Adopt b2b.next's client patterns: services, page state, feedback

Ported from the owner's b2b.next and adapted from MudBlazor to the daisyUI
components:
- LocalizableComponentBase provides CascadingState, Navigation, Toast,
  IsLoading/IsDefaultDisabled, WhenOnline/StartOnlinePolling, and after-render
  jobs that actually run.
- CascadingState starts with initialised state and polls the online status
  with a PeriodicTimer. It reports errors through ILoggingService plus a toast,
  and disposes what it holds.
- New pieces:
  - ToastService + ToastHost, the snackbar, with AddResponseError/Success/
    Warning/Exception in SUtility;
  - ErrorViewer, which shows the validation messages plus AdditionalError(s);
  - LoggingService, which writes to the console and the IndexedDB client log.
- HttpService is rebuilt and registered:
  - auth levels Get/Post/Delete, *Anon and *TotallyAnon;
  - retry with backoff;
  - classified failures (FailureCodes) instead of exceptions;
  - HTTP 410 on cancel;
  - the "default" client.
  ReadWebResult and DefaultReadFromJsonAsync read its responses.
- ClientJsonContext is source-generated, and SUtility.DefaultSerializer and
  Blazored.LocalStorage use it.
- WebResult gains a C# 14 IsInvalid extension property.

The code follows the imported rules:
- Every service and async helper takes a CancellationToken last.
- Primary constructors replace constructor-plus-fields.
- MessagesService and IStorage return Task<WebResult> / Task<List<T>>.
  MessagesService is still mock, building its results in memory; the seed
  feed and thread moved to Faker.
- Index and ExpandMessage follow the page pattern: an offline guard with
  WhenOnline, LoadData, and early returns with toasts on the results they used
  to ignore. ExpandMessage reloads on route change and shows "not found"
  instead of a null message.
- Model and state collections are [], and the fake identity defaults moved
  out of the models.
- Components:
  - no ?. chains over initialised state;
  - [Inject] instead of @inject;
  - IsDefaultDisabled on the actions;
  - autocomplete on every text input;
  - Localizer[key, args] instead of string.Format;
  - the localizer no longer leaks its inner _pLocalizer.
- Settings → General gains a language picker (English/Italiano), and
  SetDefaultCulture limits the culture to those two.

Bugs fixed along the way:
- A compose with untouched (null) content passed the empty check.
- File errors were joined with <br/> and rendered as markup.
- ClientLogs.ErrorMessage() threw on warnings.
- CoalescingStringLocalizer[key, args] showed a raw "{0}" for missing keys.
- AppStatusService exposed a call to a JS function that doesn't exist.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Components/MessageUpsertForm.razor

@@ -4,15 +4,15 @@
 	<DataAnnotationsValidator />
 
 	<div class="flex flex-col mb-3">
-		<DInput TValue="string" class="w-full rounded-t-[1.4rem] rounded-b-lg" maxlength="64"
+		<DInput TValue="string" class="w-full rounded-t-[1.4rem] rounded-b-lg" maxlength="64" autocomplete="off"
 				placeholder="@Localizer["Title (optional)"]" Value="@MessageForm.Title"
 				ValueChanged="(v) => OnTitleChanged(v)"
 				ValueExpression="() => MessageForm.Title" />
 		<div class="relative mt-1">
 			<DTextarea TValue="string" @bind-Value="MessageForm.Content" Immediate="true"
-					   class="w-full rounded-b-[1.4rem] rounded-t-lg" maxlength="5000"
+					   class="w-full rounded-b-[1.4rem] rounded-t-lg" maxlength="@MaxContentLength" autocomplete="off"
 					   placeholder="@Localizer["oh shit... here we go again"]" rows="3" />
-			<span class="absolute text-xs opacity-50 right-2 bottom-1">@(MessageForm.Content?.Length ?? 0)/5000</span>
+			<span class="absolute text-xs opacity-50 right-2 bottom-1">@ContentLength/@MaxContentLength</span>
 		</div>
 		@if (showPreviewButton && isPreviewOpen && MessageForm.Content is { Length: > 0 })
 		{
@@ -30,10 +30,6 @@
 				</div>
 			</div>
 		}
-		<div class="text-error text-sm">
-			<ValidationMessage For="() => MessageForm.Content" />
-			@contentError
-		</div>
 	</div>
 
