fix issues TUI display reliability

cmd/issues-tui/main_test.go

@@ -251,3 +251,26 @@ func TestBarAndMinimal(t *testing.T) {
 		t.Fatalf("minimal render should surface scan errors, got %q", got)
 	}
 }
+
+func TestModelKeepsLastGoodSnapshotOnScanError(t *testing.T) {
+	m := newModel(nil, modelConfig{Interval: time.Minute})
+	good := snapshot{ScannedAt: time.Now(), Issues: []issueView{{}}}
+	updated, _ := m.Update(snapshotMsg(good))
+	m = updated.(model)
+
+	failed := snapshot{Err: context.DeadlineExceeded}
+	updated, _ = m.Update(snapshotMsg(failed))
+	m = updated.(model)
+	if len(m.snap.Issues) != 1 {
+		t.Fatalf("failed scan should not erase the last good snapshot: %+v", m.snap)
+	}
+	if m.scanErr == nil {
+		t.Fatal("failed scan should be visible separately from the last good snapshot")
+	}
+
+	updated, _ = m.Update(snapshotMsg(snapshot{ScannedAt: time.Now()}))
+	m = updated.(model)
+	if m.scanErr != nil {
+		t.Fatal("successful scan should clear the previous scan error")
+	}
+}