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/agents/new_chat/test_action_log.py

@@ -11,7 +11,7 @@ from langchain_core.messages import ToolMessage
 from langchain_core.tools import tool
 
 from app.agents.shared.feature_flags import AgentFeatureFlags
-from app.agents.new_chat.middleware.action_log import ActionLogMiddleware
+from app.agents.shared.middleware.action_log import ActionLogMiddleware
 from app.agents.new_chat.tools.registry import ToolDefinition
 
 
@@ -58,7 +58,7 @@ def _disabled_flags() -> AgentFeatureFlags:
 def patch_get_flags():
     def _patch(flags: AgentFeatureFlags):
         return patch(
-            "app.agents.new_chat.middleware.action_log.get_flags",
+            "app.agents.shared.middleware.action_log.get_flags",
             return_value=flags,
         )
 
@@ -360,7 +360,7 @@ class TestActionLogDispatch:
             patch_get_flags(_enabled_flags()),
             patch("app.db.shielded_async_session", side_effect=lambda: factory()),
             patch(
-                "app.agents.new_chat.middleware.action_log.adispatch_custom_event",
+                "app.agents.shared.middleware.action_log.adispatch_custom_event",
                 dispatch_mock,
             ),
         ):
@@ -395,7 +395,7 @@ class TestActionLogDispatch:
             patch_get_flags(_enabled_flags()),
             patch("app.db.shielded_async_session", side_effect=_exploding_session),
             patch(
-                "app.agents.new_chat.middleware.action_log.adispatch_custom_event",
+                "app.agents.shared.middleware.action_log.adispatch_custom_event",
                 dispatch_mock,
             ),
         ):

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 import pytest
 
 from app.agents.shared.errors import BusyError
-from app.agents.new_chat.middleware.busy_mutex import (
+from app.agents.shared.middleware.busy_mutex import (
     BusyMutexMiddleware,
     end_turn,
     get_cancel_event,

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

@@ -10,7 +10,7 @@ from langchain_core.messages import (
     ToolMessage,
 )
 
-from app.agents.new_chat.middleware.compaction import (
+from app.agents.shared.middleware.compaction import (
     PROTECTED_SYSTEM_PREFIXES,
     _is_protected_system_message,
     _sanitize_message_content,
@@ -72,7 +72,7 @@ class TestPartitionMessages:
         # SurfSenseCompactionMiddleware without a real model, but the
         # override path needs ``_lc_helper`` to delegate to. We mock
         # that with a simple slicing partitioner equivalent to the real one.
-        from app.agents.new_chat.middleware.compaction import (
+        from app.agents.shared.middleware.compaction import (
             SurfSenseCompactionMiddleware,
         )
 

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

@@ -7,7 +7,7 @@ from typing import Any
 import pytest
 from langchain_core.messages import AIMessage, HumanMessage, ToolMessage
 
-from app.agents.new_chat.middleware.context_editing import (
+from app.agents.shared.middleware.context_editing import (
     SpillToBackendEdit,
     _build_spill_placeholder,
 )

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

@@ -6,7 +6,7 @@ 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,
 )
 
@@ -137,7 +137,7 @@ def test_full_args_dedup_keeps_distinct_calls_sharing_a_field() -> None:
 
     With :func:`dedup_key_full_args` only fully identical arg dicts dedup.
     """
-    from app.agents.new_chat.middleware.dedup_tool_calls import dedup_key_full_args
+    from app.agents.shared.middleware.dedup_tool_calls import dedup_key_full_args
 
     tool = _make_tool("createJiraIssue", dedup_key=dedup_key_full_args)
     mw = DedupHITLToolCallsMiddleware(agent_tools=[tool])
@@ -179,7 +179,7 @@ def test_full_args_dedup_keeps_distinct_calls_sharing_a_field() -> None:
 
 
 def test_full_args_dedup_drops_only_exact_duplicates() -> None:
-    from app.agents.new_chat.middleware.dedup_tool_calls import dedup_key_full_args
+    from app.agents.shared.middleware.dedup_tool_calls import dedup_key_full_args
 
     tool = _make_tool("createJiraIssue", dedup_key=dedup_key_full_args)
     mw = DedupHITLToolCallsMiddleware(agent_tools=[tool])

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

@@ -10,7 +10,7 @@ from __future__ import annotations
 
 import pytest
 
-from app.agents.new_chat.middleware.permission import PermissionMiddleware
+from app.agents.shared.middleware.permission import PermissionMiddleware
 from app.agents.shared.permissions import (
     Rule,
     Ruleset,

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 import pytest
 from langchain_core.messages import AIMessage
 
-from app.agents.new_chat.middleware.doom_loop import DoomLoopMiddleware, _signature
+from app.agents.shared.middleware.doom_loop import DoomLoopMiddleware, _signature
 
 pytestmark = pytest.mark.unit
 

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

@@ -15,7 +15,7 @@ from unittest.mock import MagicMock
 import pytest
 from langchain_core.messages import HumanMessage, SystemMessage
 
