fix(grid): pad short timestamp fractions

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

@@ -31,6 +31,36 @@ describe("dataGridCellDisplayText", () => {
       }),
     ).toBeUndefined();
   });
+
+  it.each([
+    ["2026-08-28 12:34:56.1", "2026-08-28 12:34:56.100"],
+    ["2026-08-28 12:34:56.12+08:00", "2026-08-28 12:34:56.120+08:00"],
+  ])("pads short timestamp fractions for display", (value, expected) => {
+    expect(
+      dataGridCellDisplayText({
+        value,
+        databaseType: "mysql",
+        columnInfo: { data_type: "timestamp" },
+      }),
+    ).toBe(expected);
+  });
+
+  it("leaves full-precision and non-timestamp values unchanged", () => {
+    expect(
+      dataGridCellDisplayText({
+        value: "2026-08-28 12:34:56.1234",
+        databaseType: "mysql",
+        columnInfo: { data_type: "timestamp(6)" },
+      }),
+    ).toBeUndefined();
+    expect(
+      dataGridCellDisplayText({
+        value: "2026-08-28 12:34:56.1",
+        databaseType: "mysql",
+        columnInfo: { data_type: "varchar(64)" },
+      }),
+    ).toBeUndefined();
+  });
 });
 
 describe("coerceDataGridCellValue", () => {

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

@@ -93,12 +93,22 @@ export function dataGridCellDisplayText(options: { value: GridCellValue; databas
   if (Array.isArray(options.value) && options.databaseType === "postgres" && isPostgresArrayColumn(options.columnInfo, options.value)) {
     return formatPostgresArrayText(options.value);
   }
+  if (typeof options.value === "string") {
+    const timestampDisplay = normalizeTimestampFractionDisplayText(options.value, options.columnInfo?.data_type);
+    if (timestampDisplay !== options.value) return timestampDisplay;
+  }
   if (typeof options.value === "string" && isOracleDateColumn(options.databaseType, options.columnInfo)) {
     return formatOracleDateDisplayText(options.value);
   }
   return undefined;
 }
 
+function normalizeTimestampFractionDisplayText(value: string, dataType: string | undefined): string {
+  if (!/^timestamp(?:\s*\([^)]*\))?(?:\s+(?:with|without)\s+time\s+zone)?$/i.test(dataType?.trim() ?? "")) return value;
+  const match = value.match(/^(\d{4}[-/]\d{1,2}[-/]\d{1,2}[ T]\d{1,2}:\d{1,2}:\d{1,2})\.(\d{1,2})(Z|[+-]\d{2}:?\d{2})?$/);
+  return match ? `${match[1]}.${match[2].padEnd(3, "0")}${match[3] ?? ""}` : value;
+}
+
 function coercePostgresArrayValue(options: CoerceDataGridCellValueOptions): unknown[] | undefined {
   if (options.databaseType !== "postgres") return undefined;
   if (!isPostgresArrayColumn(options.columnInfo, options.oldValue)) return undefined;