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

xtask/src/assets.rs

@@ -0,0 +1,40 @@
+//! `cargo xtask assets`: every non-code asset in the repository must have a row in
+//! ATTRIBUTION.md (author, source, licence). Icons are drawn in code and need no file.
+
+use std::path::Path;
+
+const ASSET_EXT: &[&str] =
+    &["png", "jpg", "jpeg", "svg", "ico", "icns", "ttf", "otf", "woff", "woff2", "gif", "bmp", "webp", "wav", "mp3", "stl", "step", "stp", "obj"];
+const SKIP_DIRS: &[&str] = &["target", ".git", "plan", "dist"];
+
+fn walk(dir: &Path, root: &Path, out: &mut Vec<String>) {
+    let Ok(rd) = std::fs::read_dir(dir) else { return };
+    for e in rd.flatten() {
+        let p = e.path();
+        let name = e.file_name().to_string_lossy().to_string();
+        if p.is_dir() {
+            if !SKIP_DIRS.contains(&name.as_str()) && !name.starts_with('.') {
+                walk(&p, root, out);
+            }
+        } else if let Some(ext) = p.extension().map(|x| x.to_string_lossy().to_ascii_lowercase())
+            && ASSET_EXT.contains(&ext.as_str())
+            && let Ok(rel) = p.strip_prefix(root)
+        {
+            out.push(rel.to_string_lossy().replace('\\', "/"));
+        }
+    }
+}
+
+pub fn run(root: &Path) -> Result<(), String> {
+    let attribution = std::fs::read_to_string(root.join("ATTRIBUTION.md")).map_err(|e| format!("ATTRIBUTION.md: {e}"))?;
+    let mut files = Vec::new();
+    walk(root, root, &mut files);
+    files.sort();
+    let missing: Vec<&String> = files.iter().filter(|f| !attribution.contains(f.as_str())).collect();
+    if missing.is_empty() {
+        println!("assets: {} asset file(s), all attributed", files.len());
+        Ok(())
+    } else {
+        Err(format!("assets missing from ATTRIBUTION.md:\n{}", missing.iter().map(|m| format!("  {m}")).collect::<Vec<_>>().join("\n")))
+    }
+}