-from app.agents.new_chat.middleware.flatten_system import (
+from app.agents.shared.middleware.flatten_system import (
     FlattenSystemMessageMiddleware,
     _flatten_text_blocks,
     _flattened_request,

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 import pytest
 from langchain_core.messages import AIMessage, HumanMessage
 
-from app.agents.new_chat.middleware.noop_injection import (
+from app.agents.shared.middleware.noop_injection import (
     NOOP_TOOL_NAME,
     NoopInjectionMiddleware,
     _last_ai_has_tool_calls,

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

@@ -8,7 +8,7 @@ from unittest.mock import MagicMock
 import pytest
 from langchain_core.messages import AIMessage, ToolMessage
 
-from app.agents.new_chat.middleware.otel_span import (
+from app.agents.shared.middleware.otel_span import (
     OtelSpanMiddleware,
     _annotate_model_response,
     _annotate_tool_result,
@@ -206,13 +206,13 @@ class TestMiddlewareIntegration:
         duration_calls: list[dict[str, Any]] = []
         token_calls: list[dict[str, Any]] = []
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.otel_span.ot_metrics.record_model_call_duration",
+            "app.agents.shared.middleware.otel_span.ot_metrics.record_model_call_duration",
             lambda duration_ms, **attrs: duration_calls.append(
                 {"duration_ms": duration_ms, **attrs}
             ),
         )
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.otel_span.ot_metrics.record_model_token_usage",
+            "app.agents.shared.middleware.otel_span.ot_metrics.record_model_token_usage",
             lambda **attrs: token_calls.append(attrs),
         )
 
@@ -257,11 +257,11 @@ class TestMiddlewareIntegration:
 
         errors: list[str] = []
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.otel_span.ot_metrics.record_tool_call_error",
+            "app.agents.shared.middleware.otel_span.ot_metrics.record_tool_call_error",
             lambda *, tool_name: errors.append(tool_name),
         )
         monkeypatch.setattr(
-            "app.agents.new_chat.middleware.otel_span.ot_metrics.record_tool_call_duration",
+            "app.agents.shared.middleware.otel_span.ot_metrics.record_tool_call_duration",
             lambda *args, **kwargs: None,
         )
 

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

@@ -6,7 +6,7 @@ import pytest
 from langchain_core.messages import AIMessage, ToolMessage
 
 from app.agents.shared.errors import CorrectedError, RejectedError
-from app.agents.new_chat.middleware.permission import (
+from app.agents.shared.middleware.permission import (
     PermissionMiddleware,
     _normalize_permission_decision,
 )

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

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 import pytest
 
-from app.agents.new_chat.middleware.retry_after import (
+from app.agents.shared.middleware.retry_after import (
     RetryAfterMiddleware,
     _extract_retry_after_seconds,
     _is_non_retryable,

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

@@ -21,8 +21,8 @@ from unittest.mock import AsyncMock
 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.kb_postgres_backend import KBPostgresBackend
+from app.agents.shared.middleware.filesystem import SurfSenseFilesystemMiddleware
+from app.agents.shared.middleware.kb_postgres_backend import KBPostgresBackend
 
 pytestmark = pytest.mark.unit
 

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

@@ -7,7 +7,7 @@ from pathlib import Path
 
 import pytest
 
-from app.agents.new_chat.middleware.skills_backends import (
+from app.agents.shared.middleware.skills_backends import (
     SKILLS_BUILTIN_PREFIX,
     SKILLS_SPACE_PREFIX,
     BuiltinSkillsBackend,

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

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 from langchain_core.tools import tool
 
-from app.agents.new_chat.middleware.permission import PermissionMiddleware
+from app.agents.shared.middleware.permission import PermissionMiddleware
 from app.agents.new_chat.subagents import (
     build_connector_negotiator_subagent,
     build_explore_subagent,
@@ -140,7 +140,7 @@ class TestExploreSubagent:
     def test_includes_dedup_and_patch_middleware(self) -> None:
         from deepagents.middleware.patch_tool_calls import PatchToolCallsMiddleware
 
-        from app.agents.new_chat.middleware import DedupHITLToolCallsMiddleware
+        from app.agents.shared.middleware import DedupHITLToolCallsMiddleware
 
         spec = build_explore_subagent(tools=ALL_TOOLS)
         types = {type(m) for m in spec["middleware"]}  # type: ignore[index]

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

@@ -5,7 +5,7 @@ from __future__ import annotations
 import pytest
 from langchain_core.messages import AIMessage
 
-from app.agents.new_chat.middleware.tool_call_repair import (
+from app.agents.shared.middleware.tool_call_repair import (
     ToolCallNameRepairMiddleware,
 )
 from app.agents.new_chat.tools.invalid_tool import INVALID_TOOL_NAME