feat: add batch_size setting for Phase 1 parallelism

Add a user-configurable batch_size setting (default 5, range 1-20)
that controls how many articles are processed in parallel during
Phase 1 scrape+classify. Previously hardcoded to 5.

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

CLAUDE.md

@@ -117,7 +117,7 @@ cd frontend && npx tsc --noEmit
 - `GET /api/v1/admin/users` — user list
 - `PUT /api/v1/admin/users/:id/role` — role management
 
-## Database (19 migrations)
+## Database (20 migrations)
 Tables: `users`, `sessions`, `magic_link_tokens`, `user_settings`, `sources`, `syntheses`, `admin_providers`, `admin_rate_limits`, `user_api_keys`, `audit_log`
 
 ## Environment Variables

backend/migrations/20260325000020_add_batch_size_setting.sql

@@ -0,0 +1,2 @@
+-- Add batch_size column to settings (parallelism for Phase 1 scrape+classify)
+ALTER TABLE settings ADD COLUMN batch_size INTEGER NOT NULL DEFAULT 5;

backend/src/db/settings.rs

@@ -20,6 +20,7 @@ struct SettingsRow {
     max_articles_per_source: i32,
     use_llm_for_source_links: bool,
     article_history_days: i32,
+    batch_size: i32,
     search_agent_behavior: String,
     ai_provider: String,
     ai_model: String,
@@ -46,6 +47,7 @@ impl TryFrom<SettingsRow> for UserSettings {
             max_articles_per_source: row.max_articles_per_source,
             use_llm_for_source_links: row.use_llm_for_source_links,
             article_history_days: row.article_history_days,
+            batch_size: row.batch_size,
             search_agent_behavior: row.search_agent_behavior,
             ai_provider: row.ai_provider,
             ai_model: row.ai_model,
@@ -72,10 +74,10 @@ pub async fn get_or_create_default(
 
     let row = sqlx::query_as::<_, SettingsRow>(
         r#"
-        INSERT INTO settings (user_id, theme, max_age_days, categories, max_items_per_category, search_agent_behavior, ai_provider, ai_model, ai_model_websearch, rate_limit_max_requests, rate_limit_time_window_seconds, max_articles_per_source, use_llm_for_source_links, article_history_days)
+        INSERT INTO settings (user_id, theme, max_age_days, categories, max_items_per_category, search_agent_behavior, ai_provider, ai_model, ai_model_websearch, rate_limit_max_requests, rate_limit_time_window_seconds, max_articles_per_source, use_llm_for_source_links, article_history_days, batch_size)
-        VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14)
+        VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15)
         ON CONFLICT (user_id) DO UPDATE SET user_id = settings.user_id
-        RETURNING user_id, theme, max_age_days, categories, max_items_per_category, search_agent_behavior, ai_provider, ai_model, ai_model_websearch, rate_limit_max_requests, rate_limit_time_window_seconds, max_articles_per_source, use_llm_for_source_links, article_history_days, updated_at
+        RETURNING user_id, theme, max_age_days, categories, max_items_per_category, search_agent_behavior, ai_provider, ai_model, ai_model_websearch, rate_limit_max_requests, rate_limit_time_window_seconds, max_articles_per_source, use_llm_for_source_links, article_history_days, batch_size, updated_at
         "#,
     )
     .bind(user_id)
@@ -92,6 +94,7 @@ pub async fn get_or_create_default(
     .bind(defaults.max_articles_per_source)
     .bind(defaults.use_llm_for_source_links)
     .bind(defaults.article_history_days)
+    .bind(defaults.batch_size)
     .fetch_one(pool)
     .await?;
 
