server: infer archive collected_at from source events

internal/server/source_metadata_test.go

@@ -30,6 +30,36 @@ func TestApplyArchiveSourceMetadata(t *testing.T) {
 	}
 }
 
+func TestApplyArchiveSourceMetadata_PreservesExistingCollectedAt(t *testing.T) {
+	expected := time.Date(2026, 2, 10, 15, 30, 0, 0, time.UTC)
+	result := &models.AnalysisResult{
+		CollectedAt: expected,
+	}
+
+	applyArchiveSourceMetadata(result)
+
+	if !result.CollectedAt.Equal(expected) {
+		t.Fatalf("expected collected_at to be preserved: got %s want %s", result.CollectedAt, expected)
+	}
+}
+
+func TestApplyArchiveSourceMetadata_InferCollectedAtFromEvents(t *testing.T) {
+	oldTs := time.Date(2026, 2, 10, 13, 0, 0, 0, time.UTC)
+	newTs := time.Date(2026, 2, 10, 15, 30, 0, 0, time.UTC)
+	result := &models.AnalysisResult{
+		Events: []models.Event{
+			{Timestamp: oldTs},
+			{Timestamp: newTs},
+		},
+	}
+
+	applyArchiveSourceMetadata(result)
+
+	if !result.CollectedAt.Equal(newTs) {
+		t.Fatalf("expected collected_at from latest event: got %s want %s", result.CollectedAt, newTs)
+	}
+}
+
 func TestApplyCollectSourceMetadata(t *testing.T) {
 	req := CollectRequest{
 		Host:     "bmc-api.local",