fix(benchmarks): wait for scripted event delivery

[salman1993]

Why

The Buzz-native runtime could stop a solo agent after one turn even when a scripted follow-up event was queued or already running. That could turn a harness timing race into a benchmark failure.

Follow-up to #6448.

What

• Treat solo tasks with scripted events separately from ordinary one-turn tasks.
• Wait until turn counts and authored message IDs remain idle and unchanged for several polls before stopping the agent.
• Remove the message-count shortcut that could stop an active turn.
• Add focused regressions for a delayed follow-up turn and an already-running turn with a DONE: message.

Testing

• pytest -q tests/test_container_runtime.py -k "solo_turn_end or scripted_events" — 3 passed
• ruff check on the three touched Python files
• ruff format --check on the three touched Python files
• Local buzz-native-solo-luna.yaml Harbor run, one attempt per affected task:
  • cross-thread-requests — reward 1.0; all 6 task-specific checks passed
  • interleaved-agent-reports — reward 1.0; all 7 task-specific checks passed
  • 2 completed trials, 0 exceptions, 56 seconds total

Risk

Low. This only changes completion detection for solo benchmark tasks with scripted events. Ordinary solo tasks retain immediate completion after their first turn ends.

---

Update Aug 21, 13:07 EDT: Replaced the fixed settle delay with exact delivery receipts after review feedback.

• ACP now records the event IDs delivered by each completed turn; the runtime also recognizes existing successful-steer receipts.
• Scripted trials stop only after every expected event ID is acknowledged and no turn is active. Missing receipts wait for the trial budget instead of producing partial evidence.
• TDD regression delayed delivery beyond the old five-poll boundary and failed before the implementation; the receipt parser and Rust receipt format are pinned independently.
• Focused verification: 31 container-runtime tests passed, 6 ACP delivery tests passed, plus Ruff, rustfmt, and Clippy.
• Receipt-gated Luna run: 2 completed trials and 0 exceptions. interleaved-agent-reports scored 1.0. cross-thread-requests completed both calculations and thread isolation but Luna omitted the user mention on ALPHA, so that model-output dimension scored 0.
• Risk remains low: the ACP production change adds delivery receipt logging and restores a missing turn-end log on a completed-before-control race; it does not change queue dispatch behavior.

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[philazar]

lgtm. Agent reviewer found no bugs and I didnt find anything either

[wpfleger96]

Reviewed the exact head and traced the receipt contract through the benchmark runtime, completed-batch delivery accounting, the completed-before-control race, and successful non-cancelling steer acknowledgments. The scripted-event gate now requires every expected event receipt plus a terminal turn, while ordinary solo tasks keep the existing first-turn completion behavior. CI is green, and a mutation run that restored the premature ends > 0 shortcut failed both new regressions (2 failed, 85 passed), confirming the tests observe the fix at the intended seam.