fix: an imported page margin is the one the file declares

Both importers capped every side at 10cm, which is the Layout panel's limit and
no file's: a back cover pushing its last lines to the page foot with a 21cm top
margin rendered 11cm high. fitMargins caps only what would leave the page no
strip of text at all, and the zone distances follow the page's own height.

src/lib/import/docx.ts

@@ -17,7 +17,7 @@ import { bulletCharAttr, bulletCharFromDocx } from '../utils/bulletListTypes';
 import { DATE_FORMATS, TIME_FORMATS, docxPicture, toDateValue } from '../utils/dateTime';
 import { shapeFromPrst, isLineKind, lineKindFor, parseSvgPath, parseVmlPath, fitPath } from '../utils/shapes';
 import { imageDataUrl, placeholderImage, type ConvertedImages } from './imageFormats';
-import { PX_PER_CM, cmToPx, type PageMargins } from '../storage/pageMargins';
+import { PX_PER_CM, cmToPx, fitMargins, type PageMargins } from '../storage/pageMargins';
 import type { Orientation } from '../storage/pageOrientation';
 import { formatFromCm, type PageFormat } from '../storage/pageFormat';
 import { clampTabInterval, DOCX_IMPLIED_TAB_CM } from '../storage/tabInterval';
@@ -3044,7 +3044,8 @@ function parseSectPr(sect: Element | null, ctx: Ctx, oddEven = false): {
   const { orientation, format } = sectPaper(sect);
 
   const pgMar = fc(sect, 'pgMar');
-  const clampCm = (tw: number | null) => (tw == null ? null : Math.min(10, Math.max(0, round2(twipToCm(tw)))));
+  const pageHighCm = (intAttr(fc(sect, 'pgSz'), W, 'h') ?? 16838) / 1440 * 2.54 - 1;
+  const clampCm = (tw: number | null) => (tw == null ? null : Math.min(pageHighCm, Math.max(0, round2(twipToCm(tw)))));
   const margins = sectMargins(sect);
 
   // Different first page: w:titlePg turns on the "first"-type refs for page 1.
@@ -3080,9 +3081,16 @@ function sectMargins(sect: Element | null): PageMargins | null {
   if (!pgMar) return null;
   const cm = (a: string, fallback: number) => {
     const tw = intAttr(pgMar, W, a);
-    return tw == null ? fallback : Math.min(10, Math.max(0, round2(twipToCm(tw))));
+    return tw == null ? fallback : Math.max(0, round2(twipToCm(tw)));
   };
-  return { top: cm('top', 2.54), bottom: cm('bottom', 2.54), left: cm('left', 2.12), right: cm('right', 2.12) };
+  const pgSz = sect ? fc(sect, 'pgSz') : null;
+  const dim = (a: string, fallback: number) => {
+    const tw = intAttr(pgSz, W, a);
+    return tw == null ? fallback : twipToCm(tw);
+  };
+  return fitMargins(
+    { top: cm('top', 2.54), bottom: cm('bottom', 2.54), left: cm('left', 2.12), right: cm('right', 2.12) },
+    dim('w', 21), dim('h', 29.7));
 }
 
 // One HfSet per section, in body order, resolving Word's "Link to Previous": a section

