ModelCraft foundation: workspace, quality gates, FE model, command engine, geometry boundary

A pure-Rust CAE modeling workspace following the SolidCraft conventions:
- modelcraft-model: nodes and elements by label with hostile-input validation
- modelcraft-geometry: SolidCraft's kernel (pinned git dependency) behind our own API;
  tessellation into a face-tagged boundary surface for volume meshing
- modelcraft-engine: CommandSpec registry, Session::execute with rollback and panic guard,
  scripts and a journal
- modelcraft-cli: list commands, run scripts
- xtask: layers (only geometry may use solidcraft-*), assets, licences, tests, wasm, ci
- AGENTS.md, architecture, ADR 0001 (libraries and licences), roadmap, CI

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/engine/src/cmd/mesh.rs

@@ -0,0 +1,58 @@
+use modelcraft_model::{ElementKind, MAX_LABEL};
+use serde_json::{Value, json};
+
+use super::{label, xyz};
+use crate::{CommandSpec, EngineError, Result, Session};
+
+pub const NODE_ADD: CommandSpec = CommandSpec {
+    id: "mesh.node.add",
+    label: "Add Node",
+    params: r#"{"label": 1, "xyz": [x, y, z]} — adds the node, or moves it if the label exists"#,
+    run: node_add,
+};
+
+pub const NODE_REMOVE: CommandSpec =
+    CommandSpec { id: "mesh.node.remove", label: "Remove Node", params: r#"{"label": 1} — only a node no element uses"#, run: node_remove };
+
+pub const ELEMENT_ADD: CommandSpec = CommandSpec {
+    id: "mesh.element.add",
+    label: "Add Element",
+    params: r#"{"label": 1, "kind": "rod2|beam2|tri3|tri6|quad4|quad8|tet4|tet10|wedge6|hex8|hex20", "nodes": [labels]} — adds or replaces"#,
+    run: element_add,
+};
+
+pub const ELEMENT_REMOVE: CommandSpec =
+    CommandSpec { id: "mesh.element.remove", label: "Remove Element", params: r#"{"label": 1}"#, run: element_remove };
+
+fn node_add(s: &mut Session, p: &Value) -> Result<Value> {
+    let l = label(p, "label")?;
+    s.model.set_node(l, xyz(p, "xyz")?)?;
+    Ok(json!({"label": l}))
+}
+
+fn node_remove(s: &mut Session, p: &Value) -> Result<Value> {
+    s.model.remove_node(label(p, "label")?)?;
+    Ok(Value::Null)
+}
+
+fn element_add(s: &mut Session, p: &Value) -> Result<Value> {
+    let l = label(p, "label")?;
+    let name = p.get("kind").and_then(Value::as_str).unwrap_or_default();
+    let kind = ElementKind::from_name(name).ok_or_else(|| EngineError::Params(format!("unknown element kind `{name}`")))?;
+    let raw = p.get("nodes").and_then(Value::as_array).ok_or_else(|| EngineError::Params("`nodes` must be a list of node labels".into()))?;
+    if raw.len() != kind.node_count() {
+        return Err(EngineError::Params(format!("{name} needs {} nodes, got {}", kind.node_count(), raw.len())));
+    }
+    let nodes = raw
+        .iter()
+        .map(|v| v.as_u64().and_then(|n| u32::try_from(n).ok()).filter(|n| (1..=MAX_LABEL).contains(n)))
+        .collect::<Option<Vec<u32>>>()
+        .ok_or_else(|| EngineError::Params(format!("`nodes` must be node labels in 1..={MAX_LABEL}")))?;
+    s.model.set_element(l, kind, nodes)?;
+    Ok(json!({"label": l}))
+}
+
+fn element_remove(s: &mut Session, p: &Value) -> Result<Value> {
+    s.model.remove_element(label(p, "label")?)?;
+    Ok(Value::Null)
+}