Color: Recent Colors keeps the last 30 colors used, across documents

Recent Colors now keeps up to 30 solid colors instead of 10, newest
first and each once; applying a 31st drops the oldest. The Session
holds the list, so it stays the same when another document is opened
or made active, and it lasts for the session.

The Color and Swatches panels wrap the chips onto further rows when
the panel is too narrow for one row, so every color can be clicked.
A list that fits one row draws as before.

Docs: paint.recent params text, docs/mcp.md, docs/target-app-parity.md.

crates/engine/src/tests/paintproxy.rs

@@ -185,16 +185,53 @@ fn recent_colors_are_fed_by_every_paint_command() {
     s.execute("paint.setFill", &json!({"gradient": {"kind": "linear"}})).unwrap();
     assert_eq!(hexes(&s).len(), 3);
     // The list holds the newest `RECENT_MAX` colours.
-    for i in 0..20u8 {
+    for i in 0..40u8 {
         s.execute("paint.setFill", &json!({"color": Color::rgb8(i, 0, 0).to_hex()})).unwrap();
     }
     assert_eq!(s.recent_colors.len(), Session::RECENT_MAX);
-    assert_eq!(s.recent_colors[0].to_hex(), "#130000");
+    assert_eq!(s.recent_colors[0].to_hex(), "#270000");
     let r = s.execute("paint.recent", &json!({})).unwrap();
-    assert_eq!(r["colors"][0]["hex"], "#130000");
+    assert_eq!(r["colors"][0]["hex"], "#270000");
     let _ = id;
 }
 
+#[test]
+fn recent_colors_keep_thirty_colors_across_documents() {
+    let mut s = session();
+    rect(&mut s);
+    let red = |i: u8| Color::rgb8(i, 0, 0).to_hex();
+    for i in 1..=30u8 {
+        s.execute("paint.setFill", &json!({"color": red(i)})).unwrap();
+    }
+    assert_eq!(Session::RECENT_MAX, 30);
+    let all: Vec<String> = (1..=30u8).rev().map(red).collect();
+    assert_eq!(hexes(&s), all, "30 colors are kept, newest first");
+    // The 31st drops the oldest.
+    s.execute("paint.setFill", &json!({"color": red(31)})).unwrap();
+    assert_eq!(hexes(&s).len(), 30);
+    assert_eq!(hexes(&s)[0], red(31));
+    assert_eq!(hexes(&s)[29], red(2));
+    assert!(!hexes(&s).contains(&red(1)), "the oldest color is dropped");
+    // Applying a color already in the list moves it to the front, once.
+    s.execute("paint.setStroke", &json!({"color": red(10)})).unwrap();
+    assert_eq!(hexes(&s).len(), 30);
+    assert_eq!(hexes(&s)[0], red(10));
+    assert_eq!(hexes(&s).iter().filter(|h| **h == red(10)).count(), 1);
+    let before = hexes(&s);
+    // A new document, and going back to the first one, keep the list.
+    s.execute("file.new", &json!({"width": 200, "height": 200})).unwrap();
+    assert_eq!(hexes(&s), before);
+    s.execute("document.activate", &json!({"index": 0})).unwrap();
+    assert_eq!(hexes(&s), before);
+    // A color applied in the second document joins the same list.
+    s.execute("document.activate", &json!({"index": 1})).unwrap();
+    rect(&mut s);
+    s.execute("paint.setFill", &json!({"color": "#00ff00"})).unwrap();
+    s.execute("document.activate", &json!({"index": 0})).unwrap();
+    assert_eq!(hexes(&s)[0], "#00ff00");
+    assert_eq!(hexes(&s)[1..], before[..29]);
+}
+
 #[test]
 fn live_previews_remember_only_the_committed_colour() {
     let mut s = session();