[backport core/1.34] feat: add live preview method setting for prompt execution (#7521)

## Summary

Backport of #7385 to core/1.34.

Add frontend setting to override live preview method per prompt
execution.

- **What**: New setting `Comfy.Execution.PreviewMethod` allows users to
override preview method (default/none/auto/latent2rgb/taesd) from
frontend.

## Conflict Resolution

- `src/schemas/apiSchema.ts`: Kept both `Comfy.Queue.ImageFit` (target
branch) and `Comfy.Execution.PreviewMethod` (PR addition)

Co-authored-by: Dr.Lt.Data <128333288+ltdrdata@users.noreply.github.com>

src/locales/en/settings.json

@@ -53,6 +53,17 @@
   "Comfy_EnableWorkflowViewRestore": {
     "name": "Save and restore canvas position and zoom level in workflows"
   },
+  "Comfy_Execution_PreviewMethod": {
+    "name": "Live preview method",
+    "tooltip": "Live preview method during image generation. \"default\" uses the server CLI setting.",
+    "options": {
+      "default": "default",
+      "none": "none",
+      "auto": "auto",
+      "latent2rgb": "latent2rgb",
+      "taesd": "taesd"
+    }
+  },
   "Comfy_FloatRoundingPrecision": {
     "name": "Float widget rounding decimal places [0 = auto].",
     "tooltip": "(requires page reload)"

src/platform/settings/constants/coreSettings.ts

@@ -813,6 +813,17 @@ export const CORE_SETTINGS: SettingParams[] = [
     defaultValue: 64,
     versionAdded: '1.4.12'
   },
+  {
+    id: 'Comfy.Execution.PreviewMethod',
+    category: ['Comfy', 'Execution', 'PreviewMethod'],
+    name: 'Live preview method',
+    tooltip:
+      'Live preview method during image generation. "default" uses the server CLI setting.',
+    type: 'combo',
+    options: ['default', 'none', 'auto', 'latent2rgb', 'taesd'],
+    defaultValue: 'default',
+    versionAdded: '1.36.0'
+  },
   {
     id: 'LiteGraph.Canvas.MaximumFps',
     name: 'Maximum FPS',

src/schemas/apiSchema.ts

@@ -369,6 +369,15 @@ const zNodeBadgeMode = z.enum(
   Object.values(NodeBadgeMode) as [string, ...string[]]
 )
 
+const zPreviewMethod = z.enum([
+  'default',
+  'none',
+  'auto',
+  'latent2rgb',
+  'taesd'
+])
+export type PreviewMethod = z.infer<typeof zPreviewMethod>
+
 const zSettings = z.object({
   'Comfy.ColorPalette': z.string(),
   'Comfy.CustomColorPalettes': colorPalettesSchema,
@@ -431,6 +440,7 @@ const zSettings = z.object({
   'Comfy.Validation.Workflows': z.boolean(),
   'Comfy.Workflow.SortNodeIdOnSave': z.boolean(),
   'Comfy.Queue.ImageFit': z.enum(['contain', 'cover']),
+  'Comfy.Execution.PreviewMethod': zPreviewMethod,
   'Comfy.Workflow.WorkflowTabsPosition': z.enum(['Sidebar', 'Topbar']),
   'Comfy.Node.DoubleClickTitleToEdit': z.boolean(),
   'Comfy.WidgetControlMode': z.enum(['before', 'after']),

src/scripts/api.ts

@@ -41,7 +41,8 @@ import type {
   StatusWsMessageStatus,
   SystemStats,
   User,
-  UserDataFullInfo
+  UserDataFullInfo,
+  PreviewMethod
 } from '@/schemas/apiSchema'
 import type { ComfyNodeDef } from '@/schemas/nodeDefSchema'
 import type { useFirebaseAuthStore } from '@/stores/firebaseAuthStore'
@@ -88,6 +89,11 @@ interface QueuePromptRequestBody {
      * ```
      */
     api_key_comfy_org?: string
+    /**
+     * Override the preview method for this prompt execution.
+     * 'default' uses the server's CLI setting.
+     */
+    preview_method?: PreviewMethod
   }
   front?: boolean
   number?: number
@@ -103,6 +109,11 @@ interface QueuePromptOptions {
    * Format: Colon-separated path of node IDs (e.g., "123:456:789")
    */
   partialExecutionTargets?: NodeExecutionId[]
+  /**
+   * Override the preview method for this prompt execution.
+   * 'default' uses the server's CLI setting and is not sent to backend.
+   */
+  previewMethod?: PreviewMethod
 }
 
 /** Dictionary of Frontend-generated API calls */
@@ -772,7 +783,11 @@ export class ComfyApi extends EventTarget {
       extra_data: {
         auth_token_comfy_org: this.authToken,
         api_key_comfy_org: this.apiKey,
-        extra_pnginfo: { workflow }
+        extra_pnginfo: { workflow },
+        ...(options?.previewMethod &&
+          options.previewMethod !== 'default' && {
+            preview_method: options.previewMethod
+          })
       }
     }
 

src/scripts/app.ts

@@ -1344,6 +1344,9 @@ export class ComfyApp {
     try {
       while (this.queueItems.length) {
         const { number, batchCount, queueNodeIds } = this.queueItems.pop()!
+        const previewMethod = useSettingStore().get(
+          'Comfy.Execution.PreviewMethod'
+        )
 
         for (let i = 0; i < batchCount; i++) {
           // Allow widgets to run callbacks before a prompt has been queued
@@ -1358,7 +1361,8 @@ export class ComfyApp {
             api.authToken = comfyOrgAuthToken
             api.apiKey = comfyOrgApiKey ?? undefined
             const res = await api.queuePrompt(number, p, {
-              partialExecutionTargets: queueNodeIds
+              partialExecutionTargets: queueNodeIds,
+              previewMethod
             })
             delete api.authToken
             delete api.apiKey