 	<div class="flex flex-col gap-3 mb-3 @SUtility.IfTrueThen(MessageForm.Media.Count == 0, "hidden")">
@@ -51,14 +47,14 @@
 										<i class="ion-md-image"></i> <b>@media.FileName</b>
 									</p>
 									<p class="text-xs break-all">
-										<i class="ion-md-code"></i> @media.ContentType <i class="ion-md-fitness"></i> @media.Size.GetFileSize(Localizer._pLocalizer)
+										<i class="ion-md-code"></i> @media.ContentType <i class="ion-md-fitness"></i> @media.Size.GetFileSize(Localizer)
 									</p>
 								</div>
 								<DButton Size="DSize.Sm" class="self-start" OnClick="() => RemoveFile(media)">
 									<i class="ion-md-trash text-base text-red-400"></i>
 								</DButton>
 							</div>
-							<DTextarea TValue="string" @bind-Value="media.AltText" Size="DSize.Sm" class="w-full rounded-lg!"
+							<DTextarea TValue="string" @bind-Value="media.AltText" Size="DSize.Sm" class="w-full rounded-lg!" autocomplete="off"
 									   placeholder="@Localizer["Alternative text"]" rows="1" />
 						</div>
 					</div>
@@ -74,7 +70,7 @@
 								<b>@media.FileName</b>
 							</p>
 							<p class="text-xs break-all">
-								<i class="ion-md-code"></i> @media.ContentType <i class="ion-md-fitness"></i> @media.Size.GetFileSize(Localizer._pLocalizer)
+								<i class="ion-md-code"></i> @media.ContentType <i class="ion-md-fitness"></i> @media.Size.GetFileSize(Localizer)
 							</p>
 						</div>
 						<DButton Size="DSize.Sm" OnClick="() => RemoveFile(media)">
@@ -92,7 +88,7 @@
 								<b>@media.FileName</b>
 							</p>
 							<p class="text-xs break-all">
-								<i class="ion-md-code"></i> @media.ContentType <i class="ion-md-fitness"></i> @media.Size.GetFileSize(Localizer._pLocalizer)
+								<i class="ion-md-code"></i> @media.ContentType <i class="ion-md-fitness"></i> @media.Size.GetFileSize(Localizer)
 							</p>
 							<audio controls="controls" class="w-full max-h-8">
 								<source src="@media.Base64Preview" type="@media.ContentType">
@@ -108,19 +104,14 @@
 
 	</div>
 
-	@if (fileInputErrorMessage is { Length: > 0 })
-	{
-		<div class="text-error text-sm p-1 md:p-2 mb-3 rounded-xl neo-inset neo-2xs">
-			@((MarkupString)fileInputErrorMessage)
-		</div>
-	}
+	<ErrorViewer ContainerClass="mb-3" AdditionalError="@contentError" AdditionalErrors="fileErrors" />
 
 	<div class="flex flex-wrap items-start justify-between gap-3">
 		<div class="flex flex-wrap items-start gap-3">
 			<DDropdown @bind-IsOpen="MessageForm.IsScopeOptionsOpen"
 					   TriggerClass="@(MessageForm.IsScopeOptionsOpen ? "btn btn-sm btn-active" : "btn btn-sm")"
 					   ContentClass="mt-2 flex gap-2 p-2 rounded-box"
-					   title="@string.Format(Localizer["Message scope type: {0}"], Localizer[MessageForm.MessageType.ToString()])">
+					   title="@Localizer["Message scope type: {0}", Localizer[MessageForm.MessageType.ToString()]]">
 				<Trigger>
 					<i class="@MessageForm.MessageType.GetMessageTypeIcon() text-base"></i>
 				</Trigger>
@@ -180,9 +171,6 @@
 						}
 					</ChildContent>
 				</DSelect>
-				<div class="text-error text-sm">
-					<ValidationMessage For="() => MessageForm.ContentType" />
-				</div>
 			</div>
 
 			@if (showPreviewButton)
@@ -194,7 +182,7 @@
 
 		</div>
 
-		<DButton Size="DSize.Sm" Type="submit">
+		<DButton Size="DSize.Sm" Type="submit" Disabled="IsDefaultDisabled">
 			<span>@Localizer["Post"]</span>
 			<i class="ion-md-send"></i>
 		</DButton>
@@ -204,16 +192,46 @@
 </EditForm>
 
