[BUG] OpenRouter xAI Grok 4.1 Fast doesn't comply with response format in agent block

[PlaneInABottle]

Issue Description

When using OpenRouter model xAI: Grok 4.1 Fast with a response format configured in an agent block, the model fails to comply with the specified response format and generates its own response instead.

Error Messages

1. "file_key" doesn't exist on block "agent". Available fields: model, tokens, content, toolCalls, responseFormat

   • Note: file_key is a field defined in the custom response format specification

2. "_responseFormatWarning": "LLM did not adhere to the specified structured response format. Expected valid JSON but received malformed content. Falling back to standard format."

Expected Behavior

The model should:

• Adhere to the specified structured response format provided in the agent block configuration
• Generate output that includes the file_key field as defined in the response format
• Return valid JSON matching the schema

Actual Behavior

• The model generates its own response format instead of following the specified structure
• The file_key field specified in the response format is not present in the output
• A fallback to standard format occurs due to malformed/non-compliant content
• Error indicates the custom field doesn't exist in the block output

Environment

• Model: xAI: Grok 4.1 Fast (via OpenRouter)
• Block Type: Agent
• Response Format: Custom format with file_key field defined

Reproduction

1. Create an agent block with xAI: Grok 4.1 Fast model via OpenRouter
2. Configure a custom response format that includes a file_key field
3. Execute the workflow
4. Observe the response format non-compliance warning and missing field error

Additional Context

This appears to be a model-specific issue where Grok 4.1 Fast through OpenRouter may not properly support structured output/response formats, resulting in the model ignoring the schema and generating its own response structure.

[PlaneInABottle]

I have tried more than 1 model, none of them respects to the response format.