The 'Save' button in PostIt has been returning 400 from
/api/v1/blog ever since the editor's title and article fields
were re-bound to SelectedPost.Title / SelectedPost.Article.
The user types into the editor, taps Save, the controller
rejects with 'The Title field is required', and the PostIt
status bar shows only the generic 'Response status code does
not indicate success: 400' — no field name, no reason.
Three pieces here make the regression diagnosable and pin a
test for the fix:
1. YavscApiClient: replace EnsureSuccessStatusCode() at both
call sites with a small helper that reads the response
body and embeds it in the thrown HttpRequestException. The
VM's existing catch (Exception) in ExecuteAsync forwards
ex.Message to the status bar, so the next 'click Save'
tells the user exactly which field the server rejected.
2. Yavsc.Blogs.Tests: two integration tests on the real
controller (no HTTP mock) — one pins that a well-formed
PostIt-shaped payload (Title + Article + AuthorId + dates,
Id=0) is accepted with 201, the other pins that a payload
with Title=string.Empty is rejected with 400. Together they
pin the contract the VM has to honour.
3. PostIt.Tests: a red [AvaloniaFact] UI test that mounts
MainPage inside a headless Window, types a title into the
TextBox without first selecting a post in the list, taps
Save, and asserts the body of the first POST contains
the typed title. Today this test fails with Title='',
reproducing the production 400. The matching fix (a
Title/Article buffer on MainPageViewModel that the XAML
binds to, and that Save uses to build the outgoing
BlogPost) is the next commit; the test is the safety net.
