**Fault Tolerance**: `FaultTolerantClient` wrapper (retry, circuit breaker), `SwitchableHttpClient` for HTTP client fallback

---

## Key Components

### Core Classes

- **Crawler** (`Crawler.java`): Main orchestrator - `execute()`, `addUrl()`, `cleanup()`, `stop()`

    encoding: UrlComponentEncodingTester.Encoding,
    component: Component,
  ) {
    testToUrl(codePoint, encoding, component)
    testFromUrl(codePoint, encoding, component)
    testUri(codePoint, codePointString, encoding, component)
  }

  private fun testToUrl(
    codePoint: Int,
    encoding: UrlComponentEncodingTester.Encoding,
    component: Component,
  ) {
    val encoded = encoding.encode(codePoint)

    private AndPredicate(List<? extends Predicate<? super T>> components) {
      this.components = components;
    }

    @Override
    public boolean apply(@ParametricNullness T t) {
      // Avoid using the Iterator to avoid generating garbage (issue 820).
      for (int i = 0; i < components.size(); i++) {
        if (!components.get(i).apply(t)) {
          return false;

                                            "$ref": "#/components/schemas/HTTPValidationError"
                                        }
                                    }
                                },
                            },
                        },
                    }
                },
            },
            "components": {
                "schemas": {

                                            "$ref": "#/components/schemas/HTTPValidationError"
                                        }
                                    }
                                },
                            },
                        },
                    }
                },
            },
            "components": {
                "schemas": {

                                            "$ref": "#/components/schemas/HTTPValidationError"
                                        }
                                    }
                                },
                            },
                        },
                    }
                },
            },
            "components": {
                "schemas": {

                                    "schema": {"$ref": "#/components/schemas/Item"}
                                }
                            },
                            "required": True,
                        },
                    },
                }
            },
            "components": {
                "schemas": {
                    "Item": {

                                            "$ref": "#/components/schemas/Model3"
                                        }
                                    }
                                },
                            }
                        },
                    }
                }
            },
            "components": {
                "schemas": {

                                "content": {
                                    "application/json": {
                                        "schema": {
                                            "$ref": "#/components/schemas/HTTPValidationError"
                                        }
                                    }
                                },
                            },

                                "content": {
                                    "application/json": {
                                        "schema": {
                                            "$ref": "#/components/schemas/Invoice"
                                        }
                                    }
                                },
                                "required": True,
                            },