@@ -110,8 +113,8 @@ pub async fn upsert(
 
     let row = sqlx::query_as::<_, SettingsRow>(
         r#"
-        INSERT INTO settings (user_id, theme, max_age_days, categories, max_items_per_category, search_agent_behavior, ai_provider, ai_model, ai_model_websearch, rate_limit_max_requests, rate_limit_time_window_seconds, max_articles_per_source, use_llm_for_source_links, article_history_days)
+        INSERT INTO settings (user_id, theme, max_age_days, categories, max_items_per_category, search_agent_behavior, ai_provider, ai_model, ai_model_websearch, rate_limit_max_requests, rate_limit_time_window_seconds, max_articles_per_source, use_llm_for_source_links, article_history_days, batch_size)
-        VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14)
+        VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15)
         ON CONFLICT (user_id) DO UPDATE SET
             theme = EXCLUDED.theme,
             max_age_days = EXCLUDED.max_age_days,
@@ -126,8 +129,9 @@ pub async fn upsert(
             max_articles_per_source = EXCLUDED.max_articles_per_source,
             use_llm_for_source_links = EXCLUDED.use_llm_for_source_links,
             article_history_days = EXCLUDED.article_history_days,
+            batch_size = EXCLUDED.batch_size,
             updated_at = now()
-        RETURNING user_id, theme, max_age_days, categories, max_items_per_category, search_agent_behavior, ai_provider, ai_model, ai_model_websearch, rate_limit_max_requests, rate_limit_time_window_seconds, max_articles_per_source, use_llm_for_source_links, article_history_days, updated_at
+        RETURNING user_id, theme, max_age_days, categories, max_items_per_category, search_agent_behavior, ai_provider, ai_model, ai_model_websearch, rate_limit_max_requests, rate_limit_time_window_seconds, max_articles_per_source, use_llm_for_source_links, article_history_days, batch_size, updated_at
         "#,
     )
     .bind(user_id)
@@ -144,6 +148,7 @@ pub async fn upsert(
     .bind(req.max_articles_per_source)
     .bind(req.use_llm_for_source_links)
     .bind(req.article_history_days)
+    .bind(req.batch_size)
     .fetch_one(pool)
     .await?;
 

backend/src/models/settings.rs

@@ -15,6 +15,7 @@ pub struct UserSettings {
     pub max_articles_per_source: i32,
     pub use_llm_for_source_links: bool,
     pub article_history_days: i32,
+    pub batch_size: i32,
     pub search_agent_behavior: String,
     pub ai_provider: String,
     pub ai_model: String,
@@ -34,6 +35,7 @@ pub struct SettingsResponse {
     pub max_articles_per_source: i32,
     pub use_llm_for_source_links: bool,
     pub article_history_days: i32,
+    pub batch_size: i32,
     pub search_agent_behavior: String,
     pub ai_provider: String,
     pub ai_model: String,
@@ -52,6 +54,7 @@ impl From<UserSettings> for SettingsResponse {
             max_articles_per_source: s.max_articles_per_source,
             use_llm_for_source_links: s.use_llm_for_source_links,
             article_history_days: s.article_history_days,
+            batch_size: s.batch_size,
             search_agent_behavior: s.search_agent_behavior,
             ai_provider: s.ai_provider,
             ai_model: s.ai_model,
@@ -72,6 +75,7 @@ pub struct UpdateSettingsRequest {
     pub max_articles_per_source: i32,
     pub use_llm_for_source_links: bool,
     pub article_history_days: i32,
+    pub batch_size: i32,
     pub search_agent_behavior: String,
     pub ai_provider: String,
     pub ai_model: String,
@@ -121,6 +125,9 @@ impl UpdateSettingsRequest {
         if !(0..=365).contains(&self.article_history_days) {
             return Err("article_history_days must be between 0 and 365".into());
         }
+        if !(1..=20).contains(&self.batch_size) {
+            return Err("batch_size must be between 1 and 20".into());
+        }
         if self.search_agent_behavior.len() > 2000 {
             return Err("search_agent_behavior must be at most 2000 characters".into());
         }
@@ -165,6 +172,7 @@ impl Default for UserSettings {
             max_articles_per_source: 3,
             use_llm_for_source_links: false,
             article_history_days: 90,
+            batch_size: 5,
             search_agent_behavior: String::new(),
             ai_provider: String::new(),
             ai_model: String::new(),
@@ -190,6 +198,7 @@ mod tests {
             max_articles_per_source: 3,
             use_llm_for_source_links: false,
             article_history_days: 90,
+            batch_size: 5,
             search_agent_behavior: String::new(),
             ai_provider: String::new(),
             ai_model: String::new(),
@@ -385,6 +394,26 @@ mod tests {
         assert!(err.contains("ai_model"));
     }
 
