feat: modo diff para /watch — notifica solo si hay novedades reales

src/db/database.py

@@ -159,6 +159,27 @@ class ResearchDB:
         row = await cursor.fetchone()
         return dict(row) if row else None
 
+    async def get_session_urls(self, session_id: int) -> set:
+        async with self.db.execute(
+            "SELECT url FROM sources WHERE session_id = ?", (session_id,)
+        ) as cur:
+            rows = await cur.fetchall()
+            return {r[0] for r in rows}
+
+    async def get_previous_session(self, chat_id: int, topic: str,
+                                    exclude_session_id: int) -> Optional[dict]:
+        async with self.db.execute(
+            """SELECT id, topic, status, created_at FROM research_sessions
+               WHERE telegram_chat_id = ? AND topic = ? AND id != ?
+               ORDER BY created_at DESC LIMIT 1""",
+            (chat_id, topic, exclude_session_id)
+        ) as cur:
+            row = await cur.fetchone()
+            if not row:
+                return None
+            return {"id": row[0], "topic": row[1],
+                    "status": row[2], "created_at": row[3]}
+
     async def get_active_session(self, chat_id: int) -> Optional[dict]:
         cursor = await self.db.execute(
             """SELECT * FROM research_sessions