Print: Print, Print Preview and Print Setup take a print preset by name

file.print, print.preview and print.setup took print settings only as
settings, so an agent had to read a preset with print.presets.list and
copy its settings into the call. They now take preset, the name of
[Default] or of a saved print preset in any case. The preset's settings
are used instead of the document's, settings applies over them, and
print.setup saves them with the document as one undo step. An unknown
name is a parameter error that lists the presets. The app's file.print
with params passes preset on to the engine.

Docs: docs/mcp.md, docs/target-app-parity.md.

crates/engine/src/tests_print.rs

@@ -66,6 +66,66 @@ fn print_writes_the_saved_setup_with_overrides() {
     let _ = std::fs::remove_file(&path);
 }
 
+/// A document with four 300 × 200 artboards, set up to print two copies, and a saved print preset
+/// "Sheet" that prints artboard 4 only.
+fn four_artboards_and_a_preset() -> Session {
+    let mut s = Session::new();
+    s.execute("file.new", &json!({"width": 300, "height": 200, "artboards": 4})).unwrap();
+    s.execute("print.setup", &json!({"settings": {"copies": 2}})).unwrap();
+    s.execute("print.presets.save", &json!({"name": "Sheet", "settings": {"artboards": "range", "range": "4"}})).unwrap();
+    s
+}
+
+#[test]
+fn print_takes_a_print_preset_by_name() {
+    let mut s = four_artboards_and_a_preset();
+    // The preset's settings stand in for the document's: one copy of artboard 4.
+    let (bytes, v) = print(&mut s, json!({"preset": "sheet"}));
+    assert_eq!((v["pages"].clone(), vectorcraft_pdf::info(&bytes, None).unwrap().pages.len()), (json!(1), 1));
+    let (_, v) = print(&mut s, json!({"preset": "Sheet", "settings": {"copies": 3}}));
+    assert_eq!(v["pages"], 3, "settings apply over the preset's");
+    let (_, v) = print(&mut s, json!({"preset": "[Default]"}));
+    assert_eq!(v["pages"], 4, "[Default]: every artboard, one copy");
+    assert_eq!(s.execute("print.setup", &json!({})).unwrap()["settings"]["copies"], 2, "printing doesn't change the saved setup");
+    // A PostScript file too.
+    let v = s.execute("file.print", &json!({"preset": "Sheet", "format": "postscript"})).unwrap();
+    assert_eq!(v["pages"], 1);
+}
+
+#[test]
+fn an_unknown_print_preset_is_refused_with_the_presets() {
+    let mut s = four_artboards_and_a_preset();
+    for c in ["file.print", "print.preview", "print.setup"] {
+        // Agents (MCP, the control channel) may pass `preset`.
+        s.check_params(c, &json!({"preset": "Sheet", "settings": {}})).unwrap();
+        let e = s.execute(c, &json!({"preset": "Nope"})).unwrap_err();
+        assert!(matches!(e, EngineError::BadParams { .. }), "{c}: {e}");
+        assert!(e.to_string().contains("no print preset named `Nope` (presets: [Default], Sheet)"), "{c}: {e}");
+        assert!(matches!(s.execute(c, &json!({"preset": 4})), Err(EngineError::BadParams { .. })), "{c}");
+    }
+    assert_eq!(s.doc().unwrap().doc.print_setup.as_ref().unwrap()["copies"], 2);
+}
+
+#[test]
+fn setup_with_a_preset_stores_its_settings() {
+    let mut s = four_artboards_and_a_preset();
+    let undo = s.doc().unwrap().history.undo.len();
+    let v = s.execute("print.setup", &json!({"preset": "Sheet"})).unwrap();
+    let got = (v["settings"]["copies"].clone(), v["settings"]["artboards"].clone(), v["settings"]["range"].clone());
+    assert_eq!(got, (json!(1), json!("range"), json!("4")));
+    let stored = s.doc().unwrap().doc.print_setup.clone().unwrap();
+    assert_eq!(stored, v["settings"]);
+    assert_eq!(s.doc().unwrap().history.undo.len(), undo + 1, "one undo step");
+    // The same preset again is no new step; settings apply over it.
+    s.execute("print.setup", &json!({"preset": "Sheet"})).unwrap();
+    assert_eq!(s.doc().unwrap().history.undo.len(), undo + 1);
+    let v = s.execute("print.setup", &json!({"preset": "Sheet", "settings": {"collate": false}})).unwrap();
+    assert_eq!((v["settings"]["range"].clone(), v["settings"]["collate"].clone()), (json!("4"), json!(false)));
+    s.execute("edit.undo", &json!({})).unwrap();
+    s.execute("edit.undo", &json!({})).unwrap();
+    assert_eq!(s.doc().unwrap().doc.print_setup.as_ref().unwrap()["copies"], 2);
+}
+
 #[test]
 fn preview_lists_pages_tiles_inks_and_warnings() {
     let (mut s, _) = session();