load template workflow via URL query param (#6546)

## Summary

Adds support for loading templates via URL query parameters. Users can
now share direct links to templates.

To test:

1. checkout this branch
2. start dev server on port 5173
3. go to http://localhost:5173/?template=image_qwen_image_edit_2509

**Examples:**
- `/?template=default` - Loads template with default source
- `/?template=flux_simple&source=custom` - Loads from custom source

Includes error handling with toast notifications for invalid templates
and comprehensive test coverage.

---------

Co-authored-by: Christian Byrne <c.byrne@comfy.org>

tests-ui/tests/platform/workflow/templates/composables/useTemplateUrlLoader.test.ts

@@ -0,0 +1,220 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { useTemplateUrlLoader } from '@/platform/workflow/templates/composables/useTemplateUrlLoader'
+
+/**
+ * Unit tests for useTemplateUrlLoader composable
+ *
+ * Tests the behavior of loading templates via URL query parameters:
+ * - ?template=flux_simple loads the template
+ * - ?template=flux_simple&source=custom loads from custom source
+ * - Invalid template shows error toast
+ * - Input validation for template and source parameters
+ */
+
+// Mock vue-router
+let mockQueryParams: Record<string, string | undefined> = {}
+
+vi.mock('vue-router', () => ({
+  useRoute: vi.fn(() => ({
+    query: mockQueryParams
+  }))
+}))
+
+// Mock template workflows composable
+const mockLoadTemplates = vi.fn().mockResolvedValue(true)
+const mockLoadWorkflowTemplate = vi.fn().mockResolvedValue(true)
+
+vi.mock(
+  '@/platform/workflow/templates/composables/useTemplateWorkflows',
+  () => ({
+    useTemplateWorkflows: () => ({
+      loadTemplates: mockLoadTemplates,
+      loadWorkflowTemplate: mockLoadWorkflowTemplate
+    })
+  })
+)
+
+// Mock toast
+const mockToastAdd = vi.fn()
+vi.mock('primevue/usetoast', () => ({
+  useToast: () => ({
+    add: mockToastAdd
+  })
+}))
+
+// Mock i18n
+vi.mock('vue-i18n', () => ({
+  useI18n: () => ({
+    t: vi.fn((key: string, params?: any) => {
+      if (key === 'g.error') return 'Error'
+      if (key === 'templateWorkflows.error.templateNotFound') {
+        return `Template "${params?.templateName}" not found`
+      }
+      if (key === 'g.errorLoadingTemplate') return 'Failed to load template'
+      return key
+    })
+  })
+}))
+
+describe('useTemplateUrlLoader', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+    mockQueryParams = {}
+  })
+
+  it('does not load template when no query param present', () => {
+    mockQueryParams = {}
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    void loadTemplateFromUrl()
+
+    expect(mockLoadTemplates).not.toHaveBeenCalled()
+    expect(mockLoadWorkflowTemplate).not.toHaveBeenCalled()
+  })
+
+  it('loads template when query param is present', async () => {
+    mockQueryParams = { template: 'flux_simple' }
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    await loadTemplateFromUrl()
+
+    expect(mockLoadTemplates).toHaveBeenCalledTimes(1)
+    expect(mockLoadWorkflowTemplate).toHaveBeenCalledWith(
+      'flux_simple',
+      'default'
+    )
+  })
+
+  it('uses default source when source param is not provided', async () => {
+    mockQueryParams = { template: 'flux_simple' }
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    await loadTemplateFromUrl()
+
+    expect(mockLoadWorkflowTemplate).toHaveBeenCalledWith(
+      'flux_simple',
+      'default'
+    )
+  })
+
+  it('uses custom source when source param is provided', async () => {
+    mockQueryParams = { template: 'custom-template', source: 'custom-module' }
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    await loadTemplateFromUrl()
+
+    expect(mockLoadWorkflowTemplate).toHaveBeenCalledWith(
+      'custom-template',
+      'custom-module'
+    )
+  })
+
+  it('shows error toast when template loading fails', async () => {
+    mockQueryParams = { template: 'invalid-template' }
+    mockLoadWorkflowTemplate.mockResolvedValueOnce(false)
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    await loadTemplateFromUrl()
+
+    expect(mockToastAdd).toHaveBeenCalledWith({
+      severity: 'error',
+      summary: 'Error',
+      detail: 'Template "invalid-template" not found',
+      life: 3000
+    })
+  })
+
+  it('handles array query params correctly', () => {
+    // Vue Router can return string[] for duplicate params
+    mockQueryParams = { template: ['first', 'second'] as any }
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    void loadTemplateFromUrl()
+
+    // Should not load when param is an array
+    expect(mockLoadTemplates).not.toHaveBeenCalled()
+  })
+
+  it('rejects invalid template parameter with special characters', () => {
+    // Test path traversal attempt
+    mockQueryParams = { template: '../../../etc/passwd' }
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    void loadTemplateFromUrl()
+
+    // Should not load invalid template
+    expect(mockLoadTemplates).not.toHaveBeenCalled()
+  })
+
+  it('rejects invalid template parameter with slash', () => {
+    mockQueryParams = { template: 'path/to/template' }
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    void loadTemplateFromUrl()
+
+    // Should not load invalid template
+    expect(mockLoadTemplates).not.toHaveBeenCalled()
+  })
+
+  it('accepts valid template parameter formats', async () => {
+    const validTemplates = [
+      'flux_simple',
+      'flux-kontext-dev',
+      'template123',
+      'My_Template-2'
+    ]
+
+    for (const template of validTemplates) {
+      vi.clearAllMocks()
+      mockQueryParams = { template }
+
+      const { loadTemplateFromUrl } = useTemplateUrlLoader()
+      await loadTemplateFromUrl()
+
+      expect(mockLoadWorkflowTemplate).toHaveBeenCalledWith(template, 'default')
+    }
+  })
+
+  it('rejects invalid source parameter with special characters', () => {
+    mockQueryParams = { template: 'flux_simple', source: '../malicious' }
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    void loadTemplateFromUrl()
+
+    // Should not load with invalid source
+    expect(mockLoadTemplates).not.toHaveBeenCalled()
+  })
+
+  it('accepts valid source parameter formats', async () => {
+    const validSources = ['default', 'custom-module', 'my_source', 'source123']
+
+    for (const source of validSources) {
+      vi.clearAllMocks()
+      mockQueryParams = { template: 'flux_simple', source }
+
+      const { loadTemplateFromUrl } = useTemplateUrlLoader()
+      await loadTemplateFromUrl()
+
+      expect(mockLoadWorkflowTemplate).toHaveBeenCalledWith(
+        'flux_simple',
+        source
+      )
+    }
+  })
+
+  it('shows error toast when exception is thrown', async () => {
+    mockQueryParams = { template: 'flux_simple' }
+    mockLoadTemplates.mockRejectedValueOnce(new Error('Network error'))
+
+    const { loadTemplateFromUrl } = useTemplateUrlLoader()
+    await loadTemplateFromUrl()
+
+    expect(mockToastAdd).toHaveBeenCalledWith({
+      severity: 'error',
+      summary: 'Error',
+      detail: 'Failed to load template',
+      life: 3000
+    })
+  })
+})