contract syntax

## state on the class itself

```ts
import { BigNumber } from "jsd-std";

export class Counter {
private count: BigNumber;

constructor(initialState: BigNumber) {
this.count = initialState;
}

public increment(amount: BigNumber): void {
this.count = this.count.add(amount);
}

public decrement(amount: BigNumber): void {
if (this.count.lt(amount)) {
throw new Error("Count cannot be negative");
}
this.count = this.count.sub(amount);
}

public getCount(): BigNumber {
return this.count;
}
}
```

The issue provides only a TypeScript Counter example and does not identify repository files, entry points, or tests. First clarify what “state on the class itself” and “contract syntax” should change, then locate the relevant contract-processing path and define tests that demonstrate the intended syntax is accepted.

索引モデルが issue の本文から書いたものです。