Tighten _installed_instrumentors typing once OpenInference publishes a common base

[Freezaa9]

Background

otel_lifecycle.py (PR #601) declares _installed_instrumentors: list[Any] and def attach_instrumentor(instrumentor: Any) -> None. CodeRabbit suggested a Protocol-typed list during review and the orchestrator deferred:

The four OpenInference instrumentors we attach (LangChainInstrumentor, GuardrailsInstrumentor, VertexAIInstrumentor, MCPInstrumentor) come from separate packages with no shared base class — Any is honest about the FFI boundary. A Protocol would add maintenance burden against four packages that may evolve independently.

Trigger

Open this issue when OpenInference publishes a common Instrumentor base class (or a stable Protocol) across its instrumentor packages — at which point this trade-off flips.

Fix when triggered

from typing import Protocol

class Instrumentor(Protocol):
    def instrument(self, tracer_provider: TracerProvider) -> None: ...
    def uninstrument(self) -> None: ...

_installed_instrumentors: list[Instrumentor] = []

def attach_instrumentor(instrumentor: Instrumentor) -> None: ...

Watch out for instrumentor variants that accept **kwargs in instrument(...) — the Protocol may need to be loosened.

References

• CodeRabbit review on PR feat(engine): standalone v1 traces — prep PR (lifecycle helper + user.id) #601 (nitpick, marked 💤 Low value).
• Defer rationale on PR comment: feat(engine): standalone v1 traces — prep PR (lifecycle helper + user.id) #601 (search "Protocol for _installed_instrumentors").

🤖 Filed during PR #601 wrap-up.