fix: Make Content-Disposition header RFC 2183 compliant

Changes all Content-Disposition headers from:
  filename="name.ext"
to:
  attachment; filename="name.ext"

This ensures compatibility with RFC 2183 and allows third-party
downloading libraries (e.g., Go's mime.ParseMediaType) to correctly
parse the filename.

Fixes #8914

server.py

@@ -521,7 +521,7 @@ class PromptServer():
                             buffer.seek(0)
 
                             return web.Response(body=buffer.read(), content_type=f'image/{image_format}',
-                                                headers={"Content-Disposition": f"filename=\"{filename}\""})
+                                                headers={"Content-Disposition": f"attachment; filename=\"{filename}\""})
 
                     if 'channel' not in request.rel_url.query:
                         channel = 'rgba'
@@ -541,7 +541,7 @@ class PromptServer():
                             buffer.seek(0)
 
                             return web.Response(body=buffer.read(), content_type='image/png',
-                                                headers={"Content-Disposition": f"filename=\"{filename}\""})
+                                                headers={"Content-Disposition": f"attachment; filename=\"{filename}\""})
 
                     elif channel == 'a':
                         with Image.open(file) as img:
@@ -558,7 +558,7 @@ class PromptServer():
                             alpha_buffer.seek(0)
 
                             return web.Response(body=alpha_buffer.read(), content_type='image/png',
-                                                headers={"Content-Disposition": f"filename=\"{filename}\""})
+                                                headers={"Content-Disposition": f"attachment; filename=\"{filename}\""})
                     else:
                         # Get content type from mimetype, defaulting to 'application/octet-stream'
                         content_type = mimetypes.guess_type(filename)[0] or 'application/octet-stream'
@@ -570,7 +570,7 @@ class PromptServer():
                         return web.FileResponse(
                             file,
                             headers={
-                                "Content-Disposition": f"filename=\"{filename}\"",
+                                "Content-Disposition": f"attachment; filename=\"{filename}\"",
                                 "Content-Type": content_type
                             }
                         )

test_rfc2183_fix.py

@@ -0,0 +1,49 @@
+#!/usr/bin/env python3
+"""
+Test for Content-Disposition header fix
+Verifies that the header matches RFC 2183 format
+"""
+
+import re
+
+def test_content_disposition_header():
+    """Test that Content-Disposition header is RFC 2183 compliant"""
+    
+    # Read the server.py file
+    with open('server.py', 'r') as f:
+        content = f.read()
+    
+    # Find all Content-Disposition headers
+    pattern = r'"Content-Disposition":\s*f"([^"]+)"'
+    matches = re.findall(pattern, content)
+    
+    print(f"Found {len(matches)} Content-Disposition headers")
+    
+    all_pass = True
+    for i, match in enumerate(matches, 1):
+        print(f"\nHeader {i}: {match}")
+        
+        # Check RFC 2183 compliance
+        # Should start with "attachment;" or "inline;" followed by filename
+        if match.startswith("attachment;") and "filename=" in match:
+            print(f"  ✅ RFC 2183 compliant (attachment disposition)")
+        elif match.startswith("inline;") and "filename=" in match:
+            print(f"  ✅ RFC 2183 compliant (inline disposition)")
+        elif match.startswith("filename="):
+            print(f"  ❌ NOT RFC 2183 compliant (missing disposition type)")
+            all_pass = False
+        else:
+            print(f"  ⚠️  Unknown format")
+    
+    print("\n" + "="*50)
+    if all_pass:
+        print("✅ All headers are RFC 2183 compliant!")
+    else:
+        print("❌ Some headers are NOT RFC 2183 compliant!")
+    
+    return all_pass
+
+if __name__ == "__main__":
+    import sys
+    success = test_content_disposition_header()
+    sys.exit(0 if success else 1)