Improve PostIt draft attachment and save workflow

Insert attachment links on file addition, resolve provisional links on first save, preserve the editor selection, and highlight unsaved draft changes. Include regression tests and changelog updates.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/PostIt/PostIt.Tests/BlogApiTestFakes.cs

@@ -73,6 +73,14 @@ internal sealed class RecordingYavscApiClient : YavscApiClient
     public override Task<T> CallAsync<T>(HttpMethod method, string path, Func<HttpContent> contentFactory, CancellationToken ct = default)
     {
         _recorder.Calls.Add((method, path, contentFactory));
+        if (typeof(T) == typeof(BlogPostDto))
+            return Task.FromResult((T)(object)new BlogPostDto
+            {
+                Id = 42,
+                Title = "Mon premier billet",
+                AuthorId = "tester",
+                Article = "Contenu du billet de test.",
+            });
         return Task.FromResult(default(T)!);
     }
 }

src/PostIt/PostIt.Tests/BlogAttachmentLinkTests.cs

@@ -62,18 +62,18 @@ public class BlogAttachmentLinkTests
             System.Text.Encoding.UTF8.GetBytes("payload test"),
             "text/plain"));
 
+        var expectedUrl = $"{authority}/files/tester/blogs/42/{urlName}";
+        Assert.Contains($"- [{originalName}]({expectedUrl})", vm.DraftArticle);
+        Assert.Empty(recorder.Calls);
+        var draftBeforeSave = vm.DraftArticle;
+
         await vm.SaveAsync();
 
-        // The update branch issues two PUTs: the multipart one
-        // carrying the file, then — because TryAppendAttachmentLinks
-        // appended a link — a JSON one carrying the final article.
-        var linkPut = recorder.Calls.LastOrDefault(
-            c => c.method == HttpMethod.Put);
+        var linkPut = Assert.Single(recorder.Calls, c => c.method == HttpMethod.Put);
         Assert.NotEqual(default, linkPut);
         var sent = Assert.IsType<System.Func<HttpContent>>(linkPut.body);
         var multipartContent = Assert.IsType<MultipartFormDataContent>(sent());
 
-        var expectedUrl = $"{authority}/files/tester/blogs/42/{urlName}";
         var sentStringContent = Assert.IsType<StringContent>(multipartContent.First());
 
         var sentString = await sentStringContent.ReadAsStringAsync(TestContext.Current.CancellationToken);
@@ -82,5 +82,35 @@ public class BlogAttachmentLinkTests
         Assert.Contains($"- [{originalName}]({expectedUrl})", article);
         // The regression shape: a relative, authority-less link.
         Assert.DoesNotContain("](/files/", article);
+        Assert.Equal(draftBeforeSave, vm.DraftArticle);
+        Assert.NotNull(vm.SelectedPost);
+        Assert.False(vm.IsDraftModified);
+    }
+
+    [Fact]
+    public async Task New_post_resolves_only_the_provisional_link_at_first_save()
+    {
+        var recorder = new CallRecorder();
+        var api = new RecordingYavscApiClient(recorder);
+        var vm = new BlogsViewModel(new BlogApiClient(api, "https://blogs.example.test/api/v1/"),
+            new Settings { Authentication = new AuthenticationSettings { Authority = "https://idp.example.test" } });
+        vm.DraftTitle = "Nouveau billet";
+        vm.DraftArticle = "Texte conservé.";
+        vm.DraftAttachments.Add(new BlogUploadFile("Troisi\u00e8me.PDF", new byte[] { 1 }));
+
+        Assert.Contains("postit-attachment:", vm.DraftArticle);
+        Assert.Empty(recorder.Calls);
+        await vm.SaveAsync();
+
+        Assert.Equal("Nouveau billet", vm.DraftTitle);
+        Assert.Contains("Texte conservé.", vm.DraftArticle);
+        Assert.Contains("- [Troisi\u00e8me.PDF](https://idp.example.test/files/tester/blogs/42/Troisi_232me.PDF)",
+            vm.DraftArticle);
+        Assert.DoesNotContain("postit-attachment:", vm.DraftArticle);
+        Assert.Equal(42, vm.SelectedPost?.Id);
+        Assert.Empty(vm.DraftAttachments);
+        Assert.False(vm.IsDraftModified);
+        Assert.Single(recorder.Calls, c => c.method == HttpMethod.Post);
+        Assert.Single(recorder.Calls, c => c.method == HttpMethod.Put);
     }
 }

src/PostIt/PostIt.Tests/PostItViewModelTests.cs

@@ -12,6 +12,91 @@ namespace PostIt.Tests;
 
