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/tests/unit/middleware/test_dedup_hitl_tool_calls.py

@@ -2,7 +2,7 @@ import pytest
 from langchain_core.messages import AIMessage
 from langchain_core.tools import StructuredTool
 
-from app.agents.new_chat.middleware.dedup_tool_calls import (
+from app.agents.shared.middleware.dedup_tool_calls import (
     DedupHITLToolCallsMiddleware,
     wrap_dedup_key_by_arg_name,
 )

surfsense_backend/tests/unit/middleware/test_file_intent_middleware.py

@@ -1,7 +1,7 @@
 import pytest
 from langchain_core.messages import AIMessage, HumanMessage
 
-from app.agents.new_chat.middleware.file_intent import (
+from app.agents.shared.middleware.file_intent import (
     FileIntentMiddleware,
     FileOperationIntent,
     _fallback_path,

surfsense_backend/tests/unit/middleware/test_filesystem_backends.py

@@ -9,7 +9,7 @@ from app.agents.shared.filesystem_selection import (
     FilesystemSelection,
     LocalFilesystemMount,
 )
-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/tests/unit/middleware/test_filesystem_middleware.py

@@ -19,7 +19,7 @@ from types import SimpleNamespace
 import pytest
 
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.new_chat.middleware.filesystem import (
+from app.agents.shared.middleware.filesystem import (
     SurfSenseFilesystemMiddleware,
     _build_filesystem_system_prompt,
     _build_tool_descriptions,

surfsense_backend/tests/unit/middleware/test_filesystem_verification.py

@@ -3,8 +3,8 @@ from pathlib import Path
 import pytest
 
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.new_chat.middleware.filesystem import SurfSenseFilesystemMiddleware
-from app.agents.new_chat.middleware.multi_root_local_folder_backend import (
+from app.agents.shared.middleware.filesystem import SurfSenseFilesystemMiddleware
+from app.agents.shared.middleware.multi_root_local_folder_backend import (
     MultiRootLocalFolderBackend,
 )
 

surfsense_backend/tests/unit/middleware/test_kb_persistence_filesystem_parity.py

@@ -15,7 +15,7 @@ from unittest.mock import AsyncMock
 import numpy as np
 import pytest
 
-from app.agents.new_chat.middleware import kb_persistence
+from app.agents.shared.middleware import kb_persistence
 from app.db import Document
 
 

surfsense_backend/tests/unit/middleware/test_kb_persistence_revisions.py

@@ -21,7 +21,7 @@ from unittest.mock import AsyncMock, MagicMock
 
 import pytest
 
-from app.agents.new_chat.middleware import kb_persistence
+from app.agents.shared.middleware import kb_persistence
 
 pytestmark = pytest.mark.unit
 

surfsense_backend/tests/unit/middleware/test_knowledge_search.py

@@ -6,7 +6,7 @@ import pytest
 from langchain_core.messages import AIMessage, HumanMessage
 
 from app.agents.shared.document_xml import build_document_xml as _build_document_xml
-from app.agents.new_chat.middleware.knowledge_search import (
+from app.agents.shared.middleware.knowledge_search import (
     KBSearchPlan,
     KnowledgeBaseSearchMiddleware,
     _normalize_optional_date_range,
@@ -258,7 +258,7 @@ class TestKnowledgeBaseSearchMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.search_knowledge_base",
+            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -301,7 +301,7 @@ class TestKnowledgeBaseSearchMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.search_knowledge_base",
+            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -330,7 +330,7 @@ class TestKnowledgeBaseSearchMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.search_knowledge_base",
+            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -375,11 +375,11 @@ class TestKnowledgeBaseSearchMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.browse_recent_documents",
+            "app.agents.shared.middleware.knowledge_search.browse_recent_documents",
             fake_browse_recent_documents,
         )
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.search_knowledge_base",
+            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -422,11 +422,11 @@ class TestKnowledgeBaseSearchMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.browse_recent_documents",
+            "app.agents.shared.middleware.knowledge_search.browse_recent_documents",
             fake_browse_recent_documents,
         )
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.search_knowledge_base",
+            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -549,11 +549,11 @@ class TestKnowledgePriorityMentionDrain:
             return []
 
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.fetch_mentioned_documents",
+            "app.agents.shared.middleware.knowledge_search.fetch_mentioned_documents",
             fake_fetch_mentioned_documents,
         )
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.search_knowledge_base",
+            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -597,11 +597,11 @@ class TestKnowledgePriorityMentionDrain:
             return []
 
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.fetch_mentioned_documents",
+            "app.agents.shared.middleware.knowledge_search.fetch_mentioned_documents",
             fake_fetch_mentioned_documents,
         )
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.search_knowledge_base",
+            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -642,11 +642,11 @@ class TestKnowledgePriorityMentionDrain:
             return []
 
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.fetch_mentioned_documents",
+            "app.agents.shared.middleware.knowledge_search.fetch_mentioned_documents",
             fake_fetch_mentioned_documents,
         )
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.knowledge_search.search_knowledge_base",
+            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
             fake_search_knowledge_base,
         )
 

surfsense_backend/tests/unit/middleware/test_knowledge_tree.py

@@ -9,7 +9,7 @@ contract cannot silently regress.
 
 from __future__ import annotations
 
-from app.agents.new_chat.middleware.knowledge_tree import KnowledgeTreeMiddleware
+from app.agents.shared.middleware.knowledge_tree import KnowledgeTreeMiddleware
 from app.agents.shared.path_resolver import DOCUMENTS_ROOT
 
 

surfsense_backend/tests/unit/middleware/test_local_folder_backend.py

@@ -2,7 +2,7 @@ from pathlib import Path
 
 import pytest
 
-from app.agents.new_chat.middleware.local_folder_backend import LocalFolderBackend
+from app.agents.shared.middleware.local_folder_backend import LocalFolderBackend
 
 pytestmark = pytest.mark.unit
 

surfsense_backend/tests/unit/middleware/test_multi_root_local_folder_backend.py

@@ -2,7 +2,7 @@ from pathlib import Path
 
 import pytest
 
-from app.agents.new_chat.middleware.multi_root_local_folder_backend import (
+from app.agents.shared.middleware.multi_root_local_folder_backend import (
     MultiRootLocalFolderBackend,
 )