refactor(agents): colocate main-agent middleware under main_agent/ slice

Vertical-slice colocation: all main-agent code should live under
main_agent/ instead of being split across a parallel middleware/main_agent
tree. Move multi_agent_chat/middleware/main_agent/ -> main_agent/middleware/
and its assembler middleware/stack.py -> main_agent/middleware/stack.py, so
the main-agent slice is self-contained (graph, runtime, system_prompt, tools,
middleware).

Genuinely cross-slice middleware (middleware/shared/, middleware/subagent/)
stays under multi_agent_chat/middleware/ for a later slice; the moved builders
now reference it via absolute imports.

Pure move + import rewrite (git-tracked renames). Verified: full unit suite
green (2430 passed, 1 skipped), including test_import_all and the
checkpointed-subagent middleware suite.

surfsense_backend/app/agents/multi_agent_chat/main_agent/graph/compile_graph_sync.py

@@ -11,7 +11,7 @@ from langchain_core.language_models import BaseChatModel
 from langchain_core.tools import BaseTool
 from langgraph.types import Checkpointer
 
-from app.agents.multi_agent_chat.middleware.stack import (
+from app.agents.multi_agent_chat.main_agent.middleware.stack import (
     build_main_agent_deepagent_middleware,
 )
 from app.agents.shared.context import SurfSenseContextSchema

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

@@ -8,7 +8,7 @@ from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.shared.middleware import ActionLogMiddleware
 from app.agents.shared.tools.registry import BUILTIN_TOOLS
 
-from ..shared.flags import enabled
+from app.agents.multi_agent_chat.middleware.shared.flags import enabled
 
 
 def build_action_log_mw(

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.shared.middleware import BusyMutexMiddleware
 
-from ..shared.flags import enabled
+from app.agents.multi_agent_chat.middleware.shared.flags import enabled
 
 
 def build_busy_mutex_mw(flags: AgentFeatureFlags) -> BusyMutexMiddleware | None:

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

@@ -17,7 +17,7 @@ from app.agents.shared.middleware import (
     SpillToBackendEdit,
 )
 
-from ..shared.flags import enabled
+from app.agents.multi_agent_chat.middleware.shared.flags import enabled
 
 
 def build_context_editing_mw(

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.shared.middleware import DoomLoopMiddleware
 
-from ..shared.flags import enabled
+from app.agents.multi_agent_chat.middleware.shared.flags import enabled
 
 
 def build_doom_loop_mw(flags: AgentFeatureFlags) -> DoomLoopMiddleware | None:

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.shared.middleware import NoopInjectionMiddleware
 
-from ..shared.flags import enabled
+from app.agents.multi_agent_chat.middleware.shared.flags import enabled
 
 
 def build_noop_injection_mw(flags: AgentFeatureFlags) -> NoopInjectionMiddleware | None:

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.shared.middleware import OtelSpanMiddleware
 
-from ..shared.flags import enabled
+from app.agents.multi_agent_chat.middleware.shared.flags import enabled
 
 
 def build_otel_mw(flags: AgentFeatureFlags) -> OtelSpanMiddleware | None:

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

@@ -15,7 +15,7 @@ from app.agents.shared.plugin_loader import (
 )
 from app.db import ChatVisibility
 
-from ..shared.flags import enabled
+from app.agents.multi_agent_chat.middleware.shared.flags import enabled
 
 
 def build_plugin_middlewares(

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

@@ -9,7 +9,7 @@ from langchain_core.tools import BaseTool
 from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.shared.middleware import ToolCallNameRepairMiddleware
 
-from ..shared.flags import enabled
+from app.agents.multi_agent_chat.middleware.shared.flags import enabled
 
 # deepagents-built-in tool names the repair pass treats as known.
 _DEEPAGENT_BUILTIN_TOOL_NAMES: frozenset[str] = frozenset(

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

@@ -13,7 +13,7 @@ from app.agents.shared.middleware import (
     default_skills_sources,
 )
 
-from ..shared.flags import enabled
+from app.agents.multi_agent_chat.middleware.shared.flags import enabled
 
 
 def build_skills_mw(

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

@@ -35,35 +35,37 @@ from app.agents.shared.feature_flags import AgentFeatureFlags
 from app.agents.shared.filesystem_selection import FilesystemMode
 from app.db import ChatVisibility
 
