[bot] Add instrumentation for AWSSDK.BedrockAgentRuntime (Amazon Bedrock Agents execution)

[braintrust-bot]

Summary

The AWSSDK.BedrockAgentRuntime NuGet package (v4.0.10.2, ~1.6M total downloads, updated 2026-06-22) is the official AWS SDK for executing Amazon Bedrock Agents in .NET. It is entirely distinct from the already-filed AWSSDK.BedrockRuntime (foundation model invocation): BedrockAgentRuntime targets the agent-execution, flow-execution, and retrieval-augmented generation surfaces of Bedrock, not raw model calls. None of its execution surfaces are instrumented in this SDK.

Execution surfaces missing instrumentation

• Agent invocation: AmazonBedrockAgentRuntimeClient.InvokeAgentAsync — execute a configured Bedrock Agent with a prompt; returns streaming chunks with optional trace data
• Inline agent invocation: InvokeInlineAgentAsync — execute an agent with inline configuration (no pre-configured agent required)
• Flow execution: InvokeFlowAsync / StartFlowExecutionAsync — invoke a Bedrock Flow and receive streaming node outputs
• Retrieval-augmented generation: RetrieveAndGenerateAsync / RetrieveAndGenerateStreamAsync — query a knowledge base and generate a grounded response using a foundation model
• Knowledge base retrieval: RetrieveAsync — query a Bedrock Knowledge Base and return relevant passages

Braintrust docs status

• Status: not_found — The Braintrust Bedrock integration page covers TypeScript, Go, and Java instrumentation but has no .NET/C# SDK-level instrumentation for either BedrockRuntime or BedrockAgentRuntime
• No AWSSDK.BedrockAgentRuntime-specific instrumentation is documented or referenced in Braintrust docs

Upstream sources

• NuGet: https://www.nuget.org/packages/AWSSDK.BedrockAgentRuntime (v4.0.10.2)
• API reference: https://docs.aws.amazon.com/sdkfornet/v3/apidocs/items/BedrockAgentRuntime/TBedrockAgentRuntimeClient.html
• Agents for Amazon Bedrock docs: https://docs.aws.amazon.com/bedrock/latest/userguide/agents.html
• GitHub (aws-sdk-net): https://github.com/aws/aws-sdk-net
• Recent changelog: InvokeAgentAsync extended with AgenticRetrieveStream API (June 2026), multimodal KB retrieval (December 2025), enhanced flow trace output (September 2025)

Local repo files inspected

• src/Braintrust.Sdk.OpenAI/ — instruments OpenAI SDK only
• src/Braintrust.Sdk.Anthropic/ — instruments Anthropic SDK only
• src/Braintrust.Sdk.AgentFramework/ — instruments Microsoft.Extensions.AI.IChatClient middleware only
• src/Braintrust.Sdk.AzureOpenAI/ — instruments Azure.AI.OpenAI only
• Grep for BedrockAgentRuntime, InvokeAgent, and AmazonBedrockAgentRuntimeClient across the entire repo returned zero results

Relationship to existing issue #40

Issue #40 covers AWSSDK.BedrockRuntime (ConverseAsync, InvokeModelAsync). This issue covers the separate AWSSDK.BedrockAgentRuntime package, which uses a completely different client class (AmazonBedrockAgentRuntimeClient) and targets agent orchestration execution rather than direct foundation model invocation.