feat(advisors): Enable recursive advisor execution with two new built-in advisors

Add support for recursive (repetitive) advisor execution patterns, allowing advisors to re-invoke
themselves or the remaining chain multiple times. This enables advanced patterns like retry logic,
iterative refinement, and multi-pass processing.

- Add AdvisorUtils.copyChainAfterAdvisor() utility to enable recursive chain invocation
- Implement ToolCallAdvisor for recursive tool calling with configurable tool execution
- Implement StructuredOutputValidationAdvisor for recursive output validation with retry logic
- Add MCP JSON Jackson2 dependency for JSON schema validation
- Add test suites for both new advisors and utility methods
- Add documentation for recursive advisor patterns

refactor(advisor): enhance StructuredOutputValidationAdvisor with validation feedback loop

Refactor retry logic to provide validation error feedback to LLM for self-correction.
Extract validation into separate method and augment prompts with error messages on retry.
Add comprehensive test coverage for various validation scenarios including nested objects,
lists, malformed JSON, and type mismatches.

Improve StructuredOutputValidationAdvisor logic

feat: Add return direct support and null safety to ToolCallAdvisor

Implements return direct functionality allowing tools to bypass the LLM
and return results directly to clients. Adds null safety checks for
chatResponse and comprehensive test coverage.

refactor: Move chain copying logic from AdvisorUtils to CallAdvisorChain interface

- Add CallAdvisorChain.copy(CallAdvisor after) method to replace AdvisorUtils.copyChainAfterAdvisor()
- Implement copy() method in DefaultAroundAdvisorChain
- Update StructuredOutputValidationAdvisor and ToolCallAdvisor to use new copy() API
- Add ObjectMapper parameter support to StructuredOutputValidationAdvisor for custom JSON processing
- Improve ToolCallAdvisor return direct logic using break instead of flag
- Move tests from AdvisorUtilsTests to DefaultAroundAdvisorChainTests
- Update documentation to reflect API changes

This refactoring improves the API design by moving chain manipulation logic
closer to where it belongs (on the chain itself) rather than in a utility class.

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

Author: tzolov

spring-ai-client-chat/pom.xml

@@ -44,6 +44,12 @@
 			<version>${project.version}</version>
 		</dependency>
 
+		<dependency>
+			<groupId>io.modelcontextprotocol.sdk</groupId>
+			<artifactId>mcp-json-jackson2</artifactId>
+			<version>${mcp.sdk.version}</version>
+		</dependency>
+
 		<dependency>
 			<groupId>com.fasterxml.jackson.module</groupId>
 			<artifactId>jackson-module-jsonSchema</artifactId>

spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/advisor/AdvisorUtils.java

@@ -24,6 +24,8 @@
 
 /**
  * Utilities to work with advisors.
+ *
+ * @author Christian Tzolov
  */
 public final class AdvisorUtils {
 

spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/advisor/DefaultAroundAdvisorChain.java

@@ -30,6 +30,7 @@
 import org.springframework.ai.chat.client.advisor.api.Advisor;
 import org.springframework.ai.chat.client.advisor.api.BaseAdvisorChain;
 import org.springframework.ai.chat.client.advisor.api.CallAdvisor;
+import org.springframework.ai.chat.client.advisor.api.CallAdvisorChain;
 import org.springframework.ai.chat.client.advisor.api.StreamAdvisor;
 import org.springframework.ai.chat.client.advisor.observation.AdvisorObservationContext;
 import org.springframework.ai.chat.client.advisor.observation.AdvisorObservationConvention;
@@ -133,6 +134,24 @@ public Flux<ChatClientResponse> nextStream(ChatClientRequest chatClientRequest)
 		});
 	}
 
+	@Override
+	public CallAdvisorChain copy(CallAdvisor after) {
+
+		Assert.notNull(after, "The after call advisor must not be null");
+
+		List<CallAdvisor> callAdvisors = this.getCallAdvisors();
+
+		int afterAdvisorIndex = callAdvisors.indexOf(after);
+
+		if (afterAdvisorIndex < 0) {
+			throw new IllegalArgumentException("The specified advisor is not part of the chain: " + after.getName());
+		}
+
+		var remainingCallAdvisors = callAdvisors.subList(afterAdvisorIndex + 1, callAdvisors.size());
+
+		return DefaultAroundAdvisorChain.builder(this.getObservationRegistry()).pushAll(remainingCallAdvisors).build();
+	}
+
 	@Override
 	public List<CallAdvisor> getCallAdvisors() {
 		return this.originalCallAdvisors;

spring-ai-client-chat/src/main/java/org/springframework/ai/chat/client/advisor/SimpleLoggerAdvisor.java

@@ -88,11 +88,11 @@ public Flux<ChatClientResponse> adviseStream(ChatClientRequest chatClientRequest
 		return new ChatClientMessageAggregator().aggregateChatClientResponse(chatClientResponses, this::logResponse);
 	}
 
-	private void logRequest(ChatClientRequest request) {
+	protected void logRequest(ChatClientRequest request) {
 		logger.debug("request: {}", this.requestToString.apply(request));
 	}
 
-	private void logResponse(ChatClientResponse chatClientResponse) {
+	protected void logResponse(ChatClientResponse chatClientResponse) {
 		logger.debug("response: {}", this.responseToString.apply(chatClientResponse.chatResponse()));
 	}