fix: loading api-format workflow that contains "parameters" string (#7411)

## Summary

This change extends
https://github.com/Comfy-Org/ComfyUI_frontend/pull/7154 by making sure
the `prompt` metadata tag is parsed before the legacy A1111 fallback
when files are dropped onto the canvas.

ComfyUI embeds two structured payloads into every first-class export
format we support (PNG, WEBP, WEBM, MP4/MOV/M4V, GLB, SVG, MP3,
OGG/FLAC, etc.): `workflow`, which is the full editor JSON with layout
state, and `prompt`, which is the API graph sent to `/prompt`.

During import we try format-specific decoders first and only as a last
resort look for an A1111 file by scanning text chunks for a `parameters`
entry. That compatibility path was always meant to be a best-effort
option, but when we refactored the loader it accidentally enforced the
order `workflow → parameters → prompt`. As soon as a dropped asset
contained a `parameters` chunk—something Image Saver’s “A1111
compatibility” mode always adds—the A1111 converter activated and
blocked the subsequent `prompt` loading logic.

PR #7154 already lifted `workflow` ahead of the fallback, yet any file
lacking the `workflow` chunk but holding both `prompt` and `parameters`
still regressed. Reordering to `workflow → prompt → parameters`
preserves the compatibility shim for genuine A1111 exports while
guaranteeing native Comfy metadata always wins, eliminating the entire
class of failures triggered merely by the presence of the word
`parameters` in an unrelated metadata chunk.

Fixes https://github.com/Comfy-Org/ComfyUI_frontend/issues/7096, fixes
https://github.com/Comfy-Org/ComfyUI_frontend/issues/6988

## Related 

(fixed by https://github.com/Comfy-Org/ComfyUI_frontend/pull/7154)

- https://github.com/Comfy-Org/ComfyUI_frontend/issues/6633
- https://github.com/Comfy-Org/ComfyUI_frontend/issues/6561

---------

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

src/scripts/app.ts

@@ -1468,7 +1468,21 @@ 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`.
@@ -1481,18 +1495,25 @@ 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) {