/**
 * Reducing what the model WRITES, not what it reads.
 *
 * Every other engine in this package attacks the prompt. Output is the token
 * class nobody here has touched, and on Opus-class models it bills at about
 * five times input -- so a modest reduction there is worth more than a large
 * one on the cheap side of the ledger. Much of that output is ceremony:
 * "Great, let me...", code printed straight back at you, and full reasoning
 * effort spent resuming after a file read that answered nothing.
 *
 * TWO LEVERS, BOTH DELIBERATELY TIMID.
 *
 * 1. VERBOSITY STEERING appends a short instruction to the END of the system
 *    prompt. The end matters: a provider prompt cache keys on a prefix, so
 *    anything prepended or inserted invalidates every cached token behind it.
 *    This package has already measured that mistake costing 1.77x when a
 *    reordered tool array moved bytes at the front of the prefix, so the
 *    placement here is not stylistic.
 *
 * 2. EFFORT ROUTING lowers the thinking budget when a turn is only the model
 *    resuming after a tool result -- a file read, a passing test. A new
 *    question or an error keeps whatever the client asked for.
 *
 * CLAMP-ONLY, IN ONE DIRECTION. Neither lever ever raises a setting the client
 * chose, adds a field the client omitted, or changes a request it marked as
 * needing full effort. A proxy that increases spend while advertising a saving
 * is worse than a proxy that does nothing, so every branch here can only
 * reduce or pass through.
 *
 * MEASURED, NOT ESTIMATED. Output savings are counterfactual: we never see what
 * the model would have written. So a holdout fraction of conversations is left
 * unshaped, which turns the figure from an estimate into a measurement with a
 * band. `TOKEN_OPTIMIZER_OUTPUT_HOLDOUT=0.1` leaves one in ten alone.
 */
export type WireFormat = 'messages' | 'chat-completions' | 'responses';
export interface ShaperOptions {
    readonly wireFormat: WireFormat;
    /** Off unless the operator turned it on. */
    readonly enabled?: boolean;
    /** Fraction of conversations left unshaped, so the saving can be measured. */
    readonly holdout?: number;
    /** Stable per-conversation key, so a conversation stays in or out of the holdout. */
    readonly conversationKey?: string;
}
export interface ShaperResult {
    /** The request to forward. Identical object when nothing applied. */
    readonly body: Record<string, unknown>;
    /** Labels for the accounting ledger, e.g. `output_shaper:verbosity`. */
    readonly labels: readonly string[];
    /** Why nothing was done, when nothing was done. */
    readonly skipped?: string;
}
/** Reads the switch. Absent means off: this changes what the model writes. */
export declare function shaperEnabled(env?: NodeJS.ProcessEnv): boolean;
/** The unshaped fraction. Invalid or absent means none. */
export declare function holdoutFraction(env?: NodeJS.ProcessEnv): number;
/**
 * Whether this conversation is in the unshaped control arm.
 *
 * Hashed rather than random, so a conversation does not flip arms mid-flight.
 * A conversation shaped on turn 3 and unshaped on turn 4 would pollute both
 * arms and measure nothing.
 */
export declare function inHoldout(key: string | undefined, fraction: number): boolean;
/** Is this turn only the model resuming after a tool result? */
export declare function isResumption(body: Record<string, unknown>, wireFormat: WireFormat): boolean;
/**
 * Applies both levers, or explains why it did not.
 *
 * The body is never mutated in place: a caller that decides not to forward the
 * shaped version must still hold the original bytes.
 */
export declare function shapeOutput(body: Record<string, unknown>, opts: ShaperOptions): ShaperResult;
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