test(eve): hold busy-worker until steering begins

[ruiconti]

Summary

The busy-worker eval can miss the state it intends to test: in the failed run, the child completed before the later continuation arrived. Hold the child at an approval gate and wait until that gate is visible before steering it. The eval then checks that steering cancels the held task and completes a replacement on the same agent, without relying on the five-second delay.

Extracted from #3073; this fixture fix is independent of workflow authorization.

Validation

• pnpm typecheck: 44 tasks passed, including building and typechecking fixture-tasks.
• pnpm --filter fixture-tasks validate:transitions: 19 declarations passed.
• pnpm fmt and pnpm lint passed.
• E2E execution is CI-only; the extracted branch needs its own CI run.

Checklist

• This change was requested or approved by a maintainer
• I ran the relevant checks from CONTRIBUTING.md
• I added tests and documentation where relevant
• I added a changeset if this touches the published eve package
• DCO sign-off passes for every commit (git commit --signoff)

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Project	Deployment	Actions	Updated
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