 @code {
-	[CascadingParameter] CascadingState CascadingState { get; set; }
+	const int MaxContentLength = 5_000;
+
+	[Inject] ILoggingService Logger { get; set; }
 	[Parameter] public Message AnsweringMessage { get; set; }
 	[Parameter] public EventCallback<MessageForm> OnMessageSubmit { get; set; }
 	MessageForm MessageForm { get; set; } = new();
-	int totalCharacters { get; set; } = 0;
-	string fileInputErrorMessage { get; set; }
-	string contentError { get; set; }
-	string acceptedFilesTypes { get; set; } = ".jpg,.jpeg,.png,.gif";
-	bool showPreviewButton { get; set; } = false;
-	bool isPreviewOpen { get; set; } = false;
+	List<string> fileErrors = [];
+	string contentError;
+	string acceptedFilesTypes = ".jpg,.jpeg,.png,.gif";
+	bool showPreviewButton;
+	bool isPreviewOpen;
+
+	// Content is null until the user types: a form starts without text.
+	int ContentLength => MessageForm.Content?.Length ?? 0;
+
+	int MaximumFileCount => MessageForm.MediaType switch
+	{
+		MediaType.Images => 5,
+		MediaType.Video or MediaType.Audio => 1,
+		MediaType.Documents => 3,
+		_ => 0
+	};
+
+	long MaximumFileSize => MessageForm.MediaType switch
+	{
+		MediaType.Images or MediaType.Documents => 3_145_728,
+		MediaType.Audio => 5_242_880,
+		MediaType.Video => 20_971_520,
+		_ => 0
+	};
+
+	protected override void OnInitialized()
+	{
+		IsLoading = false;
+		if (AnsweringMessage is null)
+			return;
+
+		MessageForm.Title = AnsweringMessage.Title;
+		MessageForm.RootMessageId = AnsweringMessage.RootMessageId ?? AnsweringMessage.MessageId;
+	}
 
 	void UpdateMessageType(MessageType messageType)
 	{
@@ -221,114 +239,68 @@
 		MessageForm.IsScopeOptionsOpen = false;
 	}
 
-	protected override void OnInitialized()
-	{
-		if (AnsweringMessage != default)
-		{
-			MessageForm.Title = AnsweringMessage.Title;
-			MessageForm.RootMessageId = AnsweringMessage.RootMessageId ?? AnsweringMessage.MessageId;
-		}
-	}
+	bool ShouldDisableUpload() => MessageForm.Media.Count >= MaximumFileCount;
 
-	bool ShouldDisableUpload()
-	{
-		switch (MessageForm.MediaType)
-		{
-			case MediaType.Images:
-				return MessageForm.Media.Count == 5;
-			case MediaType.Video:
-			case MediaType.Audio:
-				return MessageForm.Media.Count == 1;
-			case MediaType.Documents:
-				return MessageForm.Media.Count == 3;
-			default:
-				return true;
-		}
-	}
-
-	bool ShouldHaveMultipleUpload()
-	{
-		return MessageForm.MediaType is MediaType.Images or MediaType.Documents;
-	}
+	bool ShouldHaveMultipleUpload() => MessageForm.MediaType is MediaType.Images or MediaType.Documents;
 
