Add shared_memory backend (constants + helpers), UserMemory docstring (SUR-152)

surfsense_backend/app/agents/new_chat/tools/shared_memory.py

@@ -0,0 +1,39 @@
+"""Shared (team) memory backend for search-space-scoped AI context."""
+
+import logging
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.db import SharedMemory
+
+logger = logging.getLogger(__name__)
+
+DEFAULT_RECALL_TOP_K = 5
+MAX_MEMORIES_PER_SEARCH_SPACE = 250
+
+
+async def get_shared_memory_count(
+    db_session: AsyncSession,
+    search_space_id: int,
+) -> int:
+    result = await db_session.execute(
+        select(SharedMemory).where(SharedMemory.search_space_id == search_space_id)
+    )
+    return len(result.scalars().all())
+
+
+async def delete_oldest_shared_memory(
+    db_session: AsyncSession,
+    search_space_id: int,
+) -> None:
+    result = await db_session.execute(
+        select(SharedMemory)
+        .where(SharedMemory.search_space_id == search_space_id)
+        .order_by(SharedMemory.updated_at.asc())
+        .limit(1)
+    )
+    oldest = result.scalars().first()
+    if oldest:
+        await db_session.delete(oldest)
+        await db_session.commit()