src/lib/import/styleResolver.ts

@@ -1,4 +1,4 @@
-import type { PageMargins } from '../storage/pageMargins';
+import { fitMargins, type PageMargins } from '../storage/pageMargins';
 import type { Orientation } from '../storage/pageOrientation';
 import { formatFromCm, type PageFormat } from '../storage/pageFormat';
 import { ODF_IMPLIED_TAB_CM } from '../storage/tabInterval';
@@ -795,7 +795,7 @@ export class StyleResolver {
     const cm = (attr: string, fallback: number, extra = 0) => {
       const v = lengthToCm(props.getAttributeNS(NS.fo, attr));
       if (v == null) return fallback;
-      return Math.min(10, Math.max(0, Math.round((v + extra + inset) * 100) / 100));
+      return Math.max(0, Math.round((v + extra + inset) * 100) / 100);
     };
     const margins: PageMargins = {
       top: cm('margin-top', 2.54, hf.header ? hf.headerExtraCm : 0),
@@ -805,22 +805,24 @@ export class StyleResolver {
       left: cm('margin-left', 2.12),
       right: cm('margin-right', 2.12),
     };
-    // A page style that is one side of a book (style:page-usage left/right) mirrors as
-    // surely as one marked "mirrored"; the editor stores the odd page's pair and swaps
-    // it on an even page, so a left-hand layout hands over its mirror image.
+    // A page style that is one side of a book mirrors as surely as one marked
+    // "mirrored" — but only where the two masters really alternate: style:page-usage
+    // ="right" on a single layout is a page that starts on the right, nothing more,
+    // and swapping its pair would draw it at the wrong margin (probed).
     const usage = this.pageLayoutEl(pageName)?.getAttributeNS(NS.style, 'page-usage');
-    if (usage === 'mirrored' || usage === 'left' || usage === 'right') {
+    if (usage === 'mirrored' || ((usage === 'left' || usage === 'right') && hf.mirrorPair)) {
       margins.mirrored = true;
       if (usage === 'left') [margins.left, margins.right] = [margins.right, margins.left];
     }
     const w = lengthToCm(props.getAttributeNS(NS.fo, 'page-width'));
     const h = lengthToCm(props.getAttributeNS(NS.fo, 'page-height'));
+    const fitted = fitMargins(margins, w ?? 21, h ?? 29.7);
     const orientation: Orientation = w != null && h != null && w > h ? 'landscape' : 'portrait';
     const format: PageFormat = w != null && h != null ? (formatFromCm(w, h) ?? 'A4') : 'A4';
     // style:writing-mode: rl-tb is a right-to-left page — the columns fill from the
     // right and the text's base direction is RTL. The vertical modes are not read.
     const rtl = (props.getAttributeNS(NS.style, 'writing-mode') ?? '').startsWith('rl');
-    return { margins, orientation, format, rtl };
+    return { margins: fitted, orientation, format, rtl };
   }
 
   // The document's chapter numbering — one <text:outline-style> in styles.xml.
@@ -891,9 +893,10 @@ export class StyleResolver {
     const props = this.pageLayoutEl()?.getElementsByTagNameNS(NS.style, 'page-layout-properties')[0] ?? null;
     if (!props) return null;
     const inset = this.decorInsetCm(props);
+    const room = (lengthToCm(props.getAttributeNS(NS.fo, 'page-height')) ?? 29.7) - 1;
     const cm = (attr: string) => {
       const v = lengthToCm(props.getAttributeNS(NS.fo, attr));
-      return v == null ? null : Math.min(10, Math.max(0, Math.round((v + inset) * 100) / 100));
+      return v == null ? null : Math.min(room, Math.max(0, Math.round((v + inset) * 100) / 100));
     };
     return { top: cm('margin-top') ?? 1.25, bottom: cm('margin-bottom') ?? 1.25 };
   }

src/lib/storage/CLAUDE.md

@@ -5,7 +5,7 @@ password-protected: the protection is on the saved file, not on the browser copy
 
 ## Page layout settings
 
-- **`pageMargins.ts`** — `PageMargins` in **cm** (default `{ top: 2, bottom: 2, left: 2, right: 2 }` — LibreOffice's; clamped 0–10). `applyMarginVars` sets `--user-margin-*` (px) on `:root`; `PX_PER_CM = 96/2.54`. Optional `mirrored` (ODF `style:page-usage="mirrored"`, Word `w:mirrorMargins`) makes left/right the **inner/outer** pair, which an even page swaps: `--user-margin-mirror` carries the difference, `pageBreaks.ts` insets an even page's blocks by it and `HeaderFooterLayer.svelte` moves the band. The key is **absent**, never `false`, when off — margins are compared whole in the round-trip tests.
+- **`pageMargins.ts`** — `PageMargins` in **cm** (default `{ top: 2, bottom: 2, left: 2, right: 2 }` — LibreOffice's; `fitMargins` only caps an imported pair at what leaves the page a 1cm strip of text). `applyMarginVars` sets `--user-margin-*` (px) on `:root`; `PX_PER_CM = 96/2.54`. Optional `mirrored` (ODF `style:page-usage="mirrored"`, Word `w:mirrorMargins`) makes left/right the **inner/outer** pair, which an even page swaps: `Editor.svelte` publishes the difference per section as `--pb-section-mirror` (a cover between mirrored pages mirrors nothing), `pageBreaks.ts` insets an even page's blocks by it and `HeaderFooterLayer.svelte` moves the band. The key is **absent**, never `false`, when off — margins are compared whole in the round-trip tests.
 - **`tabInterval.ts`** — the document's default tab interval in **cm** (`DEFAULT_TAB_INTERVAL_CM = 1.25`, LibreOffice's for a new document; clamped 0.05–10). `applyTabIntervalVar` sets `--tab-interval`, which is `.tiptap`'s `tab-size`. A file that declares none falls back to its format's own value, neither of them ours: `ODF_IMPLIED_TAB_CM` 2cm (measured against LibreOffice), `DOCX_IMPLIED_TAB_CM` 1.27cm — so both exports always write the value out.
 - **`spacingModel.ts`** — how the gap between two blocks is measured: `'add'` (LibreOffice's
   own — space-below **plus** space-above) or `'max'` (the larger of the two, what it uses for a

