fix(preview): bound rich-text run walks, fold format notices, match Excel number display

- richTextPrefix visits at most maxCellTextChars + 1 runs. An empty run adds
  no text, so a length check alone walked every run of a shared string for
  every cell referencing it, on every tile.
- Two or more unsupported number format warnings in a tile fold into one
  "N unsupported number formats" entry, and the notice bar has a max-height
  and scrolls.
- General-format and unsupported-format numbers render at 15 significant
  digits, as Excel does (0.1+0.2 shows 0.3).
- TIME_FORMAT accepts a trailing AM/PM, so h:mm AM/PM renders as 2:30 PM
  instead of falling back to a date.
- SPREADSHEET_ASSET_VERSION refreshed.

test/spreadsheet-preview-worker.test.ts

@@ -986,3 +986,25 @@ describe('spreadsheet preview worker: number formats ExcelJS would rescan', () =
     expect(tile.warnings).toEqual([`Unsupported number format: ${code}`]);
   }, 60_000);
 });
+
+describe('spreadsheet preview worker: the notice bar stays bounded', () => {
+  // Each distinct unsupported code was its own notice entry; a 40 x 20 sheet
+  // with a code per cell grew the bar to thousands of pixels.
+  it('folds many distinct unsupported number formats in one tile into one counted warning', async () => {
+    const workbook = new ExcelJS.Workbook();
+    const sheet = workbook.addWorksheet('Formats');
+    for (let row = 1; row <= 40; row += 1) {
+      for (let col = 1; col <= 20; col += 1) {
+        const cell = sheet.getCell(row, col);
+        cell.value = row * col + 0.5;
+        cell.numFmt = `"c${row}-${col}"0.00E+00`;
+      }
+    }
+    const harness = createHarness();
+    const metadata = await loadMetadata(harness, await writeWorkbook(workbook));
+    const tile = await requestTile(harness, metadata.sheets[0].id, { r1: 1, c1: 1, r2: 40, c2: 20 });
+    expect(tile.type, JSON.stringify(tile).slice(0, 200)).toBe('tile');
+    expect(tile.cells).toHaveLength(800);
+    expect(tile.warnings).toEqual(['800 unsupported number formats']);
+  }, 60_000);
+});

test/spreadsheet-preview.test.ts

@@ -176,6 +176,15 @@ describe('spreadsheet preview renderer', () => {
     expect(document.body.textContent).toContain('Spreadsheet parser failed');
   });
 
+  // The bar sits above the grid in a flex column; unbounded, enough warnings
+  // pushed the grid out of view.
+  it('clamps the notice bar height and scrolls its overflow', () => {
+    const css = readFileSync(resolve(import.meta.dirname, '../src/web/public/styles.css'), 'utf8');
+    const rule = /\.spreadsheet-preview-notice\s*\{([^}]*)\}/.exec(css)?.[1] || '';
+    expect(rule).toMatch(/max-height:\s*\d/);
+    expect(rule).toMatch(/overflow-y:\s*auto/);
+  });
+
   it('shows an explicit empty-sheet state without dropping workbook warnings', async () => {
     const fetchMock = vi.fn(async () => ({ ok: true, arrayBuffer: async () => new ArrayBuffer(8) }));
     const renderer = loadRenderer(fetchMock);

test/spreadsheet-xlsx-core.test.ts

@@ -26,6 +26,7 @@ type Core = {
   computeViewport(axis: unknown, offset: number, viewportSize: number, overscan?: number): [number, number];
   intersectingMerges(merges: string[], range: { r1: number; c1: number; r2: number; c2: number }): string[];
   formatCellValue(value: unknown, format: string, date1904?: boolean): { text: string; warning?: string };
+  foldWarnings(warnings: string[]): string[];
   DEFAULT_THEME_PALETTE: string[];
   INDEXED_PALETTE: string[];
   parseThemePalette(xml?: string): string[];
@@ -428,6 +429,25 @@ describe('spreadsheet XLSX core', () => {
     expect(/[\uD800-\uDBFF](?![\uDC00-\uDFFF])/.test(emoji)).toBe(false);
   });
 
