/**
 * Per-LLM-round timing metrics (duration / TPS / TTFT) for the agent bridge.
 *
 * Pure functions — no bridge state — so the math is unit-testable in
 * isolation. The bridge stamps wall-clock `Date.now()` values while
 * translating spectral events to wire frames (spectral's
 * `AssistantMessageEvent` carries no timing) and feeds them through
 * {@link computeTpsMetrics} when `token_usage` is emitted.
 *
 * Semantics (shared contract with the landing frontend):
 *   - `durationMs`   = tEnd(message_end) − tFirstDelta  — the generation
 *     window only, excludes time-to-first-token.
 *   - `ttftMs`       = tFirstDelta − tStart(message_start).
 *   - `tokensPerSecond` = round(outputTokens / (durationMs / 1000), 1).
 *
 * Any metric that cannot be computed from sound inputs is `null` —
 * consumers must treat these fields as optional/unreliable indicators.
 */
/** Computed per-round timing metrics; every field may be null. */
export interface TpsMetrics {
    /** Generation window in ms (message_end − first streamed delta), excluding TTFT. */
    durationMs: number | null;
    /** Output tokens per second across the generation window, rounded to 1 decimal. */
    tokensPerSecond: number | null;
    /** Time-to-first-delta in ms (first streamed delta − message_start). */
    ttftMs: number | null;
}
/** A wall-clock stamp that is either missing or a finite number. */
type Stamp = number | null | undefined;
/**
 * Compute per-round timing metrics from wall-clock stamps and output token
 * count. Null-safe: missing stamps, negative windows (clock skew) and
 * non-positive token counts or durations yield `null` for the affected
 * fields rather than fabricated numbers.
 */
export declare function computeTpsMetrics(startAt: Stamp, firstDeltaAt: Stamp, endAt: Stamp, outputTokens: number | null | undefined): TpsMetrics;
/** Raw per-round sums accumulated over one subagent invocation. */
export interface TpsRoundSums {
    /** Σ durationMs over LLM rounds with a computable generation window. */
    durationMsSum: number;
    /** Σ outputTokens over TPS-eligible rounds (output > 0 and duration > 0). */
    outputTokens: number;
    /** Σ durationMs over the same TPS-eligible rounds (TPS denominator). */
    outputDurationMs: number;
    /** Σ ttftMs over rounds with a computable TTFT (mean denominator). */
    ttftMsSum: number;
    /** Count of rounds that contributed to `ttftMsSum`. */
    ttftRounds: number;
    /** TPS of the last round with outputTokens > 0. */
    lastRoundTps: number | null;
}
/** Contract-shaped TPS fields derived from raw round sums. */
export interface TpsUsageFields {
    /** Σ durationMs (ms) over the invocation's LLM rounds. */
    durationMs?: number;
    /** Token-weighted TPS: Σ outputTokens / Σ durationMs × 1000 (1 decimal). */
    tokensPerSecond?: number;
    /** Arithmetic-mean TTFT (ms) across rounds with a computable TTFT. */
    ttftMs?: number;
    /** TPS of the last round with outputTokens > 0. */
    lastRoundTps?: number;
}
/**
 * Build the contract-shaped TPS fields from raw round sums. Fields that
 * cannot be derived from sound sums are omitted rather than zero-filled —
 * consumers must treat these as optional/unreliable indicators. Shared by
 * the subagent runner (per-result snapshot) and the agent bridge
 * (`subagent_end.totalUsage` token-weighted aggregation across results).
 */
export declare function buildTpsUsageFields(sums: TpsRoundSums): TpsUsageFields;
export {};
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