 	async Task OnFileChange(InputFileChangeEventArgs eventArgs)
+	{
+		fileErrors = [];
+		var maximumFileCount = MaximumFileCount;
+		if (eventArgs.FileCount + MessageForm.Media.Count > maximumFileCount)
+		{
+			fileErrors.Add(Localizer["The maximum number of files accepted is {0}, but {1} were supplied.", maximumFileCount,
+				MessageForm.Media.Count + eventArgs.FileCount]);
+			return;
+		}
+
+		var maximumFileSize = MaximumFileSize;
+		foreach (var file in eventArgs.GetMultipleFiles(maximumFileCount))
+		{
+			if (file.Name == default || file.ContentType == default || MessageForm.Media.Any(m => m.FileName == file.Name))
+				continue;
+
+			if (file.Size > maximumFileSize)
+			{
+				fileErrors.Add(Localizer["Supplied file \"{0}\" with size {1} exceeds the maximum of {2}.", file.Name,
+					file.Size.GetFileSize(Localizer), maximumFileSize.GetFileSize(Localizer)]);
+				continue;
+			}
+
+			var uploadMedia = await ReadFile(file, maximumFileSize);
+			if (uploadMedia is null)
+			{
+				fileErrors.Add(Localizer["The file \"{0}\" could not be read.", file.Name]);
+				continue;
+			}
+
+			MessageForm.Media.Add(uploadMedia);
+		}
+	}
+
+	/// <summary>Reads a picked file into memory; null when the browser can't read it (logged).</summary>
+	async Task<UploadMedia> ReadFile(IBrowserFile file, long maximumFileSize, CancellationToken cancellationToken = default)
 	{
 		try
 		{
-			fileInputErrorMessage = string.Empty;
-			var maximumFileCount = MessageForm.MediaType switch
+			using var memoryStream = new MemoryStream();
+			await using var fileStream = file.OpenReadStream(maximumFileSize, cancellationToken);
+			await fileStream.CopyToAsync(memoryStream, cancellationToken);
+			var uploadMedia = new UploadMedia
 			{
-				MediaType.Images => 5,
-				MediaType.Audio => 1,
-				MediaType.Video => 1,
-				MediaType.Documents => 3,
-				_ => 0
+				FileName = file.Name,
+				ContentType = file.ContentType,
+				Size = file.Size,
+				Blob = memoryStream.ToArray()
 			};
-			if (eventArgs.FileCount > maximumFileCount)
-			{
-				fileInputErrorMessage = string.Format(Localizer["The maximum number of files accepted is {0}, but {1} were supplied."], maximumFileCount, eventArgs.FileCount);
-				return;
-			}
-			if (eventArgs.FileCount + MessageForm.Media.Count > maximumFileCount)
-			{
-				fileInputErrorMessage = string.Format(Localizer["The maximum number of files accepted is {0}, but {1} were supplied."], maximumFileCount, $"{MessageForm.Media.Count}+{eventArgs.FileCount}");
-				return;
-			}
-			var maxAllowedSize = MessageForm.MediaType switch
-			{
-				MediaType.Images => 3_145_728,
-				MediaType.Audio => 5_242_880,
-				MediaType.Video => 20_971_520,
-				MediaType.Documents => 3_145_728,
-				_ => 0
-			};
-			var uploadMedia = default(UploadMedia);
-			using (var memStream = new MemoryStream())
-				foreach (var file in eventArgs.GetMultipleFiles(maximumFileCount))
-				{
-					if (file.Name == default || file.ContentType == default) continue;
-					if (MessageForm.Media.Any(m => m.FileName == file.Name)) continue;
-					if (file.Size > maxAllowedSize)
-					{
-						fileInputErrorMessage += string.Format(Localizer["Supplied file \"{0}\" with size {1:N0}MBs exceeds the maximum of {2:N0}MBs."], file.Name, file.Size / 1_048_576, maxAllowedSize / 1_048_576) + "<br/>";
-						continue;
-					}
-
-					uploadMedia = new()
-						{
-							FileName = file.Name,
-							ContentType = file.ContentType,
-							Size = file.Size
-						};
-					try
-					{
-						using (var imgStream = file.OpenReadStream(maxAllowedSize))
-						{
-							await imgStream.CopyToAsync(memStream);
-							memStream.Position = 0;
-							uploadMedia.Blob = memStream.ToArray();
-							await memStream.FlushAsync();
-						}
-					}
-					catch (IOException e)
-					{
-						fileInputErrorMessage = e.Message;
-						continue;
-					}
-					catch (Exception e)
-					{
-						fileInputErrorMessage = e.Message;
-						continue;
-					}
-					if (MessageForm.MediaType is MediaType.Images or MediaType.Audio)
-						uploadMedia.Base64Preview = $"data:{uploadMedia.ContentType};base64,{Convert.ToBase64String(uploadMedia.Blob)}";
-
-					MessageForm.Media.Add(uploadMedia);
-				}
+			if (MessageForm.MediaType is MediaType.Images or MediaType.Audio)
+				uploadMedia.Base64Preview = $"data:{uploadMedia.ContentType};base64,{Convert.ToBase64String(uploadMedia.Blob)}";
+			return uploadMedia;
 		}
-		catch (Exception e)
+		catch (Exception ex)
 		{
-			fileInputErrorMessage = e.Message;
+			await Logger.ProcessError(ex, $"{nameof(MessageUpsertForm)}.{nameof(ReadFile)}:{file.Name}", cancellationToken);
+			return default;
 		}
 	}
 
@@ -342,12 +314,6 @@
 		MessageForm.Title = value;
 	}
 
-	void ContentLengthChanged()
-	{
-		totalCharacters = MessageForm.Content?.Length ?? 0;
-		StateHasChanged();
-	}
-
 	void OnContentTypeChanged(ContentType contentType)
 	{
 		MessageForm.ContentType = contentType;
@@ -375,7 +341,7 @@
 	async Task OnValidSubmit()
 	{
 		contentError = default;
-		if ((MessageForm.Content is { Length: 0 } && MessageForm.Media.Count == 0))
+		if (string.IsNullOrWhiteSpace(MessageForm.Content) && MessageForm.Media.Count == 0)
 		{
 			contentError = Localizer["Missing content, either message or media"];
 			return;
@@ -383,4 +349,4 @@
 
 		await OnMessageSubmit.InvokeAsync(MessageForm);
 	}
-}
+}