Persist SNAPUNIT and GRIDUNIT in DXF (fix #607) (#614)

Squash of PR #614 by @PedroGuille.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/cadcraft-cli/tests/drafting_spacing.rs

@@ -0,0 +1,83 @@
+//! Drawing snap/grid spacing survives saving and opening in a fresh CLI process (#607).
+
+use std::path::PathBuf;
+use std::process::Command;
+use std::sync::atomic::{AtomicU64, Ordering};
+
+use serde_json::{Value, json};
+
+static NEXT_FILE: AtomicU64 = AtomicU64::new(0);
+
+struct DxfFile(PathBuf);
+
+impl DxfFile {
+    fn new() -> Self {
+        let path =
+            std::env::temp_dir().join(format!("cadcraft-drafting-spacing-{}-{}.dxf", std::process::id(), NEXT_FILE.fetch_add(1, Ordering::Relaxed)));
+        std::fs::File::options().write(true).create_new(true).open(&path).expect("reserve test DXF");
+        Self(path)
+    }
+}
+
+impl Drop for DxfFile {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_file(&self.0);
+    }
+}
+
+fn cli(args: &[&str]) -> Vec<Value> {
+    let out = Command::new(env!("CARGO_BIN_EXE_cadcraft-cli")).args(args).output().expect("run cadcraft-cli");
+    assert!(out.status.success(), "{args:?}: {}", String::from_utf8_lossy(&out.stderr));
+    String::from_utf8_lossy(&out.stdout).lines().map(|line| serde_json::from_str(line).expect("CLI JSON reply")).collect()
+}
+
+#[test]
+fn quarter_unit_spacing_survives_save_and_reopen() {
+    let file = DxfFile::new();
+    let path = file.0.to_str().expect("test file path");
+    cli(&[
+        "run",
+        "--sample",
+        "--cmd",
+        r#"setvar {"name":"SNAPUNIT","value":[0.25,0.25]}"#,
+        "--cmd",
+        r#"setvar {"name":"GRIDUNIT","value":[0.25,0.25]}"#,
+        "--save",
+        path,
+    ]);
+    let replies = cli(&["run", path, "--cmd", r#"getvar {"name":"SNAPUNIT"}"#, "--cmd", r#"getvar {"name":"GRIDUNIT"}"#]);
+    for name in ["SNAPUNIT", "GRIDUNIT"] {
+        let reply = replies.iter().find(|r| r["name"] == name).expect("getvar reply");
+        assert_eq!(reply["value"], json!([0.25, 0.25]), "{name} reset on reopen");
+    }
+}
+
+#[test]
+fn drafting_settings_spacing_roundtrips_without_persisting_osmode() {
+    let file = DxfFile::new();
+    let path = file.0.to_str().expect("test file path");
+    cli(&[
+        "run",
+        "--sample",
+        "--cmd",
+        r#"dsettings {"snapunit":[0.25,0.125],"gridunit":[0.75,1.5]}"#,
+        "--cmd",
+        r#"setvar {"name":"OSMODE","value":0}"#,
+        "--save",
+        path,
+    ]);
+    let replies = cli(&[
+        "run",
+        path,
+        "--cmd",
+        r#"getvar {"name":"SNAPUNIT"}"#,
+        "--cmd",
+        r#"getvar {"name":"GRIDUNIT"}"#,
+        "--cmd",
+        r#"getvar {"name":"OSMODE"}"#,
+    ]);
+    for (name, expected) in [("SNAPUNIT", json!([0.25, 0.125])), ("GRIDUNIT", json!([0.75, 1.5])), ("OSMODE", json!(4133))] {
+        let reply = replies.iter().find(|r| r["name"] == name).expect("getvar reply");
+        assert_eq!(reply["value"], expected, "{name} after reopening");
+    }
+}