Graphs: invert and complement remember the color of the first object they recolor

With a graph design's art given first and an item without aligned, the
art is left out, but paint.invert and paint.complement remembered the
art's unchanged color as the last color. They now read the first object
they recolor.

crates/engine/src/cmd/graph/tests.rs

@@ -890,6 +890,9 @@ fn aligned_paint_rows_of_a_graph_designs_art_edit_the_equal_rows_of_the_other_ob
     assert_eq!(now.items[0].paint(), &green);
     let now = fill(&mut s, "paint.invert", json!({"ids": ids, "item": 1, "aligned": true}));
     assert_eq!(Some(s.last_solid), now.items[0].paint().color(), "the inverted color is the last color, not the art's");
+    // Without `aligned`, the art is left out and the item is a row of the mark.
+    let now = fill(&mut s, "paint.invert", json!({"ids": ids, "item": 0}));
+    assert_eq!(Some(s.last_solid), now.items[0].paint().color(), "the mark's inverted color is the last color, not the art's");
     let now = fill(&mut s, "paint.editGradient", json!({"ids": ids, "item": 1, "aligned": true, "kind": "linear"}));
     let Paint::Gradient(g) = now.items[0].paint() else { panic!("{:?}", now.items[0].paint()) };
     assert_eq!(&s.last_gradient, &**g, "the mark's new gradient is the last gradient");
@@ -926,6 +929,9 @@ fn aligned_paint_rows_of_a_graph_designs_art_edit_the_equal_rows_of_the_other_ob
         ("paint.setFill", json!({"ids": [art.0], "item": 1, "aligned": true, "color": "#00ff00"}), "no appearance item 1"),
         ("stroke.set", json!({"ids": [art.0], "item": 1, "aligned": true, "weight": 5}), "appearance item 1 is not a stroke"),
         ("paint.editGradient", json!({"ids": [art.0], "item": 1, "aligned": true, "kind": "linear"}), "no appearance item 1"),
+        // The weight steps take no row: they step each object's active or top stroke.
+        ("stroke.weightUp", json!({"ids": ids, "item": 2}), "unknown parameter `item`"),
+        ("stroke.weightDown", json!({"ids": ids, "aligned": true}), "unknown parameter `aligned`"),
     ] {
         let defaults = format!("{:?}", (&s.paint.fill, &s.paint.stroke, &s.last_gradient));
         let e = s.execute(cmd, &p).unwrap_err().to_string();

crates/engine/src/cmd/paint.rs

@@ -1025,7 +1025,7 @@ fn proxy_recolor(s: &mut Session, p: &Value, cmd: &str, label: &str, f: &dyn Fn(
                     ItemTarget::Item { index, .. } => Some((id, Some(index))),
                     ItemTarget::Top => None,
                 }),
-                None => ids.first().map(|id| (*id, Some(index))),
+                None => targets.first().map(|id| (*id, Some(index))),
             };
             let mut changed = 0;
             edit_items(s, &targets, item, of, cmd, label, !stroke, |n, i| {