fix: ensure ruler 0 is visible

packages/layout-engine/painters/dom/src/ruler/ruler-renderer.test.ts

@@ -88,14 +88,13 @@ describe('createRulerElement', () => {
       expect(allTicks[4].style.left).toBe('48px'); // Half tick
     });
 
-    it('adds labels to main ticks', () => {
+    it('adds labels to main ticks but skips the leading zero', () => {
       const ruler = createRulerElement({ definition, doc });
 
       const labels = ruler.querySelectorAll(`.${RULER_CLASS_NAMES.label}`);
-      expect(labels.length).toBe(2); // Two main ticks with labels
+      expect(labels.length).toBe(1); // Label 0 is hidden to prevent overflow clipping
 
-      expect(labels[0].textContent).toBe('0');
-      expect(labels[1].textContent).toBe('1');
+      expect(labels[0].textContent).toBe('1');
     });
 
     it('does not add labels to non-main ticks', () => {
@@ -264,16 +263,16 @@ describe('createRulerElement', () => {
       expect(labels.length).toBe(0);
     });
 
-    it('handles tick with label value of 0', () => {
+    it('does not render label for tick with label value of 0', () => {
       const singleTickDefinition: RulerDefinition = {
         ...definition,
         ticks: [{ size: 'main', height: '20%', label: 0, x: 0 }],
       };
 
       const ruler = createRulerElement({ definition: singleTickDefinition, doc });
 
-      const label = ruler.querySelector(`.${RULER_CLASS_NAMES.label}`);
-      expect(label?.textContent).toBe('0');
+      const labels = ruler.querySelectorAll(`.${RULER_CLASS_NAMES.label}`);
+      expect(labels.length).toBe(0);
     });
   });
 

packages/layout-engine/painters/dom/src/ruler/ruler-renderer.ts

@@ -155,7 +155,7 @@ function createTickElement(tick: RulerTick, doc: Document): HTMLElement {
   `;
 
   // Add label for main ticks
-  if (tick.label !== undefined) {
+  if (tick.label !== undefined && tick.label !== 0) {
     const label = doc.createElement('span');
     label.className = RULER_CLASS_NAMES.label;
     label.textContent = String(tick.label);

packages/super-editor/src/components/rulers/Ruler.test.ts

@@ -1,22 +1,18 @@
-/**
- * Test suite for Ruler.vue section-awareness
- *
- * NOTE: The Ruler.vue component currently has a TypeScript syntax error in its
- * emit definition (line 6). The correct syntax should be:
- *
- * const emit = defineEmits(['margin-change']);
- *
- * instead of:
- *
- * const emit = defineEmits<{
- *   'margin-change': [payload: { side: 'left' | 'right'; value: number; sectionIndex: number }]
- * }>();
- *
- * Once the Ruler.vue file is fixed, these tests can be uncommented and run.
- * For now, we document the expected behaviors that should be tested:
- */
-
 import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { mount } from '@vue/test-utils';
+import { nextTick } from 'vue';
+import Ruler from './Ruler.vue';
+
+const createMockEditor = (overrides = {}) => ({
+  options: { mode: 'docx' },
+  getPageStyles: vi.fn(() => ({
+    pageSize: { width: 8.5, height: 11 },
+    pageMargins: { left: 1, right: 1, top: 1, bottom: 1 },
+  })),
+  on: vi.fn(),
+  off: vi.fn(),
+  ...overrides,
+});
 
 /**
  * Helper to create a mock emitter for testing event handling
@@ -38,9 +34,30 @@ const createEmitter = () => {
   };
 };
 
-describe('Ruler.vue section-awareness (blocked by syntax error in Ruler.vue)', () => {
+describe('Ruler.vue rendering', () => {
+  it('renders the leading zero label and keeps it inside the ruler bounds', async () => {
+    const wrapper = mount(Ruler, {
+      props: {
+        editor: createMockEditor(),
+      },
+    });
+
+    await nextTick();
+
+    const labels = wrapper.findAll('.numbering');
+    expect(labels.length).toBeGreaterThan(1);
+    expect(labels[0].text()).toBe('0');
+    expect(labels[0].classes()).toContain('numbering--edge-start');
+    expect(labels[1].text()).toBe('1');
+    expect(labels[1].classes()).not.toContain('numbering--edge-start');
+
+    wrapper.unmount();
+  });
+});
+
+describe('Ruler.vue section-awareness coverage gaps', () => {
   /**
-   * Required test cases once Ruler.vue syntax is fixed:
+   * Remaining component test cases to add:
    *
    * 1. Updates ruler when section changes
    *    - On 'selectionUpdate' event, should call getCurrentSectionPageStyles()

packages/super-editor/src/components/rulers/Ruler.vue

@@ -459,7 +459,9 @@ onUnmounted(() => {
           :class="['ruler-tick', `ruler-tick--${tick.size}`]"
           :style="getTickStyle(tick)"
         >
-          <span v-if="tick.label !== undefined" class="numbering">{{ tick.label }}</span>
+          <span v-if="tick.label !== undefined" :class="['numbering', { 'numbering--edge-start': tick.x === 0 }]">
+            {{ tick.label }}
+          </span>
         </div>
       </template>
     </div>
@@ -531,4 +533,8 @@ onUnmounted(() => {
   pointer-events: none;
   user-select: none;
 }
+
+.numbering--edge-start {
+  left: 0;
+}
 </style>