[Enhancement]: Add Go (v2) example: Converse API with extended/adaptive thinking (Bedrock Runtime)

[vizvasrj]

Background story

The Bedrock Runtime docs for extended thinking and adaptive thinking
(https://docs.aws.amazon.com/bedrock/latest/userguide/claude-messages-extended-thinking.html
and .../claude-messages-adaptive-thinking.html) only include CLI, Python,
and TypeScript code snippets. There's no Go (v2) example anywhere in the
docs or in this repo's gov2/bedrock-runtime folder showing how to enable
thinking through the Converse API or how to parse the resulting
reasoningContent block from the response.

I had to reverse-engineer the correct approach from the generated SDK
type definitions on pkg.go.dev rather than from any example, which is
error-prone (union member names, pointer vs. value fields, etc. aren't
obvious without a working reference). A canonical Go example would save
other Go developers the same trial and error.

What does this example accomplish?

Shows how to call the Converse API with thinking enabled on a Claude
model on Bedrock, and how to read the reasoning content back out of the
response alongside the normal text block. Specifically it should cover:

1. Setting additionalModelRequestFields via the bedrockruntime/document
   package to enable thinking (both the newer adaptive mode with an
   effort level, and the older manual mode with budget_tokens, since
   support differs by model).
2. Setting InferenceConfig.MaxTokens appropriately alongside thinking.
3. Parsing types.ContentBlockMemberReasoningContent out of the response
   message content, distinct from types.ContentBlockMemberText.
4. A note on when ConverseStream is required instead of Converse (e.g.
   once MaxTokens exceeds the streaming threshold).

Which AWS service(s)?

Amazon Bedrock Runtime (Converse API)

Which AWS SDKs or tools?

• All languages
• .NET
• C++
• Go (v2)
• Java
• Java (v2)
• JavaScript
• JavaScript (v3)
• Kotlin
• PHP
• Python
• Ruby
• Rust
• Swift
• Not applicable

Are there existing code examples to leverage?

• gov2/bedrock-runtime already has a basic ConverseClaude example
  (text-only, no thinking) that this could extend or sit alongside:
  https://docs.aws.amazon.com/code-library/latest/ug/go_2_bedrock-runtime_code_examples.html
• The Python and TypeScript snippets on the adaptive thinking doc page
  show the shape of the additionalModelRequestFields payload, just not
  in Go:
  https://docs.aws.amazon.com/bedrock/latest/userguide/claude-messages-adaptive-thinking.html

Do you have any reference code?

thinkingConfig := document.NewLazyDocument(map[string]interface{}{
	"thinking": map[string]interface{}{
		"type":   "adaptive",
		"effort": "high",
	},
})

input := &bedrockruntime.ConverseInput{
	ModelId:  aws.String("us.anthropic.claude-opus-4-6-v1"),
	Messages: []types.Message{message},
	InferenceConfig: &types.InferenceConfiguration{
		MaxTokens: aws.Int32(16000),
	},
	AdditionalModelRequestFields: thinkingConfig,
}

response, err := client.Converse(ctx, input)
if err != nil {
	log.Fatalf("Error calling model: %v", err)
}

if msg, ok := response.Output.(*types.ConverseOutputMemberMessage); ok {
	for _, block := range msg.Value.Content {
		switch v := block.(type) {
		case *types.ContentBlockMemberReasoningContent:
			if rt, ok := v.Value.(*types.ReasoningContentBlockMemberReasoningText); ok {
				fmt.Println("--- Thinking ---")
				fmt.Println(aws.ToString(rt.Value.Text))
			}
		case *types.ContentBlockMemberText:
			fmt.Println(v.Value)
		}
	}
}