refactor(agents): move middleware package to app/agents/shared (slice 5c)

Relocate the entire new_chat/middleware/ package to the shared kernel as one
cohesive unit (it is live shared infrastructure: the multi-agent stack wraps
nearly every middleware via multi_agent_chat/middleware/main_agent/*, and
anonymous_agent consumes it too). Flip 69 live importers across both the
package-path and submodule-path forms.

Shims left for the frozen single-agent stack: a package __init__ re-export plus
submodule shims for permission, skills_backends, and scoped_model_fallback
(the three imported via submodule path by chat_deepagent/subagents).

Cycle break: importing shared.middleware previously reached back into
new_chat.tools at module load, which dragged in new_chat.__init__ ->
chat_deepagent -> the middleware shim -> half-initialized shared.middleware.
Made action_log's ToolDefinition import TYPE_CHECKING-only and
tool_call_repair's INVALID_TOOL_NAME import function-local. These tools-package
back-edges fully resolve in slice 6.

Asset note: skills_backends._default_builtin_root now walks to
app/agents/new_chat/skills/builtin (the skills/ tree migrates in slice 7).

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 import logging
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware import ActionLogMiddleware
+from app.agents.shared.middleware import ActionLogMiddleware
 from app.agents.new_chat.tools.registry import BUILTIN_TOOLS
 
 from ..shared.flags import enabled

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

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.new_chat.middleware import AnonymousDocumentMiddleware
+from app.agents.shared.middleware import AnonymousDocumentMiddleware
 
 
 def build_anonymous_doc_mw(

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

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware import BusyMutexMiddleware
+from app.agents.shared.middleware import BusyMutexMiddleware
 
 from ..shared.flags import enabled
 

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

@@ -11,7 +11,7 @@ from app.agents.multi_agent_chat.main_agent.context_prune.prune_tool_names impor
     safe_exclude_tools,
 )
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware import (
+from app.agents.shared.middleware import (
     ClearToolUsesEdit,
     SpillingContextEditingMiddleware,
     SpillToBackendEdit,

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

@@ -6,7 +6,7 @@ from collections.abc import Sequence
 
 from langchain_core.tools import BaseTool
 
-from app.agents.new_chat.middleware import DedupHITLToolCallsMiddleware
+from app.agents.shared.middleware import DedupHITLToolCallsMiddleware
 
 
 def build_dedup_hitl_mw(tools: Sequence[BaseTool]) -> DedupHITLToolCallsMiddleware:

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

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware import DoomLoopMiddleware
+from app.agents.shared.middleware import DoomLoopMiddleware
 
 from ..shared.flags import enabled
 

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

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.new_chat.middleware import KnowledgeBasePersistenceMiddleware
+from app.agents.shared.middleware import KnowledgeBasePersistenceMiddleware
 
 
 def build_kb_persistence_mw(

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 from langchain_core.language_models import BaseChatModel
 
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.new_chat.middleware import KnowledgePriorityMiddleware
+from app.agents.shared.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

@@ -5,7 +5,7 @@ from __future__ import annotations
 from langchain_core.language_models import BaseChatModel
 
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.new_chat.middleware import KnowledgeTreeMiddleware
+from app.agents.shared.middleware import KnowledgeTreeMiddleware
 
 
 def build_knowledge_tree_mw(

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

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware import NoopInjectionMiddleware
+from app.agents.shared.middleware import NoopInjectionMiddleware
 
 from ..shared.flags import enabled
 

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

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware import OtelSpanMiddleware
+from app.agents.shared.middleware import OtelSpanMiddleware
 
 from ..shared.flags import enabled
 

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

@@ -7,7 +7,7 @@ from collections.abc import Sequence
 from langchain_core.tools import BaseTool
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware import ToolCallNameRepairMiddleware
+from app.agents.shared.middleware import ToolCallNameRepairMiddleware
 
 from ..shared.flags import enabled
 

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

@@ -8,7 +8,7 @@ from deepagents.middleware.skills import SkillsMiddleware
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.new_chat.middleware import (
+from app.agents.shared.middleware import (
     build_skills_backend_factory,
     default_skills_sources,
 )

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

@@ -7,7 +7,7 @@ from typing import Any
 from deepagents.backends import StateBackend
 from langchain_core.language_models import BaseChatModel
 
-from app.agents.new_chat.middleware import create_surfsense_compaction_middleware
+from app.agents.shared.middleware import create_surfsense_compaction_middleware
 
 
 def build_compaction_mw(llm: BaseChatModel) -> Any:

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

@@ -9,7 +9,7 @@ from langchain.tools import ToolRuntime
 
 from app.agents.shared.filesystem_selection import FilesystemMode
 from app.agents.shared.filesystem_state import SurfSenseFilesystemState
-from app.agents.new_chat.middleware.multi_root_local_folder_backend import (
+from app.agents.shared.middleware.multi_root_local_folder_backend import (
     MultiRootLocalFolderBackend,
 )
 

