Add `wait_for_new_round` to Creator trait to eliminate round-change polling

[bagelface]

Background

The orchestrator's run loop currently polls get_payload_and_round() in a tight loop (with a 2s sleep) after executing a round, waiting for on-chain state to advance before starting the next round. This is a consequence of Creator only exposing a snapshot API — the orchestrator has no way to block until the round actually changes.

Problem

The polling approach has a few downsides:

• It requires the orchestrator to maintain a HashSet<u64> of executed rounds to avoid re-broadcasting Start for the same round
• The 2s poll interval is an arbitrary constant — too short wastes calls to the provider, too long adds latency to the start of the next round
• The orchestrator is doing work that semantically belongs to the Creator

Proposed Change

Add a wait_for_new_round(current: u64) -> Result<(Vec<u8>, u64)> method to the Creator trait that blocks until the round advances past current:

pub trait Creator {
    type TaskData;

    async fn get_payload_and_round(&self) -> Result<(Vec<u8>, u64)>;
    async fn wait_for_new_round(&self, current: u64) -> Result<(Vec<u8>, u64)>;
    fn get_task_metadata(&self) -> Self::TaskData;
}

The orchestrator's post-execution path then becomes:

// After successful execution:
executed_round = current_round;
// inner loop drains until continue_time as normal, then:
let (payload, current_round) = self.task_creator.wait_for_new_round(executed_round).await?;
// guaranteed fresh round, no HashSet needed

CounterCreator (and other implementations) can implement this by polling the provider internally with appropriate backoff, keeping that logic out of the orchestrator.

Benefits

• Eliminates executed_rounds: HashSet<u64> from the orchestrator
• Eliminates the 2s polling constant
• Correct by construction — the orchestrator cannot re-execute the same round because it blocks until a new one is available
• Provider polling strategy (interval, backoff) lives in the Creator implementation where it has context about the underlying data source

Related

Introduced as a follow-up to the fix in #[PR for bagelface/fix-retrigger-after-threshold-bug].

[bagelface]

Wired into gas-killer/roadmap#10 (Aggregation Speed) with latency + priority:medium. Notes from an audit against current code:

• Latency relevance is narrower than a critical-path fix. The 2s poll sleep (types.rs:155-163) only gates the idle inter-round start when a chain-polling creator keeps returning an already-executed round; the aggregate→execute path itself exits immediately via the break at types.rs:332. The production path uses the blocking ingress/listening creator (get_payload_and_round blocks on wait_for_task), so this mainly affects the basic CounterCreator. Probably better framed as a responsibility-placement cleanup that also trims idle next-round latency, rather than an in-flight aggregation win — and arguably priority:low.
• Overlaps Decouple the round-abandon timeout from the Start re-broadcast cadence in the orchestrator #164/Allow the orchestrator aggregation window to be driven by a runtime provider instead of a static Duration #165, which rework the same outer/inner round loop (Decouple the round-abandon timeout from the Start re-broadcast cadence in the orchestrator #164 proposes event-driven Start re-broadcast "only on a new task/block," which substantially covers this polling concern). These three should be sequenced/coordinated to avoid conflicting rewrites.
• The "Related" line is an unfilled placeholder; the originating fix was PR fix: unblock queued-task throughput in orchestrator loop (break after execution) #159 (bug report Orchestrator caps throughput at 1 round per aggregation_frequency under queued load (missing break after successful execution) #158), which introduced the executed_rounds + 2s-sleep mechanism this issue targets.
• For epic parity, Decouple the round-abandon timeout from the Start re-broadcast cadence in the orchestrator #164/Allow the orchestrator aggregation window to be driven by a runtime provider instead of a static Duration #165 each carry a "Part of gas-killer/roadmap#10" line + an Impact/Effort/Risk block; Add wait_for_new_round to Creator trait to eliminate round-change polling #153 has neither.