/**
 * compactionMeter — the instrument a window strategy is allowed to read.
 *
 * Pattern: CombinedRecorder (Convention 1 — single purpose: measurement),
 *          with a handle the window stage reads MID-run. That mid-run read is
 *          deliberate and has precedent: the causal-evidence recorder is
 *          attached inline for the same reason (the memory write stage
 *          consumes its accumulators before the run ends).
 * Role:    recorders/core layer. Attached ONLY when a window strategy is
 *          configured (`.window()` / `.compaction()`), and always INLINE — a
 *          window decision cannot ride one beat behind the loop it is
 *          deciding for.
 * Emits:   nothing. It only measures.
 *
 * It answers two questions a stage function cannot answer for itself:
 *
 *   1. "How big was the last window, as the PROVIDER counted it?" — from the
 *      `stream.llm_end` usage the adapter reported. Counted, not guessed. Fed
 *      by the agent's REAL-value event path (`noteLlmEnd`), never by a served
 *      event: the window decides on this number, so a redaction policy can
 *      never take it away (`src/redaction/runRedaction.ts`).
 *   2. "Which stage put each message in the window?" — from the
 *      `runtimeStageId` on every write to `history`. A stage function has no
 *      access to its own runtimeStageId (footprintjs exposes no such scope
 *      method), so the recorder channel is the ONLY honest source for the
 *      `removedStageIds` a strategy has to name. That channel is a RECORD:
 *      under a redaction policy that selects `history` whole, footprintjs
 *      serves the write masked, the meter cannot see the window's length, and
 *      an eviction's provenance reads as unknown (`removedStageIds` names none,
 *      `survivalMs` is 0 — the documented "birth unknown"). The record of a
 *      masked key loses its shape; the window's decision does not change.
 */
import type { WriteEvent } from 'footprintjs';
/** What the provider reported for the most recent completed LLM call. */
export interface MeteredCall {
    readonly input: number;
    readonly output: number;
    /**
     * The ReAct iteration whose call produced this reading, from the
     * `stream.llm_end` payload. It is what makes the reading EXPIRE (8.14.0):
     * before it existed, a provider that reported usage once and then stopped
     * left this number standing forever, and every later window decision was
     * made on it. Messages were evicted on a count nobody had taken.
     */
    readonly meteredAtIteration: number;
}
/** Per-message provenance for the CURRENT window. */
export interface MessageOrigin {
    /** runtimeStageId of the stage whose write first put this message in. */
    readonly stageId: string;
    /** Wall clock when that write happened — the message's birth. */
    readonly bornAtMs: number;
}
export interface CompactionMeterHandle {
    readonly id: string;
    /**
     * The last completed LLM call's reported usage — **only if it is still
     * current**. `undefined` before call #1, and `undefined` again once the
     * reading has expired.
     *
     * A reading is current for the iteration that follows the call that
     * produced it, and no longer. The window stage runs at the loop head: at
     * iteration N the last completed call was made during iteration N−1, so a
     * reading stamped older than N−1 means the most recent call reported
     * nothing usable. That is not a smaller number or an older number — it is
     * an ABSENT number, and this returns `undefined` for it. Every strategy
     * already treats `undefined` as "do not act", which is the honest response
     * to a provider that stopped counting.
     *
     * @param currentIteration the iteration the caller is deciding for
     */
    lastCall(currentIteration: number): MeteredCall | undefined;
    /**
     * How many `stream.llm_end` events carried no usable usage since the last
     * good reading. Non-zero means the provider is answering without counting;
     * the window stage turns it into one warning per run.
     */
    unmeteredSinceLastGood(): number;
    /** Origins aligned index-for-index with the current window. */
    origins(): readonly MessageOrigin[];
    /**
     * Tell the meter a window strategy is about to change the window, so it can
     * re-align origins to the new one — `[...head, (inserted)?, ...tail]`:
     * `head` is the leading messages the strategy stepped over (turns that
     * refused to leave), `tail` is the messages kept after the removed span.
     *
     * `insertedAtMs` is the birth of the ONE message the strategy put in the
     * span's place (compaction's summary, a drop's authored notice). Omit it
     * when the strategy removed messages and inserted nothing.
     *
     * Called by the stage that performs the change, BEFORE it writes — the
     * shape change is the one thing the meter cannot infer, because the
     * TypedScope set trap JSON-round-trips every write and destroys object
     * identity.
     */
    rebaseForWindowChange(headCount: number, keptTailCount: number, insertedAtMs?: number): void;
    clear(): void;
    /**
     * Take one `stream.llm_end` reading. Fed from the agent's REAL-value event
     * path (`EventDispatcher · onRealEvent`), never from a served event: the
     * count is a measurement the window decides on, and a redaction policy whose
     * pattern happens to match `input` must not quietly switch compaction off.
     */
    noteLlmEnd(payload: unknown): void;
    onWrite(event: WriteEvent): void;
}
export interface CompactionMeterOptions {
    /** Recorder id (default 'compaction-meter'). */
    readonly id?: string;
    /** Scope key holding the window. Default 'history'. */
    readonly key?: string;
    /** Injectable clock, so tests can pin `survivalMs`. */
    readonly now?: () => number;
}
/**
 * Build the meter.
 *
 * Origin tracking assumes the ONE shape the agent's window actually has:
 * writes either replace the window wholesale (seed, and resume seeding) or
 * append to it (tool-calls). Growth fills the new tail with the writing
 * stage's id; a wholesale replacement re-stamps everything with the writer
 * that produced it — which is exactly true, since that writer is where those
 * messages entered THIS run. Shrink only ever comes from a window strategy,
 * and the stage announces it through `rebaseForWindowChange`.
 */
export declare function compactionMeter(options?: CompactionMeterOptions): CompactionMeterHandle;