Add modal cross-reference validation for action.type="modal" → page existence check

Follows the same pattern as flow validation: when pages are defined,
modal-type action targets are validated against the page names collection.
When no pages are defined, validation is skipped (plugin may provide them).

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/spec/src/stack.test.ts

@@ -1038,9 +1038,69 @@ describe('defineStack - Action Cross-Reference Validation', () => {
 });
 
 // ============================================================================
-// Example-Level Strict Validation — mirrors examples/app-todo & examples/app-crm
+// Action → Modal Cross-Reference Validation — ensures modal targets resolve to pages
 // ============================================================================
 
+describe('defineStack - Modal Cross-Reference Validation', () => {
+  const baseManifest = {
+    id: 'com.example.test',
+    name: 'test-project',
+    version: '1.0.0',
+    type: 'app' as const,
+  };
+
+  const makePage = (name: string) => ({
+    name,
+    label: name,
+    regions: [{ name: 'main', components: [] }],
+  });
+
+  it('should detect modal action referencing undefined page', () => {
+    const config = {
+      manifest: baseManifest,
+      objects: [
+        { name: 'task', label: 'Task', fields: { title: { type: 'text' as const } } },
+      ],
+      pages: [makePage('existing_page')],
+      actions: [
+        { name: 'open_modal', label: 'Open Modal', type: 'modal' as const, target: 'nonexistent_page' },
+      ],
+    };
+
+    expect(() => defineStack(config)).toThrow('cross-reference validation failed');
+    expect(() => defineStack(config)).toThrow('nonexistent_page');
+  });
+
+  it('should pass when modal action references a defined page', () => {
+    const config = {
+      manifest: baseManifest,
+      objects: [
+        { name: 'task', label: 'Task', fields: { title: { type: 'text' as const } } },
+      ],
+      pages: [makePage('defer_task_modal')],
+      actions: [
+        { name: 'defer_task', label: 'Defer Task', type: 'modal' as const, target: 'defer_task_modal' },
+      ],
+    };
+
+    expect(() => defineStack(config)).not.toThrow();
+  });
+
+  it('should skip modal validation when no pages are defined', () => {
+    const config = {
+      manifest: baseManifest,
+      objects: [
+        { name: 'task', label: 'Task', fields: { title: { type: 'text' as const } } },
+      ],
+      actions: [
+        { name: 'open_modal', label: 'Open Modal', type: 'modal' as const, target: 'some_modal' },
+      ],
+    };
+
+    expect(() => defineStack(config)).not.toThrow();
+  });
+});
+
 describe('defineStack - Example-Level Strict Validation', () => {
   it('should validate a Todo-style app config (strict mode)', () => {
     const todoConfig = {

packages/spec/src/stack.zod.ts

@@ -400,9 +400,9 @@ function validateCrossReferences(config: ObjectStackDefinition): string[] {
     }
   }
 
-  // Validate action → flow/target cross-references
-  // Note: When no flows are defined (flowNames.size === 0), flow-type action targets
-  // are not validated because the referenced flow may be provided by a plugin.
+  // Validate action → flow/modal cross-references
+  // Note: When no flows/pages are defined (size === 0), targets are not validated
+  // because the referenced items may be provided by a plugin.
   // This is consistent with dashboard/page/report validation in navigation.
   if (config.actions) {
     const flowNames = new Set<string>();
@@ -412,13 +412,27 @@ function validateCrossReferences(config: ObjectStackDefinition): string[] {
       }
     }
 
+    const pageNames = new Set<string>();
+    if (config.pages) {
+      for (const page of config.pages) {
+        pageNames.add(page.name);
+      }
+    }
+
     for (const action of config.actions) {
       // Validate flow-type actions reference a defined flow
       if (action.type === 'flow' && action.target && flowNames.size > 0 && !flowNames.has(action.target)) {
         errors.push(
           `Action '${action.name}' references flow '${action.target}' which is not defined in flows.`,
         );
       }
+
+      // Validate modal-type actions reference a defined page
+      if (action.type === 'modal' && action.target && pageNames.size > 0 && !pageNames.has(action.target)) {
+        errors.push(
+          `Action '${action.name}' references modal '${action.target}' which is not defined in pages.`,
+        );
+      }
     }
   }