refactor(agents): extract subagent-invocation contract to subagents/shared

The knowledge_base subagent imported subagent_invoke_config + EXCLUDED_STATE_KEYS
from main_agent's checkpointed_subagent_middleware -- a subagent reaching into
main-agent internals. Both symbols (plus the recursion-limit constant they need)
are a subagent-invocation contract shared by the orchestrator's task middleware
and any nested-invoking subagent. Move them to subagents/shared/invocation.py;
config.py keeps the HITL resume side-channel and constants.py keeps the
main-agent tuning knobs. All consumers (task_tool, kb tool, tests) repointed.

surfsense_backend/app/agents/chat/multi_agent_chat/main_agent/middleware/checkpointed_subagent_middleware/config.py

@@ -1,7 +1,9 @@
-"""RunnableConfig wiring for nested subagent invocations.
+"""HITL resume side-channel for nested subagent invocations.
 
-Forwards the parent's ``runtime.config`` (thread_id, …) into the subagent and
+Exposes the configurable side-channel ``stream_resume_chat`` uses to ferry
-exposes the side-channel ``stream_resume_chat`` uses to ferry resume payloads.
+resume payloads into a mid-flight subagent. The ``RunnableConfig`` builder and
+state-key filter shared with subagents live in
+``app.agents.chat.multi_agent_chat.subagents.shared.invocation``.
 """
 
 from __future__ import annotations
@@ -11,8 +13,6 @@ from typing import Any
 
 from langchain.tools import ToolRuntime
 
-from .constants import DEFAULT_SUBAGENT_RECURSION_LIMIT
-
 logger = logging.getLogger(__name__)
 
 # langgraph stores the parent task's scratchpad under this configurable key;
@@ -20,39 +20,6 @@ logger = logging.getLogger(__name__)
 _LANGGRAPH_SCRATCHPAD_KEY = "__pregel_scratchpad"
 
 
-def subagent_invoke_config(runtime: ToolRuntime) -> dict[str, Any]:
-    """RunnableConfig for the nested invoke; raises ``recursion_limit`` and isolates ``thread_id``.
-
-    Each parallel subagent invocation lands in its own checkpoint slot keyed
-    by an extended ``thread_id`` of the form ``{parent_thread}::task:{tool_call_id}``.
-    The same call across the resume cycle keeps reading from the same snapshot
-    (``tool_call_id`` is stable per LLM-emitted call).
-
-    We namespace via ``thread_id`` rather than ``checkpoint_ns`` because
-    langgraph's ``aget_state`` interprets a non-empty ``checkpoint_ns`` as a
-    subgraph path and raises ``ValueError("Subgraph X not found")``.
-    """
-    merged: dict[str, Any] = dict(runtime.config) if runtime.config else {}
-    current_limit = merged.get("recursion_limit")
-    try:
-        current_int = int(current_limit) if current_limit is not None else 0
-    except (TypeError, ValueError):
-        current_int = 0
-    if current_int < DEFAULT_SUBAGENT_RECURSION_LIMIT:
-        merged["recursion_limit"] = DEFAULT_SUBAGENT_RECURSION_LIMIT
-
-    configurable: dict[str, Any] = dict(merged.get("configurable") or {})
-    parent_thread_id = configurable.get("thread_id")
-    per_call_suffix = f"task:{runtime.tool_call_id}"
-    configurable["thread_id"] = (
-        f"{parent_thread_id}::{per_call_suffix}"
-        if parent_thread_id
-        else per_call_suffix
-    )
-    merged["configurable"] = configurable
-    return merged
-
-
 def consume_surfsense_resume(runtime: ToolRuntime) -> Any:
     """Pop the resume payload for *this* call's ``tool_call_id``.
 

surfsense_backend/app/agents/chat/multi_agent_chat/main_agent/middleware/checkpointed_subagent_middleware/constants.py

@@ -1,24 +1,14 @@
-"""Constants shared by the checkpointed subagent middleware."""
+"""Tuning constants for the checkpointed subagent middleware.
+
+``EXCLUDED_STATE_KEYS`` and ``DEFAULT_SUBAGENT_RECURSION_LIMIT`` are part of the
+subagent-invocation contract shared with subagents and now live in
+``app.agents.chat.multi_agent_chat.subagents.shared.invocation``.
+"""
 
 from __future__ import annotations
 
 import os
 
-# Mirror of deepagents.middleware.subagents._EXCLUDED_STATE_KEYS.
-EXCLUDED_STATE_KEYS = frozenset(
-    {
-        "messages",
-        "todos",
-        "structured_response",
-        "skills_metadata",
-        "memory_contents",
-    }
-)
-
-# Match the parent graph's budget; the LangGraph default of 25 trips on
-# multi-step subagent runs.
-DEFAULT_SUBAGENT_RECURSION_LIMIT = 10_000
-
 
 def _read_timeout_env(name: str, default: float) -> float:
     """Parse ``name`` from the environment; fall back to ``default`` on bad values.

surfsense_backend/app/agents/chat/multi_agent_chat/main_agent/middleware/checkpointed_subagent_middleware/task_tool.py

@@ -23,6 +23,10 @@ from langchain_core.tools import StructuredTool
 from langgraph.errors import GraphInterrupt
 from langgraph.types import Command, Interrupt
 
