OptionalagentAgent run ID for tracing
OptionalOnCalled with the rerank's run step as soon as it is created, so the agent can add it to its run's
steps. When the rerank finishes, the step's PromptRun is the rerank's MJ: AI Prompt Runs row,
whose TotalCost and token rollups include a prompt-backed reranker's own prompt runs, so the
agent run's cost and token totals, and its MaxCostPerRun / MaxTokensPerRun guardrails, count
the rerank.
OptionalparentParent step ID for hierarchical step logging
OptionalstepStep sequence number
Options for observability integration.