Type: Highlight Substituted Fonts moves to Preferences › Type and applies to every document

Highlight Substituted Fonts is now a preference in Preferences › Type,
next to Highlight Alternate Glyphs, on by default and saved with the
other preferences (`prefs.set highlightSubstitutedFonts`). The canvas
reads it through `RenderOptions::highlight_substituted_fonts` for every
open document; a document's own setup no longer decides it. File ›
Document Setup no longer shows the checkbox and keeps Highlight
Substituted Glyphs.

A file saved with Document Setup's Highlight Substituted Fonts off now
shows the pink highlight when it opens, while the preference is on.
The file still opens with the stored value, and saving it again keeps
that value.

`document.setup` no longer reports `highlightSubstitutedFonts`. It
ignores the key and adds a `warnings` entry that names `prefs.set` to
its reply, so an older reply passed back still applies its other keys.

The raster cache of type under a raster effect now also redraws when
Highlight Alternate Glyphs changes.

docs/control-protocol.md

@@ -466,7 +466,7 @@ string is points). The `preferences` dialog's `unitsGeneral` starts as the activ
 
 Document Setup: File → Document Setup… (`file.documentSetup`, Cmd+Alt+P) opens the `documentSetup` dialog. Its fields
 are what `document.setup` reports (`units`, `bleed` [top, bottom, left, right] in pt, `outlineImages`,
-`highlightSubstitutedFonts`, `highlightSubstitutedGlyphs`, `gridSize`, `gridColors`, `simulatePaper`, `flattenerPreset`,
+`highlightSubstitutedGlyphs`, `gridSize`, `gridColors`, `simulatePaper`, `flattenerPreset`,
 `discardWhiteOverprint`, `language`, `quotes`, `typographersQuotes`, `superscript`, `subscript`, `smallCapsSize`,
 `exportText`, `backgroundContents`) plus `tab` (`General`, `Transparency` or `Type`) and `bleedLinked`.
 `ui.dialog.confirm` runs `document.setup` with them as one undo step; a bad value answers with an error and the dialog

docs/mcp.md

@@ -2784,8 +2784,9 @@ off, an empty window, and the Home button or `app.home` still shows the screen),
 default: on, a click away from a panel popped out of the icon column puts it away), `displayPrintSize` (off by
 default: View › Actual Size / `view.actualSize` is one document point per screen point; on, one document inch fills
 96 screen points, an inch at the system's reference density whatever the display scaling). `highlightAlternateGlyphs` (off by default: on, the canvas paints a pink cell behind glyphs OpenType features
-substituted — ligatures, contextual forms — on screen; Document Setup's Highlight Substituted Fonts / Glyphs stay
-separate). `blackOnScreen`
+substituted — ligatures, contextual forms — on screen; Document Setup's Highlight Substituted Glyphs stays
+separate). `highlightSubstitutedFonts` (on by default: the canvas paints pink behind text drawn in a substitute for a
+missing font, in every document). `blackOnScreen`
 (Appearance of Black › On Screen, `accurate` by default) sets how the canvas shows pure CMYK black, black ink alone
 at 100%: `accurate` shows it through the CMYK profile, a dark grey, and `rich` shows it as RGB black. Rich blacks,
 black tints and images show the same either way, and exports are unchanged. `blackOutput` (Appearance of Black ›
@@ -2901,8 +2902,13 @@ Pen's second anchor at (150, 431), in line with the square's centre.
   matched without regard to case: a word with no hyphens is never hyphenated (`typography`), and a word with hyphens
   breaks only where they are (`hap-pen`). `prefs.set` pushes the list into the hyphenator and reflows open documents.
 - `highlightAlternateGlyphs` (off by default): Preferences › Type › Highlight Alternate Glyphs. On, the canvas paints
-  pink behind OpenType substitutions (ligatures, contextual forms). Document Setup's Highlight Substituted Fonts /
-  Glyphs stay separate. Agents set it with `prefs.set`; the desktop canvas reads it on the next paint.
+  pink behind OpenType substitutions (ligatures, contextual forms). Document Setup's Highlight Substituted Glyphs
+  stays separate. Agents set it with `prefs.set`; the desktop canvas reads it on the next paint.
+- `highlightSubstitutedFonts` (on by default): Preferences › Type › Highlight Substituted Fonts. On, the canvas paints
+  pink behind text drawn in a substitute for a missing font, in every open document. Off, no document shows that
+  highlight. `document.setup` ignores this key and adds a `warnings` entry that names `prefs.set` to its reply. A file
+  saved with the key in its Document Setup still opens and keeps the value it was saved with, and the preference
+  decides whether that file shows the highlight.
 
 ```json
 {"name":"run_command","arguments":{"command":"prefs.set","params":{"values":{"typeSizeIncrement":4,"trackingIncrement":50}}}}