diff --git a/crates/engine/src/cmd/geometry.rs b/crates/engine/src/cmd/geometry.rs
index d186de4..9f0d53a 100644
--- a/crates/engine/src/cmd/geometry.rs
+++ b/crates/engine/src/cmd/geometry.rs
@@ -16,7 +16,7 @@ use crate::{CommandKind, CommandSpec, EngineError, Result, Session};
 pub const OPEN: CommandSpec = CommandSpec {
     id: "geometry.open",
     label: "Open Design",
-    params: r#"{"path": "part.solidcraft", "model"?: "keep"} — rebuilds the SolidCraft design and makes its bodies the geometry. `model`: "keep" (default) keeps the mesh and every definition, so opening the same design again after an edit picks up the change and sets follow their persistent face names; "new" starts a new model with the design (no mesh, sets, materials, sections, BCs, loads or steps; the unit system stays; the model is untitled until saved, and undo restores the previous file). The reply's `related` is false when the model (before the open) refers to bodies (mesh tags, set geometry) and the design has none of them, and `stale` lists what no longer resolves: `mesh_bodies` (bodies the mesh is tagged with that the design lacks) `sets` (sets naming a body or face it lacks) and `seeds` (edge seeds on edges it lacks). One undo step"#,
+    params: r#"{"path": "part.solidcraft", "model"?: "keep"} — rebuilds the SolidCraft design and makes its bodies the geometry. `model`: "keep" (default) keeps the mesh and every definition, so opening the same design again after an edit picks up the change and sets follow their persistent face names; "new" starts a new model with the design (no mesh, sets, materials, sections, BCs, loads or steps; the unit system stays; the model is untitled until saved, and undo restores the previous file). The reply's `related` is false when the model (before the open) refers to bodies (mesh tags, set geometry) and the design has none of them, and `stale` lists what no longer resolves: `mesh_bodies` (bodies the mesh is tagged with that the design lacks) `sets` (sets naming a body or face it lacks) and `seeds` (edge seeds on edges it lacks). `errors` lists the features that failed to rebuild with the `bodies` each may change, and `warnings` says so in one line each. One undo step"#,
     form: Some(super::forms::OPEN_DESIGN),
     kind: CommandKind::Model,
     requires: &[],
@@ -86,7 +86,9 @@ fn open(s: &mut Session, p: &Value) -> Result<Value> {
     let out = json!({
         "name": design.name,
         "bodies": design.bodies.iter().map(|b| b.name.as_str()).collect::<Vec<_>>(),
-        "errors": design.errors.iter().map(|e| json!({"feature": e.feature, "message": e.message})).collect::<Vec<_>>(),
+        "errors": design.errors.iter().map(|e| json!({"feature": e.feature, "message": e.message, "bodies": e.bodies})).collect::<Vec<_>>(),
+        // Shown with the open: a body that differs from the design is never silent.
+        "warnings": design.errors.iter().map(|e| e.warning()).collect::<Vec<_>>(),
         "model": if new_model { "new" } else { "kept" },
         "related": fit.related,
         "stale": {"mesh_bodies": fit.mesh_bodies, "sets": fit.sets, "seeds": fit.seeds},
diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index b1f31a8..3ebcf90 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -734,6 +734,7 @@ mod tests {
         let opened = s.execute("geometry.open", &json!({"path": path})).unwrap();
         assert_eq!(opened["bodies"], json!(["Body1"]));
         assert_eq!(opened["errors"], json!([]));
+        assert_eq!(opened["warnings"], json!([]));
         assert_eq!(s.journal.len(), 1);
 
         let bodies = s.execute("geometry.bodies", &json!({})).unwrap();
diff --git a/crates/geometry/Cargo.toml b/crates/geometry/Cargo.toml
index 897cd06..30ba374 100644
--- a/crates/geometry/Cargo.toml
+++ b/crates/geometry/Cargo.toml
@@ -18,9 +18,9 @@ thiserror = { workspace = true }
 zip = { workspace = true }
 quick-xml = { workspace = true }
 solidcraft-engine = { workspace = true, optional = true }
-serde_json = { workspace = true, optional = true }
+serde_json = { workspace = true }
 
