Chart builder: escape ./[/] in built field names

src/core/chart-builder.test.ts

@@ -674,6 +674,20 @@ describe('buildChartSpec', () => {
       expect((spec.mark as { type: string }).type).toBe(mark);
     }
   });
+
+  it('escapes `.`/`[`/`]` in encoded field names so they read as literal columns', () => {
+    const spec = buildChartSpec({
+      datasetName: 'D',
+      mark: 'point',
+      encodings: {
+        x: { field: 'user.age', type: 'quantitative' },
+        y: { field: 'cols[0]', type: 'quantitative' },
+      },
+    });
+    const enc = spec.encoding as Record<string, { field: string }>;
+    expect(enc.x.field).toBe('user\\.age');
+    expect(enc.y.field).toBe('cols\\[0\\]');
+  });
 });
 
 describe('transforms — aggregate / bin / timeUnit', () => {
@@ -940,6 +954,13 @@ describe('buildTransforms (predicate coercion + shape)', () => {
     expect(t).toEqual([{ filter: 'datum.value > 0' }]);
   });
 
+  it('escapes `.`/`[`/`]` in a predicate field so it reads as a literal column', () => {
+    const t = buildTransforms(
+      withFilters(filter({ field: 'user.age', fieldType: 'quantitative', op: 'gt', value: '10' })),
+    );
+    expect(t).toEqual([{ filter: { field: 'user\\.age', gt: 10 } }]);
+  });
+
   it('skips incomplete entries (blank value, blank range bound, blank expression)', () => {
     const t = buildTransforms(
       withFilters(