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]>

tests/test_xlsx_viewer.py

@@ -519,6 +519,173 @@ class TestXlsxWriteLock:
         assert openpyxl.load_workbook(xlsx_file)["Budget"]["A1"].value == "premier"
 
 
+@pytest.fixture
+def wide_xlsx(test_vault_dir: str) -> str:
+    """Workbook whose sheet exceeds BOTH render caps (501 rows x 45 cols).
+
+    Sparse on purpose: a cell in A501 and one in AS1 are enough for openpyxl
+    to declare those dimensions, without writing 20 000 cells to disk.
+    """
+    from openpyxl import Workbook
+
+    path = Path(test_vault_dir) / "grand.xlsx"
+    wb = Workbook()
+    ws = wb.active
+    ws.title = "Data"
+    ws["A1"] = "tête"
+    ws["A501"] = "dernière ligne"
+    ws["AS1"] = "colonne 45"
+    wb.save(path)
+    return str(path)
+
+
+@pytest.fixture
+def edge_xlsx(test_vault_dir: str) -> str:
+    """Sheet exactly on the caps (500 rows x 40 cols) — must NOT be truncated."""
+    from openpyxl import Workbook
+
+    path = Path(test_vault_dir) / "limite.xlsx"
+    wb = Workbook()
+    ws = wb.active
+    ws.title = "Data"
+    ws["A1"] = "bord"
+    ws["A500"] = "ligne 500"
+    ws["AN1"] = "colonne 40"
+    wb.save(path)
+    return str(path)
+
+
+# ── #153 A8 — silent truncation made visible ─────────────────────────────
+
+
+class TestXlsxTruncationNotice:
+    """A sheet bigger than the caps must SAY so instead of looking complete."""
+
+    def test_render_reports_the_real_dimensions(self, client, wide_xlsx):
+        resp = client.get(f"/api/file/{VAULT}", params={"path": "grand.xlsx"})
+        sheet = resp.json()["xlsx_sheets"][0]
+        assert (sheet["total_rows"], sheet["total_cols"]) == (501, 45)
+        assert sheet["truncated"] is True
+        # The caps are the coverage the banner announces — `rows`/`cols` are
+        # post-trim and would understate it on a sparse sheet.
+        assert (sheet["max_rows"], sheet["max_cols"]) == (500, 40)
+        assert (sheet["rows"], sheet["cols"]) == (1, 1)  # only 3 filled cells
+
+    def test_a_sheet_on_the_caps_is_not_flagged(self, client, edge_xlsx):
+        """Boundary: 500x40 is exactly what the renderer supports."""
+        resp = client.get(f"/api/file/{VAULT}", params={"path": "limite.xlsx"})
+        sheet = resp.json()["xlsx_sheets"][0]
+        assert sheet["truncated"] is False
+        assert (sheet["total_rows"], sheet["total_cols"]) == (500, 40)
+
+    def test_a_normal_sheet_is_not_flagged(self, client, xlsx_file):
+        resp = client.get(f"/api/file/{VAULT}", params={"path": "budget.xlsx"})
+        assert all(not s["truncated"] for s in resp.json()["xlsx_sheets"])
+
+    def test_blank_tail_is_not_reported_as_truncation(self, client, test_vault_dir):
+        """A sheet with empty rows below its data fits in the caps."""
+        from openpyxl import Workbook
+
+        path = Path(test_vault_dir) / "blanc.xlsx"
+        wb = Workbook()
+        ws = wb.active
+        ws.title = "Data"
+        ws["A1"] = "seule ligne"
+        ws["A300"] = None  # formatted-but-empty row inside the caps
+        wb.save(path)
+        resp = client.get(f"/api/file/{VAULT}", params={"path": "blanc.xlsx"})
+        sheet = resp.json()["xlsx_sheets"][0]
+        assert sheet["truncated"] is False
+        assert sheet["rows"] == 1  # trailing blanks dropped by _trim
+
+
+# ── #153 A9 — lazy per-sheet loading ─────────────────────────────────────
+
+
+class TestXlsxSheetWindow:
+    """GET /api/file/{vault}/xlsx/sheet — one window of one sheet."""
+
+    def _get(self, client, path="budget.xlsx", **params):
+        return client.get(
+            f"/api/file/{VAULT}/xlsx/sheet", params={"path": path, **params}
+        )
+
+    def test_window_returns_rows_and_totals(self, client, xlsx_file):
+        resp = self._get(client, sheet="Budget", offset=0, limit=10)