+from app.agents.chat.multi_agent_chat.subagents.shared.invocation import (
+    EXCLUDED_STATE_KEYS,
+    subagent_invoke_config,
+)
 from app.agents.chat.multi_agent_chat.subagents.shared.spec import (
     SURF_CONTEXT_HINT_PROVIDER_KEY,
     ContextHintProvider,
@@ -34,13 +38,11 @@ from .config import (
     consume_surfsense_resume,
     drain_parent_null_resume,
     has_surfsense_resume,
-    subagent_invoke_config,
 )
 from .constants import (
     DEFAULT_SUBAGENT_BATCH_CONCURRENCY,
     DEFAULT_SUBAGENT_BILLABLE_THRESHOLD,
     DEFAULT_SUBAGENT_INVOKE_TIMEOUT_SECONDS,
-    EXCLUDED_STATE_KEYS,
     MAX_SUBAGENT_BATCH_SIZE,
 )
 from .propagation import wrap_with_tool_call_id

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

@@ -10,11 +10,9 @@ from langchain_core.runnables import Runnable
 from langchain_core.tools import StructuredTool
 from langgraph.types import Command
 
-from app.agents.chat.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.config import (
+from app.agents.chat.multi_agent_chat.subagents.shared.invocation import (
-    subagent_invoke_config,
-)
-from app.agents.chat.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.constants import (
     EXCLUDED_STATE_KEYS,
+    subagent_invoke_config,
 )
 
 from .prompts import load_readonly_description

surfsense_backend/app/agents/chat/multi_agent_chat/subagents/shared/invocation.py

@@ -0,0 +1,69 @@
+"""Subagent-invocation contract shared by the orchestrator and nested subagents.
+
+Both the main-agent ``task`` middleware (``checkpointed_subagent_middleware``)
+and subagents that themselves invoke another subagent (e.g.
+``ask_knowledge_base``) need the same two things when spawning a child run:
+
+- a ``RunnableConfig`` that raises the recursion limit and isolates the child's
+  ``thread_id`` so each invocation lands in its own checkpoint slot
+  (``subagent_invoke_config``), and
+- the set of parent state keys that must *not* be forwarded into / merged back
+  from the child (``EXCLUDED_STATE_KEYS``).
+
+Keeping this here (rather than inside the main-agent middleware) lets subagents
+reuse the contract without importing main-agent internals.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from langchain.tools import ToolRuntime
+
+# Mirror of deepagents.middleware.subagents._EXCLUDED_STATE_KEYS.
+EXCLUDED_STATE_KEYS = frozenset(
+    {
+        "messages",
+        "todos",
+        "structured_response",
+        "skills_metadata",
+        "memory_contents",
+    }
+)
+
+# Match the parent graph's budget; the LangGraph default of 25 trips on
+# multi-step subagent runs.
+DEFAULT_SUBAGENT_RECURSION_LIMIT = 10_000
+
+
+def subagent_invoke_config(runtime: ToolRuntime) -> dict[str, Any]:
+    """RunnableConfig for the nested invoke; raises ``recursion_limit`` and isolates ``thread_id``.
+
+    Each parallel subagent invocation lands in its own checkpoint slot keyed
+    by an extended ``thread_id`` of the form ``{parent_thread}::task:{tool_call_id}``.
+    The same call across the resume cycle keeps reading from the same snapshot
+    (``tool_call_id`` is stable per LLM-emitted call).
+
+    We namespace via ``thread_id`` rather than ``checkpoint_ns`` because
+    langgraph's ``aget_state`` interprets a non-empty ``checkpoint_ns`` as a
+    subgraph path and raises ``ValueError("Subgraph X not found")``.
+    """
+    merged: dict[str, Any] = dict(runtime.config) if runtime.config else {}
+    current_limit = merged.get("recursion_limit")
+    try:
+        current_int = int(current_limit) if current_limit is not None else 0
+    except (TypeError, ValueError):
+        current_int = 0
+    if current_int < DEFAULT_SUBAGENT_RECURSION_LIMIT:
+        merged["recursion_limit"] = DEFAULT_SUBAGENT_RECURSION_LIMIT
+
+    configurable: dict[str, Any] = dict(merged.get("configurable") or {})
+    parent_thread_id = configurable.get("thread_id")
+    per_call_suffix = f"task:{runtime.tool_call_id}"
+    configurable["thread_id"] = (
+        f"{parent_thread_id}::{per_call_suffix}"
+        if parent_thread_id
+        else per_call_suffix
+    )
+    merged["configurable"] = configurable
+    return merged

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

@@ -14,9 +14,6 @@ from langgraph.graph import END, START, StateGraph
 from langgraph.types import Command, interrupt
 from typing_extensions import TypedDict
 
-from app.agents.chat.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.config import (
-    subagent_invoke_config,
-)
 from app.agents.chat.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.resume_routing import (
     collect_pending_tool_calls,
     slice_decisions_by_tool_call,
@@ -24,6 +21,9 @@ from app.agents.chat.multi_agent_chat.main_agent.middleware.checkpointed_subagen
 from app.agents.chat.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.task_tool import (
     build_task_tool_with_parent_config,
 )
+from app.agents.chat.multi_agent_chat.subagents.shared.invocation import (
+    subagent_invoke_config,
+)
 
 
 class _SubagentState(TypedDict, total=False):

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.chat.multi_agent_chat.main_agent.middleware.checkpointed_subagent_middleware.config import (
+from app.agents.chat.multi_agent_chat.subagents.shared.invocation import (
     subagent_invoke_config,
 )