Fix Bedrock Anthropic line separator handling on Windows

  Resolves an issue where Bedrock Anthropic failed to handle line separators properly on Windows.

  Resolves #404

Author: tzolov

models/spring-ai-bedrock/src/main/java/org/springframework/ai/bedrock/MessageToPromptConverter.java

@@ -37,11 +37,18 @@ public class MessageToPromptConverter {
 
 	private String assistantPrompt = ASSISTANT_PROMPT;
 
-	private MessageToPromptConverter() {
+	private final String lineSeparator;
+
+	private MessageToPromptConverter(String lineSeparator) {
+		this.lineSeparator = lineSeparator;
 	}
 
 	public static MessageToPromptConverter create() {
-		return new MessageToPromptConverter();
+		return create(System.lineSeparator());
+	}
+
+	public static MessageToPromptConverter create(String lineSeparator) {
+		return new MessageToPromptConverter(lineSeparator);
 	}
 
 	public MessageToPromptConverter withHumanPrompt(String humanPrompt) {
@@ -67,8 +74,9 @@ public String toPrompt(List<Message> messages) {
 			.map(this::messageToString)
 			.collect(Collectors.joining(System.lineSeparator()));
 
-		final String prompt = systemMessages + System.lineSeparator() + System.lineSeparator() + userMessages
-				+ System.lineSeparator() + ASSISTANT_PROMPT;
+		// Related to: https://github.com/spring-projects/spring-ai/issues/404
+		final String prompt = systemMessages + this.lineSeparator + this.lineSeparator + userMessages
+				+ this.lineSeparator + ASSISTANT_PROMPT;
 
 		return prompt;
 	}

models/spring-ai-bedrock/src/main/java/org/springframework/ai/bedrock/anthropic/BedrockAnthropicChatClient.java

@@ -93,7 +93,8 @@ public Flux<ChatResponse> stream(Prompt prompt) {
 	 */
 	AnthropicChatRequest createRequest(Prompt prompt) {
 
-		final String promptValue = MessageToPromptConverter.create().toPrompt(prompt.getInstructions());
+		// Related to: https://github.com/spring-projects/spring-ai/issues/404
+		final String promptValue = MessageToPromptConverter.create("\n").toPrompt(prompt.getInstructions());
 
 		AnthropicChatRequest request = AnthropicChatRequest.builder(promptValue).build();