private HttpClient NewClient(string subject)
+    {
+        var handler = new HttpClientHandler
+        {
+            ServerCertificateCustomValidationCallback = (_, _, _, _) => true
+        };
+        var http = new HttpClient(handler)
+        {
+            BaseAddress = new Uri(_fixture.Addresses.First(a => a.StartsWith("https://")))
+        };
+        http.DefaultRequestHeaders.Authorization =
+            new System.Net.Http.Headers.AuthenticationHeaderValue(
+                "Bearer", TestTokenIssuer.Issue(subject));
+        return http;
+    }
+
+    [Fact]
+    public async Task GetMembers_returns_200_with_empty_list_when_no_members()
+    {
+        ResetDatabaseWithUsers();
+        var circleId = SeedCircle("alice", "Famille");
+        using var http = NewClient("alice");
+
+        var response = await http.GetAsync(MembersUrl(circleId));
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        using var doc = JsonDocument.Parse(await response.Content.ReadAsStringAsync());
+        Assert.Equal(JsonValueKind.Array, doc.RootElement.ValueKind);
+        Assert.Equal(0, doc.RootElement.GetArrayLength());
+    }
+
+    [Fact]
+    public async Task PostMember_returns_201_then_Get_returns_the_member()
+    {
+        ResetDatabaseWithUsers();
+        var circleId = SeedCircle("alice", "Famille");
+        using var http = NewClient("alice");
+
+        var postResponse = await http.PostAsJsonAsync(
+            MembersUrl(circleId),
+            new { userId = "bob" });
+
+        Assert.Equal(HttpStatusCode.Created, postResponse.StatusCode);
+
+        var getResponse = await http.GetAsync(MembersUrl(circleId));
+        Assert.Equal(HttpStatusCode.OK, getResponse.StatusCode);
+
+        using var doc = JsonDocument.Parse(await getResponse.Content.ReadAsStringAsync());
+        Assert.Equal(JsonValueKind.Array, doc.RootElement.ValueKind);
+        Assert.Equal(1, doc.RootElement.GetArrayLength());
+        var member = doc.RootElement[0];
+        Assert.Equal("bob", member.GetProperty("id").GetString());
+        Assert.Equal("bob", member.GetProperty("userName").GetString());
+        Assert.Equal("Bob Martin", member.GetProperty("fullName").GetString());
+    }
+
+    [Fact]
+    public async Task PostMember_returns_409_when_user_already_in_circle()
+    {
+        ResetDatabaseWithUsers();
+        var circleId = SeedCircle("alice", "Famille");
+        using var http = NewClient("alice");
+
+        var first = await http.PostAsJsonAsync(
+            MembersUrl(circleId),
+            new { userId = "bob" });
+        Assert.Equal(HttpStatusCode.Created, first.StatusCode);
+
+        var second = await http.PostAsJsonAsync(
+            MembersUrl(circleId),
+            new { userId = "bob" });
+        Assert.Equal(HttpStatusCode.Conflict, second.StatusCode);
+    }
+
+    [Fact]
+    public async Task DeleteMember_returns_200_then_Get_does_not_include_member()
+    {
+        ResetDatabaseWithUsers();
+        var circleId = SeedCircle("alice", "Famille");
+        using var http = NewClient("alice");
+
+        await http.PostAsJsonAsync(MembersUrl(circleId), new { userId = "bob" });
+
+        var deleteResponse = await http.DeleteAsync(
+            $"{MembersUrl(circleId)}/bob");
+        Assert.Equal(HttpStatusCode.OK, deleteResponse.StatusCode);
+
+        var getResponse = await http.GetAsync(MembersUrl(circleId));
+        using var doc = JsonDocument.Parse(await getResponse.Content.ReadAsStringAsync());
+        Assert.Equal(0, doc.RootElement.GetArrayLength());
+    }
+
+    [Fact]
+    public async Task GetMembers_returns_404_when_circle_not_owned_by_caller()
+    {
+        ResetDatabaseWithUsers();
+        // Alice's circle, Bob tries to read its members.
+        var circleId = SeedCircle("alice", "Famille");
+        using var http = NewClient("bob");
+
+        var response = await http.GetAsync(MembersUrl(circleId));
+
+        // 404, not 403 — the controller deliberately avoids leaking
+        // the existence of someone else's circle.
+        Assert.Equal(HttpStatusCode.NotFound, response.StatusCode);
+    }
+}

