fix(instrumentation): preserve context attributes in async coroutine decorators (#3583) - #3662

Why

contextlib.ContextDecorator runs its __exit__ as soon as the decorated call returns. For an async def function or a generator function, that call only builds the coroutine or generator object, so OpenInference context attributes detached before the body ran. Issue #3583 reports the coroutine case.

_UsingAttributesContextManager now owns the decorator protocol and handles each kind of callable. A coroutine attaches when the body starts. A generator body runs each step under a rolling OpenTelemetry context.

Scope

• Drop contextlib.ContextDecorator as the base class. __call__ routes async generator functions, generator functions, coroutine functions, and plain functions.
• Add _RollingOtelContext, _drive_sync_generator_in_rolling_otel, and _AwaitRollingOtelStep. Each generator invocation gets its own rolling context. After every successful body step, the saved context becomes get_current(), so a span the body holds across yield stays current when the body resumes.
• Isolate only OpenTelemetry state. An earlier revision used one contextvars.copy_context() snapshot per generator, which froze every application ContextVar for the life of the generator. That snapshot is gone.
• Keep one attach token per decorated invocation in a wrapper local. One decorator instance serves every call of the function it wraps, so a token on self would break concurrent and re-entrant calls. Only with and async with still store self._token.
• Restore _context_with_attributes, the expanded using_* docstrings, and the corrected version / variables keywords in the using_prompt_template example.
• Add the README decorator section and examples/async_context_attribute_decorators.py, with the matching mypy exclude in pyproject.toml.

The PR does not include the unrelated Anthropic token-count change from the original branch.

Tradeoffs

The generator drivers forward send, throw, close, asend, athrow, and aclose by hand, which is more code than yield from. The gain is that a generator body keeps its attributes and its open span across yield while application ContextVar values stay on the caller's live map.

Blast Radius

The change affects Python callers that use a using_* helper as a decorator. Context-manager behavior is unchanged. Sync decorators keep their existing semantics and additionally survive re-entrant calls. Generator decorators gain attribute and span scoping that the stdlib decorator never provided.

Verification

• The issue reproduction returned {'session.id': 'async-session'}. Main returned {}.
• py310-ci-instrumentation on tests/test_context_managers.py passed Ruff formatting, Ruff lint, strict mypy, and 39 tests.
• New tests cover live ContextVar updates across yield for sync and async generators, a body-owned ContextVar surviving resume, a consumer span between yields not becoming the parent of body spans, and an abandoned generator running its finally with attributes attached.
• Ported tests cover attributes in the body but not the consumer, span parentage across yield, bidirectional send / throw / asend / athrow / aclose, re-entrant sync decorators, concurrent coroutine calls, exception detach, and using_session stacked above tracer.agent.