[backport core/1.34] fix: loading api-format workflow that contains "parameters" string (#7516)

Backport of #7411 to `core/1.34`

Automatically created by backport workflow.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7516-backport-core-1-34-fix-loading-api-format-workflow-that-contains-parameters-string-2ca6d73d365081438d19fd6ed3272684)
by [Unito](https://www.unito.io)

Co-authored-by: Christian Byrne <cbyrne@comfy.org>
Co-authored-by: github-actions <github-actions@github.com>
Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

browser_tests/tests/loadWorkflowInMedia.spec.ts

@@ -12,6 +12,7 @@ test.describe('Load Workflow in Media', () => {
     'edited_workflow.webp',
     'no_workflow.webp',
     'large_workflow.webp',
+    'workflow_prompt_parameters.png',
     'workflow.webm',
     // Skipped due to 3d widget unstable visual result.
     // 3d widget shows grid after fully loaded.

src/scripts/app.ts

@@ -1469,7 +1469,21 @@ export class ComfyApp {
       }
     }
 
-    // Use parameters as fallback when no workflow exists
+    if (prompt) {
+      try {
+        const promptObj =
+          typeof prompt === 'string' ? JSON.parse(prompt) : prompt
+        if (this.isApiJson(promptObj)) {
+          this.loadApiJson(promptObj, fileName)
+          return
+        }
+      } catch (err) {
+        console.error('Failed to parse prompt:', err)
+      }
+      // Fall through to parameters as a last resort
+    }
+
+    // Use parameters strictly as the final fallback
     if (parameters) {
       // Note: Not putting this in `importA1111` as it is mostly not used
       // by external callers, and `importA1111` has no access to `app`.
@@ -1482,18 +1496,25 @@ export class ComfyApp {
       return
     }
 
-    if (prompt) {
-      const promptObj = typeof prompt === 'string' ? JSON.parse(prompt) : prompt
-      this.loadApiJson(promptObj, fileName)
-      return
-    }
-
     this.showErrorOnFileLoad(file)
   }
 
   // @deprecated
-  isApiJson(data: unknown) {
-    return _.isObject(data) && Object.values(data).every((v) => v.class_type)
+  isApiJson(data: unknown): data is ComfyApiWorkflow {
+    if (!_.isObject(data) || Array.isArray(data)) {
+      return false
+    }
+    if (Object.keys(data).length === 0) return false
+
+    return Object.values(data).every((node) => {
+      if (!node || typeof node !== 'object' || Array.isArray(node)) {
+        return false
+      }
+
+      const { class_type: classType, inputs } = node as Record<string, unknown>
+      const inputsIsRecord = _.isObject(inputs) && !Array.isArray(inputs)
+      return typeof classType === 'string' && inputsIsRecord
+    })
   }
 
   loadApiJson(apiData: ComfyApiWorkflow, fileName: string) {