Never lose work: atomic saves (temporary file, flush, rename) keeping the replaced version as <file>.bak; autosave of unsaved changes into a recovery folder (every 5 min, preference autosave_minutes, and after commands over 1.5 s; skipped when unchanged; entries locked while their app runs); Recover unsaved design? at launch; doc.recovery_list / doc.recover / doc.recovery_discard; kill-mid-save test

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

apps/solvecraft-cli/tests/kill_mid_save.rs

@@ -0,0 +1,45 @@
+//! Kill the process while it saves: the design file is always the old version or the new one,
+//! whole, and opens.
+
+use std::process::Command;
+use std::time::Duration;
+
+fn round_of(path: &std::path::Path) -> Option<String> {
+    let bytes = std::fs::read(path).ok()?;
+    let doc = solvecraft_engine::io::read_design(&bytes).ok()?;
+    doc.params.iter().find(|p| p.name == "save_round").map(|p| p.expr.clone())
+}
+
+#[test]
+fn killed_mid_save_the_old_file_survives() {
+    let exe = env!("CARGO_BIN_EXE_solvecraft-cli");
+    let dir = std::env::temp_dir().join(format!("solvecraft-kill-mid-save-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    let path = dir.join("design.solvecraft");
+    let ok = Command::new(exe).args(["save-stress", &path.to_string_lossy(), "1"]).status().unwrap();
+    assert!(ok.success());
+    assert_eq!(round_of(&path).as_deref(), Some("0"));
+    let mut kills = 0;
+    let mut seen = std::collections::BTreeSet::new();
+    for i in 0..25u64 {
+        let mut child = Command::new(exe).args(["save-stress", &path.to_string_lossy(), "100000"]).spawn().unwrap();
+        // Let it get into its save loop (building the design takes a moment), then kill it.
+        std::thread::sleep(Duration::from_millis(150 + (i * 37) % 200));
+        if child.try_wait().unwrap().is_none() {
+            child.kill().unwrap();
+            kills += 1;
+        }
+        let _ = child.wait();
+        let round = round_of(&path);
+        assert!(round.is_some(), "after kill {i} the design file is torn or missing");
+        seen.insert(round);
+        let bak = solvecraft_engine::io::backup_path(&path);
+        if bak.exists() {
+            assert!(round_of(&bak).is_some(), "after kill {i} the backup is torn");
+        }
+    }
+    assert!(kills > 20, "the saver was killed while running ({kills})");
+    assert!(seen.len() > 5, "the saver got to saving before it was killed ({seen:?})");
+    let _ = std::fs::remove_dir_all(&dir);
+}