feat: parallel source extraction, shuffle candidates, clear history endpoint

- Remove 10-source cap; all sources are now processed
- Increase max links per source from 10 to 15
- Extract article links in parallel (up to 5 concurrent) using JoinSet
- Shuffle candidate URLs after history filtering to interleave sources
- Add DELETE /api/v1/article-history endpoint to clear all history for a user

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

backend/src/db/article_history.rs

@@ -201,6 +201,15 @@ pub async fn get_last_source_url(
     Ok(result)
 }
 
+/// Delete ALL article history entries for a user.
+pub async fn delete_all_for_user(pool: &PgPool, user_id: Uuid) -> Result<u64, AppError> {
+    let result = sqlx::query("DELETE FROM article_history WHERE user_id = $1")
+        .bind(user_id)
+        .execute(pool)
+        .await?;
+    Ok(result.rows_affected())
+}
+
 /// Delete history entries older than N days for this user.
 ///
 /// Only removes entries where synthesis_id IS NULL (dropped articles).

backend/src/handlers/article_history.rs

@@ -54,6 +54,18 @@ pub async fn list_history(
     })))
 }
 
+/// DELETE /api/v1/article-history
+///
+/// Deletes ALL article history entries for the authenticated user.
+pub async fn clear_history(
+    auth_user: AuthUser,
+    State(state): State<AppState>,
+) -> Result<impl IntoResponse, AppError> {
+    let deleted = db::article_history::delete_all_for_user(&state.pool, auth_user.id).await?;
+    tracing::info!(user_id = %auth_user.id, deleted = deleted, "Cleared article history");
+    Ok(Json(serde_json::json!({ "deleted": deleted })))
+}
+
 /// GET /api/v1/syntheses/:id/provenance
 ///
 /// Returns all article history entries for the generation run

backend/src/router.rs

@@ -55,7 +55,7 @@ pub fn build_router(state: AppState, config: &AppConfig) -> Router {
         .route("/syntheses/generate", post(handlers::generation::trigger_generate))
         .route("/syntheses/generate/{job_id}/progress", get(handlers::generation::progress_stream))
         // Article history & provenance routes (authenticated)
-        .route("/article-history", get(handlers::article_history::list_history))
+        .route("/article-history", get(handlers::article_history::list_history).delete(handlers::article_history::clear_history))
         .route("/syntheses/{id}/provenance", get(handlers::article_history::get_provenance))
         // LLM call log routes (authenticated)
         .route("/llm-logs/{job_id}", get(handlers::llm_logs::get_logs))

backend/src/services/synthesis.rs

@@ -281,32 +281,79 @@ async fn run_generation_inner(
 
         let last_source = db::article_history::get_last_source_url(&state.pool, user_id).await.unwrap_or(None);
         let rotated_sources = rotate_sources(sources.clone(), last_source.as_deref());
-        let max_sources = rotated_sources.len().min(10);
+        let max_links = 15usize;
-        let max_links = 10usize;
 
-        // 1a. Extract article links + filter against history
+        // 1a. Extract article links from source pages (parallel, max 5 concurrent)
-        let mut candidate_urls: Vec<(String, String)> = Vec::new(); // (article_url, source_url)
+        let mut candidate_urls: Vec<(String, String)> = Vec::new();
-
+        {
-        for source in rotated_sources.iter().take(max_sources) {
+            let mut join_set = tokio::task::JoinSet::new();
-            let links = if settings.use_llm_for_source_links {
+            let mut pending = rotated_sources.iter().peekable();
+            let max_concurrent = 5;
+
+            // Seed initial tasks
+            for _ in 0..max_concurrent {
+                if let Some(source) = pending.next() {
+                    let client = state.http_client.clone();
+                    let source_url = source.url.clone();
+                    let source_title = source.title.clone();
+                    let use_llm = settings.use_llm_for_source_links;
+                    let provider_clone = std::sync::Arc::clone(&provider);
+                    let model = model_research.clone();
+                    let max_l = max_links;
+                    join_set.spawn(async move {
+                        let links = if use_llm {
                             source_scraper::extract_article_links_with_llm(
-                    &state.http_client, &source.url, max_links, &provider, &model_research,
+                                &client, &source_url, max_l, &provider_clone, &model,
                             ).await
                         } else {
                             source_scraper::extract_article_links(
-                    &state.http_client, &source.url, max_links,
+                                &client, &source_url, max_l,
                             ).await
                         };
+                        (source_url, source_title, links)
+                    });
+                }
+            }
 
-            if let Ok(links) = links {
+            while let Some(join_result) = join_set.join_next().await {
-                tracing::info!(source = %source.title, links = links.len(), "Extracted links from source");
+                if let Ok((source_url, source_title, links_result)) = join_result {
+                    match links_result {
+                        Ok(links) => {
+                            tracing::info!(source = %source_title, links = links.len(), "Extracted links from source");
                             for link in links {
                                 if seen_urls.insert(link.to_lowercase()) {
-                        candidate_urls.push((link, source.url.clone()));
+                                    candidate_urls.push((link, source_url.clone()));
+                                }
+                            }
+                        }
+                        Err(e) => {
+                            tracing::warn!(source = %source_title, error = %e, "Failed to extract links");
+                        }
                     }
                 }
-            } else if let Err(e) = links {
+
-                tracing::warn!(source = %source.title, error = %e, "Failed to extract links");
+                // Spawn next task
+                if let Some(source) = pending.next() {
+                    let client = state.http_client.clone();
+                    let source_url = source.url.clone();
+                    let source_title = source.title.clone();
+                    let use_llm = settings.use_llm_for_source_links;
+                    let provider_clone = std::sync::Arc::clone(&provider);
+                    let model = model_research.clone();
+                    let max_l = max_links;
+                    join_set.spawn(async move {
+                        let links = if use_llm {
+                            source_scraper::extract_article_links_with_llm(
+                                &client, &source_url, max_l, &provider_clone, &model,
+                            ).await
+                        } else {
+                            source_scraper::extract_article_links(
+                                &client, &source_url, max_l,
+                            ).await
+                        };
+                        (source_url, source_title, links)
+                    });
+                }
             }
         }
 
@@ -324,6 +371,10 @@ async fn run_generation_inner(
             }
         }
 
+        // Shuffle candidates to interleave articles from different sources
+        use rand::seq::SliceRandom;
+        candidate_urls.shuffle(&mut rand::thread_rng());
+
         // Track url -> source
         for (url, source_url) in &candidate_urls {
             url_source.insert(url.clone(), source_url.clone());