feat: troncature annoncee et lecture par fenetres des tableurs #153

- BUG-090 (#153 A8) : render_sheets() expose total_rows/total_cols,
  max_rows/max_cols et truncated ; la visionneuse affiche un bandeau
  « Feuille tronquée » (i18n FR/EN) au lieu de couper en silence, et la
  ligne d'en-têtes devient sticky (top:auto sur les numéros de ligne).
- #153 A9 : GET /api/file/{vault}/xlsx/sheet?sheet&offset&limit sert une
  fenêtre de 1 à 1000 lignes avec les vraies coordonnées A1, has_more de
  pagination et valeurs calculées A12 ; 404 feuille inconnue, 415 non-xlsx.
- Tests : TestXlsxTruncationNotice (4) + TestXlsxSheetWindow (11) avec
  contre-preuves, xlsx-viewer.test.mjs 14/14, E2E 7/7 (fixture
  sample-xlsx-large.xlsx 520 lignes), suite 1417 passed / 6 skipped,
  ruff/mypy 0, i18n parity.

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <[email protected]>

frontend/js/viewer.js

@@ -1005,6 +1005,35 @@ export function renderVideoViewer(area, data) {
 // confirmation before retrying with `force: true`. A value starting with "=" or
 // "@" is stored as text unless the user turns the formula toggle on, so a typed
 // `=cmd|…` cannot execute when the file is later opened in Excel.
+// #153 A8 — a sheet bigger than the render caps used to be silently cut: the
+// user saw a short table and no way to tell the rest of the workbook still
+// existed. The backend now reports the real dimensions of every sheet, so the
+// note states exactly what is hidden (and that those cells are not editable
+// here — the workbook itself is untouched). A payload without those fields
+// (older cache) simply shows no note.
+function truncationNote(sheet) {
+  // The cap is the real "shown" figure, not `rows`/`cols`: those are post-trim
+  // (a sparse sheet renders 1x1) while the note must say how far the view
+  // reaches.
+  const cap = { rows: Number(sheet.max_rows) || 0, cols: Number(sheet.max_cols) || 0 };
+  const reasons = [];
+  if (Number(sheet.total_rows) > cap.rows) {
+    reasons.push(t("xlsx.truncated_rows", { shown: cap.rows, total: Number(sheet.total_rows) }));
+  }
+  if (Number(sheet.total_cols) > cap.cols) {
+    reasons.push(t("xlsx.truncated_cols", { shown: cap.cols, total: Number(sheet.total_cols) }));
+  }
+  if (!reasons.length) return "";
+  return `<div class="xlsx-truncated" role="note">
+      <i data-lucide="scissors" class="xlsx-truncated-icon"></i>
+      <div class="xlsx-warning-body">
+        <strong>${escapeHtml(t("xlsx.truncated_title"))}</strong>
+        <span>${escapeHtml(reasons.join(" "))}</span>
+        <span class="xlsx-warning-hint">${escapeHtml(t("xlsx.truncated_hint"))}</span>
+      </div>
+    </div>`;
+}
+
 export function renderXlsxViewer(area, data) {
   const sheets = data.xlsx_sheets || [];
   const lossy = data.xlsx_lossy_features || [];
@@ -1019,7 +1048,7 @@ export function renderXlsxViewer(area, data) {
       ).join("")}</div>`
     : "";
   const panels = sheets.map((s, i) =>
-    `<div class="xlsx-panel" data-sheet="${i}"${i === 0 ? "" : ' style="display:none"'}>${s.html}</div>`
+    `<div class="xlsx-panel" data-sheet="${i}"${i === 0 ? "" : ' style="display:none"'}>${truncationNote(s)}${s.html}</div>`
   ).join("");
   const lossWarning = lossy.length
     ? `<div class="xlsx-warning" role="note">

frontend/locales/en.json

@@ -1829,6 +1829,10 @@
   "xlsx.lossy_cancelled": "Save cancelled",
   "xlsx.formula_toggle_title": "Treat “=” and “@” as formulas (off by default)",
   "xlsx.cached_value_title": "Last value calculated by Excel",
+  "xlsx.truncated_title": "Truncated sheet",
+  "xlsx.truncated_rows": "{shown} of {total} rows displayed.",
+  "xlsx.truncated_cols": "{shown} of {total} columns displayed.",
+  "xlsx.truncated_hint": "Cells outside the displayed area cannot be edited here; the workbook is unchanged.",
   "xlsx.feature_cached_values": "cached values",
   "xlsx.feature_slicers": "slicers and timelines",
   "xlsx.feature_form_controls": "form controls",

frontend/locales/fr.json

@@ -1829,6 +1829,10 @@
   "xlsx.lossy_cancelled": "Sauvegarde annulée",
   "xlsx.formula_toggle_title": "Interpréter « = » et « @ » comme des formules (désactivé par défaut)",
   "xlsx.cached_value_title": "Dernière valeur calculée par Excel",
+  "xlsx.truncated_title": "Feuille tronquée",
+  "xlsx.truncated_rows": "{shown} lignes affichées sur {total}.",
+  "xlsx.truncated_cols": "{shown} colonnes affichées sur {total}.",
+  "xlsx.truncated_hint": "Les cellules hors de l'affichage ne sont pas éditables ici ; le classeur n'est pas modifié.",
   "xlsx.feature_cached_values": "valeurs calculées",
   "xlsx.feature_slicers": "segments et chronologies",
   "xlsx.feature_form_controls": "contrôles de formulaire",

frontend/style.css

@@ -10967,12 +10967,25 @@ body.desktop-mode .editor-container {
   border-right: 1px solid var(--border-light, var(--border));
   position: sticky;
   left: 0;
-  z-index: 1;
+  /* #153 A8 — `top: auto` is load-bearing: `.csv-table th` pins EVERY `th`
+     at `top: 0`, so a row number left sticky on both axes piles up in the
+     top-left corner instead of tracking its own row. */
+  top: auto;
+  z-index: 2;
 }
 .xlsx-table th.xlsx-corner {
   left: 0;
   top: 0;
-  z-index: 2;
+  z-index: 4;
+}
+/* #153 A8 — the column headers stay visible while the sheet scrolls down.
+   Declared explicitly (and not inherited from `.csv-table th`) so the stacking
+   order is intentional: thead (3) < row numbers (2) < corner (4). */
+.xlsx-table thead th {
+  position: sticky;
+  top: 0;
+  z-index: 3;
+  background: var(--surface);
 }
 .xlsx-table td[contenteditable] {
   cursor: text;
@@ -11051,6 +11064,31 @@ body.desktop-mode .editor-container {
   color: var(--text-secondary);
   opacity: 0.85;
 }
+/* #153 A8 — "feuille tronquée" notice. Deliberately NOT the `.xlsx-warning`
+   look: that one is a data-loss alert, this one only says part of the sheet is
+   out of view. */
+.xlsx-truncated {
+  display: flex;
+  align-items: flex-start;
+  gap: 8px;
+  padding: 8px 10px;
+  margin-bottom: 8px;
+  border: 1px solid var(--border);
+  border-left: 3px solid var(--accent, #4a90d9);
+  border-radius: 4px;
+  background: var(--bg-secondary);
+  color: var(--text-secondary);
+  font-size: 0.82rem;
+  line-height: 1.45;
+}
+.xlsx-truncated-icon {
+  width: 16px;
+  height: 16px;
+  flex: 0 0 auto;
+  margin-top: 1px;
+  color: var(--accent, #4a90d9);
+}
+
 .xlsx-formula-toggle {
   font-family: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;
   font-weight: 600;