feat(rag): modularize knowledge retrieval pipeline

src/main/java/com/superbiz/agent/service/KnowledgeQueryTransformer.java

@@ -0,0 +1,38 @@
+package com.superbiz.agent.service;
+
+import com.superbiz.agent.dto.KnowledgeQuery;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+
+/**
+ * Converts a raw Agent query into retrieval-control hints.
+ */
+@Service
+public class KnowledgeQueryTransformer {
+
+    private final KnowledgeIndexService knowledgeIndexService;
+
+    public KnowledgeQueryTransformer(KnowledgeIndexService knowledgeIndexService) {
+        this.knowledgeIndexService = knowledgeIndexService;
+    }
+
+    public KnowledgeQuery transform(String rawQuery) {
+        String normalized = rawQuery == null ? "" : rawQuery.trim();
+        KnowledgeIndexService.L0Hint hint = knowledgeIndexService.analyzeQuery(normalized);
+        return KnowledgeQuery.builder()
+                .originalQuery(normalized)
+                .rewrittenQuery(normalized)
+                .domainHints(safeList(hint.domains()))
+                .matchedKeywords(safeList(hint.matchedKeywords()))
+                .entities(safeList(hint.entities()))
+                .categoryFilter(hint.singleDomainOrNull())
+                .l0Titles(safeList(hint.titles()))
+                .l0MatchCount(hint.matches() == null ? 0 : hint.matches().size())
+                .build();
+    }
+
+    private List<String> safeList(List<String> values) {
+        return values == null ? List.of() : values;
+    }
+}