To mitigate the risk of circular fragments in GraphQL, consider the following steps:

### 1. Circular Fragment Detection via Schema Analysis

Implement static analysis on your GraphQL schema and queries to detect and prevent circular references before they can be exploited. Some GraphQL server libraries provide tools for analyzing schemas.

 - **Tooling:** Use GraphQL linting tools such as GraphQL Code Generator or GraphQL Inspector to detect circular fragments and prevent them from reaching production.

**Example using GraphQL Code Generator:**

```
npm install @graphql-codegen/cli
npx graphql-codegen init
```

You can configure the code generator to output schema validations that detect potential circular fragment issues in your GraphQL queries.

### 2. Implement Query Cost Analysis
Use query complexity analysis to assign a "cost" to each field, fragment, or query. When a query or fragment exceeds a predefined cost threshold, it can be automatically rejected.

 - **Tooling:** You can use libraries like graphql-query-complexity to calculate query cost and limit the impact of circular fragments.

**Example in JavaScript using graphql-query-complexity:**

```javascript
const { getComplexity, simpleEstimator } = require('graphql-query-complexity');

const server = new ApolloServer({
  schema,
  validationRules: [
    queryComplexity({
      estimators: [
        simpleEstimator({ defaultComplexity: 1 })
      ],
      maximumComplexity: 1000,  // Queries that exceed this complexity will be rejected
      onComplete: (complexity) => {
        console.log('Query Complexity:', complexity);
      },
    }),
  ],
});
```

### 3. Enforce Depth and Recursion Limits

Some GraphQL server implementations allow you to define limits for query depth and recursion to prevent resource exhaustion. This helps avoid infinite loops caused by circular fragments.

 - **Tooling:** Apollo Server, for example, supports query depth limits, which can prevent excessive recursion.

**Example using query depth limit in Apollo Server:**

```javascript
const { ApolloServer } = require('apollo-server');
const depthLimit = require('graphql-depth-limit');

const server = new ApolloServer({
  schema,
  validationRules: [depthLimit(5)],  // Set query depth limit to 5
});
```

### 4. Use Fragments Wisely

Avoid overusing fragments in complex queries. Overuse can lead to performance degradation and opens up possibilities for circular references. Instead, consider splitting complex queries into multiple smaller queries.

 - **Recommendation:** Review query design and limit fragment usage to specific, modular pieces of data.

**Example:**

```graphql
query {
  user(id: "1") {
    name
    email
    posts {
      title
      content
    }
  }
}
```

Rather than nesting multiple fragments within each other, use a simpler query like this.
