[feat] Add async model upload with WebSocket progress tracking (#7746)

## Summary
- Adds asynchronous model upload support with HTTP 202 responses
- Implements WebSocket-based real-time download progress tracking via
`asset_download` events
- Creates `assetDownloadStore` for centralized download state management
and toast notifications
- Updates upload wizard UI to show "processing" state when downloads
continue in background

## Changes
- **Core**: New `assetDownloadStore` for managing async downloads with
WebSocket events
- **API**: Support for HTTP 202 async upload responses with task
tracking
- **UI**: Upload wizard now shows "processing" state and allows closing
dialog during download
- **Progress**: Periodic toast notifications (every 5s) during active
downloads with completion/error toasts
- **Schema**: Updated task statuses (`created`, `running`, `completed`,
`failed`) and WebSocket message types

## Review Focus
- WebSocket event handling and download state management in
`assetDownloadStore`
- Upload flow UX - users can now close the dialog and download continues
in background
- Toast notification frequency and timing
- Schema alignment with backend async upload API

Fixes #7748

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7746-feat-Add-async-model-upload-with-WebSocket-progress-tracking-2d36d73d3650811cb79ae06f470dcded)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: GitHub Action <action@github.com>

src/platform/assets/services/assetService.ts

@@ -3,12 +3,14 @@ import { fromZodError } from 'zod-validation-error'
 import { st } from '@/i18n'
 import {
   assetItemSchema,
-  assetResponseSchema
+  assetResponseSchema,
+  asyncUploadResponseSchema
 } from '@/platform/assets/schemas/assetSchema'
 import type {
   AssetItem,
   AssetMetadata,
   AssetResponse,
+  AsyncUploadResponse,
   ModelFile,
   ModelFolder
 } from '@/platform/assets/schemas/assetSchema'
@@ -46,6 +48,7 @@ function getLocalizedErrorMessage(errorCode: string): string {
 }
 
 const ASSETS_ENDPOINT = '/assets'
+const ASSETS_DOWNLOAD_ENDPOINT = '/assets/download'
 const EXPERIMENTAL_WARNING = `EXPERIMENTAL: If you are seeing this please make sure "Comfy.Assets.UseAssetAPI" is set to "false" in your ComfyUI Settings.\n`
 const DEFAULT_LIMIT = 500
 
@@ -445,6 +448,72 @@ function createAssetService() {
     return await res.json()
   }
 
+  /**
+   * Uploads an asset asynchronously using the /api/assets/download endpoint
+   * Returns immediately with either the asset (if already exists) or a task to track
+   *
+   * @param params - Upload parameters
+   * @param params.source_url - HTTP/HTTPS URL to download from
+   * @param params.tags - Optional freeform tags
+   * @param params.user_metadata - Optional custom metadata object
+   * @param params.preview_id - Optional UUID for preview asset
+   * @returns Promise<AsyncUploadResponse> - Either sync asset or async task info
+   * @throws Error if upload fails
+   */
+  async function uploadAssetAsync(params: {
+    source_url: string
+    tags?: string[]
+    user_metadata?: Record<string, unknown>
+    preview_id?: string
+  }): Promise<AsyncUploadResponse> {
+    const res = await api.fetchApi(ASSETS_DOWNLOAD_ENDPOINT, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify(params)
+    })
+
+    if (!res.ok) {
+      throw new Error(
+        st(
+          'assetBrowser.errorUploadFailed',
+          'Failed to upload asset. Please try again.'
+        )
+      )
+    }
+
+    const data = await res.json()
+
+    if (res.status === 202) {
+      const result = asyncUploadResponseSchema.safeParse({
+        type: 'async',
+        task: data
+      })
+      if (!result.success) {
+        throw new Error(
+          st(
+            'assetBrowser.errorUploadFailed',
+            'Failed to parse async upload response. Please try again.'
+          )
+        )
+      }
+      return result.data
+    }
+
+    const result = asyncUploadResponseSchema.safeParse({
+      type: 'sync',
+      asset: data
+    })
+    if (!result.success) {
+      throw new Error(
+        st(
+          'assetBrowser.errorUploadFailed',
+          'Failed to parse sync upload response. Please try again.'
+        )
+      )
+    }
+    return result.data
+  }
+
   return {
     getAssetModelFolders,
     getAssetModels,
@@ -456,7 +525,8 @@ function createAssetService() {
     updateAsset,
     getAssetMetadata,
     uploadAssetFromUrl,
-    uploadAssetFromBase64
+    uploadAssetFromBase64,
+    uploadAssetAsync
   }
 }