mesh: report a kernel failure to partition as the kernel's, not a plane that misses (#283)

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/cmd/datum.rs

@@ -94,7 +94,7 @@ pub const DATUM_DELETE: CommandSpec = CommandSpec {
 pub const PARTITION: CommandSpec = CommandSpec {
     id: "geometry.partition",
     label: "Partition",
-    params: r#"{"name": "Half", "datum": "Mid", "bodies"?: ["Body1"] (default: every body the plane divides)} — cuts bodies of the open design into cells by a datum plane, in memory (the design file is not changed); the model keeps the partition and applies it again whenever the design is opened, after the partitions before it. A cut body `B` becomes the cells `B/a` (on the plane's negative side) and `B/b` (several pieces on a side: `B/a1`, `B/a2`, …). The two faces of the cut are paired by name: `partition:<name>:a` on the cells on the negative side, `partition:<name>:b` on the positive side (`…#0`, `…#1` where a cell has several); every other face keeps the persistent name of the face it is a piece of (`<face>#k` for several pieces on one cell), so sets by face name still select it. Reports the cells made and the cut faces named; a plane that divides no body, or a listed body it does not divide, is an error"#,
+    params: r#"{"name": "Half", "datum": "Mid", "bodies"?: ["Body1"] (default: every body the plane divides)} — cuts bodies of the open design into cells by a datum plane, in memory (the design file is not changed); the model keeps the partition and applies it again whenever the design is opened, after the partitions before it. A cut body `B` becomes the cells `B/a` (on the plane's negative side) and `B/b` (several pieces on a side: `B/a1`, `B/a2`, …). The two faces of the cut are paired by name: `partition:<name>:a` on the cells on the negative side, `partition:<name>:b` on the positive side (`…#0`, `…#1` where a cell has several); every other face keeps the persistent name of the face it is a piece of (`<face>#k` for several pieces on one cell), so sets by face name still select it. Reports the cells made and the cut faces named; a plane that divides no body, a listed body it does not divide, or a body the kernel fails to cut (its message) is an error"#,
     form: Some(super::forms::PARTITION),
     kind: CommandKind::Model,
     requires: &[Requirement::Design, Requirement::DatumPlane],