test(agents-core): stabilize leak detection harness

[wsk-builds]

This pull request fixes the flaky leak-detection harness used by packages/agents-core/test/result.test.ts.

The previous regression checks spawned separate Node processes and asserted on stdout, which made the harness brittle under coverage and worker execution. This change keeps the manual scripts runnable from the CLI, but refactors them into importable helpers with structured results so the Vitest suite can assert directly.

It also adds a shared gcRuntime test helper that lazily exposes gc inside the worker when Node was not launched with --expose-gc, and adds the required patch changeset for @openai/agents-core.

Validation notes:

• Passed: pnpm vitest run packages/agents-core/test/result.test.ts --reporter=dot
• Passed: pnpm vitest run packages/agents-core/test/result.test.ts --coverage --reporter=dot
• Passed: node --expose-gc --import tsx packages/agents-core/test/manual/streamedRunResultLeakCheck.ts
• Passed: node --expose-gc --import tsx packages/agents-core/test/manual/streamedRunResultLeakStress.ts with the reduced stress env from the test
• Passed: pnpm -F @openai/agents-core build-check
• Passed: pnpm -F @openai/agents-core dist:check
• Passed: pnpm lint
• Full bash .agents/skills/code-change-verification/scripts/run.sh still stops on packages/agents-core/test/logger.test.ts, which times out during the full pnpm test run under load. That test was not changed in this branch.

[changeset-bot]

🦋 Changeset detected

Latest commit: 27750bd

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@openai/agents-core	Patch
@openai/agents-extensions	Patch
@openai/agents-openai	Patch
@openai/agents-realtime	Patch
@openai/agents	Patch

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