Fix #319: exports warn when type in a missing font is written in the fallback font

Opening a PDF whose fonts aren't installed keeps the text live in the fallback font (as
Illustrator substitutes and highlights missing fonts), and opening said so, but every export
then wrote the fallback font silently ("warnings": []), so a headless convert re-set the type
without a word.

- Exports that draw type now say so in their warnings, naming the missing families and the
  fallback font: PDF (outlined or real text, also .ai and Save As), EPS, EMF/WMF, raster images
  and SVG with outlined or embedded fonts. Live SVG text, DXF, text and native files name the
  font itself and don't warn. Replacing the font (Find Font) clears it.
- The fonts a document uses (text.fonts' scope, Package's font list) come from one helper.
- textAs: outlines already keeps the glyphs the PDF draws (its embedded font program, installed
  or not): now covered by a test with an embedded serif font that isn't installed, checked
  against the installed font's and the fallback's outlines.
- docs/mcp.md and ROADMAP describe the warning.

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

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

@@ -355,7 +355,8 @@ pub fn encode(doc: &Document, format: &str, p: &Value) -> Result<Vec<u8>> {
 }
 
 /// Like [`encode`], also returning the encoder's warnings (PDF and SVG: options not applied yet,
-/// features approximated or left out; the other formats have none).
+/// features approximated or left out; every format that draws type: fonts written in the fallback
+/// font).
 pub fn encode_with_warnings(doc: &Document, format: &str, p: &Value) -> Result<(Vec<u8>, Vec<String>)> {
     let f = super::writable(C, Some(format), None)?;
     encode_all(doc, f.id, p)?.single(f)
@@ -364,6 +365,19 @@ pub fn encode_with_warnings(doc: &Document, format: &str, p: &Value) -> Result<(
 /// [`encode`], with every file the export writes.
 pub fn encode_all(doc: &Document, format: &str, p: &Value) -> Result<Encoded> {
     let f = super::writable(C, Some(format), None)?;
+    let mut enc = encode_files(doc, f, p)?;
+    // Formats that draw type: missing fonts come out in the fallback font (PDF and SVG say so
+    // themselves: SVG only when it outlines or embeds fonts).
+    if (f.raster || matches!(f.id, "eps" | "emf" | "wmf"))
+        && let Some(w) = crate::cmd::fonts::substitution_warning(doc)
+    {
+        enc.warnings.push(w);
+    }
+    Ok(enc)
+}
+
+/// [`encode_all`] without the font substitution warning.
+fn encode_files(doc: &Document, f: &Format, p: &Value) -> Result<Encoded> {
     let doc = &*doc.without_edit_modes();
     let n = doc.artboards.len();
     // SVG reads its own `useArtboards` (an SVG option).
@@ -374,7 +388,7 @@ pub fn encode_all(doc: &Document, format: &str, p: &Value) -> Result<Encoded> {
         if let Some(o) = q.as_object_mut() {
             o.remove("useArtboards");
         }
-        return encode_all(&single_artboard(doc, bounds, "Art"), f.id, &q);
+        return encode_files(&single_artboard(doc, bounds, "Art"), f, &q);
     }
     let bytes = match f.id {
         "vectorcraft" => super::native::encode(C, f, doc, p)?,

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

@@ -276,6 +276,7 @@ pub(super) fn encode_carrying(cmd: &str, doc: &Document, p: &Value, native: impl
     }
     let r = super::super::rasterfx::export_pdf_with_report(flat.as_ref().unwrap_or(doc), &opts).map_err(|e| pdf_error(cmd, e))?;
     warnings.extend(r.warnings);
+    warnings.extend(crate::cmd::fonts::substitution_warning(doc));
     Ok((r.bytes, warnings))
 }
 

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

@@ -166,5 +166,11 @@ pub(super) fn encode(doc: &Document, p: &Value, compressed: bool) -> Result<Enco
         }
         enc.files.push((artboard, if compressed { vectorcraft_svg::compress_bytes(&bytes) } else { bytes }));
     }
+    // Live type names its fonts; outlines and embedded fonts are the fallback font's.
+    if (opts.outline_text || opts.embed_fonts)
+        && let Some(w) = crate::cmd::fonts::substitution_warning(doc)
+    {
+        enc.warnings.push(w);
+    }
     Ok(enc)
 }

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

@@ -67,3 +67,40 @@ fn load_options_read_text_and_layers() {
     let d = LoadOptions::default();
     assert_eq!((d.text_as, d.layers, d.is_partial()), (TextAs::Text, true, false));
 }
+
+#[test]
+fn exports_that_draw_type_in_a_missing_font_say_it_is_the_fallback_font() {
+    let page = PdfPage {
+        resources: "/Font << /F1 << /Type /Font /Subtype /Type1 /BaseFont /Zyxwvu-Serif >> >>".into(),
+        ..PdfPage::new(200.0, 100.0, "BT /F1 12 Tf 10 50 Td (Hello) Tj ET")
+    };
+    let mut s = Session::new();
+    let r = open(&mut s, &pdf(&[page], None), json!({})).unwrap();
+    let fonts = s.execute("text.fonts", &json!({})).unwrap();
+    let family = fonts[0]["family"].as_str().unwrap().to_string();
+    assert_eq!(fonts[0]["status"], "missing", "{fonts}");
+    assert!(r["warnings"].to_string().contains(&family), "opening lists it: {r}");
+    let warned = |s: &mut Session, p: Value| {
+        let w = s.execute("document.serialize", &p).unwrap()["warnings"].to_string();
+        w.contains(&family) && w.contains(vectorcraft_text::FALLBACK_FAMILY)
+    };
+    for p in [
+        json!({"format": "pdf"}),
+        json!({"format": "pdf", "advanced": {"outlineText": false}}),
+        json!({"format": "png"}),
+        json!({"format": "eps"}),
+        json!({"format": "emf"}),
+        json!({"format": "svg", "outlineText": true}),
+        json!({"format": "svg", "embedFonts": true}),
+    ] {
+        assert!(warned(&mut s, p.clone()), "{p}");
+    }
+    // Live SVG type and the native file name the font itself.
+    for p in [json!({"format": "svg", "outlineText": false}), json!({"format": "vectorcraft"}), json!({"format": "txt"})] {
+        assert!(!warned(&mut s, p.clone()), "{p}");
+    }
+    let pdf_export = s.execute("document.exportPdf", &json!({})).unwrap();
+    assert!(pdf_export["warnings"].to_string().contains(&family), "{pdf_export}");
+    s.execute("text.replaceFont", &json!({"from": {"family": family}, "to": {"family": "Source Serif 4"}})).unwrap();
+    assert!(!warned(&mut s, json!({"format": "pdf"})), "replaced: nothing is substituted");
+}