-from .main_agent.action_log import build_action_log_mw
-from .main_agent.anonymous_doc import build_anonymous_doc_mw
-from .main_agent.busy_mutex import build_busy_mutex_mw
-from .main_agent.checkpointed_subagent_middleware import (
+from .action_log import build_action_log_mw
+from .anonymous_doc import build_anonymous_doc_mw
+from .busy_mutex import build_busy_mutex_mw
+from .checkpointed_subagent_middleware import (
     SurfSenseCheckpointedSubAgentMiddleware,
 )
-from .main_agent.checkpointed_subagent_middleware.task_description import (
+from .checkpointed_subagent_middleware.task_description import (
     TASK_TOOL_DESCRIPTION,
 )
-from .main_agent.context_editing import build_context_editing_mw
-from .main_agent.dedup_hitl import build_dedup_hitl_mw
-from .main_agent.doom_loop import build_doom_loop_mw
-from .main_agent.kb_persistence import build_kb_persistence_mw
-from .main_agent.knowledge_priority import build_knowledge_priority_mw
-from .main_agent.knowledge_tree import build_knowledge_tree_mw
-from .main_agent.noop_injection import build_noop_injection_mw
-from .main_agent.otel import build_otel_mw
-from .main_agent.plugins import build_plugin_middlewares
-from .main_agent.repair import build_repair_mw
-from .main_agent.skills import build_skills_mw
-from .shared.anthropic_cache import build_anthropic_cache_mw
-from .shared.compaction import build_compaction_mw
-from .shared.kb_context_projection import build_kb_context_projection_mw
-from .shared.memory import build_memory_mw
-from .shared.patch_tool_calls import build_patch_tool_calls_mw
-from .shared.permissions import build_permission_mw
-from .shared.resilience import build_resilience_middlewares
-from .shared.todos import build_todos_mw
-from .subagent.middleware_stack import build_subagent_middleware_stack
+from .context_editing import build_context_editing_mw
+from .dedup_hitl import build_dedup_hitl_mw
+from .doom_loop import build_doom_loop_mw
+from .kb_persistence import build_kb_persistence_mw
+from .knowledge_priority import build_knowledge_priority_mw
+from .knowledge_tree import build_knowledge_tree_mw
+from .noop_injection import build_noop_injection_mw
+from .otel import build_otel_mw
+from .plugins import build_plugin_middlewares
+from .repair import build_repair_mw
+from .skills import build_skills_mw
+from app.agents.multi_agent_chat.middleware.shared.anthropic_cache import build_anthropic_cache_mw
+from app.agents.multi_agent_chat.middleware.shared.compaction import build_compaction_mw
+from app.agents.multi_agent_chat.middleware.shared.kb_context_projection import build_kb_context_projection_mw
+from app.agents.multi_agent_chat.middleware.shared.memory import build_memory_mw
+from app.agents.multi_agent_chat.middleware.shared.patch_tool_calls import build_patch_tool_calls_mw
+from app.agents.multi_agent_chat.middleware.shared.permissions import build_permission_mw
+from app.agents.multi_agent_chat.middleware.shared.resilience import build_resilience_middlewares
+from app.agents.multi_agent_chat.middleware.shared.todos import build_todos_mw
+from app.agents.multi_agent_chat.middleware.subagent.middleware_stack import (
+    build_subagent_middleware_stack,
+)
 
 
 def build_main_agent_deepagent_middleware(

surfsense_backend/app/agents/multi_agent_chat/subagents/builtins/knowledge_base/ask_knowledge_base_tool.py

@@ -10,10 +10,10 @@ from langchain_core.runnables import Runnable
 from langchain_core.tools import StructuredTool
 from langgraph.types import Command
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.config import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.config import (
     subagent_invoke_config,
 )
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.constants import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.constants import (
     EXCLUDED_STATE_KEYS,
 )
 

surfsense_backend/app/tasks/chat/streaming/flows/resume_chat/resume_routing.py

@@ -41,7 +41,7 @@ async def build_resume_routing(
     ``surfsense_resume_value`` configurable; parallel siblings each pop their
     own entry so they never race.
     """
-    from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.resume_routing import (
+    from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume_routing import (
         build_lg_resume_map,
         collect_pending_tool_calls,
         slice_decisions_by_tool_call,

