docs: node relaxation in features, MCP guide, control protocol, literature and the meshing skill (#398)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/catalogue.rs

@@ -354,6 +354,14 @@ pub static CATALOGUE: &[Capability] = &[
     soon("mesh.smooth", "Smooth", Mesh, "Improve", "M6", "Smooth node positions, keeping every element valid"),
     soon("mesh.untangle", "Untangle", Mesh, "Improve", "M6", "Repair inverted elements"),
     soon("mesh.layers", "Layers", Mesh, "Improve", "M6", "Boundary padding and layers through thin walls"),
+    ready_more(
+        "mesh.node.relax",
+        "Relax Nodes",
+        Mesh,
+        "Improve",
+        "Relax the nodes inside a sphere to fix spikes and slivers; surface nodes slide on the geometry; kept as a field to apply again after a remesh",
+        &["mesh.node.relax.apply"],
+    ),
     ready_more("mesh.node.add", "Node", Mesh, "Edit", "Add a node", &["mesh.node.remove"]),
     ready_more("mesh.element.add", "Element", Mesh, "Edit", "Add an element on existing nodes", &["mesh.element.remove", "mesh.clear"]),
     ready("mesh.mirror", "Mirror Mesh", Mesh, "Edit", "Mirror a body's mesh across a plane, joined on the plane (mesh half a symmetric part)"),
@@ -365,14 +373,6 @@ pub static CATALOGUE: &[Capability] = &[
         "Merge coincident nodes, keeping sets, loads and boundary conditions on the survivors; check for duplicates and cracks, renumber",
         &["mesh.check.duplicates", "mesh.renumber"],
     ),
-    ready_more(
-        "mesh.node.relax",
-        "Relax Nodes",
-        Mesh,
-        "Improve",
-        "Relax the nodes inside a sphere to fix spikes and slivers; surface nodes slide on the geometry; kept as a field to apply again after a remesh",
-        &["mesh.node.relax.apply"],
-    ),
     soon("mesh.region.remesh", "Remesh Region", Mesh, "Edit", "M6", "Remesh a region in place; split and collapse elements"),
     soon("mesh.import.orphan", "Orphan Mesh", Mesh, "Edit", "M6", "Import a mesh without geometry"),
     ready("mesh.quality", "Quality", Mesh, "Verify", "Quality metrics and the certified validity check, failing elements listed"),

crates/engine/src/cmd/forms.rs

@@ -1891,6 +1891,7 @@ mod tests {
         "has a result",
         "no crash report",
         "FIELDCRAFT_CRASH_TEST",
+        "no relaxation field",
     ];
 
     /// Fill top-level required names (a fresh one) and references (the first existing item).

crates/engine/src/cmd/relax.rs

@@ -374,7 +374,7 @@ pub(crate) fn weights(model: &Model, p: &Value) -> Result<(BTreeMap<u32, f64>, O
         nodes.extend(el.nodes.iter().copied());
     }
     if listed == 0 {
-        return Err(EngineError::Params("say which nodes to relax: `center` and `radius`, `around_element`, `nodes`, `elements` or `set`".into()));
+        return Err(EngineError::Params("say which nodes to relax: give one of `center` and `radius`, `around_element`, `nodes`, `elements` or `set`".into()));
     }
     if let Some(only) = &only {
         nodes.retain(|n| only.contains(n));