Python: [Feature]: Python: BedrockChatClient — support Converse API outputConfig.textFormat for structured output

[ankit-singh16]

Description

BedrockChatClient hard-codes response_format: None in BedrockChatOptions, which blocks structured output entirely. The Converse API now supports outputConfig.textFormat with a jsonSchema type for API-enforced structured output (GA since February 2026, works with Converse, ConverseStream, InvokeModel, and InvokeModelWithResponseStream). The Anthropic, Gemini, and OpenAI clients in MAF all support response_format already. Bedrock is the odd one out.

What needs to change

1. Remove the response_format: None override so ChatOptions.response_format can flow through naturally.

2. Add a _prepare_output_config() helper that converts Pydantic models or dict schemas into the Bedrock wire format:

def _prepare_output_config(self, response_format):
    if response_format is None:
        return None

    if isinstance(response_format, dict):
        schema = response_format.get("json_schema", {}).get("schema", response_format)
        name = response_format.get("json_schema", {}).get("name", "output_schema")
    else:
        schema = response_format.model_json_schema()
        name = response_format.__name__

    self._set_additional_properties_false(schema)

    return {
        "textFormat": {
            "type": "jsonSchema",
            "jsonSchema": {
                "name": name,
                "schema": json.dumps(schema),  # Bedrock wants a JSON string, not a dict
            },
        }
    }

The recursive _set_additional_properties_false helper mirrors what AnthropicChatClient._prepare_response_format() does (lines 659-693).

3. Wire it into _prepare_options() after the toolConfig block:

if output_config := self._prepare_output_config(options.get("response_format")):
    run_options["outputConfig"] = output_config

4. Populate ChatResponse.value by passing response_format through to _build_response, same as the Anthropic client does.

Compatibility notes

• When response_format is omitted, nothing changes. No outputConfig gets sent.
• Models that don't support outputConfig.textFormat will return a ValidationException from Bedrock. Surface that clearly rather than silently falling back to unstructured text.
• Agent.run(response_format=...) might need a separate follow-up to pass the option down to the client layer.

Acceptance criteria

• outputConfig.textFormat.jsonSchema.schema is serialized as a JSON string (not a dict)
• additionalProperties: false is set recursively on all object schemas
• No outputConfig in the request when response_format is not provided
• Clear error when a model doesn't support it (no silent downgrade)
• ChatResponse.value is populated with a parsed Pydantic model
• Unit tests covering request shape, string serialization, and the no-op path

[karthik-0306]

I've now verified the correct wire format against the AWS CLI reference and the Feb 4, 2026 Bedrock API changelog.

The issue description's proposed _prepare_output_config() has two problems in the generated shape:

1. Missing structure wrapper — the correct nesting is textFormat -> structure -> jsonSchema, not textFormat -> jsonSchema.

2. Wrong type string — the correct value is "json_schema" (underscore), not "jsonSchema" (camelCase).

The correct wire format is:

{
  "outputConfig": {
    "textFormat": {
      "type": "json_schema",
      "structure": {
        "jsonSchema": {
          "name": "output_schema",
          "schema": "{...}"
        }
      }
    }
  }
}

My implementation plan accounts for both of these. I'll follow the 4-step approach:

1. Remove the response_format: None override
2. Generate _prepare_output_config() with the correct structure
3. Wire it into _prepare_options()
4. Populate ChatResponse.value in _build_response()

I’ll also add unit tests covering:

• correct wire shape
• JSON string serialization
• no-op path behavior

Happy to open a draft PR shortly.