Fix #255: selection exports report the encoder's warnings

document.exportSelection (the MCP export tool's `selection: true`) now
replies with `format` and the encoder's `warnings`, the same list a
whole-document export gives: lossy WebP written lossless, blend modes left
out of SVG Tiny 1.2, PDF layers at 1.4 and the rest. A selection export
that approximates nothing replies with an empty list.

Root cause: export_selection encoded with `encode`, which drops the
warnings encode_with_warnings returns, and its reply carried only path,
bytes and bounds. The params doc and docs/mcp.md now describe the reply.

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

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

@@ -11,7 +11,7 @@ use crate::DocState;
 
 use super::super::*;
 use super::encode::single_artboard;
-use super::{ARTBOARD_PARAMS, Format, default_name, encode, encode_all, merge, writable, write_encoded, write_or_return};
+use super::{ARTBOARD_PARAMS, Format, default_name, encode, encode_all, encode_with_warnings, merge, writable, write_encoded, write_or_return};
 
 pub(super) fn serialize(s: &mut Session, p: &Value) -> Result<Value> {
     let f = writable("document.serialize", Some(str_param(p, "format").unwrap_or("vectorcraft")), None)?;
@@ -151,8 +151,10 @@ pub(super) fn export_selection(s: &mut Session, p: &Value) -> Result<Value> {
     let expanded = expand_presets(s, C, p)?;
     let p = &*expanded;
     let (d, bounds) = selection(s, C)?;
-    let bytes = encode(&d, f.id, &without_artboards(p))?;
+    // The encoder's warnings (options accepted but not applied, features approximated or left
-    write_or_return(path, &bytes, json!({ "bounds": [bounds.x0, bounds.y0, bounds.width(), bounds.height()] }))
+    // out), as document.export reports them.
+    let (bytes, warnings) = encode_with_warnings(&d, f.id, &without_artboards(p))?;
+    write_or_return(path, &bytes, json!({ "format": f.id, "warnings": warnings, "bounds": [bounds.x0, bounds.y0, bounds.width(), bounds.height()] }))
 }
 
 /// File → Save for Office Documents: one artboard as a PNG at `ppi`, on white unless

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

@@ -105,7 +105,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Export Selection…",
             ["File"],
             None,
-            "{path?, format?: png|jpg|webp|svg|svgz|pdf (default: from the extension, else png), scale?: 1, …the format's options} the selected objects cropped to their bounds (template layers left out) → {path, bytes, bounds} (no path → {dataBase64, bounds})",
+            "{path?, format?: png|jpg|webp|svg|svgz|pdf (default: from the extension, else png), scale?: 1, …the format's options} the selected objects cropped to their bounds (template layers left out) → {path, format, bytes, warnings, bounds} (no path → {dataBase64, format, bytes, warnings, bounds}); warnings say what the format approximated or left out, as for document.export",
             has_selection,
             export::export_selection
         ),

crates/engine/src/tests_file.rs

@@ -168,6 +168,33 @@ fn export_selection_crops_to_the_selection() {
     assert_eq!(text.matches("<path").count(), 1, "{text}");
 }
 
+/// A selection export reports the encoder's warnings like a whole-document export, and an empty
+/// list when nothing was approximated.
+#[test]
+fn export_selection_reports_the_encoders_warnings() {
+    let mut s = session();
+    s.execute("shape.rectangle", &json!({"x": 10, "y": 10, "width": 50, "height": 50})).unwrap();
+    s.execute("transparency.set", &json!({"blend": "Multiply"})).unwrap();
+    let warnings = |v: &serde_json::Value| v["warnings"].as_array().cloned().unwrap_or_else(|| panic!("no warnings key: {v}"));
+    // Control: nothing approximated.
+    let plain = s.execute("document.exportSelection", &json!({"format": "svg"})).unwrap();
+    assert_eq!(plain["format"], "svg");
+    assert!(warnings(&plain).is_empty(), "{plain}");
+    for (format, options, says) in [
+        ("webp", json!({"lossless": false}), "lossless"),
+        ("svg", json!({"profile": "tiny12"}), "blend"),
+        ("pdf", json!({"createLayers": true, "compatibility": "1.4"}), "layers"),
+    ] {
+        let mut p = options.clone();
+        p["format"] = json!(format);
+        let sel = s.execute("document.exportSelection", &p).unwrap();
+        let doc = s.execute("document.export", &p).unwrap();
+        let w = warnings(&sel);
+        assert!(w.iter().any(|w| w.as_str().unwrap_or("").to_lowercase().contains(says)), "{format}: {sel}");
+        assert_eq!(w, warnings(&doc), "{format}: the same warnings as a whole-document export");
+    }
+}
+
 #[test]
 fn template_opens_as_untitled() {
     let mut s = session();