crates/engine/src/cmd/fonts.rs

@@ -2,10 +2,10 @@
 //! another everywhere or in the selection, and selecting the text that uses a font. Also the fonts
 //! available (the bundled and installed ones) and rescanning the installed fonts.
 
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, BTreeSet};
 
 use serde_json::{Value, json};
-use vectorcraft_doc::{Document, NodeId, NodeKind};
+use vectorcraft_doc::{Document, Node, NodeId, NodeKind};
 
 use super::typecmd::refresh_bounds;
 use super::*;
@@ -85,6 +85,41 @@ fn scope(s: &Session, selection_only: bool) -> Result<Vec<NodeId>> {
     Ok(v)
 }
 
+/// The fonts (family, style) of the type in the layers and symbols of `d`.
+pub(super) fn used_fonts(d: &Document) -> BTreeSet<(String, String)> {
+    let mut fonts = BTreeSet::new();
+    let mut add = |n: &Node| {
+        if let NodeKind::Text(t) = &n.kind {
+            fonts.extend(t.runs.iter().map(|r| (r.style.font_family.clone(), r.style.font_style.clone())));
+        }
+    };
+    d.walk(&mut add);
+    for s in &d.symbols {
+        s.art.walk(&mut add);
+    }
+    fonts
+}
+
+/// What an export that draws type (as outlines, embedded fonts or pixels) says when `d` uses font
+/// families that aren't available: their type is drawn in the fallback font, not the font it names.
+pub(super) fn substitution_warning(d: &Document) -> Option<String> {
+    let db = vectorcraft_text::FontDb::global();
+    let mut missing: Vec<String> = used_fonts(d)
+        .into_iter()
+        .filter(|(family, style)| db.resolve(family, style).is_none_or(|(_, m)| m == vectorcraft_text::FontMatch::Missing))
+        .map(|(family, _)| family)
+        .collect();
+    // Sorted by family: its styles are neighbours.
+    missing.dedup();
+    (!missing.is_empty()).then(|| {
+        format!(
+            "fonts that aren't available were written in the fallback font, {}: {} (install them, or replace them with Find Font)",
+            vectorcraft_text::FALLBACK_FAMILY,
+            missing.join(", ")
+        )
+    })
+}
+
 fn text(d: &Document, id: NodeId) -> Option<&vectorcraft_doc::TextObject> {
     match d.node(id).map(|n| &n.kind) {
         Some(NodeKind::Text(t)) => Some(t),

crates/engine/src/cmd/package.rs

@@ -4,12 +4,11 @@
 //! report). The packaged document links to the copies (Relink); the open document doesn't change.
 //! Without a folder (the web, agents) the same files come back as a zip archive.
 
-use std::collections::{BTreeMap, BTreeSet, HashSet};
+use std::collections::{BTreeMap, HashSet};
 use std::io::Write;
 use std::path::Path;
 
 use serde_json::{Value, json};
-use vectorcraft_doc::{Document, Node, NodeKind};
 
 use super::fileio::{create_dir, write_file};
 use super::*;
@@ -51,21 +50,6 @@ fn font_ext(bytes: &[u8]) -> &'static str {
     }
 }
 
-/// The fonts (family, style) of the type in the layers and symbols of `d`.
-fn used_fonts(d: &Document) -> BTreeSet<(String, String)> {
-    let mut fonts = BTreeSet::new();
-    let mut add = |n: &Node| {
-        if let NodeKind::Text(t) = &n.kind {
-            fonts.extend(t.runs.iter().map(|r| (r.style.font_family.clone(), r.style.font_style.clone())));
-        }
-    };
-    d.walk(&mut add);
-    for s in &d.symbols {
-        s.art.walk(&mut add);
-    }
-    fonts
-}
-
 /// The options of a package.
 struct Options {
     copy_links: bool,
@@ -123,7 +107,7 @@ fn package(s: &mut Session, p: &Value) -> Result<Value> {
         let db = vectorcraft_text::FontDb::global();
         let mut files = HashSet::new();
         lines.push("FONTS".to_string());
-        for (family, style) in used_fonts(&st.doc) {
+        for (family, style) in super::fonts::used_fonts(&st.doc) {
             let font = format!("{family} {style}");
             let reason = match db.face(&family, &style) {
                 Some(f) if f.family.eq_ignore_ascii_case(&family) && f.embeddable() => {