 [features]
 # Build designs from SolidCraft command scripts (`script_design`): the test corpus and tooling.
 # Off by default; the library itself only opens designs.
-scripts = ["dep:solidcraft-engine", "dep:serde_json"]
+scripts = ["dep:solidcraft-engine"]
diff --git a/crates/geometry/src/design.rs b/crates/geometry/src/design.rs
index 277c4b4..ccb30f2 100644
--- a/crates/geometry/src/design.rs
+++ b/crates/geometry/src/design.rs
@@ -34,6 +34,42 @@ pub struct Design {
 pub struct FeatureError {
     pub feature: String,
     pub message: String,
+    /// The bodies that may differ from the design as SolidCraft builds it: those the feature
+    /// names, or every body when it names none of them.
+    pub bodies: Vec<String>,
+}
+
+impl FeatureError {
+    /// One line for the person opening the design, naming the bodies it may change.
+    pub fn warning(&self) -> String {
+        format!("{} failed to build, so {} may differ from the design: {}", self.feature, quoted(&self.bodies), self.message)
+    }
+}
+
+fn quoted(bodies: &[String]) -> String {
+    match bodies {
+        [] => "the design".into(),
+        [b] => format!("body \"{b}\""),
+        _ => format!("bodies {}", bodies.iter().map(|b| format!("\"{b}\"")).collect::<Vec<_>>().join(", ")),
+    }
+}
+
+/// The bodies of `bodies` that `feature` names anywhere in its saved form (targets, tools,
+/// selections); all of them when it names none.
+fn bodies_of(feature: Option<&solidcraft_doc::Feature>, bodies: &[Shape]) -> Vec<String> {
+    fn strings<'a>(v: &'a serde_json::Value, out: &mut Vec<&'a str>) {
+        match v {
+            serde_json::Value::String(s) => out.push(s),
+            serde_json::Value::Array(a) => a.iter().for_each(|v| strings(v, out)),
+            serde_json::Value::Object(o) => o.values().for_each(|v| strings(v, out)),
+            _ => {}
+        }
+    }
+    let value = feature.and_then(|f| serde_json::to_value(f).ok()).unwrap_or_default();
+    let mut named = Vec::new();
+    strings(&value, &mut named);
+    let hit: Vec<String> = bodies.iter().filter(|b| named.contains(&b.name.as_str())).map(|b| b.name.clone()).collect();
+    if hit.is_empty() { bodies.iter().map(|b| b.name.clone()).collect() } else { hit }
 }
 
 impl Design {
@@ -55,12 +91,6 @@ pub(crate) fn rebuild(doc: &Document) -> Result<Design> {
         m.evaluate(doc);
         Ok(m)
     })?;
-    let errors = model
-        .results
-        .iter()
-        .filter(|r| !r.skipped)
-        .filter_map(|r| r.error.as_ref().map(|e| FeatureError { feature: r.name.clone(), message: e.clone() }))
-        .collect();
     // Placed in the world: a component's bodies through every occurrence of it (an instance is a
     // body of its own, named after its occurrence path), as SolidCraft displays and exports them.
     let state = guard("place components", || Ok(solidcraft_doc::world_state(doc, &model.state())))?;
@@ -72,6 +102,18 @@ pub(crate) fn rebuild(doc: &Document) -> Result<Design> {
         })?;
         bodies.push(Shape { name: b.name.clone(), body: b.body.clone(), faces });
     }
+    // A feature that failed leaves a different solid than SolidCraft's: each one names the bodies
+    // it would have changed, so opening never hands back a silently different solid.
+    let errors = model
+        .results
+        .iter()
+        .filter(|r| !r.skipped)
+        .filter_map(|r| {
+            let message = r.error.clone()?;
+            let bodies = bodies_of(doc.features.iter().find(|f| f.id == r.id), &bodies);
+            Some(FeatureError { feature: r.name.clone(), message, bodies })
+        })
+        .collect();
     Ok(Design { name: doc.name.clone(), source: std::sync::Arc::new(bodies.clone()), bodies, errors, cuts: Vec::new() })
 }
 
diff --git a/crates/geometry/src/partition.rs b/crates/geometry/src/partition.rs
index e3e1bcf..76810c5 100644
--- a/crates/geometry/src/partition.rs
+++ b/crates/geometry/src/partition.rs
@@ -104,7 +104,7 @@ impl Design {
             let feature = format!("partition {}", cut.name);
             for b in &cut.bodies {
                 if !bodies.iter().any(|x| &x.name == b) {
-                    errors.push(FeatureError { feature: feature.clone(), message: format!("no body `{b}` to cut") });
+                    errors.push(FeatureError { feature: feature.clone(), message: format!("no body `{b}` to cut"), bodies: vec![b.clone()] });
                 }
             }
             let mut report = CutReport { name: cut.name.clone(), split: Vec::new(), faces: 0 };
@@ -123,7 +123,11 @@ impl Design {
                     }
                     None => {
                         if listed {
-                            errors.push(FeatureError { feature: feature.clone(), message: format!("the plane does not divide `{}`", body.name) });
+                            errors.push(FeatureError {
+                                feature: feature.clone(),
+                                message: format!("the plane does not divide `{}`", body.name),
+                                bodies: vec![body.name.clone()],
+                            });
                         }
                         next.push(body);
                     }