Add kernel solid operations and complete Solid3D (create and rigid move)

An additive HostApi::solid_operation builds cadkernel primitives and applies
rigid transforms, verifying each result lifts back losslessly and refusing a
payload it cannot lift. Exposed as doc.solids in Python; Solid3D, Body and
Region are mapped read-only with the opaque payload preserved. The lifecycle
test passes through the real runner with analytic volumes and exact extents as
oracles, DWG and DXF reopen with re-edit, and undo restores exactly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/ocs_plugin_api/src/ipc/v4/client.rs

@@ -784,6 +784,18 @@ impl HostApi for V4PluginHostApi {
         }
     }
 
+    fn solid_operation(&mut self, operation: crate::host::SolidOperation) -> Result<Handle, String> {
+        match self.request(PluginRequest::SolidOperation { operation }) {
+            Ok(PluginResponse::SolidResult(result)) => {
+                if result.is_ok() { self.document_cache = OnceCell::new(); }
+                result
+            }
+            Ok(PluginResponse::Error(error)) => Err(error),
+            Ok(other) => Err(format!("unexpected solid operation response: {other:?}")),
+            Err(error) => Err(error.to_string()),
+        }
+    }
+
     fn set_selection(&mut self, handles: &[Handle]) -> Result<(), String> {
         match self.request(PluginRequest::SetSelection { handles: handles.to_vec() }) {
             Ok(PluginResponse::SelectionResult(result)) => result,

crates/ocs_plugin_api/src/ipc/v4/protocol.rs

@@ -105,6 +105,27 @@ mod tests {
         assert_eq!(decoded, changed);
     }
 
+    #[test]
+    fn solid_operation_request_and_response_roundtrip() {
+        use crate::host::{SolidOperation, SolidPrimitive};
+        for operation in [
+            SolidOperation::Create {
+                primitive: SolidPrimitive::Pyramid { center: [1.0, 2.0, 3.0], radius: 4.0, height: 5.0, sides: 6 },
+                layer: Some("SOLIDS".into()),
+            },
+            SolidOperation::Transform { handle: acadrust::Handle::new(7), matrix: [1.0; 16] },
+        ] {
+            let bytes = bincode::serialize(&PluginRequest::SolidOperation { operation: operation.clone() }).unwrap();
+            assert!(matches!(bincode::deserialize::<PluginRequest>(&bytes).unwrap(),
+                PluginRequest::SolidOperation { operation: decoded } if decoded == operation));
+        }
+        for result in [Ok(acadrust::Handle::new(9)), Err("refused".to_owned())] {
+            let bytes = bincode::serialize(&PluginResponse::SolidResult(result.clone())).unwrap();
+            assert!(matches!(bincode::deserialize::<PluginResponse>(&bytes).unwrap(),
+                PluginResponse::SolidResult(decoded) if decoded == result));
+        }
+    }
+
     #[test]
     fn selection_request_and_response_roundtrip() {
         let request = PluginRequest::SetSelection { handles: vec![acadrust::Handle::new(9)] };