src/lib/storage/pageMargins.ts

@@ -10,6 +10,22 @@ const KEY = 'edentext-page-margins';
 // document gets these — an imported one always adopts its own page geometry.
 export const DEFAULT_MARGINS: PageMargins = { top: 2, bottom: 2, left: 2, right: 2 };
 
+// An imported margin is laid out as the file declares it — a back cover really does push
+// its five lines to the page foot with a 21cm top. The only cap is that the page keeps a
+// strip of text, or the flow would measure a column of no height at all.
+export const MIN_CONTENT_CM = 1;
+
+export function fitMargins(m: PageMargins, pageWidthCm: number, pageHeightCm: number): PageMargins {
+  const pair = (a: number, b: number, page: number): [number, number] => {
+    const room = Math.max(0, page - MIN_CONTENT_CM);
+    const first = Math.min(Math.max(0, a), room);
+    return [first, Math.min(Math.max(0, b), room - first)];
+  };
+  const [top, bottom] = pair(m.top, m.bottom, pageHeightCm);
+  const [left, right] = pair(m.left, m.right, pageWidthCm);
+  return { ...m, top, bottom, left, right };
+}
+
 export const PX_PER_CM = 96 / 2.54; // 37.795 — A4 @96dpi
 export const cmToPx = (cm: number) => cm * PX_PER_CM;
 
@@ -51,7 +67,4 @@ export function applyMarginVars(m: PageMargins): void {
   root.setProperty('--user-margin-bottom', `${cmToPx(m.bottom)}px`);
   root.setProperty('--user-margin-left',   `${cmToPx(m.left)}px`);
   root.setProperty('--user-margin-right',  `${cmToPx(m.right)}px`);
-  // How far an even page's text block moves right; .tiptap's padding draws the odd
-  // page's pair, so pageBreaks.ts insets the even one by the difference.
-  root.setProperty('--user-margin-mirror', `${m.mirrored ? cmToPx(m.right - m.left) : 0}px`);
 }

tests/unit/page-margins.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { PX_PER_CM, cmToPx, DEFAULT_MARGINS } from '../../src/lib/storage/pageMargins';
+import { PX_PER_CM, cmToPx, DEFAULT_MARGINS, fitMargins } from '../../src/lib/storage/pageMargins';
 
 describe('pageMargins units', () => {
   it('PX_PER_CM is A4 @96dpi (96 / 2.54)', () => {
@@ -21,4 +21,18 @@ describe('pageMargins units', () => {
   it("default margins are LibreOffice's 2cm all round", () => {
     expect(DEFAULT_MARGINS).toEqual({ top: 2, bottom: 2, left: 2, right: 2 });
   });
+
+  it('keeps a margin the file declares, however large', () => {
+    // A back cover pushes its last lines to the page foot with a 21cm top margin.
+    expect(fitMargins({ top: 21, bottom: 2, left: 3.6, right: 2.7 }, 21, 29.7))
+      .toEqual({ top: 21, bottom: 2, left: 3.6, right: 2.7 });
+  });
+
+  it('leaves the page a strip of text where the pair would take it all', () => {
+    const m = fitMargins({ top: 28, bottom: 5, left: 30, right: 5 }, 21, 29.7);
+    expect(m.top).toBe(28);
+    expect(m.bottom).toBeCloseTo(0.7, 6);
+    expect(m.left).toBe(20);
+    expect(m.right).toBe(0);
+  });
 });