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["sheet"] == "Budget"
+        assert (data["offset"], data["limit"]) == (0, 10)
+        assert data["rows"] == 2 and data["cols"] == 2
+        assert data["total_rows"] == 2 and data["truncated"] is False
+        assert (data["max_rows"], data["max_cols"]) == (500, 40)
+        assert data["has_more"] is False
+        assert 'data-cell="A1"' in data["html"]
+
+    def test_window_keeps_the_real_a1_coordinates(self, client, xlsx_file):
+        """A window must be indistinguishable from a full render: the A1
+        references and the row numbers have to be the sheet's, not the
+        window's, or an edit would land on the wrong cell. The CONTENT matters
+        as much as the label — row 2 of "Budget" is "Total", not "Poste"."""
+        data = self._get(client, sheet="Budget", offset=1, limit=1).json()
+        assert data["rows"] == 1
+        assert 'data-cell="A2"' in data["html"]
+        assert 'data-cell="A1"' not in data["html"]
+        assert "<th class=\"xlsx-rownum\">2</th>" in data["html"]
+        assert "Total" in data["html"] and "Poste" not in data["html"]
+
+    def test_window_offsets_walk_the_whole_sheet(self, client, wide_xlsx):
+        first = self._get(client, path="grand.xlsx", sheet="Data", offset=0, limit=10).json()
+        last = self._get(client, path="grand.xlsx", sheet="Data", offset=500, limit=10).json()
+        assert first["truncated"] is True and first["has_more"] is True
+        assert 'data-cell="A501"' in last["html"]  # the row the caps used to hide
+        assert "dernière ligne" in last["html"]
+        assert "dernière ligne" not in first["html"]
+        assert last["rows"] == 1 and last["has_more"] is False
+
+    def test_offset_past_the_end_is_empty_not_an_error(self, client, xlsx_file):
+        resp = self._get(client, sheet="Budget", offset=9999, limit=10)
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["rows"] == 0
+        assert data["has_more"] is False
+
+    def test_cached_result_survives_the_window(self, client, lossy_xlsx):
+        """A12 must not be lost on the lazy path."""
+        data = self._get(client, path="risky.xlsx", sheet="Data", offset=0, limit=10).json()
+        assert "xlsx-cached" in data["html"]
+
+    def test_unknown_sheet_is_404(self, client, xlsx_file):
+        resp = self._get(client, sheet="Nope")
+        assert resp.status_code == 404
+        assert "Feuille introuvable" in resp.json()["detail"]
+
+    def test_missing_file_is_404(self, client, test_vault_dir):
+        assert self._get(client, path="absent.xlsx", sheet="Budget").status_code == 404
+
+    def test_non_xlsx_file_is_415(self, client, test_vault_dir):
+        (Path(test_vault_dir) / "note.md").write_text("# hi", encoding="utf-8")
+        resp = self._get(client, path="note.md", sheet="Budget")
+        assert resp.status_code == 415
+
+    def test_limit_above_the_server_cap_is_rejected(self, client, xlsx_file):
+        """The cap is a contract, not a silent truncation of the request."""
+        assert self._get(client, sheet="Budget", limit=100_000).status_code == 422
+
+    def test_reader_clamps_a_hostile_limit(self, xlsx_file):
+        """Belt and braces: the reader caps too, whoever calls it."""
+        from backend.xlsx_reader import MAX_WINDOW_ROWS, read_sheet_window
+
+        window = read_sheet_window(Path(xlsx_file), "Budget", offset=0, limit=10**9)
+        assert window["limit"] == MAX_WINDOW_ROWS
+
+    def test_reader_rejects_a_negative_offset(self, xlsx_file):
+        from backend.xlsx_reader import read_sheet_window
+
+        window = read_sheet_window(Path(xlsx_file), "Budget", offset=-5, limit=10)
+        assert window["offset"] == 0
+
+
 # ── #153 A4 — formula injection ──────────────────────────────────────────