The .modelcraft file, undo/redo on the journal, atomic saves and autosave recovery (M3) (#21)

* modelcraft-io: the .modelcraft file (modelcraft/1), atomic writes, autosave storage

A stored ZIP of a manifest (format tag, geometry sources with SHA-256,
part sizes and hashes), the model definition as stable pretty JSON, the
mesh and geometry tags in a compact binary part, and the journal one
command per line. Reading caps every size, checks every checksum and
replays the model through its checked methods. Model::without_mesh and
empty mesh fields left out of the model's JSON; geometry::read_file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* engine: undo/redo on the journal, file.open/save/save_as, autosave and recovery

CommandSpec gains a kind: Model commands are journalled and become undo
steps; Session commands (file.*, edit.*) manage the session. Undo history
is bounded by steps and estimated memory. Geometry sources are recorded
with content hashes and reopened on file.open (missing or changed files
are warnings). Desktop app autosaves every 30 s and reports recoverable
models; Ctrl/Cmd+Z and Shift+Z/Y undo and redo.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* docs: the .modelcraft format, undo history, roadmap and parity status

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* simplify: shared path parameter, one load path for open/recover, history accounting in History

Session commands skip the per-command model copy; saved revision is an
Option; journal written from borrowed entries and read without an
intermediate tree; backups copied by the file system; recovery lock and
error helpers; geometry file wrappers use read_file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/mesh.rs

@@ -8,32 +8,40 @@ use modelcraft_model::{ElementKind, MAX_ELEMENTS};
 use serde_json::{Value, json};
 
 use super::{label, labels, listed, optional_number, points, xyz};
-use crate::{CommandSpec, EngineError, Result, Session};
+use crate::{CommandKind, 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"#,
+    kind: CommandKind::Model,
     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 NODE_REMOVE: CommandSpec = CommandSpec {
+    id: "mesh.node.remove",
+    label: "Remove Node",
+    params: r#"{"label": 1} — only a node no element uses"#,
+    kind: CommandKind::Model,
+    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"#,
+    kind: CommandKind::Model,
     run: element_add,
 };
 
 pub const ELEMENT_REMOVE: CommandSpec =
-    CommandSpec { id: "mesh.element.remove", label: "Remove Element", params: r#"{"label": 1}"#, run: element_remove };
+    CommandSpec { id: "mesh.element.remove", label: "Remove Element", params: r#"{"label": 1}"#, kind: CommandKind::Model, run: element_remove };
 
 pub const QUALITY: CommandSpec = CommandSpec {
     id: "mesh.quality",
     label: "Mesh Quality",
     params: r#"{"elements": [labels] (optional, default all), "bins": 10 (1..=1000)} — certified validity (det J > 0 everywhere), volume, and min/max/mean/worst/histogram per metric (angles in degrees; histograms over each metric's fixed range, out-of-range values in the end bins)"#,
+    kind: CommandKind::Model,
     run: quality_report,
 };
 
@@ -41,6 +49,7 @@ pub const DELAUNAY_POINTS: CommandSpec = CommandSpec {
     id: "mesh.delaunay.points",
     label: "Delaunay of Points",
     params: r#"{"points": [[x, y, z], ...] (at most 20000)} — the exact Delaunay tetrahedralization (a debugging report; the model is not changed): {"dimension", "vertices", "duplicates": [[point, kept point], ...], "tets": [[i, j, k, l], ...]} with 0-based point indices in tet4 order; collinear or coplanar points give no tets"#,
+    kind: CommandKind::Model,
     run: delaunay_points,
 };
 
@@ -65,6 +74,7 @@ pub const SURFACE_CHECK: CommandSpec = CommandSpec {
     id: "mesh.surface.check",
     label: "Check Boundary Surface",
     params: r#"{"body": "Body1", "tolerance": 0.05} or {"surface": 0}, optional "weld": 1e-9 (0 or 1e-15..=1e-3 of the bounding-box diagonal), "weld_distance": mm (default: the surface's own, twice SolidCraft's linear tolerance for a tessellated body, 0 for an imported mesh), "feature_angle": 45 (degrees, (0, 180]) — welds the tessellated body or imported surface and checks it can bound a volume mesh: closed, manifold, outward, no self-intersections; reports shells, genus, volume and feature edges, or the located defects"#,
+    kind: CommandKind::Model,
     run: surface_check,
 };