refactor: centralize all download utils across app and apply special cloud-specific behavior (#6188)

## Summary

Centralized all download functionalities across app. Then changed
downloadFile on the cloud distribution to stream assets via blob fetches
while desktop/local retains direct anchor downloads. This fixes issue
where trying to download cross-origin resources opens them in the
window, potentially losing the user's unsaved changes.

## Changes

- **What**: Moved `downloadBlob` into `downloadUtil`, routed all callers
(3D exporter, recording manager, node template export, workflow/palette
export, Litegraph save, ~~`useDownload` consumers~~) through shared
helpers, and changed `downloadFile` to `fetch` first when `isCloud` so
cross-origin URLs download reliably
- `useDownload` is the exception since we simply cannot do model
downloads through blob (forcing user to transfer the entire model data
twice is bad). Fortunately on cloud, the user doesn't need to download
models locally anyway.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6188-refactor-centralize-all-download-utils-across-app-and-apply-special-cloud-specific-behav-2946d73d365081de9f27f0994950511d)
by [Unito](https://www.unito.io)

tests-ui/tests/base/common/downloadUtil.test.ts

@@ -2,15 +2,38 @@ import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
 import { downloadFile } from '@/base/common/downloadUtil'
 
+let mockIsCloud = false
+
+vi.mock('@/platform/distribution/types', () => ({
+  get isCloud() {
+    return mockIsCloud
+  }
+}))
+
+// Global stubs
+const createObjectURLSpy = vi
+  .spyOn(URL, 'createObjectURL')
+  .mockReturnValue('blob:mock-url')
+const revokeObjectURLSpy = vi
+  .spyOn(URL, 'revokeObjectURL')
+  .mockImplementation(() => {})
+
 describe('downloadUtil', () => {
   let mockLink: HTMLAnchorElement
+  let fetchMock: ReturnType<typeof vi.fn>
 
   beforeEach(() => {
+    mockIsCloud = false
+    fetchMock = vi.fn()
+    vi.stubGlobal('fetch', fetchMock)
+    createObjectURLSpy.mockClear().mockReturnValue('blob:mock-url')
+    revokeObjectURLSpy.mockClear().mockImplementation(() => {})
     // Create a mock anchor element
     mockLink = {
       href: '',
       download: '',
-      click: vi.fn()
+      click: vi.fn(),
+      style: { display: '' }
     } as unknown as HTMLAnchorElement
 
     // Spy on DOM methods
@@ -20,7 +43,7 @@ describe('downloadUtil', () => {
   })
 
   afterEach(() => {
-    vi.restoreAllMocks()
+    vi.unstubAllGlobals()
   })
 
   describe('downloadFile', () => {
@@ -35,6 +58,8 @@ describe('downloadUtil', () => {
       expect(document.body.appendChild).toHaveBeenCalledWith(mockLink)
       expect(mockLink.click).toHaveBeenCalled()
       expect(document.body.removeChild).toHaveBeenCalledWith(mockLink)
+      expect(fetchMock).not.toHaveBeenCalled()
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
     })
 
     it('should use custom filename when provided', () => {
@@ -45,6 +70,8 @@ describe('downloadUtil', () => {
 
       expect(mockLink.href).toBe(testUrl)
       expect(mockLink.download).toBe(customFilename)
+      expect(fetchMock).not.toHaveBeenCalled()
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
     })
 
     it('should extract filename from URL query parameters', () => {
@@ -55,6 +82,7 @@ describe('downloadUtil', () => {
 
       expect(mockLink.href).toBe(testUrl)
       expect(mockLink.download).toBe('extracted-image.jpg')
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
     })
 
     it('should use default filename when URL has no filename parameter', () => {
@@ -64,6 +92,7 @@ describe('downloadUtil', () => {
 
       expect(mockLink.href).toBe(testUrl)
       expect(mockLink.download).toBe('download.png')
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
     })
 
     it('should handle invalid URLs gracefully', () => {
@@ -74,6 +103,8 @@ describe('downloadUtil', () => {
       expect(mockLink.href).toBe(invalidUrl)
       expect(mockLink.download).toBe('download.png')
       expect(mockLink.click).toHaveBeenCalled()
+      expect(fetchMock).not.toHaveBeenCalled()
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
     })
 
     it('should prefer custom filename over extracted filename', () => {
@@ -84,6 +115,7 @@ describe('downloadUtil', () => {
       downloadFile(testUrl, customFilename)
 
       expect(mockLink.download).toBe(customFilename)
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
     })
 
     it('should handle URLs with empty filename parameter', () => {
@@ -92,6 +124,7 @@ describe('downloadUtil', () => {
       downloadFile(testUrl)
 
       expect(mockLink.download).toBe('download.png')
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
     })
 
     it('should handle relative URLs by using window.location.origin', () => {
@@ -101,6 +134,8 @@ describe('downloadUtil', () => {
 
       expect(mockLink.href).toBe(relativeUrl)
       expect(mockLink.download).toBe('relative-image.png')
+      expect(fetchMock).not.toHaveBeenCalled()
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
     })
 
     it('should clean up DOM elements after download', () => {
@@ -111,6 +146,54 @@ describe('downloadUtil', () => {
       // Verify the element was added and then removed
       expect(document.body.appendChild).toHaveBeenCalledWith(mockLink)
       expect(document.body.removeChild).toHaveBeenCalledWith(mockLink)
+      expect(fetchMock).not.toHaveBeenCalled()
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
+    })
+
+    it('streams downloads via blob when running in cloud', async () => {
+      mockIsCloud = true
+      const testUrl = 'https://storage.googleapis.com/bucket/file.bin'
+      const blob = new Blob(['test'])
+      const blobFn = vi.fn().mockResolvedValue(blob)
+      fetchMock.mockResolvedValue({
+        ok: true,
+        status: 200,
+        blob: blobFn
+      } as unknown as Response)
+
+      downloadFile(testUrl)
+
+      expect(fetchMock).toHaveBeenCalledWith(testUrl)
+      const fetchPromise = fetchMock.mock.results[0].value as Promise<Response>
+      await fetchPromise
+      const blobPromise = blobFn.mock.results[0].value as Promise<Blob>
+      await blobPromise
+      await Promise.resolve()
+      expect(blobFn).toHaveBeenCalled()
+      expect(createObjectURLSpy).toHaveBeenCalledWith(blob)
+      expect(revokeObjectURLSpy).toHaveBeenCalledWith('blob:mock-url')
+      expect(mockLink.click).toHaveBeenCalled()
+    })
+
+    it('logs an error when cloud fetch fails', async () => {
+      mockIsCloud = true
+      const testUrl = 'https://storage.googleapis.com/bucket/missing.bin'
+      const consoleSpy = vi.spyOn(console, 'error').mockImplementation(() => {})
+      fetchMock.mockResolvedValue({
+        ok: false,
+        status: 404,
+        blob: vi.fn()
+      } as unknown as Response)
+
+      downloadFile(testUrl)
+
+      expect(fetchMock).toHaveBeenCalledWith(testUrl)
+      const fetchPromise = fetchMock.mock.results[0].value as Promise<Response>
+      await fetchPromise
+      await Promise.resolve()
+      expect(consoleSpy).toHaveBeenCalled()
+      expect(createObjectURLSpy).not.toHaveBeenCalled()
+      consoleSpy.mockRestore()
     })
   })
 })