feat: RSS embeddings, semantic news in chat, article-to-chat, richer briefings

- Embed RSS items at fetch time (nomic-embed-text); backfill at startup
- Semantic news search injected into chat system prompt ("Recent News You've Seen")
  when items match query above 0.55 cosine threshold (independent of note RAG)
- "Discuss in chat" button on news cards — creates a seeded conversation with
  the article title + full content, navigates directly to the new chat
- Briefing compilation now passes 500-char article excerpts (not just headlines)
  to the LLM and uses 8192 num_ctx to accommodate the larger prompt

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

src/fabledassistant/services/embeddings.py

@@ -1,6 +1,7 @@
 """Semantic note search via Ollama embedding model (nomic-embed-text).
 
 Embeddings are stored in the note_embeddings table (one row per note).
+RSS item embeddings are stored in rss_item_embeddings (one row per item).
 All search operations degrade gracefully — if the embedding model is
 unavailable the callers fall back to keyword search.
 """
@@ -8,6 +9,7 @@ unavailable the callers fall back to keyword search.
 import asyncio
 import logging
 import math
+from datetime import datetime, timedelta, timezone
 
 import httpx
 from sqlalchemy import delete, select
@@ -16,6 +18,8 @@ from fabledassistant.config import Config
 from fabledassistant.models import async_session
 from fabledassistant.models.embedding import NoteEmbedding
 from fabledassistant.models.note import Note
+from fabledassistant.models.rss_feed import RssItem
+from fabledassistant.models.rss_item_embedding import RssItemEmbedding
 
 logger = logging.getLogger(__name__)
 
@@ -24,6 +28,10 @@ logger = logging.getLogger(__name__)
 # 0.45 keeps only genuinely relevant notes; lower values like 0.30 let in
 # loosely-related results that pad the sidebar without adding real value.
 _SIMILARITY_THRESHOLD = 0.45
+_RSS_SIMILARITY_THRESHOLD = 0.55
+_RSS_SEARCH_LIMIT = 3
+_RSS_SEARCH_DAYS = 30
+_RSS_SNIPPET_CHARS = 500
 
 
 async def get_embedding(text: str, model: str | None = None) -> list[float]:
@@ -172,3 +180,120 @@ async def backfill_note_embeddings() -> None:
         await asyncio.sleep(0.05)  # gentle pacing
 
     logger.info("Embedding backfill complete: %d/%d notes embedded", success, len(notes_to_embed))
+
+
+# ── RSS item embeddings ───────────────────────────────────────────────────────
+
+async def upsert_rss_item_embedding(item_id: int, user_id: int, title: str, content: str) -> None:
+    """Generate and persist an embedding for an RSS item. Safe to fire-and-forget."""
+    text = f"{title}\n{content}".strip()
+    if not text:
+        return
+    try:
+        embedding = await get_embedding(text)
+    except Exception:
+        logger.debug("Skipping embedding for RSS item %d — model unavailable", item_id)
+        return
+
+    try:
+        async with async_session() as session:
+            await session.execute(
+                delete(RssItemEmbedding).where(RssItemEmbedding.rss_item_id == item_id)
+            )
+            session.add(RssItemEmbedding(rss_item_id=item_id, user_id=user_id, embedding=embedding))
+            await session.commit()
+        logger.debug("Upserted embedding for RSS item %d", item_id)
+    except Exception:
+        logger.warning("Failed to persist embedding for RSS item %d", item_id, exc_info=True)
+
+
+async def semantic_search_rss_items(
+    user_id: int,
+    query_vector: list[float],
+    limit: int = _RSS_SEARCH_LIMIT,
+    days: int = _RSS_SEARCH_DAYS,
+) -> list[tuple[float, RssItem]]:
+    """Return up to *limit* (score, RssItem) pairs most relevant to *query_vector*.
+
+    Only considers items fetched within the last *days* days.
+    Returns an empty list on any error.
+    """
+    since = datetime.now(timezone.utc) - timedelta(days=days)
+    try:
+        async with async_session() as session:
+            stmt = (
+                select(RssItemEmbedding, RssItem)
+                .join(RssItem, RssItemEmbedding.rss_item_id == RssItem.id)
+                .where(
+                    RssItemEmbedding.user_id == user_id,
+                    RssItem.fetched_at >= since,
+                )
+            )
+            rows = list((await session.execute(stmt)).all())
+    except Exception:
+        logger.warning("Failed to query RSS item embeddings", exc_info=True)
+        return []
+
+    if not rows:
+        return []
+
+    scored: list[tuple[float, RssItem]] = []
+    for rie, item in rows:
+        try:
+            sim = _cosine_similarity(query_vector, rie.embedding)
+        except Exception:
+            continue
+        if sim >= _RSS_SIMILARITY_THRESHOLD:
+            scored.append((sim, item))
+
+    scored.sort(key=lambda x: x[0], reverse=True)
+    return scored[:limit]
+
+
+async def backfill_rss_item_embeddings() -> None:
+    """Generate embeddings for all RSS items that don't have one yet.
+
+    Runs as a background task at startup. Adds a small sleep between items
+    to avoid overwhelming Ollama.
+    """
+    try:
+        async with async_session() as session:
+            existing = {
+                row[0]
+                for row in (
+                    await session.execute(select(RssItemEmbedding.rss_item_id))
+                ).fetchall()
+            }
+            result = await session.execute(
+                select(RssItem.id, RssItem.feed_id, RssItem.title, RssItem.content)
+            )
+            items_to_embed = [row for row in result.fetchall() if row[0] not in existing]
+    except Exception:
+        logger.warning("RSS embedding backfill: failed to query items", exc_info=True)
+        return
+
+    if not items_to_embed:
+        logger.info("RSS embedding backfill: all items already have embeddings")
+        return
+
+    # Resolve user_id per feed_id
+    try:
+        from fabledassistant.models.rss_feed import RssFeed
+        async with async_session() as session:
+            result = await session.execute(select(RssFeed.id, RssFeed.user_id))
+            feed_user_map = {fid: uid for fid, uid in result.fetchall()}
+    except Exception:
+        logger.warning("RSS embedding backfill: failed to load feed user map", exc_info=True)
+        return
+
+    logger.info("RSS embedding backfill: generating embeddings for %d items", len(items_to_embed))
+    success = 0
+    for item_id, feed_id, title, content in items_to_embed:
+        user_id = feed_user_map.get(feed_id)
+        if user_id is None:
+            continue
+        await upsert_rss_item_embedding(item_id, user_id, title or "", content or "")
+        success += 1
+        await asyncio.sleep(0.05)
+
+    logger.info("RSS embedding backfill complete: %d/%d items embedded", success, len(items_to_embed))