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

@@ -12,7 +12,7 @@ from langchain_core.tools import BaseTool, StructuredTool
 from langgraph.types import Command
 
 from app.agents.shared.filesystem_state import SurfSenseFilesystemState
-from app.agents.new_chat.middleware.kb_postgres_backend import KBPostgresBackend
+from app.agents.shared.middleware.kb_postgres_backend import KBPostgresBackend
 
 from ...middleware.async_dispatch import run_async_blocking
 from ...middleware.mode import is_cloud

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

@@ -10,7 +10,7 @@ from langchain.tools import ToolRuntime
 from langchain_core.tools import BaseTool, StructuredTool
 
 from app.agents.shared.filesystem_state import SurfSenseFilesystemState
-from app.agents.new_chat.middleware.kb_postgres_backend import KBPostgresBackend
+from app.agents.shared.middleware.kb_postgres_backend import KBPostgresBackend
 
 from ...middleware.async_dispatch import run_async_blocking
 from ...middleware.path_resolution import resolve_list_target_path

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

@@ -9,7 +9,7 @@ from langchain.tools import ToolRuntime
 from langchain_core.tools import BaseTool, StructuredTool
 
 from app.agents.shared.filesystem_state import SurfSenseFilesystemState
-from app.agents.new_chat.middleware.kb_postgres_backend import paginate_listing
+from app.agents.shared.middleware.kb_postgres_backend import paginate_listing
 
 from ...middleware.async_dispatch import run_async_blocking
 from ...middleware.path_resolution import resolve_list_target_path

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

@@ -9,7 +9,7 @@ from langchain_core.messages import ToolMessage
 from langgraph.types import Command
 
 from app.agents.shared.filesystem_state import SurfSenseFilesystemState
-from app.agents.new_chat.middleware.kb_postgres_backend import KBPostgresBackend
+from app.agents.shared.middleware.kb_postgres_backend import KBPostgresBackend
 from app.agents.shared.path_resolver import DOCUMENTS_ROOT
 from app.agents.shared.state_reducers import _CLEAR
 

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

@@ -11,7 +11,7 @@ from langchain_core.tools import BaseTool, StructuredTool
 from langgraph.types import Command
 
 from app.agents.shared.filesystem_state import SurfSenseFilesystemState
-from app.agents.new_chat.middleware.kb_postgres_backend import KBPostgresBackend
+from app.agents.shared.middleware.kb_postgres_backend import KBPostgresBackend
 
 from ...middleware.async_dispatch import run_async_blocking
 from ...middleware.path_resolution import resolve_relative

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

@@ -13,7 +13,7 @@ from langchain_core.messages import ToolMessage
 from langgraph.types import Command
 
 from app.agents.shared.filesystem_state import SurfSenseFilesystemState
-from app.agents.new_chat.middleware.kb_postgres_backend import KBPostgresBackend
+from app.agents.shared.middleware.kb_postgres_backend import KBPostgresBackend
 from app.agents.shared.path_resolver import DOCUMENTS_ROOT
 from app.agents.shared.state_reducers import _CLEAR
 

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

@@ -14,7 +14,7 @@ from langchain_core.messages import ToolMessage
 from langgraph.types import Command
 
 from app.agents.shared.filesystem_state import SurfSenseFilesystemState
-from app.agents.new_chat.middleware.kb_postgres_backend import KBPostgresBackend
+from app.agents.shared.middleware.kb_postgres_backend import KBPostgresBackend
 from app.agents.shared.path_resolver import DOCUMENTS_ROOT
 from app.agents.shared.state_reducers import _CLEAR
 

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

@@ -10,7 +10,7 @@ from langchain_core.messages import SystemMessage
 from langgraph.runtime import Runtime
 
 from app.agents.shared.filesystem_state import SurfSenseFilesystemState
-from app.agents.new_chat.middleware.knowledge_search import _render_priority_message
+from app.agents.shared.middleware.knowledge_search import _render_priority_message
 from app.utils.perf import get_perf_logger
 
 _perf_log = get_perf_logger()

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

@@ -2,7 +2,7 @@
 
 from __future__ import annotations
 
-from app.agents.new_chat.middleware import MemoryInjectionMiddleware
+from app.agents.shared.middleware import MemoryInjectionMiddleware
 from app.db import ChatVisibility
 
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/resilience/bundle.py

@@ -11,8 +11,8 @@ from langchain.agents.middleware import (
 )
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware import RetryAfterMiddleware
-from app.agents.new_chat.middleware.scoped_model_fallback import (
+from app.agents.shared.middleware import RetryAfterMiddleware
+from app.agents.shared.middleware.scoped_model_fallback import (
     ScopedModelFallbackMiddleware,
 )
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/resilience/fallback.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 import logging
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware.scoped_model_fallback import (
+from app.agents.shared.middleware.scoped_model_fallback import (
     ScopedModelFallbackMiddleware,
 )
 

surfsense_backend/app/agents/multi_agent_chat/middleware/shared/resilience/retry.py

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware import RetryAfterMiddleware
+from app.agents.shared.middleware import RetryAfterMiddleware
 
 from ..flags import enabled