T02: unique temp file per save, parse errors name the field

Cargo.toml

@@ -18,6 +18,7 @@ gpui_platform = { package = "gpui-pre-platform", version = "=0.3.8", features =
 log = "0.4"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
+serde_path_to_error = "0.1.20"
 
 [lints.rust]
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(feature, values("cargo-clippy"))'] }