/**
 * Canonical duration → human label (ADR-0144).
 *
 * Sub-second: whole milliseconds. Sub-minute: one-decimal seconds via tenths
 * rounding. Minute scale: `"Nm Y.Ys"`.
 *
 * Non-finite and negative inputs fall back to the `0` path (never throw).
 */
/**
 * Format a millisecond duration as `"Xms"` under one second, `"X.Ys"` for
 * sub-minute durations, or `"Xm Y.Ys"` at minute scale.
 *
 * @example formatDuration(450)   // "450ms"
 * @example formatDuration(19850) // "19.9s"
 * @example formatDuration(1471600) // "24m 31.6s"
 */
export declare function formatDuration(ms: number): string;
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