+    #[test]
+    fn test_validate_batch_size_below_range() {
+        let req = UpdateSettingsRequest {
+            batch_size: 0,
+            ..valid_request()
+        };
+        let err = req.validate().unwrap_err();
+        assert!(err.contains("batch_size"));
+    }
+
+    #[test]
+    fn test_validate_batch_size_above_range() {
+        let req = UpdateSettingsRequest {
+            batch_size: 21,
+            ..valid_request()
+        };
+        let err = req.validate().unwrap_err();
+        assert!(err.contains("batch_size"));
+    }
+
     #[test]
     fn test_validate_ai_model_websearch_too_long_rejected() {
         let req = UpdateSettingsRequest {

backend/src/services/prompts.rs

@@ -199,6 +199,7 @@ mod tests {
             max_articles_per_source: 3,
             use_llm_for_source_links: false,
             article_history_days: 90,
+            batch_size: 5,
             search_agent_behavior: String::new(),
             ai_provider: String::new(),
             ai_model: String::new(),

backend/src/services/synthesis.rs

@@ -398,7 +398,7 @@ async fn run_generation_inner(
         // 1b. Scrape, classify, summarize in batches of 5
         emit_progress(tx, "processing", "Traitement des articles...", 25);
         let total_candidates = candidate_urls.len();
-        let batch_size = 5;
+        let batch_size = settings.batch_size.max(1) as usize;
         let mut processed = 0usize;
         let mut candidates_iter = candidate_urls.into_iter();
         let mut done = false;

backend/tests/api_syntheses_test.rs

@@ -633,7 +633,8 @@ async fn generate_pipeline_resolves_model_from_admin_config() {
         "ai_model_websearch": "",
         "use_llm_for_source_links": false,
         "use_llm_for_article_extraction": false,
-        "article_history_days": 90
+        "article_history_days": 90,
+        "batch_size": 5
     });
     let (settings_status, _) = app
         .put_with_session("/api/v1/settings", &settings, &session)

e2e/tests/generation-live.spec.ts

@@ -143,6 +143,7 @@ test.describe('Live generation with OpenAI', () => {
       ai_model_websearch: 'gpt-4o-mini',
       use_llm_for_source_links: false,
       article_history_days: 90,
+      batch_size: 5,
     });
     expect(settingsResp.status).toBe(200);
 

frontend/src/i18n/fr.ts

@@ -153,6 +153,8 @@ const fr = {
   'settings.advancedExtraction': 'Extraction avancee',
   'settings.useLlmForSourceLinks': "Utiliser l'IA pour extraire les liens",
   'settings.articleHistoryDays': 'Historique des articles (jours)',
+  'settings.batchSize': 'Taille du lot de traitement',
+  'settings.batchSizeHelp': 'Nombre d\'articles traites en parallele lors de la generation (defaut: 5).',
   'settings.export': 'Exporter',
   'settings.import': 'Importer',
   'settings.exportIncludeKeys': 'Inclure les cles API',

frontend/src/pages/Settings.tsx

@@ -458,6 +458,33 @@ const Settings: Component = () => {
                 </A>
               </div>
             </div>
+
+            <div>
+              <label
+                for="batchSize"
+                class="block text-sm font-medium text-gray-700"
+              >
+                {t('settings.batchSize')}
+              </label>
+              <p class="text-xs text-gray-500 mb-1">{t('settings.batchSizeHelp')}</p>
+              <div class="mt-1">
+                <input
+                  type="number"
+                  id="batchSize"
+                  min="1"
+                  max="20"
+                  class="shadow-sm focus:ring-indigo-500 focus:border-indigo-500 block w-full sm:text-sm border-gray-300 rounded-md py-2 px-3 border"
+                  value={settings().batch_size}
+                  onInput={(e) =>
+                    setSettings((prev) => ({
+                      ...prev,
+                      batch_size:
+                        parseInt(e.currentTarget.value) || 5,
+                    }))
+                  }
+                />
+              </div>
+            </div>
           </div>
 
           {/* Advanced extraction */}

frontend/src/types.ts

@@ -46,6 +46,7 @@ export interface UserSettings {
   max_articles_per_source: number;
   use_llm_for_source_links: boolean;
   article_history_days: number;
+  batch_size: number;
   search_agent_behavior: string;
   ai_model: string;
   ai_model_websearch: string;
@@ -62,6 +63,7 @@ export const DEFAULT_SETTINGS: UserSettings = {
   max_articles_per_source: 3,
   use_llm_for_source_links: false,
   article_history_days: 90,
+  batch_size: 5,
   search_agent_behavior:
     "Tu peux egalement utiliser d'autres sources pertinentes trouvees via la recherche Google.",
   ai_model: '',