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_hitl_bridge.py

@@ -14,14 +14,14 @@ from langgraph.graph import END, START, StateGraph
 from langgraph.types import Command, interrupt
 from typing_extensions import TypedDict
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.config import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.config import (
     subagent_invoke_config,
 )
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.resume_routing import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume_routing import (
     collect_pending_tool_calls,
     slice_decisions_by_tool_call,
 )
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.task_tool import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_parallel_heterogeneous_decisions.py

@@ -40,12 +40,12 @@ from langgraph.graph.message import add_messages
 from langgraph.types import Command, Send, interrupt
 from typing_extensions import TypedDict
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.resume_routing import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume_routing import (
     build_lg_resume_map,
     collect_pending_tool_calls,
     slice_decisions_by_tool_call,
 )
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.task_tool import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_parallel_partial_pause_routing.py

@@ -47,12 +47,12 @@ from langgraph.graph.message import add_messages
 from langgraph.types import Command, Send, interrupt
 from typing_extensions import TypedDict
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.resume_routing import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume_routing import (
     build_lg_resume_map,
     collect_pending_tool_calls,
     slice_decisions_by_tool_call,
 )
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.task_tool import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_parallel_reject_only_routing.py

@@ -37,12 +37,12 @@ from langgraph.graph.message import add_messages
 from langgraph.types import Command, Send, interrupt
 from typing_extensions import TypedDict
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.resume_routing import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume_routing import (
     build_lg_resume_map,
     collect_pending_tool_calls,
     slice_decisions_by_tool_call,
 )
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.task_tool import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_parallel_resume_command_keying.py

@@ -37,12 +37,12 @@ from langgraph.graph.message import add_messages
 from langgraph.types import Command, Send, interrupt
 from typing_extensions import TypedDict
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.resume_routing import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume_routing import (
     build_lg_resume_map,
     collect_pending_tool_calls,
     slice_decisions_by_tool_call,
 )
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.task_tool import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_parallel_self_and_middleware_gated.py

@@ -35,12 +35,12 @@ from langgraph.graph.message import add_messages
 from langgraph.types import Command, Send
 from typing_extensions import TypedDict
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.resume_routing import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume_routing import (
     build_lg_resume_map,
     collect_pending_tool_calls,
     slice_decisions_by_tool_call,
 )
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.task_tool import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
 from app.agents.multi_agent_chat.middleware.shared.permissions.ask.request import (

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_parallel_tasks.py

@@ -18,7 +18,7 @@ from langgraph.graph import END, START, StateGraph
 from langgraph.types import Command
 from typing_extensions import TypedDict
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.task_tool import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_pending_interrupt.py

@@ -9,7 +9,7 @@ from __future__ import annotations
 
 from types import SimpleNamespace
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.resume import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume import (
     get_first_pending_subagent_interrupt,
 )
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_resume_decision_routing.py

@@ -17,7 +17,7 @@ from types import SimpleNamespace
 
 import pytest
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.resume_routing import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume_routing import (
     collect_pending_tool_calls,
     slice_decisions_by_tool_call,
 )

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_resume_helpers.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 from langchain.tools import ToolRuntime
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.config import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.config import (
     consume_surfsense_resume,
     has_surfsense_resume,
 )

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_subagent_interrupt_stamping.py

@@ -30,7 +30,7 @@ from langgraph.graph import END, START, StateGraph
 from langgraph.types import Send, interrupt
 from typing_extensions import TypedDict
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.task_tool import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
 

surfsense_backend/tests/unit/agents/multi_agent_chat/middleware/checkpointed_subagent_middleware/test_subagent_invoke_config.py

@@ -16,7 +16,7 @@ from __future__ import annotations
 
 from langchain.tools import ToolRuntime
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.config import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.config import (
     subagent_invoke_config,
 )
 

surfsense_backend/tests/unit/tasks/chat/streaming/test_interrupt_inspector_all.py

@@ -18,7 +18,7 @@ from langgraph.graph import END, START, StateGraph
 from langgraph.types import Send, interrupt
 from typing_extensions import TypedDict
 
-from app.agents.multi_agent_chat.middleware.main_agent.checkpointed_subagent_middleware.task_tool import (
+from app.agents.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
 from app.tasks.chat.streaming.helpers.interrupt_inspector import (