src/Yavsc.Blogs/Controllers/CircleApiController.cs

@@ -1,5 +1,4 @@
 using System.Linq;
-using System.Security.Claims;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.EntityFrameworkCore;
 using Yavsc.Models;
@@ -27,7 +26,7 @@ namespace Yavsc.Blogs.Controllers
         [HttpGet]
         public IEnumerable<Circle> GetCircle()
         {
-            var uid = User.FindFirstValue(ClaimTypes.NameIdentifier);
+            var uid = User.GetUserId();
             return _context.Circle.Where(c => c.OwnerId == uid);
         }
 
@@ -43,7 +42,7 @@ namespace Yavsc.Blogs.Controllers
                 return BadRequest(ModelState);
             }
 
-            var uid = User.FindFirstValue(ClaimTypes.NameIdentifier);
+            var uid = User.GetUserId();
             Circle circle = await _context.Circle.SingleOrDefaultAsync(
                 m => m.Id == id && m.OwnerId == uid);
 
@@ -74,7 +73,7 @@ namespace Yavsc.Blogs.Controllers
                 return BadRequest();
             }
 
-            var uid = User.FindFirstValue(ClaimTypes.NameIdentifier);
+            var uid = User.GetUserId();
             var existing = await _context.Circle.SingleOrDefaultAsync(
                 c => c.Id == id && c.OwnerId == uid);
             if (existing is null)
@@ -118,7 +117,7 @@ namespace Yavsc.Blogs.Controllers
                 return BadRequest(ModelState);
             }
 
-            var uid = User.FindFirstValue(ClaimTypes.NameIdentifier);
+            var uid = User.GetUserId();
             circle.OwnerId = uid;
 
             _context.Circle.Add(circle);
@@ -156,7 +155,7 @@ namespace Yavsc.Blogs.Controllers
                 return BadRequest(ModelState);
             }
 
-            var uid = User.FindFirstValue(ClaimTypes.NameIdentifier);
+            var uid = User.GetUserId();
             Circle circle = await _context.Circle.SingleOrDefaultAsync(
                 m => m.Id == id && m.OwnerId == uid);
             if (circle == null)
@@ -170,6 +169,143 @@ namespace Yavsc.Blogs.Controllers
             return Ok(circle);
         }
 
