fix: enforce max_items_per_category in JSON schema and prompt

The LLM was returning only 1 article per category despite the user setting 4.
- Added minItems/maxItems to the category array schema (enforced by OpenAI strict mode)
- Changed prompt from "au maximum N actualites" to "exactement N actualites"
- Schema builder now takes max_items_per_category parameter

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/services/llm/schema.rs

@@ -35,7 +35,7 @@ use serde_json::Value;
 ///   "required": ["category_0", "category_1"]
 /// }
 /// ```
-pub fn build_category_schema(categories: &[String]) -> Value {
+pub fn build_category_schema(categories: &[String], max_items_per_category: i32) -> Value {
     let news_item_schema = serde_json::json!({
         "type": "object",
         "properties": {
@@ -66,7 +66,9 @@ pub fn build_category_schema(categories: &[String]) -> Value {
             serde_json::json!({
                 "type": "array",
                 "description": category_name,
-                "items": news_item_schema
+                "items": news_item_schema,
+                "minItems": max_items_per_category,
+                "maxItems": max_items_per_category
             }),
         );
         required.push(Value::String(key));
@@ -87,7 +89,7 @@ mod tests {
     #[test]
     fn schema_with_one_category() {
         let categories = vec!["AI News".to_string()];
-        let schema = build_category_schema(&categories);
+        let schema = build_category_schema(&categories, 5);
 
         assert_eq!(schema["type"], "object");
 
@@ -124,7 +126,7 @@ mod tests {
             "Recherche".to_string(),
             "Secteur public".to_string(),
         ];
-        let schema = build_category_schema(&categories);
+        let schema = build_category_schema(&categories, 5);
 
         let props = schema["properties"].as_object().unwrap();
         assert_eq!(props.len(), 3);
@@ -141,7 +143,7 @@ mod tests {
         let categories: Vec<String> = (0..5)
             .map(|i| format!("Category {}", i))
             .collect();
-        let schema = build_category_schema(&categories);
+        let schema = build_category_schema(&categories, 5);
 
         let props = schema["properties"].as_object().unwrap();
         assert_eq!(props.len(), 5);
@@ -162,7 +164,7 @@ mod tests {
     #[test]
     fn schema_with_empty_categories() {
         let categories: Vec<String> = vec![];
-        let schema = build_category_schema(&categories);
+        let schema = build_category_schema(&categories, 5);
 
         let props = schema["properties"].as_object().unwrap();
         assert_eq!(props.len(), 0);
@@ -174,7 +176,7 @@ mod tests {
     #[test]
     fn schema_news_item_has_required_fields() {
         let categories = vec!["Test".to_string()];
-        let schema = build_category_schema(&categories);
+        let schema = build_category_schema(&categories, 5);
 
         let items = &schema["properties"]["category_0"]["items"];
         let item_required = items["required"].as_array().unwrap();
@@ -191,7 +193,7 @@ mod tests {
     #[test]
     fn schema_meets_openai_strict_mode_requirements() {
         let categories = vec!["Test".to_string(), "Other".to_string()];
-        let schema = build_category_schema(&categories);
+        let schema = build_category_schema(&categories, 5);
 
         // Every "type": "object" must have "additionalProperties": false
         assert_eq!(
@@ -253,7 +255,7 @@ mod tests {
             "AI & Machine Learning".to_string(),
             "R&D / Innovation".to_string(),
         ];
-        let schema = build_category_schema(&categories);
+        let schema = build_category_schema(&categories, 5);
 
         let props = schema["properties"].as_object().unwrap();
         assert_eq!(props["category_0"]["description"], "AI & Machine Learning");

backend/src/services/prompts.rs

@@ -71,7 +71,7 @@ pub fn build_search_prompt(
          {behavior}\n\n\
          La synthese doit etre divisee en {count} grandes sections :\n\
          {categories}\n\n\
-         Pour chaque categorie, fournis au maximum {max_items} actualites.\n\
+         Pour chaque categorie, fournis exactement {max_items} actualites.\n\
          Pour chaque actualite, fournis un titre provisoire, l'URL source exacte et complete, \
          et un resume provisoire.\n\
          Ne retourne JAMAIS des URLs de pages d'accueil (homepage). Fournis toujours des liens \

backend/src/services/synthesis.rs

@@ -275,7 +275,7 @@ async fn run_generation_inner(
     let provider = create_provider(&provider_name, api_key)?;
 
     // Step 4: Build schema from categories
-    let schema = build_category_schema(&settings.categories);
+    let schema = build_category_schema(&settings.categories, settings.max_items_per_category);
 
     // Step 4b: Resolve models — user overrides take priority over admin config
     let model_research = if !settings.ai_model.is_empty() {