refactor(agents): move MAC middleware impls out of shared kernel

knowledge_search, memory_injection and scoped_model_fallback no longer
belong in the cross-agent kernel (app/agents/shared/middleware): they are
consumed only inside multi_agent_chat. Relocate each impl next to the
builder that uses it:

- knowledge_search.py -> multi_agent_chat/shared/middleware/ (genuinely
  shared: its _render_priority_message feeds kb_context_projection, used by
  both the main agent and the KB subagent)
- memory_injection.py -> multi_agent_chat/shared/middleware/ (beside its
  memory.py builder)
- scoped_model_fallback.py -> multi_agent_chat/shared/middleware/resilience/
  (beside fallback.py/bundle.py)

Impls moved verbatim (git rename). Builders/consumers now import the local
sibling; main_agent knowledge_priority imports the new shared path; shared
middleware barrel trimmed.

Tests: repoint imports; convert the knowledge_search monkeypatch targets
from brittle dotted-string form to object-based patching (monkeypatch.setattr
on the imported module), which is robust to import ordering. No behavior
change.

surfsense_backend/tests/integration/retriever/test_knowledge_search_date_filters.py

@@ -8,7 +8,10 @@ from datetime import UTC, datetime, timedelta
 import numpy as np
 import pytest
 
-from app.agents.shared.middleware.knowledge_search import search_knowledge_base
+from app.agents.multi_agent_chat.shared.middleware import knowledge_search as ks
+from app.agents.multi_agent_chat.shared.middleware.knowledge_search import (
+    search_knowledge_base,
+)
 
 from .conftest import DUMMY_EMBEDDING
 
@@ -26,13 +29,9 @@ async def test_search_knowledge_base_applies_date_filters(
     async def fake_shielded_async_session():
         yield db_session
 
+    monkeypatch.setattr(ks, "shielded_async_session", fake_shielded_async_session)
     monkeypatch.setattr(
-        "app.agents.shared.middleware.knowledge_search.shielded_async_session",
-        fake_shielded_async_session,
-    )
-    monkeypatch.setattr(
-        "app.agents.shared.middleware.knowledge_search.embed_texts",
-        lambda texts: [np.array(DUMMY_EMBEDDING) for _ in texts],
+        ks, "embed_texts", lambda texts: [np.array(DUMMY_EMBEDDING) for _ in texts]
     )
 
     space_id = seed_date_filtered_docs["search_space"].id

surfsense_backend/tests/unit/agents/new_chat/middleware/test_scoped_model_fallback.py

@@ -87,7 +87,7 @@ class RateLimitError(Exception):
 def _build_agent(primary: BaseChatModel, fallback: BaseChatModel):
     from langchain.agents import create_agent
 
-    from app.agents.shared.middleware.scoped_model_fallback import (
+    from app.agents.multi_agent_chat.shared.middleware.resilience.scoped_model_fallback import (
         ScopedModelFallbackMiddleware,
     )
 

surfsense_backend/tests/unit/middleware/test_knowledge_search.py

@@ -5,10 +5,11 @@ import json
 import pytest
 from langchain_core.messages import AIMessage, HumanMessage
 
+from app.agents.multi_agent_chat.shared.middleware import knowledge_search as ks
 from app.agents.multi_agent_chat.shared.middleware.filesystem.backends.document_xml import (
     build_document_xml as _build_document_xml,
 )
-from app.agents.shared.middleware.knowledge_search import (
+from app.agents.multi_agent_chat.shared.middleware.knowledge_search import (
     KBSearchPlan,
     KnowledgePriorityMiddleware,
     _normalize_optional_date_range,
@@ -260,7 +261,7 @@ class TestKnowledgePriorityMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
+            ks, "search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -303,7 +304,7 @@ class TestKnowledgePriorityMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
+            ks, "search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -332,7 +333,7 @@ class TestKnowledgePriorityMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
+            ks, "search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -377,11 +378,11 @@ class TestKnowledgePriorityMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.browse_recent_documents",
+            ks, "browse_recent_documents",
             fake_browse_recent_documents,
         )
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
+            ks, "search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -424,11 +425,11 @@ class TestKnowledgePriorityMiddlewarePlanner:
             return []
 
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.browse_recent_documents",
+            ks, "browse_recent_documents",
             fake_browse_recent_documents,
         )
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
+            ks, "search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -551,11 +552,11 @@ class TestKnowledgePriorityMentionDrain:
             return []
 
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.fetch_mentioned_documents",
+            ks, "fetch_mentioned_documents",
             fake_fetch_mentioned_documents,
         )
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
+            ks, "search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -599,11 +600,11 @@ class TestKnowledgePriorityMentionDrain:
             return []
 
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.fetch_mentioned_documents",
+            ks, "fetch_mentioned_documents",
             fake_fetch_mentioned_documents,
         )
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
+            ks, "search_knowledge_base",
             fake_search_knowledge_base,
         )
 
@@ -644,11 +645,11 @@ class TestKnowledgePriorityMentionDrain:
             return []
 
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.fetch_mentioned_documents",
+            ks, "fetch_mentioned_documents",
             fake_fetch_mentioned_documents,
         )
         monkeypatch.setattr(
-            "app.agents.shared.middleware.knowledge_search.search_knowledge_base",
+            ks, "search_knowledge_base",
             fake_search_knowledge_base,
         )