+        /// <summary>
+        /// Returns the members of one of the caller's circles.
+        /// Returns 404 (not 403) when the circle does not exist
+        /// or is not owned by the caller, mirroring the scoping
+        /// of the rest of this controller.
+        /// </summary>
+        // GET: api/circle/5/members
+        [HttpGet("{id}/members")]
+        public async Task<IActionResult> GetMembers([FromRoute] long id)
+        {
+            if (!ModelState.IsValid)
+            {
+                return BadRequest(ModelState);
+            }
+
+            var uid = User.GetUserId();
+            var ownsIt = await _context.Circle.AnyAsync(c => c.Id == id && c.OwnerId == uid);
+            if (!ownsIt)
+            {
+                return NotFound();
+            }
+
+            var members = await _context.CircleMembers
+                .Where(m => m.CircleId == id)
+                .Select(m => new CircleMemberDto
+                {
+                    Id = m.MemberId,
+                    UserName = m.Member.UserName ?? string.Empty,
+                    FullName = m.Member.FullName,
+                    Avatar = m.Member.Avatar,
+                })
+                .ToListAsync();
+
+            return Ok(members);
+        }
+
+        /// <summary>
+        /// Adds a Yavsc user to one of the caller's circles. The
+        /// body carries the user id (resolved client-side via the
+        /// central <c>/api/user-search</c> endpoint). Returns
+        /// 404 (not 403) when the circle does not exist or is not
+        /// owned by the caller, and 404 when the target user does
+        /// not exist, so the caller can't probe whether an email
+        /// belongs to a real account.
+        ///
+        /// <para>Returns 409 Conflict if the user is already a
+        /// member of the circle; the client treats this as a
+        /// no-op success.</para>
+        /// </summary>
+        // POST: api/circle/5/members
+        // body: { "userId": "..." }
+        [HttpPost("{id}/members")]
+        public async Task<IActionResult> AddMember(
+            [FromRoute] long id,
+            [FromBody] AddCircleMemberDto body)
+        {
+            if (!ModelState.IsValid)
+            {
+                return BadRequest(ModelState);
+            }
+
+            var uid = User.GetUserId();
+            var ownsIt = await _context.Circle.AnyAsync(c => c.Id == id && c.OwnerId == uid);
+            if (!ownsIt)
+            {
+                return NotFound();
+            }
+
+            // Reject unknown user ids the same way as an unknown
+            // circle: 404. Probing the user table by id should not
+            // be possible through this endpoint.
+            var userExists = await _context.Users.AnyAsync(u => u.Id == body.UserId);
+            if (!userExists)
+            {
+                return NotFound();
+            }
+
+            // Idempotency: re-adding an existing member is a
+            // 409, not a silent success. Clients that don't
+            // dedupe beforehand will at least get an actionable
+            // status code rather than a misleading "created".
+            var alreadyMember = await _context.CircleMembers.AnyAsync(
+                m => m.CircleId == id && m.MemberId == body.UserId);
+            if (alreadyMember)
+            {
+                return new StatusCodeResult(StatusCodes.Status409Conflict);
+            }
+
+            _context.CircleMembers.Add(new CircleMember
+            {
+                CircleId = id,
+                MemberId = body.UserId,
+            });
+            await _context.SaveChangesAsync(User.GetUserId());
+
+            return CreatedAtRoute("GetCircle", new { id }, body);
+        }
+
+        /// <summary>
+        /// Removes a user from one of the caller's circles.
+        /// Returns 404 when the circle does not exist or is not
+        /// owned by the caller, mirroring the rest of this
+        /// controller's scoping. Returns 404 when the user is
+        /// not a member of the circle (idempotent: removing a
+        /// non-member is the same as having nothing to remove).
+        /// </summary>
+        // DELETE: api/circle/5/members/tester
+        [HttpDelete("{id}/members/{userId}")]
+        public async Task<IActionResult> RemoveMember(
+            [FromRoute] long id,
+            [FromRoute] string userId)
+        {
+            if (!ModelState.IsValid)
+            {
+                return BadRequest(ModelState);
+            }
+
+            var uid = User.GetUserId();
+            var ownsIt = await _context.Circle.AnyAsync(c => c.Id == id && c.OwnerId == uid);
+            if (!ownsIt)
+            {
+                return NotFound();
+            }
+
+            var membership = await _context.CircleMembers.SingleOrDefaultAsync(
+                m => m.CircleId == id && m.MemberId == userId);
+            if (membership is null)
+            {
+                return NotFound();
+            }
+
+            _context.CircleMembers.Remove(membership);
+            await _context.SaveChangesAsync(User.GetUserId());
+
+            return Ok();
+        }
+
         protected override void Dispose(bool disposing)
         {
             if (disposing)
@@ -184,4 +320,30 @@ namespace Yavsc.Blogs.Controllers
             return _context.Circle.Count(e => e.Id == id) > 0;
         }
     }
+
+    /// <summary>
+    /// Wire shape for <c>GET /api/circle/{id}/members</c>.
+    /// Mirrors <see cref="UserSearchResultDto"/> but stops
+    /// short of the Email field — circle membership UI only
+    /// needs to render a name and an avatar, not contact
+    /// details.
+    /// </summary>
+    public sealed class CircleMemberDto
+    {
+        public string Id { get; set; } = string.Empty;
+        public string UserName { get; set; } = string.Empty;
+        public string? FullName { get; set; }
+        public string? Avatar { get; set; }
+    }
+
+    /// <summary>
+    /// Wire shape for <c>POST /api/circle/{id}/members</c>.
+    /// The body is intentionally tiny: the client resolves
+    /// the user id via <c>/api/user-search</c> before
+    /// posting, so all we need is the resolved id.
+    /// </summary>
+    public sealed class AddCircleMemberDto
+    {
+        public string UserId { get; set; } = string.Empty;
+    }
 }