refactor(agents): move checkpointer + mention_resolver to app/agents/shared (slice 5b)

Two independent leaf modules (no intra-new_chat deps, no frozen importer),
consumed only by flows/routes/tests. Flipped 8 importers across both the
dotted-path and module-style (from app.agents.new_chat import mention_resolver)
forms. No shims needed.

surfsense_backend/app/app.py

@@ -23,7 +23,7 @@ from starlette.requests import Request as StarletteRequest
 from starlette.responses import Response as StarletteResponse
 from uvicorn.middleware.proxy_headers import ProxyHeadersMiddleware
 
-from app.agents.new_chat.checkpointer import (
+from app.agents.shared.checkpointer import (
     close_checkpointer,
     setup_checkpointer_tables,
 )

surfsense_backend/app/automations/actions/builtin/agent_task/invoke.py

@@ -12,7 +12,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.agents.multi_agent_chat import create_multi_agent_chat_deep_agent
 from app.agents.shared.context import SurfSenseContextSchema
-from app.agents.new_chat.mention_resolver import resolve_mentions, substitute_in_text
+from app.agents.shared.mention_resolver import resolve_mentions, substitute_in_text
 from app.db import ChatVisibility, async_session_maker
 from app.schemas.new_chat import MentionedDocumentInfo
 

surfsense_backend/app/routes/anonymous_chat_routes.py

@@ -352,7 +352,7 @@ async def stream_anonymous_chat(
         from langchain_core.messages import AIMessage, HumanMessage
 
         from app.agents.new_chat.anonymous_agent import create_anonymous_chat_agent
-        from app.agents.new_chat.checkpointer import get_checkpointer
+        from app.agents.shared.checkpointer import get_checkpointer
         from app.db import shielded_async_session
         from app.services.new_streaming_service import VercelStreamingService
         from app.services.token_tracking_service import start_turn

surfsense_backend/app/routes/new_chat_routes.py

@@ -1934,7 +1934,7 @@ async def regenerate_response(
     """
     from langchain_core.messages import HumanMessage
 
-    from app.agents.new_chat.checkpointer import get_checkpointer
+    from app.agents.shared.checkpointer import get_checkpointer
 
     try:
         # Verify thread exists and user has permission

surfsense_backend/app/tasks/chat/stream_new_chat.py

@@ -28,7 +28,7 @@ from sqlalchemy.future import select
 
 from app.agents.multi_agent_chat import create_multi_agent_chat_deep_agent
 from app.agents.new_chat.chat_deepagent import create_surfsense_deep_agent
-from app.agents.new_chat.checkpointer import get_checkpointer
+from app.agents.shared.checkpointer import get_checkpointer
 from app.agents.shared.context import SurfSenseContextSchema
 from app.agents.shared.errors import BusyError
 from app.agents.shared.filesystem_selection import FilesystemMode, FilesystemSelection
@@ -39,7 +39,7 @@ from app.agents.shared.llm_config import (
     load_agent_config,
     load_global_llm_config_by_id,
 )
-from app.agents.new_chat.mention_resolver import resolve_mentions, substitute_in_text
+from app.agents.shared.mention_resolver import resolve_mentions, substitute_in_text
 from app.agents.new_chat.middleware.busy_mutex import (
     end_turn,
     get_cancel_state,

surfsense_backend/app/tasks/chat/streaming/flows/new_chat/input_state.py

@@ -29,7 +29,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.future import select
 
 from app.agents.shared.filesystem_selection import FilesystemMode
-from app.agents.new_chat.mention_resolver import resolve_mentions, substitute_in_text
+from app.agents.shared.mention_resolver import resolve_mentions, substitute_in_text
 from app.db import (
     ChatVisibility,
     NewChatThread,

surfsense_backend/app/tasks/chat/streaming/flows/shared/pre_stream_setup.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.agents.new_chat.checkpointer import get_checkpointer
+from app.agents.shared.checkpointer import get_checkpointer
 from app.db import SearchSourceConnectorType
 from app.services.connector_service import ConnectorService
 
@@ -33,7 +33,7 @@ async def setup_connector_and_firecrawl(
 async def get_chat_checkpointer():
     """Resolve the PostgreSQL checkpointer for persistent conversation memory.
 
-    Thin wrapper around ``app.agents.new_chat.checkpointer.get_checkpointer`` so
+    Thin wrapper around ``app.agents.shared.checkpointer.get_checkpointer`` so
     flow orchestrators can rely on a streaming-local symbol and we have a hook
     point if the checkpointer source ever needs to vary per flow.
     """

surfsense_backend/tests/unit/agents/new_chat/test_mention_resolver.py

@@ -15,8 +15,8 @@ from unittest.mock import AsyncMock, MagicMock
 
 import pytest
 
-from app.agents.new_chat import mention_resolver
-from app.agents.new_chat.mention_resolver import (
+from app.agents.shared import mention_resolver
+from app.agents.shared.mention_resolver import (
     ResolvedMention,
     ResolvedMentionSet,
     resolve_mentions,