docs: embed the rendered class diagram in the event-carried state transfer README

Render etc/event-carried-state-transfer.urm.puml to PNG and embed it in the detailed explanation section, matching the other modules, instead of the inline mermaid block. The producer and consumer snippets now show the plain long sequence counters the code uses.

Author: ylcn91

event-carried-state-transfer/README.md

@@ -57,6 +57,8 @@ sequenceDiagram
     OS->>R: apply (version 1 <= 2, ignored)
 ```
 
+![Event-Carried State Transfer class diagram](./etc/event-carried-state-transfer.urm.png)
+
 ## Programmatic Example of Event-Carried State Transfer Pattern in Java
 
 The example has a producer, a channel and a consumer. The producer is the customer service, the channel is a tiny in-memory event bus and the consumer is the order service with its local customer replica.
@@ -116,7 +118,7 @@ public CustomerState changeShippingAddress(String customerId, String newAddress)
 
 private CustomerState store(CustomerState state) {
   customers.put(state.customerId(), state);
-  var event = new CustomerUpdatedEvent(eventSequence.incrementAndGet(), Instant.now(), state);
+  var event = new CustomerUpdatedEvent(++eventSequence, Instant.now(), state);
   bus.publish(event);
   return state;
 }
@@ -166,7 +168,7 @@ public Order placeOrder(String customerId, BigDecimal amount) {
         "Amount " + amount + " exceeds credit limit " + customer.creditLimit() + " of " + customerId);
   }
   return new Order(
-      "ORD-" + orderSequence.incrementAndGet(), customerId, customer.shippingAddress(), amount);
+      "ORD-" + ++orderSequence, customerId, customer.shippingAddress(), amount);
 }
 ```
 
@@ -232,81 +234,6 @@ INFO OrderService -- Accepted ORD-2 for C-1 (900.00) shipping to '42 Ocean Avenu
 INFO App -- Order ORD-2 accepted
 ```
 
-## Class Diagram
-
-```mermaid
-classDiagram
-    class CustomerState {
-        +String customerId
-        +String name
-        +String shippingAddress
-        +BigDecimal creditLimit
-        +long version
-        +withShippingAddress(newAddress) CustomerState
-        +withCreditLimit(newLimit) CustomerState
-    }
-    class CustomerUpdatedEvent {
-        +long eventId
-        +Instant occurredAt
-        +CustomerState state
-    }
-    class EventListener~E~ {
-        <<interface>>
-        +onEvent(event) void
-    }
-    class EventBus {
-        -Map~Class, List~ listeners
-        +subscribe(eventType, listener) void
-        +publish(event) void
-    }
-    class CustomerService {
-        -Map~String, CustomerState~ customers
-        -EventBus bus
-        -long eventSequence
-        -boolean online
-        +register(customerId, name, shippingAddress, creditLimit) CustomerState
-        +changeShippingAddress(customerId, newAddress) CustomerState
-        +changeCreditLimit(customerId, newLimit) CustomerState
-        +findCustomer(customerId) Optional~CustomerState~
-        +shutdown() void
-        +isOnline() boolean
-    }
-    class CustomerReplica {
-        -Map~String, CustomerState~ customers
-        +apply(event) boolean
-        +find(customerId) Optional~CustomerState~
-        +size() int
-    }
-    class OrderService {
-        -CustomerReplica replica
-        -long orderSequence
-        +placeOrder(customerId, amount) Order
-        +replica() CustomerReplica
-    }
-    class Order {
-        +String orderId
-        +String customerId
-        +String shippingAddress
-        +BigDecimal amount
-    }
-    class OrderRejectedException {
-        +OrderRejectedException(message)
-    }
-
-    CustomerUpdatedEvent --> CustomerState
-    EventBus "1" --> "*" EventListener
-    CustomerService --> EventBus
-    CustomerService "1" --> "*" CustomerState
-    CustomerService ..> CustomerUpdatedEvent : publishes
-    CustomerReplica "1" --> "*" CustomerState
-    CustomerReplica ..> CustomerUpdatedEvent : applies
-    OrderService --> CustomerReplica
-    OrderService ..> EventListener : adapts the replica
-    OrderService ..> EventBus : subscribes
-    OrderService ..> Order : creates
-    OrderService ..> OrderRejectedException : throws
-```
-
 ## When to Use the Event-Carried State Transfer Pattern in Java
 
 * Consumers need data owned by another service on every request and a synchronous call would add latency, load, or a hard availability dependency.