[bot] Bedrock Converse `reasoningContent` blocks not normalized — extended thinking traces break UI schema

Bắt đầu trong braintrust-sdk/src/main/java/dev/braintrust/instrumentation/InstrumentationSemConv.java, đọc tagBedrockRequest, tagBedrockResponse và normalizeBedrockMessage quanh các dòng 339–501. Sau đó kiểm tra BraintrustAWSBedrockTest.java và bổ sung coverage cho một reasoningContent block của Bedrock. Hoàn tất khi reasoningContent được chuẩn hóa với kiểu mong đợi, vẫn giữ nguyên nội dung của nó, và việc xử lý block hiện có vẫn nguyên vẹn.

<!-- provider-gap-audit: bedrock-reasoningcontent-not-normalized -->

Summary

InstrumentationSemConv.normalizeBedrockMessage() — the function that normalizes Bedrock Converse content blocks so they carry an explicit "type" field the Braintrust UI schema requires — recognizes text, toolUse, toolResult, and image blocks, but does not recognize reasoningContent, the official Bedrock Converse block type for extended thinking / Chain-of-Thought output (Claude 3.7+ and Amazon Nova reasoning models via additionalModelRequestFields.reasoning_config).

This is the same code path issue #85 describes as working correctly for tool use ("Non-streaming Converse calls handle tool use correctly — normalizeBedrockMessage() ... already recognizes toolUse, toolResult, and image"), but that issue is scoped to the streaming (ConverseStream) tool-use path and does not mention reasoningContent at all — this is a distinct gap in the shared, non-streaming-safe normalization helper used by both request and response tagging.

What is missing

In braintrust-sdk/src/main/java/dev/braintrust/instrumentation/InstrumentationSemConv.java, normalizeBedrockMessage() (lines 467–501):

if (block.has("text")) {
    normalized.put("type", "text");
    changed = true;
} else if (block.has("toolUse")) {
    normalized.put("type", "tool_use");
    changed = true;
} else if (block.has("toolResult")) {
    normalized.put("type", "tool_result");
    changed = true;
} else if (block.has("image")) {
    normalized.put("type", "image");
    changed = true;
}

There is no else if (block.has("reasoningContent")) branch. When a Bedrock Converse (or ConverseStream, once #85 is fixed) response contains a reasoningContent block ({"reasoningContent": {"reasoningText": {"text": "...", "signature": "..."}}}), it is left without a type field — unlike every sibling content-block type in the same array — so it doesn't match the schema the UI validates against for thread rendering (per this same method's own doc comment: "both the OpenAI and Anthropic schemas the UI validates against require an explicit type field").

This function is shared by both:

• tagBedrockRequest() (line 389: inputArray.add(normalizeBedrockMessage(msg))) — affects multi-turn conversations that echo back a prior assistant reasoningContent block (required by some models to preserve the reasoning trace across turns)
• tagBedrockResponse() (line 408: outputArray.add(normalizeBedrockMessage(message))) — affects the model's own reasoning output on the current turn

Braintrust docs status

unclear — the Braintrust docs list Bedrock as a supported provider (https://www.braintrust.dev/docs/integrations/ai-providers) but do not specifically document extended-thinking/reasoning content handling for Bedrock Converse.

Upstream sources

• AWS Bedrock Converse API — reasoningContent block, part of the ContentBlock union: https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_ContentBlock.html
• Amazon Nova extended reasoning guide (documents reasoningContent/reasoningText response shape): https://docs.aws.amazon.com/nova/latest/userguide/extended-thinking.html
• Using Claude 3.7 Sonnet extended thinking via the Bedrock Converse API (additionalModelRequestFields.reasoning_config, response reasoningContent): https://seobs.medium.com/using-sonnet-3-7-reasoning-with-the-converse-api-on-aws-bedrock-6c838c685ad9

Local files inspected

• braintrust-sdk/src/main/java/dev/braintrust/instrumentation/InstrumentationSemConv.java — lines 339–429 (tagBedrockRequest/tagBedrockResponse), lines 460–501 (normalizeBedrockMessage: only text/toolUse/toolResult/image handled)
• braintrust-sdk/instrumentation/aws_bedrock_2_30_0/src/test/java/dev/braintrust/instrumentation/awsbedrock/v2_30_0/BraintrustAWSBedrockTest.java — no test exercises a reasoning/extended-thinking model response
• Confirmed via issue #85 that this shared helper is treated as the "correct" reference implementation for non-streaming content-block normalization, but it does not cover reasoningContent