feat(client): add long-lived multi-server client that reuses sessions…#419
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kulikrch wants to merge 2 commits intolangchain-ai:mainfrom
Open
feat(client): add long-lived multi-server client that reuses sessions…#419kulikrch wants to merge 2 commits intolangchain-ai:mainfrom
kulikrch wants to merge 2 commits intolangchain-ai:mainfrom
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… for tools/prompts/resources - add `LongLivedMultiServerMCPClient` inheriting `MultiServerMCPClient` - support async lifecycle with `start()` / `stop()` and `__aenter__` / `__aexit__` - override `get_tools()` to pass persistent `ClientSession` into `load_mcp_tools` - override `get_prompt()` and `get_resources()` to prefer persistent sessions - export new client from package `__init__` - add tests validating persistent-session reuse paths Refs: langchain-ai#362, langchain-ai#189
- refactor LongLivedMultiServerMCPClient session lifecycle to use AsyncExitStack - ensure partial startup failures close already-opened sessions safely - centralize server validation via _validate_server_name() - add _session_for_server() helper to unify persistent/ephemeral session resolution - keep get_tools() connection-based fallback when no persistent session exists to avoid tools bound to closed ephemeral sessions - update get_prompt() and get_resources() to use shared session-resolution helper - add tests for persistent-session reuse and partial-start cleanup Refs: langchain-ai#362, langchain-ai#189
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Summary
This PR adds a new client class,
LongLivedMultiServerMCPClient, to enable long-lived MCP sessions and ensure those sessions are actually reused by high-level APIs.Problem
Even when a long-lived session was opened,
get_tools()could still load tools throughload_mcp_tools(session=None, connection=...), which caused tool execution to create fresh sessions instead of using the persistent one.Changes
LongLivedMultiServerMCPClientinlangchain_mcp_adapters/client.py.start()stop()__aenter__()__aexit__()get_tools()to useself.sessions[server_name]when available.get_prompt()to use persistent sessions when available.get_resources()to use persistent sessions when available (single server and all servers modes).LongLivedMultiServerMCPClientvialangchain_mcp_adapters/__init__.py.tests/test_client.pyto verify persistent-session reuse for:get_tools()get_prompt()get_resources()Why this fixes it
When a persistent session exists, all three APIs now call loaders with that active
ClientSessiondirectly. This avoids per-call session creation and preserves server-side state in long-lived workflows.Related issues
Testing
Added targeted unit tests for the new behavior.