+  // An empty run adds no text, so stopping on the text length alone still
+  // visited every run, once per cell referencing the shared string, per tile.
+  it('visits at most maxCellTextChars + 1 rich-text runs, however many are empty', () => {
+    const bound = core.LIMITS.maxCellTextChars + 1;
+    const runs: Array<{ text: string }> = Array.from({ length: 5_000 }, () => ({ text: '' }));
+    runs[0] = { text: 'head' };
+    for (let index = bound; index < runs.length; index += 1) {
+      Object.defineProperty(runs, index, {
+        get() {
+          throw new Error(`rich-text run ${index} visited`);
+        },
+      });
+    }
+    expect(core.formatCellValue({ richText: runs }, 'General')).toEqual({ text: 'head' });
+    // A run inside the bound still contributes.
+    runs[bound - 1] = { text: 'tail' };
+    expect(core.formatCellValue({ richText: runs }, 'General').text).toBe('headtail');
+  });
+
   it('refuses an entry whose declared compressed size runs past the file', () => {
     const zip = workbookZip();
     const view = new DataView(zip.buffer, zip.byteOffset, zip.byteLength);
@@ -483,6 +503,38 @@ describe('spreadsheet XLSX core', () => {
     expect(core.formatCellValue({ formula: 'SUM(A1:A2)' }, 'General')).toMatchObject({ text: '=SUM(A1:A2)' });
   });
 
+  // Excel displays at most 15 significant digits; String() printed the binary noise.
+  it('shows General and unsupported-format numbers at 15 significant digits, as Excel does', () => {
+    expect(core.formatCellValue(0.1 + 0.2, 'General').text).toBe('0.3');
+    expect(core.formatCellValue(10.1 * 3, 'General').text).toBe('30.3');
+    expect(core.formatCellValue({ formula: '0.1+0.2', result: 0.1 + 0.2 }, 'General').text).toBe('0.3');
+    expect(core.formatCellValue(0.1 + 0.2, '0.00E+00')).toEqual({
+      text: '0.3',
+      warning: 'Unsupported number format: 0.00E+00',
+    });
+    expect(core.formatCellValue(1234.5, 'General').text).toBe('1234.5');
+    expect(core.formatCellValue(-42, 'General').text).toBe('-42');
+  });
+
+  it('renders a time-only AM/PM format as a 12-hour time, not a date', () => {
+    expect(core.formatCellValue(14.5 / 24, 'h:mm AM/PM')).toEqual({ text: '2:30 PM' });
+    expect(core.formatCellValue(0, 'h:mm AM/PM').text).toBe('12:00 AM');
+    expect(core.formatCellValue(0.5, 'h:mm AM/PM').text).toBe('12:00 PM');
+    expect(core.formatCellValue(9.25 / 24, 'hh:mm:ss AM/PM').text).toBe('09:15:00 AM');
+    // ExcelJS loads a time-formatted cell as a Date on the 1899-12-31 epoch day.
+    expect(core.formatCellValue(new Date(Date.UTC(1899, 11, 31, 14, 30)), 'h:mm AM/PM')).toEqual({
+      text: '2:30 PM',
+    });
+  });
+
+  it('folds unsupported number format warnings into one counted entry', () => {
+    const many = Array.from({ length: 800 }, (_, index) => `Unsupported number format: 0.0${'0'.repeat(index)}E+0`);
+    const folded = core.foldWarnings(['charts', ...many, 'Formula has no cached result']);
+    expect(folded).toEqual(['charts', '800 unsupported number formats', 'Formula has no cached result']);
+    expect(core.foldWarnings(['Unsupported number format: 0.00E+00'])).toEqual(['Unsupported number format: 0.00E+00']);
+    expect(core.foldWarnings(['charts'])).toEqual(['charts']);
+  });
+
   // toLocaleString throws a RangeError above 100 fraction digits; Excel caps at 30.
   it('caps a number format at 30 decimals instead of throwing', () => {
     expect(core.formatCellValue(1.5, `0.${'0'.repeat(120)}`).text).toBe(`1.5${'0'.repeat(29)}`);