feat: chargement à la demande des lignes cachées des tableurs #153

A9bis : sous une feuille tronquée, un pied de page « N lignes affichées
sur M · Charger la suite » fetch la fenêtre suivante (limit=500) au clic
ou à l'approche du bas du tableau (sentinelle de défilement, marge 120px).
Les lignes ajoutées passent par le même pipeline d'édition que le rendu
initial (setupCell factorisé) : éditables et sauvegardables immédiatement.
Fetch échoué → bouton restauré (retry) + toast ; feuille complète → pied
de page masqué (class done).

Vérifié : xlsx-viewer.test.mjs 19/19 (5 nouveaux, contre-preuve
wireLazyRows désactivé → 5 échecs), E2E 8/8 (A520 visible et éditable
après clic), validate-imports 40 modules, unit.test.mjs 12/12, i18n parity.

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

frontend/js/viewer.js

@@ -1085,14 +1085,80 @@ export function renderXlsxViewer(area, data) {
   const dirtyCount = () => area.querySelectorAll("td.xlsx-dirty").length;
   const refreshSaveState = () => { saveBtn.disabled = dirtyCount() === 0; };
 
-  // #153 A12 — the backend marks the last value Excel computed; the wording is
-  // translated here so the tooltip follows the UI language.
-  area.querySelectorAll(".xlsx-cached[data-cached-value]").forEach((el) => {
-    el.title = t("xlsx.cached_value_title");
-  });
+  // #153 A9bis — the first render stops at MAX_ROWS/MAX_COLS; the tail is
+  // fetched window by window from GET …/xlsx/sheet when the user reaches the
+  // end of a truncated sheet (scroll sentinel) or clicks « Charger la suite ».
+  // Appended rows reuse the exact same edit pipeline as the initial render.
+  const wireLazyRows = (panel) => {
+    const meta = sheets[Number(panel.dataset.sheet)] || {};
+    if (!meta.truncated) return;
+    const wrapper = panel.querySelector(".csv-table-wrapper");
+    const table = panel.querySelector(".xlsx-table tbody");
+    if (!wrapper || !table) return;
 
-  // Editable cells: Enter blurs, Escape reverts, paste stays single-line.
-  area.querySelectorAll(".xlsx-table td").forEach((td) => {
+    let offset = Number(meta.rows) || 0;
+    const total = Number(meta.total_rows) || 0;
+    let loading = false;
+    let done = offset >= total;
+
+    const foot = document.createElement("div");
+    foot.className = "xlsx-load-more";
+    const refreshFoot = () => {
+      foot.textContent = done
+        ? ""
+        : `${t("xlsx.truncated_rows", { shown: offset, total })} · ${t("xlsx.load_more")}`;
+      foot.classList.toggle("done", done);
+    };
+    refreshFoot();
+    foot.addEventListener("click", () => { if (!done) loadMore(); });
+    wrapper.insertAdjacentElement("afterend", foot);
+
+    const appendWindow = (win) => {
+      const doc = new DOMParser().parseFromString(`<table>${win.html}</table>`, "text/html");
+      // No `tbody` selector: the fragment embeds its own wrapper div, so the
+      // parse yields bare `<tr>` inside `<table>` (the rows we want) — while
+      // any `tbody` in the fragment belongs to the *embedded* wrapper table.
+      doc.querySelectorAll("tr").forEach((tr) => table.appendChild(tr));
+      offset = win.offset + win.rows;
+      done = !win.has_more;
+      refreshFoot();
+      // The new rows must behave like the initial ones: contenteditable,
+      // dirty tracking, cached-value tooltip, icons in the fresh footnote.
+      panel.querySelectorAll("tbody tr:not([data-wired]) td").forEach(setupCell);
+      panel.querySelectorAll("tbody tr").forEach((tr) => tr.setAttribute("data-wired", "1"));
+      const cachedEls = panel.querySelectorAll(".xlsx-cached[data-cached-value]");
+      cachedEls.forEach((el) => { if (!el.title) el.title = t("xlsx.cached_value_title"); });
+      safeCreateIcons();
+    };
+
+    const loadMore = async () => {
+      if (loading || done) return;
+      loading = true;
+      const label = foot.textContent;
+      foot.textContent = t("xlsx.loading_more");
+      try {
+        const win = await api(
+          `/api/file/${encodeURIComponent(data.vault)}/xlsx/sheet?path=${encodeURIComponent(data.path)}` +
+          `&sheet=${encodeURIComponent(sheets[Number(panel.dataset.sheet)].name)}` +
+          `&offset=${offset}&limit=500`,
+        );
+        appendWindow(win);
+      } catch (err) {
+        foot.textContent = label; // restore: a failed fetch must not eat the button
+        showToast(`${t("xlsx.load_error")}: ${err.message || err}`, "error");
+      } finally {
+        loading = false;
+      }
+    };
+
+    // Scroll sentinel: near the bottom of the wrapper, pull the next window.
+    wrapper.addEventListener("scroll", () => {
+      if (loading || done) return;
+      if (wrapper.scrollTop + wrapper.clientHeight >= wrapper.scrollHeight - 120) loadMore();
+    });
+  };
+
+  const setupCell = (td) => {
     td.contentEditable = "true";
     td.spellcheck = false;
     td.dataset.orig = td.textContent;
@@ -1113,8 +1179,18 @@ export function renderXlsxViewer(area, data) {
       const text = (e.clipboardData || window.clipboardData).getData("text").replace(/\r?\n/g, " ");
       document.execCommand("insertText", false, text);
     });
+  };
+
+  // #153 A12 — the backend marks the last value Excel computed; the wording is
+  // translated here so the tooltip follows the UI language.
+  area.querySelectorAll(".xlsx-cached[data-cached-value]").forEach((el) => {
+    el.title = t("xlsx.cached_value_title");
   });
 
+  // Editable cells: Enter blurs, Escape reverts, paste stays single-line.
+  area.querySelectorAll(".xlsx-table td").forEach(setupCell);
+  panelEls.forEach(wireLazyRows);
+
   area.querySelectorAll(".xlsx-tab").forEach((tab) => {
     tab.addEventListener("click", () => {
       const idx = tab.dataset.sheet;