Add multi_agent_chat package exports and implementation layout doc.

surfsense_backend/app/agents/multi_agent_chat/IMPLEMENTATION_PLAN.md

@@ -0,0 +1,35 @@
+# `multi_agent_chat` — vertical slices + shared
+
+```
+multi_agent_chat/
+  __init__.py
+
+  shared/                     # Cross-domain helpers (one level)
+    deps.py                   # connector_binding for new_chat factories
+    prompt_loader.py          # read_prompt_md(package, stem)
+    domain_agent_factory.py   # build_domain_agent(..., prompt_package=...)
+    invoke_output.py          # extract_last_assistant_text (invoke result parsing)
+
+  gmail/                      # Gmail slice (agent + tooling + prompt)
+    domain_prompt.md
+    connector_tools.py
+    agent.py
+
+  calendar/                   # Google Calendar slice
+    domain_prompt.md
+    connector_tools.py
+    agent.py
+
+  routing/
+    from_domain_agents.py
+    supervisor_routing.py
+
+  supervisor/
+    supervisor_prompt.md
+    graph.py
+
+  integration/
+    create_multi_agent_chat.py
+```
+
+**References:** [Multi-agent](https://docs.langchain.com/oss/python/langchain/multi-agent), [Subagents](https://docs.langchain.com/oss/python/langchain/multi-agent/subagents).

surfsense_backend/app/agents/multi_agent_chat/__init__.py

@@ -0,0 +1,60 @@
+"""
+Multi-agent chat (LangChain Subagents pattern).
+
+**Vertical slices**
+
+- :mod:`gmail` — connector tools, domain agent, ``domain_prompt.md``
+- :mod:`calendar` — connector tools, domain agent, ``domain_prompt.md``
+
+**Shared**
+
+- :mod:`shared` — prompt loader, ``build_domain_agent``, connector deps, invoke result parsing
+
+**Cross-cutting**
+
+- :mod:`routing` — supervisor routing tools + invoke helpers
+- :mod:`supervisor` — top graph + ``supervisor_prompt.md``
+- :mod:`integration` — ``create_multi_agent_chat``
+
+Documentation:
+https://docs.langchain.com/oss/python/langchain/multi-agent
+https://docs.langchain.com/oss/python/langchain/multi-agent/subagents
+
+Display name: ``multi-agent-chat`` — Python package: ``multi_agent_chat``.
+"""
+
+from app.agents.multi_agent_chat.calendar import (
+    build_calendar_domain_agent,
+    build_google_calendar_connector_tools,
+)
+from app.agents.multi_agent_chat.gmail import (
+    build_gmail_connector_tools,
+    build_gmail_domain_agent,
+)
+from app.agents.multi_agent_chat.integration import create_multi_agent_chat
+from app.agents.multi_agent_chat.shared import (
+    build_domain_agent,
+    connector_binding,
+    extract_last_assistant_text,
+    read_prompt_md,
+)
+from app.agents.multi_agent_chat.routing import (
+    build_supervisor_routing_tools,
+    routing_tools_from_domain_agents,
+)
+from app.agents.multi_agent_chat.supervisor import build_supervisor_agent
+
+__all__ = [
+    "build_calendar_domain_agent",
+    "build_domain_agent",
+    "build_gmail_connector_tools",
+    "build_gmail_domain_agent",
+    "build_google_calendar_connector_tools",
+    "build_supervisor_agent",
+    "build_supervisor_routing_tools",
+    "connector_binding",
+    "create_multi_agent_chat",
+    "extract_last_assistant_text",
+    "read_prompt_md",
+    "routing_tools_from_domain_agents",
+]