fix(studio): a line keeps its own colour when a theme is applied, adopted or described

shared/src/book/design/design-theme.ts

@@ -111,6 +111,8 @@ function linkToLook(el: BookElement, spread: BookSpread, look: BookDesignLook):
   switch (el.kind) {
     case 'photo':
     case 'sticker':
+    // A line keeps the colour it was drawn in (book-line.schema.ts has no theme link).
+    case 'line':
       return el;
     case 'text': {
       const token = lookToken(el.color, look, true);

shared/src/book/theme/book-theme-adopt.ts

@@ -61,6 +61,8 @@ function chromaticInks(el: BookElement): string[] {
   switch (el.kind) {
     case 'photo':
     case 'sticker':
+    // A line keeps the colour it was drawn in (book-line.schema.ts has no theme link).
+    case 'line':
       return [];
     case 'text':
     case 'icon':
@@ -157,6 +159,8 @@ function adoptElement(
     // A sticker keeps the colours of its slots: they are a drawing, not the page's inks.
     case 'photo':
     case 'sticker':
+    // A line keeps the colour it was drawn in (book-line.schema.ts has no theme link).
+    case 'line':
       return el;
     case 'text': {
       const token = el.token ?? inkToken(el.color, ground, map, prev, el.size <= 9);

shared/src/book/theme/book-theme-apply.ts

@@ -66,6 +66,8 @@ export function themedElement<E extends BookElement>(el: E, theme: BookTheme): E
   switch (el.kind) {
     case 'photo':
     case 'sticker':
+    // A line keeps the colour it was drawn in (book-line.schema.ts has no theme link).
+    case 'line':
       return el;
     case 'text': {
       tokenColour(next, theme, 'color', el.token);

shared/src/book/theme/book-theme-describe.ts

@@ -23,7 +23,7 @@ export function bookThemeLine(theme: BookTheme | undefined): string {
 
 /** What an element follows of the theme, as words for its line ('' when nothing). */
 export function themeLinkWords(el: BookElement): string {
-  if (el.kind === 'photo' || el.kind === 'sticker') return '';
+  if (el.kind === 'photo' || el.kind === 'sticker' || el.kind === 'line') return '';
   const parts: string[] = [];
   if (el.token) parts.push(`${el.kind === 'shape' ? 'fill' : 'colour'} ${el.token}`);
   if (el.kind === 'shape' && el.strokeToken) parts.push(`stroke ${el.strokeToken}`);