From 963f489eab4947936cf770f8e01710c50298f69b Mon Sep 17 00:00:00 2001
From: Madhav Agarwal <connectmadhav09@gmail.com>
Date: Thu, 22 Oct 2026 18:47:59 +0530
Subject: [PATCH] engine: resolve effect match-name paths in prop_ref (#2064)

---
 crates/engine/src/commands/prop.rs |  7 +++++--
 crates/engine/src/tests_effects.rs | 21 +++++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/crates/engine/src/commands/prop.rs b/crates/engine/src/commands/prop.rs
index 3af877d34..596164b42 100644
--- a/crates/engine/src/commands/prop.rs
+++ b/crates/engine/src/commands/prop.rs
@@ -22,8 +22,11 @@ pub(crate) fn prop_ref(s: &Session, p: &Value, cmd: &str) -> Result<(ItemId, Lay
         });
     }
     let path = str_p(p, "path").ok_or_else(|| bad(cmd, "missing `path` (e.g. transform/position) or `prop` uid"))?;
-    let pr = layer.props.prop(path).ok_or_else(|| {
-        let group = layer.props.group(path).or_else(|| path.trim().strip_prefix('@')?.parse().ok().and_then(|uid| layer.props.find_group(uid)));
+    // `effects/<match name>[#n]/<property>` is how `essential.list`, presets and Copy write an
+    // effect property; turn it into the uid path `PropGroup::prop` parses (#2064).
+    let resolved = super::resolve_effect_path(layer, path);
+    let pr = layer.props.prop(&resolved).ok_or_else(|| {
+        let group = layer.props.group(&resolved).or_else(|| path.trim().strip_prefix('@')?.parse().ok().and_then(|uid| layer.props.find_group(uid)));
         if group.is_some() {
             bad(cmd, format!("`{path}` is a property group; use layer.tree (MCP: get_layer) to inspect its children, then select a leaf property"))
         } else {
diff --git a/crates/engine/src/tests_effects.rs b/crates/engine/src/tests_effects.rs
index 18fcc6f84..1ea57f4cf 100644
--- a/crates/engine/src/tests_effects.rs
+++ b/crates/engine/src/tests_effects.rs
@@ -772,6 +772,27 @@ fn preset_round_trips_effect_properties_by_match_name() {
     }
 }
 
+/// #2064: `prop.addKey` accepts the `effects/<match name>[#n]/<property>` path that
+/// `essential.list` reports.
+#[test]
+fn add_key_resolves_effect_match_name_paths() {
+    let (mut s, a, _) = comp_with_two_solids();
+    apply(&mut s, a, "Slider Control");
+    apply(&mut s, a, "Slider Control");
+    let slider = |s: &Session, n: usize| match layer(s, a).effects().unwrap().groups().nth(n).unwrap().get("slider").unwrap().value {
+        KV::Scalar(v) => v,
+        ref other => panic!("not a scalar: {other:?}"),
+    };
+    for (path, n, value) in [("effects/ec.control.slider/slider", 0, 30.0), ("effects/ec.control.slider#2/slider", 1, 70.0)] {
+        let reply = s.execute("prop.addKey", json!({"layer": a, "path": path, "time": 0, "value": value})).unwrap();
+        assert_eq!(reply, json!(1), "{path}");
+        let got = s.execute("prop.get", json!({"layer": a, "path": path, "time": 0})).unwrap();
+        assert_eq!(got["value"], json!(value), "{path}");
+        assert_eq!(got["keys"].as_array().unwrap().len(), 1, "{path}");
+        assert_eq!(slider(&s, n), 0.0, "the static value stays put; the key carries {value}");
+    }
+}
+
 /// #1746: Edit ▸ Copy of an effect property writes the same `effects/ec.blur.gaussian/blurriness` path,
 /// and Paste (the value, or Copy Expression Only) sets that property of the other layer's effect.
 #[test]