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/geometry/src/design.rs

@@ -9,7 +9,7 @@
 use solidcraft_doc::{Document, Model, naming};
 use solidcraft_kernel::{KernelError, guard};
 
-use crate::{Error, Face, Result, Shape};
+use crate::{Face, Result, Shape};
 
 /// Largest design file opened (SolidCraft's own limit).
 pub const MAX_DESIGN_BYTES: usize = solidcraft_io::MAX_DESIGN_BYTES;
@@ -47,8 +47,7 @@ pub fn open_design(bytes: &[u8]) -> Result<Design> {
 
 /// Read a design file (a regular file of at most [`MAX_DESIGN_BYTES`]) and rebuild it.
 pub fn open_design_file(path: &str) -> Result<Design> {
-    let bytes = solidcraft_io::vfs::read(path, MAX_DESIGN_BYTES).map_err(|e| Error::Invalid(format!("cannot read `{path}`: {e}")))?;
-    open_design(&bytes)
+    open_design(&crate::read_file(path, MAX_DESIGN_BYTES)?)
 }
 
 /// Rebuild an in-memory document (the design half of [`open_design`]).

crates/geometry/src/lib.rs

@@ -47,6 +47,14 @@ impl From<KernelError> for Error {
     }
 }
 
+/// Read a regular file of at most `max_bytes` through SolidCraft's file access (in the browser,
+/// the in-memory files the web host loaded). Opening a design or a 3MF package from these bytes
+/// ([`open_design`], [`tagged_mesh::read_3mf`]) lets the caller record a hash of exactly what it
+/// opened.
+pub fn read_file(path: &str, max_bytes: usize) -> Result<Vec<u8>> {
+    solidcraft_io::vfs::read(path, max_bytes).map_err(|e| Error::Invalid(format!("cannot read `{path}`: {e}")))
+}
+
 /// SolidCraft's linear modelling tolerance (mm): points closer than this are the same point.
 const LINEAR_TOLERANCE: f64 = solidcraft_geom::LINEAR_TOL;
 

crates/geometry/src/tagged_mesh.rs

@@ -347,8 +347,7 @@ fn surface(mut o: Object, k: usize, id: u32, xf: &Xf, unit: f64) -> Result<Tagge
 /// [`read_3mf`] of a file: a regular file of at most [`MAX_FILE_BYTES`] (SolidCraft's virtual
 /// file system, so the browser's in-memory files work too).
 pub fn read_3mf_file(path: &str) -> Result<Vec<TaggedSurface>> {
-    let bytes = solidcraft_io::vfs::read(path, MAX_FILE_BYTES).map_err(|e| Error::Invalid(format!("cannot read `{path}`: {e}")))?;
-    read_3mf(&bytes)
+    read_3mf(&crate::read_file(path, MAX_FILE_BYTES)?)
 }
 
 /// The surfaces of a 3MF package, one per build item, in millimetres.