fix: a header/footer band is as tall as its own font, not the body's

The zone is one paragraph, so its mark sizes every line of the band. Runs
that agree on a font now set that strut (applyUniformRunFont, as the body
already does), the zone schema carries blockFontSize so it renders, and
hfReachPx measures a line by the family's natural height instead of a flat
1.15. A 10pt footer reserved 12pt lines and sat 1.6mm high on every page.

src/lib/components/Editor.svelte

@@ -28,7 +28,7 @@
   import { findBookmark } from '../editor/extensions/bookmark';
   import { recordTransaction, resetHistoryLog } from '../utils/historyLog.svelte';
   import { wheelZoomFactor } from '../utils/zoom';
-  import { styleCss } from '../styles/styleSheet';
+  import { styleCss, singleLineHeight } from '../styles/styleSheet';
   import { styleSheet } from '../styles/sheet.svelte';
   import { t } from '../i18n/i18n.svelte';
   import { withShortcut } from '../i18n/shortcut';
@@ -103,19 +103,23 @@
   const HF_LINE_PX = 16 * 1.15;
   function hfReachPx(doc: HfDoc, distPx: number, footer = false): number {
     if (!doc || hfIsEmpty(doc)) return 0;
-    type Run = { type?: string; attrs?: { height?: number; wrap?: string }; marks?: { type?: string; attrs?: { fontSize?: string } }[] };
-    const para = doc.content?.[0] as { content?: Run[]; attrs?: { spaceBefore?: number; spaceAfter?: number } } | undefined;
+    type Run = { type?: string; attrs?: { height?: number; wrap?: string }; marks?: { type?: string; attrs?: { fontSize?: string; fontFamily?: string } }[] };
+    const para = doc.content?.[0] as { content?: Run[]; attrs?: { spaceBefore?: number; spaceAfter?: number; fontSize?: string; fontFamily?: string } } | undefined;
     const inline = para?.content ?? [];
     // The zone's biggest text run sizes its lines: LibreOffice grows the band to hold them
     // when fo:min-height is smaller (probed, a 3-line header), and a zone set throughout in
     // 10pt reserves 10pt — the body default only stands in for a run that declares none.
-    let linePx = 0;
+    // A line is its font's own natural height, which is what the band renders at.
+    const line = (size?: string, family?: string) =>
+      size ? (parseFloat(size) * 96) / 72 * singleLineHeight(family) : HF_LINE_PX;
+    // The paragraph mark is the strut every run that declares no size of its own takes.
+    const base = line(para?.attrs?.fontSize, para?.attrs?.fontFamily);
+    let linePx = base;
     for (const n of inline) {
       if (n.type === 'image') continue;
-      const size = n.marks?.find((m) => m.type === 'textStyle')?.attrs?.fontSize;
-      linePx = Math.max(linePx, size ? (parseFloat(size) * 96) / 72 * 1.15 : HF_LINE_PX);
+      const ts = n.marks?.find((m) => m.type === 'textStyle')?.attrs;
+      linePx = Math.max(linePx, ts?.fontSize ? line(ts.fontSize, ts.fontFamily) : base);
     }
-    if (!linePx) linePx = HF_LINE_PX;
     // Per line, since an as-character image (a letterhead logo) makes its own line
     // as tall as it is; the others are one text line each. A positioned frame is out
     // of flow — a page-sized background would otherwise reserve the whole page.

src/lib/editor/extensions/headerFooter.ts

@@ -21,6 +21,7 @@ import { Image } from './image';
 import { Shortcuts } from './shortcuts';
 import { TabStops } from './tabStops';
 import { ParagraphSpacing } from './paragraphSpacing';
+import { BlockFontSize } from './blockFontSize';
 
 // Schema for the header/footer mini editors: exactly one paragraph of formatted
 // runs, line breaks, page fields, and inline (as-character) images. Marks mirror
@@ -65,6 +66,9 @@ export function hfExtensions(placeholder = '') {
     // The zone style's own margins: what the band has to be tall enough for
     // (Editor.svelte's hfReachPx), not a gap the bottom-anchored footer moves by.
     ParagraphSpacing.configure({ types: ['paragraph'] }),
+    // The zone is one paragraph, so its mark's font is the band's line height: a 10pt
+    // footer reserves 10pt lines, not the body's 12pt.
+    BlockFontSize.configure({ types: ['paragraph'] }),
     CharacterStyle,
     Highlight.configure({ multicolor: true }),
     HfHardBreak,

src/lib/import/docx.ts

@@ -2022,6 +2022,9 @@ function convertHfPart(relId: string | null, ctx: Ctx): HfDoc {
 
   const para: Node = { type: 'paragraph', content: inline };
   const attrs: Record<string, string> = {};
+  // The zone is one paragraph here, so its strut is the whole band's line height —
+  // runs that agree on a size must set it, or a 10pt footer reserves 12pt lines.
+  applyUniformRunFont(attrs, inline);
   if (textAlign) attrs.textAlign = textAlign;
   if (stops) attrs.tabStops = stops;
   Object.assign(attrs, box);

src/lib/import/odt.ts

@@ -736,6 +736,9 @@ function convertHfZone(zoneEl: Element, ctx: Ctx): HfDoc {
 
   const para: Node = { type: 'paragraph', content };
   const attrs: Record<string, string | number> = {};
+  // The zone is one paragraph here, so its strut is the whole band's line height —
+  // runs that agree on a size must set it, or a 10pt footer reserves 12pt lines.
+  applyUniformRunFont(attrs, content);
   if (textAlign) attrs.textAlign = textAlign;
   if (stops) attrs.tabStops = stops;
   if (spaceBefore) attrs.spaceBefore = spaceBefore;

tests/roundtrip.test.ts

@@ -932,10 +932,12 @@ describe('Leg 3a: different first page header/footer → buildOdt → importOdt'
     // Arial 10pt on the runs AND the page-field atoms, so the field digits keep the font.
     const arial = [{ type: 'textStyle', attrs: { fontFamily: 'Arial', fontSize: '10pt' } }];
     const header: N = { type: 'doc', content: [{ type: 'paragraph', content: [{ type: 'text', text: 'Default header' }] }] };
-    const footer: N = { type: 'doc', content: [{ type: 'paragraph', attrs: { textAlign: 'center' }, content: [
+    // The strut follows runs that agree on a font (applyUniformRunFont), so the zone
+    // paragraph carries it either way — stating it keeps the round trip an identity.
+    const footer: N = { type: 'doc', content: [{ type: 'paragraph', attrs: { textAlign: 'center', fontFamily: 'Arial', fontSize: '10pt' }, content: [
       { type: 'text', text: 'Seite ', marks: arial }, { type: 'pageNumber', marks: arial }, { type: 'text', text: ' von ', marks: arial }, { type: 'pageCount', marks: arial },
     ] }] };
-    const headerFirst: N = { type: 'doc', content: [{ type: 'paragraph', content: [
+    const headerFirst: N = { type: 'doc', content: [{ type: 'paragraph', attrs: { fontFamily: 'Arial', fontSize: '10pt' }, content: [
       { type: 'text', text: 'Cover', marks: [{ type: 'bold' }, ...arial] },
     ] }] };
     const footerFirst: N = { type: 'doc', content: [{ type: 'paragraph', content: [