docs/mcp.md

@@ -161,7 +161,7 @@ objects' fills or strokes differ (`fillMixed` / `strokeMixed`, drawn as a "?" pr
 | `screenshot` | `{path?, scale?, artboard?, window?}` | Returns MCP image content (`image/png`, base64) plus a text block. Renders the artboard; `window:true` captures the app window (remote only). |
 | `open_file` | `{path}` | Opens any readable file as a new active document: `.vectorcraft`/`.drawcraft`, `.svg`/`.svgz`, `.pdf`/`.ai`, `.ait`, PNG, JPEG, GIF, WebP, TIFF, BMP (an image opens as a document of its pixel size). Templates open as a new untitled document. PDF, `.ai` and SVG files saved with Preserve Editing reopen as the document they carry. `run_command document.formats` lists the formats. |
 | `save_file` | `{path?}` | Runs `document.save`: the document's own file in its own format (native `.vectorcraft` unless it was opened from or saved as SVG, PDF or a restorable `.ai`; then `warnings` say what that format loses). A path's extension picks the format (`.vectorcraft`, `.vctemplate`, `.pdf`, `.svg`, `.svgz`, `.ai`: a PDF carrying the native document, which reopens editable). |
-| `export` | `{path?, format?, scale?, artboard?, range?, selection?, outlineText?, options?}` | `svg`, `pdf`, `png`, `jpg`, `webp`, `gif`, `png8` (an indexed `.png`), `tiff`, `bmp`, `tga`, `psd` (layered), `txt` (the document's text) or `vectorcraft` (the list comes from `document.formats`). When `format` is omitted, it comes from the path's extension. PDF writes one page per artboard: all of them, or `artboard` (0-based) / `range` (`"1-3, 5"`, 1-based); the other formats write one artboard. `options` carries more format options (e.g. `{"quality": 80}` for JPEG). `selection: true` exports the selected objects cropped to their bounds; `outlineText: true` writes SVG text as paths. Template layers are left out, live effects are kept, and exporting `vectorcraft` never changes the document's path. Without `path` the bytes come back as `dataBase64`. Both backends run the same `document.export` call. |
+| `export` | `{path?, format?, scale?, artboard?, range?, selection?, outlineText?, options?}` | `svg`, `pdf`, `png`, `jpg`, `webp`, `gif`, `png8` (an indexed `.png`), `tiff`, `bmp`, `tga`, `psd` (layered), `txt` (the document's text) or `vectorcraft` (the list comes from `document.formats`). When `format` is omitted, it comes from the path's extension. PDF writes one page per artboard: all of them, or `artboard` (0-based) / `range` (`"1-3, 5"`, 1-based); the other formats write one artboard. `options` carries more format options (e.g. `{"quality": 80}` for JPEG). `selection: true` exports the selected objects cropped to their bounds (the reply adds their `bounds`, and reports `format` and the encoder's `warnings` as a whole-document export does); `outlineText: true` writes SVG text as paths. Template layers are left out, live effects are kept, and exporting `vectorcraft` never changes the document's path. Without `path` the bytes come back as `dataBase64`. Both backends run the same `document.export` call. |
 | `add_text` | `{text, x?, y?, width?, height?, path?, mode?, pathEffect?, size?, font?, color?}` | Point type at (x, y); area type with `width`/`height`; or `path` + `mode` (`area`/`onPath`) to flow text in or along a path, with `pathEffect` (`rainbow`, `skew`, `3dRibbon`, `stairStep`, `gravity`). |
 | `apply_effect` | `{effect?, params?, ids?}` | Appends a live effect. Without `effect`, returns the effect catalogue with parameters and defaults. |
 | `pathfinder` | `{operation, ids?}` | `unite`, `minusFront`, `intersect`, `exclude`, `divide`, `trim`, `merge`, `crop`, `outline`, `minusBack`. For a live version, apply the `pathfinder.*` effect to a group (`effect.apply` groups several loose selected objects first). |