export interface SessionCap {
    tasks?: number;
    tokens?: number;
}
export type CapReason = 'tasks' | 'tokens';
export interface PendingRotation {
    reason: CapReason;
    cap: number;
    /** What the generation that just ended had processed. */
    previous: {
        tasks: number;
        tokens: number;
    };
    overshoot: number;
}
export interface GenerationState {
    generation: number;
    tasks: string[];
    tokens: number;
    /** Rotations in a row after which no further task was done (R22). */
    stalled_rotations: number;
    done_at_last_rotation: number;
    usage_missing: number;
    started_at: number;
    /** Set at rotation, cleared once the new generation's first message carries the digest. */
    pending_rotation?: PendingRotation;
}
/** Which threshold the generation has reached, if any. With `incoming` (the
 *  task ids the next message carries) the tasks cap fires only for a message
 *  that brings a task the generation lacks: a reminder about a task already in
 *  it, or untagged mail, adds no task and so is no reason to rotate. The tokens
 *  cap does not look at the message. */
export declare function capReached(s: Pick<GenerationState, 'tasks' | 'tokens'>, cap: SessionCap | undefined, incoming?: readonly string[]): {
    reason: CapReason;
    value: number;
    cap: number;
} | undefined;
export declare function loadCounters(runDir: string, role: string, key: string): GenerationState;
export declare function saveCounters(runDir: string, role: string, key: string, state: GenerationState): void;
export declare class SessionCounters {
    private readonly runDir;
    private readonly role;
    private readonly key;
    constructor(runDir: string, role: string, key: string);
    /** The persisted state, read fresh. */
    get state(): GenerationState;
    private update;
    /** A message was admitted; each task id it names is added once. */
    admit(taskIds: readonly string[]): void;
    addTokens(n: number): void;
    /** A turn reported no usage. Returns how many have in this generation. */
    noteUsageMissing(): number;
    /** End the generation: the next one starts empty, with a digest owed to its first message. */
    rotate(hit: {
        reason: CapReason;
        cap: number;
    }, doneTasks: number): {
        from: GenerationState;
        overshoot: number;
    };
    clearPendingRotation(): void;
}
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