fix(data-grid): show first nonblank cell preview line

Closes #5977

apps/desktop/src/lib/__tests__/dataGrid/cellValue.spec.ts

@@ -6,5 +6,19 @@ describe("firstLineCellDisplayValue", () => {
     expect(firstLineCellDisplayValue("111\n222")).toBe("111");
     expect(firstLineCellDisplayValue("111\r\n222")).toBe("111");
     expect(firstLineCellDisplayValue("111\r222")).toBe("111");
+    expect(firstLineCellDisplayValue("single line")).toBe("single line");
+  });
+
+  it("skips leading blank lines without stripping content indentation", () => {
+    expect(firstLineCellDisplayValue("\nINNODB MONITOR OUTPUT\nbody")).toBe("INNODB MONITOR OUTPUT");
+    expect(firstLineCellDisplayValue("\r\nINNODB MONITOR OUTPUT\r\nbody")).toBe("INNODB MONITOR OUTPUT");
+    expect(firstLineCellDisplayValue("\rINNODB MONITOR OUTPUT\rbody")).toBe("INNODB MONITOR OUTPUT");
+    expect(firstLineCellDisplayValue("  \n  indented content\nbody")).toBe("  indented content");
+  });
+
+  it("preserves values that do not contain a content line", () => {
+    expect(firstLineCellDisplayValue("")).toBe("");
+    expect(firstLineCellDisplayValue("   ")).toBe("   ");
+    expect(firstLineCellDisplayValue("\n\r\n  \r")).toBe("\n\r\n  \r");
   });
 });

apps/desktop/src/lib/dataGrid/cellValue.ts

@@ -11,8 +11,25 @@ export function displayCellValue(value: CellValue): string {
 }
 
 export function firstLineCellDisplayValue(value: string): string {
-  const lineBreakIndex = value.search(/\r\n|\r|\n/);
-  return lineBreakIndex === -1 ? value : value.slice(0, lineBreakIndex);
+  const lineBreakPattern = /\r\n|\r|\n/g;
+  const firstLineBreak = lineBreakPattern.exec(value);
+  if (!firstLineBreak) return value;
+
+  const firstLine = value.slice(0, firstLineBreak.index);
+  if (/\S/u.test(firstLine)) return firstLine;
+
+  let lineStart = lineBreakPattern.lastIndex;
+
+  while (lineStart <= value.length) {
+    const lineBreak = lineBreakPattern.exec(value);
+    const lineEnd = lineBreak?.index ?? value.length;
+    const line = value.slice(lineStart, lineEnd);
+    if (/\S/u.test(line)) return line;
+    if (!lineBreak) return value;
+    lineStart = lineBreakPattern.lastIndex;
+  }
+
+  return value;
 }
 
 export function limitDataGridCellDisplay(value: string, maxLength = DATA_GRID_CELL_DISPLAY_MAX_LENGTH): string {