fix(cli): build exporters once, clarify --format all doc

crates/bin/src/cli.rs

@@ -34,7 +34,7 @@ struct Cli {
     #[arg(short, long, default_value = "output")]
     out: PathBuf,
 
-    /// Output format(s): mcfunction, litematica, or all (repeatable)
+    /// Output format(s): mcfunction, litematica, all (overrides others), or repeatable values
     #[arg(long, value_name = "FORMAT")]
     format: Vec<String>,
 
@@ -160,15 +160,16 @@ pub fn run() -> anyhow::Result<()> {
         .filter(|&name| seen.insert(name))
         .collect();
 
-    // Pre-validate all names before writing anything
-    for name in &format_names {
-        if exporters::build(name, &palette).is_none() {
-            anyhow::bail!("unknown format '{}'. Available: {}", name, all_names.join(", "));
-        }
-    }
+    // Build and validate in one pass
+    let exporters_to_run = format_names
+        .iter()
+        .map(|&name| -> anyhow::Result<_> {
+            exporters::build(name, &palette)
+                .ok_or_else(|| anyhow::anyhow!("unknown format '{}'. Available: {}", name, all_names.join(", ")))
+        })
+        .collect::<anyhow::Result<Vec<_>>>()?;
 
-    for name in format_names {
-        let exporter = exporters::build(name, &palette).unwrap(); // safe: pre-validated
+    for (name, exporter) in format_names.iter().zip(exporters_to_run) {
         let output_bytes = exporter.export(&grid)?;
         let mut out_path = cli.out.clone();
         out_path.set_extension(exporter.file_extension());