From fb9a3a813be450f79d6424cc32b2b1e411800ab8 Mon Sep 17 00:00:00 2001
From: HassanKhan <ch.hasni.khan@gmail.com>
Date: Thu, 12 Nov 2026 13:57:30 +0500
Subject: [PATCH] Blend: pinning a closed replaced spine gives its end keys
 points of their own (#6809)

Pinning a closed spine from Replace Spine (a spine edit, Reverse Spine)
stored it closed with both end keys on its first point, so moving the
first key afterwards landed it on the last. Pinning now opens the spine
there as the layout of a moved key does.
---
 crates/doc/src/blend.rs         |  8 ++++++--
 crates/engine/src/tests/live.rs | 27 +++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/crates/doc/src/blend.rs b/crates/doc/src/blend.rs
index ac9f99c4f6..4e51777060 100644
--- a/crates/doc/src/blend.rs
+++ b/crates/doc/src/blend.rs
@@ -1116,8 +1116,12 @@ pub fn pin_spine(keys: &[Arc<Node>], spec: &BlendSpec) -> Option<(PathData, Vec<
         && pinned(spec, keys.len(), first.anchors.len()).is_none()
     {
         let mut path = PathData::single(first.clone());
-        let out = spread_anchors(&mut path, keys.len())?;
-        return Some((path, out));
+        let mut out = spread_anchors(&mut path, keys.len())?;
+        // A closed spine's end keys get points of their own, so that once pinned each still
+        // moves only its own end.
+        let mut sp = path.subpaths.into_iter().next()?;
+        open_at_start(&mut sp, &mut out);
+        return Some((PathData::single(sp), out));
     }
     let (path, anchors) = blend_spine(keys, spec)?;
     Some((path, anchors?))
diff --git a/crates/engine/src/tests/live.rs b/crates/engine/src/tests/live.rs
index 429542827e..0cc01bdae5 100644
--- a/crates/engine/src/tests/live.rs
+++ b/crates/engine/src/tests/live.rs
@@ -484,6 +484,33 @@ fn moving_the_first_key_of_a_closed_replaced_spine_blend_moves_what_is_drawn() {
     assert!(center(&back[1]).distance(center(&before[1])) < 1e-6);
 }
 
+/// #6809 on a closed spine pinned by a spine edit: the end keys get points of their own, so
+/// moving the first key afterwards still moves only its end.
+#[test]
+fn moving_the_first_key_of_a_pinned_closed_spine_blend_moves_what_is_drawn() {
+    let mut s = session();
+    let (a, _, g) = blend(&mut s, json!({"steps": 5}));
+    let square = id_of(&s.execute("path.create", &json!({"d": "M100 100 L300 100 L300 300 L100 300 Z"})).unwrap());
+    sel(&mut s, &[g, square]);
+    s.execute("object.blend.replaceSpine", &json!({})).unwrap();
+    // Dragging a corner away from the keys pins the spine to them.
+    s.execute("object.blend.spine.moveAnchor", &json!({"id": g.0, "anchor": 2, "x": 320, "y": 320})).unwrap();
+    let NodeKind::Blend { spec, .. } = node(&s, g).kind else { panic!() };
+    assert_eq!(spec.key_anchors.len(), 2, "{:?}", spec.key_anchors);
+    let center = |n: &Node| n.geometric_bounds().unwrap().center();
+    let before = steps_of(&s, g);
+    sel(&mut s, &[a]);
+    s.execute("object.move", &json!({"dx": -50, "dy": -40})).unwrap();
+    let key = center(&node(&s, a));
+    assert!(key.distance(Point::new(50.0, 60.0)) < 1e-6, "{key:?}");
+    let after = steps_of(&s, g);
+    assert_eq!(after.len(), before.len());
+    let drawn = center(&after[0]);
+    assert!(drawn.distance(key) < 1e-6, "the key is drawn where it was moved to: {drawn:?}, outline at {key:?}");
+    let last = center(&after[after.len() - 1]);
+    assert!(last.distance(Point::new(100.0, 100.0)) < 1e-6, "the other key stays put: {last:?}");
+}
+
 #[test]
 fn blend_align_to_path_rotates_steps() {
     let mut s = session();