 public class PostItViewModelTests
 {
+    [Fact]
+    public void Draft_modified_tracks_title_body_and_attachments_not_publication()
+    {
+        var vm = new BlogsViewModel(new BlogApiClient(new ThrowingYavscApiClient(), "http://localhost/"));
+        vm.SelectedPost = new BlogPostDto { Id = 42, AuthorId = "tester", Title = "Titre", Article = "Corps" };
+        Assert.False(vm.IsDraftModified);
+        vm.DraftIsPublished = true;
+        Assert.False(vm.IsDraftModified);
+        vm.DraftTitle = "Autre";
+        Assert.True(vm.IsDraftModified);
+        vm.DraftTitle = "Titre";
+        Assert.False(vm.IsDraftModified);
+        vm.DraftArticleDocument!.Insert(0, "Edit ");
+        Assert.True(vm.IsDraftModified);
+        vm.DraftArticle = "Corps";
+        Assert.False(vm.IsDraftModified);
+        vm.DraftAttachments.Add(new BlogUploadFile("note.txt", new byte[] { 1 }));
+        Assert.True(vm.IsDraftModified);
+    }
+
+    [AvaloniaFact]
+    public async Task Save_keeps_selection_and_editor_open_and_resets_highlight()
+    {
+        var recorder = new CallRecorder();
+        var vm = new BlogsViewModel(new BlogApiClient(new RecordingYavscApiClient(recorder),
+            "https://blogs.example.test/api/v1/"));
+        var selected = new BlogPostDto { Id = 42, AuthorId = "tester", Title = "Titre", Article = "Corps" };
+        vm.Posts.Add(selected);
+        vm.SearchText = "";
+        vm.SelectedPost = selected;
+        var page = new BlogsPage { DataContext = vm };
+        var navigation = new NavigationPage();
+        await navigation.PushAsync(page);
+        var window = new Window { Content = navigation };
+        try
+        {
+            window.Show();
+            Dispatcher.UIThread.RunJobs();
+            selected = Assert.Single(vm.FilteredPosts);
+            selected.AuthorId = "tester";
+            selected.Title = "Titre";
+            selected.Article = "Corps";
+            page.PostsListBox.SelectedItem = selected;
+            Dispatcher.UIThread.RunJobs();
+            Assert.Same(selected, page.PostsListBox.SelectedItem);
+            Assert.Same(selected, vm.SelectedPost);
+            Assert.DoesNotContain("modified", page.SaveButton.Classes);
+            vm.DraftTitle = "Titre modifié";
+            Dispatcher.UIThread.RunJobs();
+            Assert.Contains("modified", page.SaveButton.Classes);
+            Assert.Equal(Avalonia.Media.FontWeight.Bold, page.SaveButton.FontWeight);
+            Assert.Same(vm.SaveCommand, page.SaveButton.Command);
+            await vm.SaveAsync();
+            Dispatcher.UIThread.RunJobs();
+            Assert.Same(page, navigation.NavigationStack.Last());
+            Assert.Same(selected, vm.SelectedPost);
+            Assert.Same(selected, page.PostsListBox.SelectedItem);
+            Assert.Equal("Titre modifié", vm.DraftTitle);
+            Assert.Equal("Corps", vm.DraftArticle);
+            Assert.DoesNotContain("modified", page.SaveButton.Classes);
+        }
+        finally
+        {
+            window.Close();
+        }
+    }
+
+    [Fact]
+    public async Task Failed_save_preserves_draft_attachments_and_modified_state()
+    {
+        var vm = new BlogsViewModel(new BlogApiClient(new ThrowingYavscApiClient(), "http://localhost/"));
+        var post = new BlogPostDto { Id = 42, AuthorId = "tester", Title = "Titre", Article = "Corps" };
+        vm.SelectedPost = post;
+        vm.DraftTitle = "Titre modifié";
+        vm.DraftAttachments.Add(new BlogUploadFile("note.txt", new byte[] { 1 }));
+        var article = vm.DraftArticle;
+        await vm.SaveAsync();
+        Assert.Same(post, vm.SelectedPost);
+        Assert.Equal("Titre modifié", vm.DraftTitle);
+        Assert.Equal(article, vm.DraftArticle);
+        Assert.Single(vm.DraftAttachments);
+        Assert.True(vm.IsDraftModified);
+        Assert.False(vm.IsBusy);
+    }
+
     [AvaloniaFact]
     public void Published_badge_tracks_post_publication_state()
     {