Migrated openai instrumentation to new integration API

[delner]

Purpose

This PR migrates the OpenAI instrumentation from a monolithic implementation (lib/braintrust/trace/contrib/openai.rb) to the new Integration API framework. By putting this behind a consistent programmatic interface, it will help facilitate the implementation of auto-instrumentation.

Architectural Overview

The new integration uses a three-layer architecture:

Integration → Patcher(s) → Instrumentation Modules

1. Integration (lib/braintrust/contrib/openai/integration.rb)

• Defines metadata: gem names, version requirements, detection logic
• Implements instrument! for high-level API
• Delegates to one or more Patchers

2. Patcher (lib/braintrust/contrib/openai/patcher.rb)

• ChatPatcher - Patches chat.completions methods
• ResponsesPatcher - Patches responses API (new OpenAI feature)
• Thread-safe via per-patcher mutex
• Handles both class-level and instance-level patching

3. Instrumentation Modules (lib/braintrust/contrib/openai/instrumentation/)

• Chat::Completions - Wraps create(), stream(), stream_raw()
• Responses - Wraps responses API methods
• Common - Shared utilities for parsing usage, aggregating streams

The instrumentation modules use Module#prepend to wrap methods, creating OpenTelemetry spans with input/output/metrics attributes.

Usage Examples

Class-level instrumentation (all clients):

require "braintrust"
require "openai"

Braintrust.init
Braintrust.instrument!(:openai)

# All OpenAI::Client instances are now traced
client = OpenAI::Client.new
client.chat.completions.create(...)  # Automatically traced

Instance-level instrumentation (specific client):

require "braintrust"
require "openai"

Braintrust.init

client_traced = OpenAI::Client.new
client_untraced = OpenAI::Client.new

# Only instrument the specific client
Braintrust.instrument!(:openai, target: client_traced)

client_traced.chat.completions.create(...)    # ✓ Traced
client_untraced.chat.completions.create(...)  # ✗ Not traced

Files Changed

• Removed: lib/braintrust/trace/contrib/openai.rb (611 lines) - Monolithic implementation
• Added: Modular structure under lib/braintrust/contrib/openai/:
  • integration.rb - Integration metadata and discovery
  • patcher.rb - ChatPatcher and ResponsesPatcher classes
  • instrumentation/chat.rb - Chat completions instrumentation
  • instrumentation/responses.rb - Responses API instrumentation
  • instrumentation/common.rb - Shared utilities
• Added: Comprehensive test coverage with VCR cassettes for streaming and responses API

[realark]

ran this branch in sdk-test: https://github.com/braintrustdata/braintrust-sdk-test/pull/23