/** W3C Trace Context headers, exported to a child as TRACEPARENT and TRACESTATE. */
export interface FabricTraceContextV1 {
    traceparent: string;
    tracestate?: string;
}
/** The launch a trace context is requested for. */
export interface FabricChildTraceContextLaunch {
    /** The outer tool call (normally `fabric_exec`) that started the child; absent for actor turns. */
    parentToolCallId?: string;
    /** The nested `agents.*` call, as carried by its audit and proxied `tool_result`. */
    nestedToolCallId?: string;
    /** Absent when a durable resident host mints the id after the request leaves the session. */
    runId?: string;
    runner: string;
    name: string;
}
/**
 * Host-local synchronous request emitted before each child launch and
 * relaunch. The first valid `reply` made before the listener's first await
 * wins; with none, the child keeps the environment it would inherit.
 */
export interface FabricChildTraceContextRequestV1 extends FabricChildTraceContextLaunch {
    version: 1;
    reply: (context: FabricTraceContextV1) => void;
}
/**
 * Only the two headers, in their wire grammar: a reply reaches a child's
 * environment, so it can never name another variable or span a line.
 */
export declare const readTraceContext: (value: unknown) => FabricTraceContextV1 | undefined;
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