[Abhijeet Prasad (AbhiPrasad)]

🤖 This text was AI-generated.

With BRAINTRUST_OTEL_COMPAT=true, async frameworks such as LangGraph can start a span in one asyncio task and end it in another. Each task runs in its own contextvars.Context, so the token saved when the span became current belongs to a different Context than the one ending it:

task A (Context 1)             task B (Context 2)
on_chain_start                 on_chain_end
  span.set_current()             span.unset_current()
    token = attach(ctx)            context.detach(token)
                                     -> ValueError (other Context)
                                     -> OTel logs it at ERROR

OpenTelemetry's context.detach() catches that ValueError itself and logs "Failed to detach context" with a traceback. Nothing reaches Braintrust, so the except ValueError guard in the LangChain callback handler never ran. Every such run printed an ERROR, even though span parenting was correct (#1062).

The OTel ContextManager now resets OTel's default contextvars token directly instead of calling context.detach():

try:
    token.var.reset(token)
except ValueError:
    # token came from another Context; leave both contexts as-is
    log.debug(...)
except Exception:
    log.exception("Failed to detach context")

• A token from another Context is logged at DEBUG. Neither context is changed, so an unrelated span that is active where the run ends stays current.
• Other failures, such as reusing a token, are still logged at ERROR and not raised, same as before.
• Tokens from other OTel runtime implementations still go through context.detach().

The dead try/except ValueError around span.unset_current() in the LangChain handler is removed, since unset_current() never raises.

Limitation: the Context where the span started still treats the ended span as current. BraintrustContextManager skips ended spans when it looks up the current one; the OTel manager does not yet.

Fixes #1062

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-05T04:05:09.314615Z	c816ac5	PR opened

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