Fix Kotlin coroutine context loss during thread handoffs

[amarziali]

What Does This Do

Kotlin coroutines can resume on another worker before the previous worker restores its context. This can lose the active span and leave manual scopes unclosed.

Give each coroutine an isolated, movable scope stack so late restoration cannot overwrite newer context.

flowchart LR
  A["Worker A suspends with active scopes"]
  B["Worker B resumes using the same scope stack"]
  C["Worker A restores its previous worker context"]
  D["Worker B retains the coroutine's active scopes"]

  A --> B --> C --> D
  linkStyle 0,1,2 stroke:#289447

Loading

Add deterministic regression coverage for overlapping callbacks, nested scopes, and closed scopes staying closed.

Validation: 807 test executions passed across JDK 8 and 17, covering coroutine versions 1.3.0, 1.6.4, 1.8.1, and 1.11.0. Muzzle and formatting checks passed.

Motivation

Additional Notes

Contributor Checklist

• Format the title according to the contribution guidelines
• Assign the type: and (comp: or inst:) labels in addition to any other useful labels
• Avoid using close, fix, or any linking keywords when referencing an issue
  Use solves instead, and assign the PR milestone to the issue
• Update the CODEOWNERS file on source file addition, migration, or deletion
• Update public documentation with any new configuration flags or behaviors
• Once approved, use merge queue to merge the PR

Jira ticket: [PROJ-IDENT]

[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	13.90 s	13.90 s	[-0.8%; +0.9%] (no difference)
startup:insecure-bank:tracing:Agent	12.78 s	12.89 s	[-1.7%; -0.1%] (maybe better)
startup:petclinic:appsec:Agent	17.07 s	17.06 s	[-0.8%; +1.0%] (no difference)
startup:petclinic:iast:Agent	16.97 s	17.01 s	[-1.0%; +0.6%] (no difference)
startup:petclinic:profiling:Agent	16.61 s	16.76 s	[-1.8%; +0.1%] (no difference)
startup:petclinic:sca:Agent	17.06 s	17.01 s	[-0.5%; +1.2%] (no difference)
startup:petclinic:tracing:Agent	16.01 s	16.26 s	[-2.6%; -0.5%] (maybe better)

Commit: 408e4b33 · CI Pipeline · Benchmarking Platform UI

---

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

[mcculls]

Note my followup Kotlin PR is not yet merged - at first glance it basically does the same thing as this PR

[amarziali]

closing as the linked PR is effectively not yet in master