Describe the bug

When using the opentelemetry-ktor plugin, Spans start to have a wrong parent context after some requests.
This only happens if the Ktor client is used within a route or when withContext with a explicit dispatcher is used.

Steps to reproduce

Create a ktor server project with ktor 3.4.1 and add the opentelemetry plugin (Default configuration works).
Add a route that either invokes a ktor client or uses withContext with any Dispatcher.
Call it a few times (on my machine it seems to happen after 12 successful invocations, might depend on the eventLoop threadpool size).

Expected behavior

Every server route invocation creates a separate span.

Actual behavior

After the initial working calls, at some point spans start having a wrong parent context, leading to nesting or spans being missing if their parent span was dropped by a custom sampler.

Javaagent or library instrumentation version

opentelemetry-ktor-2.25.0-alpha

Environment

JDK: Temurin 21.0.10
OS: macOS 26.3.1 and Amazon Linux 2023 (latest)

Additional context

This might be related to this: #14763

The issue does not appear with the latest ktor version, potentially due to a change of the event loop dispatcher from Unconfined here: ktorio/ktor#5364

I am not entirely sure if this issue is caused by ktor or this library but I assume the cause is in this library since it seems to be related to a context from a previous call leaking to the current one.

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