refactor(agents): move filesystem_selection to app/agents/shared (slice 3a)

Promote the filesystem mode contracts (FilesystemMode, FilesystemSelection,
ClientPlatform, LocalFilesystemMount) out of `new_chat` into the cross-agent
`app/agents/shared` kernel.

Pure leaf consumed across the whole multi-agent filesystem middleware/tool tree,
the chat flows/monolith, routes and tests. git mv (content unchanged) + flipped
all ~48 importers. A re-export shim remains at new_chat/filesystem_selection.py
only for the not-yet-retired single-agent (chat_deepagent).

Also updated the stream parity test's annotation normalizer to strip the new
app.agents.shared.filesystem_selection. prefix (the dataclasses' __module__
changed with the move), keeping monolith<->flows signature parity intact.

Behavior-preserving: only import paths change. 1326 tests green.

surfsense_backend/app/agents/multi_agent_chat/middleware/main_agent/anonymous_doc.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 from app.agents.new_chat.middleware import AnonymousDocumentMiddleware
 
 

surfsense_backend/app/agents/multi_agent_chat/middleware/main_agent/kb_persistence.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 from app.agents.new_chat.middleware import KnowledgeBasePersistenceMiddleware
 
 

surfsense_backend/app/agents/multi_agent_chat/middleware/main_agent/knowledge_priority.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 from langchain_core.language_models import BaseChatModel
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 from app.agents.new_chat.middleware import KnowledgePriorityMiddleware
 from app.services.llm_service import get_planner_llm
 

surfsense_backend/app/agents/multi_agent_chat/middleware/main_agent/knowledge_tree.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 from langchain_core.language_models import BaseChatModel
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 from app.agents.new_chat.middleware import KnowledgeTreeMiddleware
 
 

surfsense_backend/app/agents/multi_agent_chat/middleware/main_agent/skills.py

@@ -7,7 +7,7 @@ import logging
 from deepagents.middleware.skills import SkillsMiddleware
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 from app.agents.new_chat.middleware import (
     build_skills_backend_factory,
     default_skills_sources,

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/index.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 from typing import Any
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 from .middleware import SurfSenseFilesystemMiddleware
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/middleware/middleware.py

@@ -7,7 +7,7 @@ from typing import Any
 from deepagents import FilesystemMiddleware
 from langchain_core.tools import BaseTool
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 from app.agents.new_chat.filesystem_state import SurfSenseFilesystemState
 from app.agents.new_chat.sandbox import is_sandbox_enabled
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/middleware/mode.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 from app.agents.new_chat.path_resolver import DOCUMENTS_ROOT
 
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/middleware/path_resolution.py

@@ -7,7 +7,7 @@ from typing import TYPE_CHECKING
 
 from langchain.tools import ToolRuntime
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 from app.agents.new_chat.filesystem_state import SurfSenseFilesystemState
 from app.agents.new_chat.middleware.multi_root_local_folder_backend import (
     MultiRootLocalFolderBackend,

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/system_prompt/index.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 from .cloud import BODY as CLOUD_BODY
 from .common import HEADER, SANDBOX_ADDENDUM

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/cd/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _DESCRIPTION = """Changes the current working directory (cwd).
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/edit_file/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _CLOUD_DESCRIPTION = """Performs exact string replacements in files.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/execute_code/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _DESCRIPTION = """Executes Python code in an isolated sandbox environment.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/glob/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _DESCRIPTION = """Find files matching a glob pattern.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/grep/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _CLOUD_DESCRIPTION = """Search for a literal text pattern across files.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/list_tree/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _CLOUD_DESCRIPTION = """Lists files/folders recursively in a single bounded call.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/ls/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _CLOUD_DESCRIPTION = """Lists files and directories at the given path.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/mkdir/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _CLOUD_DESCRIPTION = """Creates a directory under `/documents/`.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/move_file/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _CLOUD_DESCRIPTION = """Moves or renames a file or folder.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/pwd/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _DESCRIPTION = """Prints the current working directory."""
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/read_file/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _DESCRIPTION = """Reads a file from the filesystem.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/rm/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _CLOUD_DESCRIPTION = """Deletes a single file under `/documents/`.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/rmdir/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _CLOUD_DESCRIPTION = """Deletes an empty directory under `/documents/`.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/filesystem/tools/write_file/description.py

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 
 _CLOUD_DESCRIPTION = """Writes a new text file to the workspace.
 

surfsense_backend/app/agents/multi_agent_chat/middleware/stack.py

@@ -32,7 +32,7 @@ from app.agents.multi_agent_chat.subagents.builtins.knowledge_base.ask_knowledge
     build_ask_knowledge_base_tool,
 )
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.filesystem_selection import FilesystemMode
+from app.agents.shared.filesystem_selection import FilesystemMode
 from app.db import ChatVisibility
 
 from .main_agent.action_log import build_action_log_mw