feat(together): add Braintrust tracing for the Together AI Go SDK

[Atharva Mhaske (atharvamhaske)]

Summary

• Adds a new trace/contrib/togethercomputer/together integration for the official Together AI Go SDK (github.com/togethercomputer/together-go), covering Chat.Completions.New/NewStreaming, Completions.New, and Embeddings.New
• Together's client is Stainless-generated with the same option.WithMiddleware() extension point as openai-go/anthropic-sdk-go, so this follows trace/contrib/openai's middleware pattern directly
• chatcompletions.go — traces Chat Completion spans, both streaming and non-streaming; streaming responses accumulate delta content/tool calls into one merged choice, matching the non-streaming shape
• completions.go — traces together.completions.create spans
• embeddings.go — traces together.embeddings.create spans; output is a count + dimension summary, not the raw vectors
• Orchestrion — auto-instruments together.NewClient by appending option.WithMiddleware(...) to its variadic options
• Examples — examples/internal/together

Changes

• trace/contrib/togethercomputer/together/ — new module (tracetogether.go, chatcompletions.go, completions.go, embeddings.go, orchestrion.go, orchestrion.yml, tests)
• examples/internal/together/ — new example
• examples/go.mod, go.work, scripts/nested_modules.txt — registered the new module
• trace/contrib/all/ — registered together in the meta-module and regenerated orchestrion.yml
• trace/contrib/orchestrion_test.go — added together to the fixture's local replace-directive map and the "individual" import list
• trace/contrib/testdata/orchestrion/ — added TestTogether
• internal/genorchestrion/genorchestrion_test.go — bumped expected aspect count 18 → 19 (1 new: together-newclient-middleware)

Notes

• The originating issue cites together-go v0.10.0; verified against the real upstream repo that current latest is v0.12.0 (no import-path break, just a version bump).
• Blocker: no VCR cassettes recorded yet. Together AI requires a funded account for real API access, which isn't available in this environment. All test/build/lint steps pass except the 5 tests that need a recorded cassette (TestChatCompletion, TestChatCompletionStreaming, TestCompletion, TestEmbeddings, and the orchestrion fixture's TestTogether) — these currently fail with "requested cassette not found". A partial run against a real (but unfunded) key confirmed the wiring itself is correct: requests reach api.together.ai with the right path/shape and the orchestrion-injected middleware fires, they just get rejected with a genuine 401 invalid_api_key rather than any compile/injection error.
• Whoever has a funded TOGETHER_API_KEY needs to run VCR_MODE=record go test ./... in trace/contrib/togethercomputer/together and trace/contrib/testdata/orchestrion (-run TestTogether) before this can merge. Opened as a draft for that reason.
• make lint and go build ./... clean locally; go vet clean.

Closes #142

[chatgpt-codex-connector]

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[Atharva Mhaske (atharvamhaske)]

Abhijeet Prasad (@AbhiPrasad) now CI on this PR will be red until real cassettes are recorded and pushed, as you wanted. PTAL and LMK