From 4d1eb16424ef189c5a9e7c54740ddf73f0102424 Mon Sep 17 00:00:00 2001
From: Brandon Thomas <echelon@gmail.com>
Date: Thu, 1 Oct 2026 10:32:58 -0400
Subject: [PATCH] M1: fix paste into a compound path when undo made a new
 object reuse the active layer's id (active layer / isolation must still be a
 layer / group); regression test

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 crates/engine/src/cmd/clipboard.rs | 19 +++++++++++++++++++
 crates/engine/src/lib.rs           |  8 +++++---
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/crates/engine/src/cmd/clipboard.rs b/crates/engine/src/cmd/clipboard.rs
index 6a9c7c06..110ab49d 100644
--- a/crates/engine/src/cmd/clipboard.rs
+++ b/crates/engine/src/cmd/clipboard.rs
@@ -115,6 +115,25 @@ mod tests {
         assert!((b.width() - 30.0).abs() < 1e-6 && (b.height() - 40.0).abs() < 1e-6);
     }
 
+    #[test]
+    fn paste_never_lands_in_an_object_that_reused_an_undone_layers_id() {
+        // Found by the model-based test: undo restores the id counter, so a compound path made
+        // after undoing New Layer gets the dead layer's id, which was still the active layer.
+        let mut s = session();
+        let r = s.execute("shape.rectangle", &json!({"x": 0, "y": 0, "width": 10, "height": 10})).unwrap()["id"].clone();
+        s.execute("select.set", &json!({"ids": [r]})).unwrap();
+        s.execute("edit.copy", &json!({})).unwrap();
+        let layer = s.execute("layer.new", &json!({})).unwrap()["id"].as_u64().unwrap();
+        s.execute("edit.undo", &json!({})).unwrap();
+        s.execute("select.set", &json!({"ids": [r]})).unwrap();
+        let c = s.execute("object.compoundPath.make", &json!({})).unwrap()["id"].as_u64().unwrap();
+        assert_eq!(c, layer, "the scenario needs the id to be reused");
+        s.execute("edit.paste", &json!({})).unwrap();
+        let d = &s.doc().unwrap().doc;
+        let compound = d.node(NodeId(c)).unwrap();
+        assert!(compound.children().unwrap().iter().all(|ch| matches!(ch.kind, drawcraft_doc::NodeKind::Path { .. })));
+    }
+
     #[test]
     fn foreign_svg_and_non_svg_text() {
         let mut s = session();
diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index 398872cd..b2e17596 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -13,7 +13,7 @@ mod tooling;
 use std::sync::Arc;
 
 use drawcraft_color::{Color, Paint};
-use drawcraft_doc::{Document, NodeId, Selection};
+use drawcraft_doc::{Document, NodeId, NodeKind, Selection};
 use drawcraft_geom::Affine;
 use drawcraft_tools::{PaintDefaults, Tool};
 use serde_json::Value;
@@ -130,12 +130,14 @@ impl DocState {
     }
     /// Where new art is inserted: the isolation container, else the active layer.
     pub fn insertion_parent(&self) -> Option<NodeId> {
+        // Ids are reused after undo (the id counter is part of the document), so a remembered
+        // layer or isolated group must still be one: a pasted group must never land in a path.
         if let Some(i) = self.isolation
-            && self.doc.node(i).is_some()
+            && self.doc.node(i).is_some_and(|n| matches!(n.kind, NodeKind::Group { .. } | NodeKind::Layer { .. }))
         {
             return Some(i);
         }
-        self.active_layer.filter(|l| self.doc.node(*l).is_some_and(|n| !n.locked)).or_else(|| self.doc.default_layer())
+        self.active_layer.filter(|l| self.doc.node(*l).is_some_and(|n| n.is_layer() && !n.locked)).or_else(|| self.doc.default_layer())
     }
 }