on type safety in LangChain TS

snippet-2.ts

async call(
    arg: (z.output<T> extends string ? string : never) | z.input<T>,
    configArg?: Callbacks | RunnableConfig,
    /** @deprecated */
    tags?: string[]
  ): Promise<string> {
    let parsed;
    try {
      parsed = await this.schema.parseAsync(arg);
    } catch (e) {
      throw new ToolInputParsingException(
        `Received tool input did not match expected schema`,
        JSON.stringify(arg)
      );
    }
    // ... more code