/** * Configuration for exponential reconnect backoff. */export interface ReconnectBackoffConfig {  /** Base delay in milliseconds before the first retry. */  readonly initialDelayMs: number;  /** Multiplier applied per retry (exponential factor). */  readonly backoffFactor: number;  /** Hard upper bound on delay in milliseconds. */  readonly maxDelayMs: number;  /** Maximum number of retries (0-based). `null` means unlimited. */  readonly maxRetries: number | null;} /** * Sensible defaults for WebSocket reconnect backoff. * * - 1 s initial delay, doubling each retry, capped at 64 s, up to 7 retries. */export const DEFAULT_RECONNECT_BACKOFF: ReconnectBackoffConfig = {  initialDelayMs: 1_000,  backoffFactor: 2,  maxDelayMs: 64_000,  maxRetries: 7,}; /** * Calculate the reconnect delay for a given retry index using exponential * backoff. Returns `null` when `retryIndex` exceeds the configured maximum. */export function getReconnectDelayMs(  retryIndex: number,  config: ReconnectBackoffConfig = DEFAULT_RECONNECT_BACKOFF,): number | null {  if (!Number.isInteger(retryIndex) || retryIndex < 0) {    return null;  }   if (config.maxRetries !== null && retryIndex >= config.maxRetries) {    return null;  }   return Math.min(    Math.round(config.initialDelayMs * config.backoffFactor ** retryIndex),    config.maxDelayMs,  );}