test(domain): malware is reported infected even when the file is not a PDF (refs #192)

clamd matches EICAR only at the start of a file, so a %PDF- check ahead of the
scan made the infected path unreachable for the EICAR test file.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

services/domain/Big.Tests/ProvideDocumentsTests.cs

@@ -113,24 +113,38 @@ public class ProvideDocumentsTests
     }
 
     [Fact]
-    public async Task A_file_that_is_not_a_pdf_is_refused_without_being_scanned()
+    public async Task A_clean_file_that_is_not_a_pdf_is_refused()
     {
         var store = new FakeRegistrationStore();
         var registration = Submitted();
         store.Seed(registration);
         var workflow = new FakeWorkflowClient();
         var acl = new FakeAclClient();
-        var scanner = new FakeDocumentScanner();
+        var handler = new ProvideDocuments(store, workflow, acl, new FakeDocumentScanner());
-        var handler = new ProvideDocuments(store, workflow, acl, scanner);
 
         var outcome = await handler.HandleAsync(Command(registration.Id, content: "MZ not a pdf"u8.ToArray()));
 
         Assert.Equal(ProvideDocumentsOutcome.NotAPdf, outcome);
-        Assert.Null(scanner.Scanned);
         Assert.Null(acl.StoredDiploma);
         Assert.Null(workflow.CompletedDocumentWaitFor);
     }
 
+    [Fact]
+    public async Task Malware_is_reported_as_infected_even_when_it_is_not_a_pdf()
+    {
+        // Scan first: clamd matches EICAR (and much real malware) only at the start of a file, so a file
+        // that fails the PDF check must still be scanned, and the citizen told it is infected.
+        var store = new FakeRegistrationStore();
+        var registration = Submitted();
+        store.Seed(registration);
+        var handler = new ProvideDocuments(store, new FakeWorkflowClient(), new FakeAclClient(),
+            new FakeDocumentScanner(ScanVerdict.Infected));
+
+        var outcome = await handler.HandleAsync(Command(registration.Id, content: "X5O!P not a pdf"u8.ToArray()));
+
+        Assert.Equal(ProvideDocumentsOutcome.Infected, outcome);
+    }
+
     [Fact]
     public async Task A_clean_pdf_is_scanned_before_it_is_stored()
     {