fix: use plain String for PS multilingual fields; add Dolibarr diagnostic endpoint

PS WebService GET responses return name/description as plain strings, not
language-array objects. Using List<LangValue> caused Jackson to throw
HttpMessageConversionException on every getProductByReference call.

Also adds GET /api/sync/diagnostics/dolibarr to verify Dolibarr connectivity
and product count from the Railway environment.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

sync-service/src/main/java/com/teterialosjuanjos/tfg/sync_service/api/controller/SyncController.java

@@ -1,6 +1,8 @@
 package com.teterialosjuanjos.tfg.sync_service.api.controller;
 
 import com.teterialosjuanjos.tfg.sync_service.api.dto.SyncTriggerResponse;
+import com.teterialosjuanjos.tfg.sync_service.integration.dolibarr.DolibarrClient;
+import com.teterialosjuanjos.tfg.sync_service.integration.dolibarr.dto.DolibarrProductDto;
 import com.teterialosjuanjos.tfg.sync_service.sync.OrderSyncService;
 import com.teterialosjuanjos.tfg.sync_service.sync.ProductSyncService;
 import com.teterialosjuanjos.tfg.sync_service.sync.StockSyncService;
@@ -8,10 +10,14 @@ import com.teterialosjuanjos.tfg.sync_service.sync.SyncResult;
 import io.swagger.v3.oas.annotations.Operation;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import lombok.RequiredArgsConstructor;
+import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
 
+import java.util.List;
+import java.util.Map;
+
 /**
  * REST endpoints for manually triggering synchronization flows.
  * Useful in development (where scheduling is disabled) and for on-demand resync in production.
@@ -25,6 +31,7 @@ import org.springframework.web.bind.annotation.RestController;
 @RequiredArgsConstructor
 public class SyncController {
 
+    private final DolibarrClient dolibarrClient;
     private final ProductSyncService productSyncService;
     private final StockSyncService stockSyncService;
     private final OrderSyncService orderSyncService;
@@ -47,6 +54,14 @@ public class SyncController {
         return toResponse("ORDER_PULL", orderSyncService.synchronize());
     }
 
+    @Operation(summary = "Diagnostic: list products returned by Dolibarr API (verifies connectivity)")
+    @GetMapping("/diagnostics/dolibarr")
+    public Map<String, Object> dolibarrDiagnostics() {
+        List<DolibarrProductDto> products = dolibarrClient.getProducts();
+        List<String> refs = products.stream().map(DolibarrProductDto::ref).toList();
+        return Map.of("count", products.size(), "refs", refs);
+    }
+
     private static SyncTriggerResponse toResponse(String syncType, SyncResult result) {
         return new SyncTriggerResponse(
                 syncType,

sync-service/src/main/java/com/teterialosjuanjos/tfg/sync_service/integration/prestashop/PrestashopClient.java

@@ -209,9 +209,9 @@ public class PrestashopClient {
     // PS WebService requires XML body for writes; output_format=JSON only affects the response.
 
     private String toProductXml(PrestashopProductDto dto) {
-        String name = firstLangValue(dto.name());
-        String description = firstLangValue(dto.description());
-        String descShort = firstLangValue(dto.descriptionShort());
+        String name = dto.name() != null ? dto.name() : "";
+        String description = dto.description() != null ? dto.description() : "";
+        String descShort = dto.descriptionShort() != null ? dto.descriptionShort() : "";
         String slug = toSlug(dto.reference());
 
         StringBuilder sb = new StringBuilder(512);
@@ -260,12 +260,6 @@ public class PrestashopClient {
         return sb.toString();
     }
 
-    private static String firstLangValue(List<PrestashopProductDto.LangValue> langs) {
-        if (langs == null || langs.isEmpty()) return "";
-        String v = langs.get(0).value();
-        return v != null ? v : "";
-    }
-
     /** Generates a URL-safe slug from any string (used for PS link_rewrite). */
     private static String toSlug(String text) {
         if (text == null || text.isBlank()) return "product";

sync-service/src/main/java/com/teterialosjuanjos/tfg/sync_service/integration/prestashop/dto/PrestashopProductDto.java

@@ -9,8 +9,10 @@ import java.util.List;
 /**
  * Represents a PrestaShop product.
  *
- * <p>Multilingual fields (name, description) are returned as arrays of {@link LangValue}
- * objects, one per configured shop language.</p>
+ * <p>The PS WebService GET response (both list and single) returns multilingual fields
+ * ({@code name}, {@code description}, {@code description_short}) as plain {@link String}
+ * values — NOT as language-array objects. The XML request bodies we send for create/update
+ * wrap these strings inside {@code <language id="1">} elements.</p>
  *
  * <p>Response wrappers ({@link ListResponse}, {@link SingleResponse}) match the JSON envelope
  * PrestaShop adds around resources: {@code {"products":[...]}} and {@code {"product":{...}}}.</p>
@@ -25,15 +27,11 @@ public record PrestashopProductDto(
         /** "1" = active, "0" = inactive */
         String active,
         @JsonProperty("id_category_default") String idCategoryDefault,
-        List<LangValue> name,
-        List<LangValue> description,
-        @JsonProperty("description_short") List<LangValue> descriptionShort
+        String name,
+        String description,
+        @JsonProperty("description_short") String descriptionShort
 ) {
 
-    /** One language entry for a multilingual field, e.g. {@code {"id":"1","value":"Name"}}. */
-    @JsonIgnoreProperties(ignoreUnknown = true)
-    public record LangValue(String id, String value) {}
-
     /** Envelope for {@code GET /api/products?display=full} */
     @JsonIgnoreProperties(ignoreUnknown = true)
     public record ListResponse(List<PrestashopProductDto> products) {}

sync-service/src/main/java/com/teterialosjuanjos/tfg/sync_service/sync/ProductSyncService.java

@@ -144,9 +144,9 @@ public class ProductSyncService {
                 src.price(),
                 active,
                 categoryId,
-                List.of(new PrestashopProductDto.LangValue("1", label)),
-                List.of(new PrestashopProductDto.LangValue("1", description)),
-                List.of(new PrestashopProductDto.LangValue("1", ""))
+                label,
+                description,
+                ""
         );
     }
 }