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 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/engine/src/cmd/mod.rs

@@ -0,0 +1,29 @@
+//! The command registry. Each area has its own module; [`ALL`] lists every command.
+
+mod mesh;
+mod model;
+
+use serde_json::Value;
+
+use crate::{CommandSpec, EngineError, Result};
+
+pub static ALL: &[CommandSpec] = &[model::INFO, mesh::NODE_ADD, mesh::NODE_REMOVE, mesh::ELEMENT_ADD, mesh::ELEMENT_REMOVE];
+
+/// A required label parameter (1..=u32::MAX; the model checks its own range).
+pub(crate) fn label(p: &Value, key: &str) -> Result<u32> {
+    p.get(key)
+        .and_then(Value::as_u64)
+        .and_then(|v| u32::try_from(v).ok())
+        .ok_or_else(|| EngineError::Params(format!("`{key}` must be a positive whole number")))
+}
+
+/// A required `[x, y, z]` parameter.
+pub(crate) fn xyz(p: &Value, key: &str) -> Result<[f64; 3]> {
+    let bad = || EngineError::Params(format!("`{key}` must be [x, y, z]"));
+    let a = p.get(key).and_then(Value::as_array).filter(|a| a.len() == 3).ok_or_else(bad)?;
+    let mut out = [0.0; 3];
+    for (o, v) in out.iter_mut().zip(a) {
+        *o = v.as_f64().ok_or_else(bad)?;
+    }
+    Ok(out)
+}