test(runtime): wait for sandbox boundary requests by deadline

[mikemikimike]

Summary

Fixes #4383

The sandbox-boundary test helper now waits until a bounded 5-second deadline instead of polling a fixed 100 macrotask ticks. It still polls without changing production behavior, but filesystem setup that takes longer than the old tick budget no longer flakes solely because of scheduler timing.

Verification

• npm run build:test
• node --test packages/runtime/dist/__tests__/tool-runtime-sandbox-boundary.test.js (15 passed)
• npm run lint
• npm run format:check
• npm run typecheck
• npm run build
• git diff --check
• npm test was run; the full matrix reports Windows-only Rive/remote-access/SQLite failures and workspace timeouts in unrelated suites. The changed sandbox-boundary test passes independently.

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Codex authored the focused test-helper change and validation commands. The commit includes the required Generated-by: Codex trailer.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

[mikemikimike]

Withdrawing this PR after verifying that #4383 had already been claimed and assigned before this PR was prepared. No maintainer action is needed on this duplicate contribution.