Add structured-output module: entity() mapping to records/lists/maps, StructuredOutputValidationAdvisor retries

ChatClient.CallResponseSpec.entity() mapping LLM JSON to a record (TicketTriage, with a real
enum-constrained Priority field), a List<ActionItem>, and a Map<String,Object> -- every case driven
by a hand-written ScriptedChatModel with no live LLM anywhere.

Key findings, all confirmed by disassembling spring-ai-client-chat-2.0.1.jar and spring-ai-model-2.0.1.jar
rather than trusting docs:

- StructuredOutputValidationAdvisor lives in org.springframework.ai.chat.client.advisor, in the same
  spring-ai-client-chat artifact as ToolCallingAdvisor -- unlike the tool-calling module's Tool Search
  Advisor pieces, it needs no separate Maven Central artifact or version pin.
- entity(Class, spec -> spec.validateSchema()) is sugar: DefaultCallResponseSpec.resolveAdvisorChain
  builds a real StructuredOutputValidationAdvisor from the same JSON schema BeanOutputConverter uses
  to parse the response, and pushes it onto the advisor chain for that one call.
- The schema/format instructions are baked into the user message once, up front, by entity() itself,
  before the advisor chain runs at all. A validation retry's only contribution is one appended line:
  "Output JSON validation failed because of: <the real schema-validator error>" -- each retry
  re-augments the ORIGINAL request, not the previous attempt's, so corrections never stack.
- Default maxRepeatAttempts is 3 (4 total attempts); default advisorOrder is 2147481647, near
  Ordered.LOWEST_PRECEDENCE.
- Exhausting every retry does NOT throw -- adviseCall's loop just returns the last (still invalid)
  response to the caller. Plain entity() with no validation, by contrast, throws immediately on the
  same bad JSON, since BeanOutputConverter.convert() is a separate Jackson deserialization step with
  no retry loop of its own. Both behaviors are captured from real runs (output/02, output/06).
- Spring AI 2.0's JSON stack is Jackson 3 (tools.jackson.databind), not classic com.fasterxml.jackson --
  visible directly in every one of this advisor's constructor and field signatures.

Companion module for "Structured Output in Spring AI 2.0: Records, JSON Schema and Self-Correcting
Responses" on ankurm.com.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01FtpJvZfg4nvLvtzgJTDWpB

structured-output/src/test/java/com/ankurm/structuredoutput/EntityBindingMapTest.java

@@ -0,0 +1,44 @@
+package com.ankurm.structuredoutput;
+
+import java.util.Map;
+
+import com.ankurm.structuredoutput.support.ScriptedChatModel;
+import com.ankurm.structuredoutput.support.Transcript;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.ai.chat.client.ChatClient;
+import org.springframework.core.ParameterizedTypeReference;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Sometimes there's no record worth declaring -- a one-off extraction, a shape that varies call
+ * to call. {@code entity()} maps straight to a {@code Map<String, Object>} for that case, the
+ * same converter machinery as the record and list cases, just with a looser target type.
+ */
+class EntityBindingMapTest {
+
+	@Test
+	void mapsAJsonObjectToAMapWhenNoRecordIsWorthDeclaring() {
+		ScriptedChatModel model = ScriptedChatModel.builder()
+			.thenRespond("""
+					{"darkModeEnabled":true,"maxUploadSizeMb":25,"betaFeatures":["new-dashboard","ai-search"]}
+					""")
+			.build();
+		ChatClient client = ChatClient.builder(model).build();
+
+		Map<String, Object> flags = client.prompt()
+			.user("Extract the feature flags mentioned here: dark mode is on, max upload size is 25MB, "
+					+ "and the beta features enabled are new-dashboard and ai-search.")
+			.call()
+			.entity(new ParameterizedTypeReference<Map<String, Object>>() {
+			});
+
+		assertThat(flags).containsEntry("darkModeEnabled", true).containsEntry("maxUploadSizeMb", 25);
+		assertThat(model.callCount()).isEqualTo(1);
+
+		Transcript.write("04-entity-map",
+				"model call count: " + model.callCount() + "\n\n" + "mapped map: " + flags);
+	}
+
+}