[openai-agents / OpenRouter] OpenRouterResponses injects additionalProperties:false into schemas for non-OpenAI providers

## Observed symptom [Bug] OpenRouterResponses injects additionalProperties: false into schemas for non-OpenAI providers (xAI/Grok rejects with 400) Copied from https://github.com/agno-agi/agno/issues/7455 ### Description When using `OpenRouterResponses` with `x-ai/grok-4.20`, all requests with `output_schema` (structured output) are rejected by the xAI provider with HTTP 400: ``` Schema validation failed: [standard_violation] /properties/properties/additionalProperties: property schema 'false' is not supported ``` The root cause is that `OpenRouterResponses` inherits from `OpenAIResponses`, which unconditionally sanitizes JSON schemas to comply with OpenAI's structured output spec — specifically injecting `additionalProperties: false` into all object-type schemas. xAI does not support this schema property. Setting `strict_output=False` does **not** prevent this — it only controls the `format.strict` flag in the API request, not t ## Literal error text ``` additionalProperties: false ``` ## Environment GitHub issue DeadantCo/agno #469; state=open ## Trigger / context Copied from https://github.com/agno-agi/agno/issues/7455 ### Description When using `OpenRouterResponses` with `x-ai/grok-4.20`, all requests with `output_schema` (structured output) are rejected by the xAI provider with HTTP 400: ``` Schema validation failed: [standard_violation] /properties/properties/additionalProperties: property schema 'false' is not supported ``` The root cause is that `OpenRouterResponses` inherits from `OpenAIResponses`, which unconditionally sanitizes JSON schemas to comply with OpenAI's structured output spec — specifically injecting `additionalProperties: false` into all object-type schemas. xAI does not support this schema property. Setting `strict_output=False` does **not** prevent this — it only controls the `format.strict` flag in the API request, not the schema content itself. ### Steps to Reproduce ```python from agno.agent import Agent from agno.models.openrouter import OpenRouterResponses from pydantic import BaseModel, Field class MyDecision(BaseModel): action: str = Field(min_length=1) reason: str = Field(min_length=1) agent = Agent( model=OpenRouterResponses( id="x-ai/grok-4.20", strict_output=False, # does not help ), output_schema=MyDecision, use_json_mode=False, ) agent.print_response("What should I do today?") # → HTTP 400: additionalProperties: property schema 'false' is not supported ``` ### Agent Configuration (if applicable) Any agent using `OpenRouterResponses` with a non-Open ## Source evidence - https://github.com/DeadantCo/agno/issues/469 (2026-09-28T19:26:49Z) — GitHub issue #469 (open) ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:39:37.643698Z - scout_id: C2dc7df0ae0 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome.