Fix Docker sandbox exec for AgentBeats runtime

[Yiminnn]

Summary

• disable pseudo-TTY allocation for Docker sandbox exec commands with
• keep multi-service exec behavior intact
• unblocks SkillsBench AgentBeats worker runs from nested/non-interactive runners

Verification

• ...... [100%]
  6 passed in 0.25s
• .........sss.....ssssssssss..s....................... [100%]
  39 passed, 14 skipped in 0.30s

This branch is used by via a pinned commit for the AgentBeats runtime image.

---

[Yiminnn]

This branch is now the BenchFlow dependency for SkillsBench AgentBeats runtime-first smoke.

Evidence:

• Head: d64cad1
• CI test workflow is green: https://github.com/benchflow-ai/benchflow/actions/runs/26316233825
• Local full suite: 1343 passed, 30 skipped, 1 deselected.
• Focused local check: Docker sandbox service exec tests passed with compose exec -T.
• SkillsBench live AgentBeats run using the runtime fix completed without sandbox infra failures: https://github.com/benchflow-ai/skillsbench-leaderboard/actions/runs/26315996067

The functional runtime fix remains the Docker compose exec -T change; the latest commit only updates a scene metadata test fixture for the A2A role metadata already emitted by the SDK.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 6 additional findings.