refactor(agents): move MAC graph-state schema into multi_agent_chat/shared/state/

filesystem_state.py (the multi-agent graph state) and state_reducers.py
(its merge reducers) are consumed only by multi_agent_chat (filesystem
tools/middleware, kb projection, and the MAC-only shared middleware) plus
two unit tests -- no external app code. Relocate them into a dedicated
multi_agent_chat/shared/state/ package (filesystem_state.py + reducers.py)
and repoint every importer.

No behavior change; import-all + the full unit/middleware + unit/agents
suites (1066 tests) stay green.

surfsense_backend/app/agents/shared/middleware/anonymous_document.py

@@ -24,7 +24,9 @@ from typing import Any
 from langchain.agents.middleware import AgentMiddleware, AgentState
 from langgraph.runtime import Runtime
 
-from app.agents.shared.filesystem_state import SurfSenseFilesystemState
+from app.agents.multi_agent_chat.shared.state.filesystem_state import (
+    SurfSenseFilesystemState,
+)
 from app.agents.shared.path_resolver import DOCUMENTS_ROOT, safe_filename
 
 logger = logging.getLogger(__name__)

surfsense_backend/app/agents/shared/middleware/kb_persistence.py

@@ -45,16 +45,18 @@ from sqlalchemy import delete, select, update
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from app.agents.multi_agent_chat.shared.state.filesystem_state import (
+    SurfSenseFilesystemState,
+)
+from app.agents.multi_agent_chat.shared.state.reducers import _CLEAR
 from app.agents.shared.feature_flags import get_flags
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.shared.filesystem_state import SurfSenseFilesystemState
 from app.agents.shared.path_resolver import (
     DOCUMENTS_ROOT,
     parse_documents_path,
     safe_folder_segment,
     virtual_path_to_doc,
 )
-from app.agents.shared.state_reducers import _CLEAR
 from app.agents.shared.receipt import Receipt, make_receipt
 from app.db import (
     AgentActionLog,

surfsense_backend/app/agents/shared/middleware/knowledge_search.py

@@ -45,9 +45,11 @@ from app.agents.multi_agent_chat.shared.date_filters import (
     parse_date_or_datetime,
     resolve_date_range,
 )
+from app.agents.multi_agent_chat.shared.state.filesystem_state import (
+    SurfSenseFilesystemState,
+)
 from app.agents.shared.feature_flags import get_flags
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.shared.filesystem_state import SurfSenseFilesystemState
 from app.agents.shared.path_resolver import (
     PathIndex,
     build_path_index,

surfsense_backend/app/agents/shared/middleware/knowledge_tree.py

@@ -33,8 +33,10 @@ from langchain_core.messages import SystemMessage
 from langgraph.runtime import Runtime
 from sqlalchemy import select
 
+from app.agents.multi_agent_chat.shared.state.filesystem_state import (
+    SurfSenseFilesystemState,
+)
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.shared.filesystem_state import SurfSenseFilesystemState
 from app.agents.shared.path_resolver import (
     DOCUMENTS_ROOT,
     PathIndex,