M4.12: one loader and encoder for every frontend — engine fileio (load/encode/export/save, append-only FORMATS table, OPEN_EXTS, document.formats query, typed per-format options, parse_range); document.open reads native/legacy, SVG/SVGZ, PDF/.ai, .ait (opens untitled like native templates) and PNG/JPEG/GIF/WebP/TIFF/BMP; desktop, web, control channel, headless MCP and the CLI open and encode through it; open dialogs list "All readable files" plus one filter per format

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

crates/engine/src/cmd/fileio/batch.rs

@@ -0,0 +1,37 @@
+//! `command.batch`: several commands as one undo step.
+
+use serde_json::{Value, json};
+
+use super::super::*;
+use crate::EngineError;
+
+pub(super) fn batch(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmds = p.get("commands").and_then(Value::as_array).ok_or_else(|| bad("command.batch", "missing commands"))?.clone();
+    let label = str_param(p, "label").unwrap_or("Batch").to_string();
+    s.begin_interaction(&label)?;
+    // Session-level state a step may change (paint defaults, drawing mode) rolls back too.
+    let saved = (s.paint.clone(), s.fill_active, s.draw_mode, s.draw_inside, s.clipboard.clone());
+    let mut results = vec![];
+    for c in &cmds {
+        let id = c.get("command").and_then(Value::as_str).unwrap_or("");
+        if id == "command.batch" {
+            s.cancel_interaction()?;
+            return Err(bad("command.batch", "batches cannot nest"));
+        }
+        let params = c.get("params").cloned().unwrap_or(json!({}));
+        match s.execute(id, &params) {
+            Ok(v) => results.push(v),
+            Err(e) => {
+                s.cancel_interaction()?;
+                (s.paint, s.fill_active, s.draw_mode, s.draw_inside, s.clipboard) = saved;
+                return Err(EngineError::Other(format!("batch step {} (`{id}`) failed: {e}", results.len())));
+            }
+        }
+    }
+    // Commit as one undo step (the interaction's "preview" is the batch itself).
+    if let Some(it) = s.doc_mut()?.interaction.as_mut() {
+        it.preview = Some(("command.batch".into(), p.clone()));
+    }
+    s.commit_interaction()?;
+    Ok(json!({ "results": results }))
+}