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Multi-Turn Tool Execution with State Carryover

Critical rule — tool annotations must resolve

from __future__ import annotations is supported, but every type used by @tool() must resolve when schema generation runs.

Overview

Use ctx.agent_context.metadata to persist state across multiple tool calls within a single runner.run() call. Read via ctx.get_metadata(key, default), write via ctx.agent_context.metadata[key] = value.

Important: AgentContext.metadata persists for the duration of one runner.run() call (one user turn). It is NOT shared across separate runner.run() calls. For cross-run persistence, use a conversation store or external database.

Do not use ctx.state for cross-tool-call state — ctx.state is reset per tool call, not per run.

Shopping cart example (function-form tool)

# tools/shopping_cart.py — future annotations are allowed; keep tool types importable
from lauren_ai import tool, ToolContext

CART_KEY = "shopping_cart"

@tool()
async def shopping_cart_tool(
    action: str,
    item: str = "",
    quantity: int = 1,
    ctx: ToolContext | None = None,
) -> dict:
    """Manage a shopping cart with persistent state across tool calls.

    Args:
        action: 'add', 'remove', 'view', or 'clear'.
        item: Item name (for add/remove).
        quantity: Quantity (for add, default 1).
    """
    if ctx is None:
        return {"error": "No context provided"}

    cart: dict = dict(ctx.get_metadata(CART_KEY, {}))

    if action == "add":
        if not item:
            return {"error": "item is required for add"}
        cart[item] = cart.get(item, 0) + quantity
        ctx.agent_context.metadata[CART_KEY] = cart
        return {"added": item, "quantity": cart[item], "cart": dict(cart)}

    elif action == "remove":
        if item in cart:
            del cart[item]
            ctx.agent_context.metadata[CART_KEY] = cart
        return {"removed": item, "cart": dict(cart)}

    elif action == "view":
        return {"cart": dict(cart), "total_items": sum(cart.values())}

    elif action == "clear":
        ctx.agent_context.metadata[CART_KEY] = {}
        return {"cleared": True}

    return {"error": f"Unknown action: {action}"}

How state flows

Turn 1:  add "apple" → ctx.agent_context.metadata["shopping_cart"] = {"apple": 1}
Turn 2:  add "banana" → ctx.agent_context.metadata["shopping_cart"] = {"apple": 1, "banana": 1}
Turn 3:  view → returns both items

ctx.get_metadata(CART_KEY, {}) reads from AgentContext.metadata (after checking tool-level static metadata via @set_metadata first).

AgentRunner test pattern

Queue multiple tool calls in one client.run() — the runner processes them in sequence within a single AgentContext, so metadata accumulates correctly.

import json
from lauren_ai._agents import AgentContext, agent, use_tools
from lauren_ai._tools import ToolContext, ToolResult, tool
from lauren_ai._transport import Completion, TokenUsage
from lauren_ai.testing import TestClient


class _Capture:
    def __init__(self):
        self.captured: list[ToolResult] = []

    async def on_tool_result(self, result: ToolResult, ctx: AgentContext) -> ToolResult | None:
        self.captured.append(result)
        return None


@agent(model=None, system="Shopping cart agent")
@use_tools(shopping_cart_tool)
class CartAgent(_Capture):
    def __init__(self):
        _Capture.__init__(self)


def _c(text):
    return Completion(id="c1", model="mock", content=text, tool_calls=[],
                      stop_reason="end_turn", usage=TokenUsage(10, 5))


def test_cart_accumulates_across_calls():
    agent_inst = CartAgent()
    client = TestClient(agent_inst)
    client.mock.queue_tool_use(
        "shopping_cart_tool", {"action": "add", "item": "Widget", "quantity": 2}
    )
    client.mock.queue_tool_use(
        "shopping_cart_tool", {"action": "add", "item": "Gadget", "quantity": 1}
    )
    client.mock.queue_response(_c("Cart updated."))
    client.run("Add Widget x2 and Gadget x1")

    add1 = json.loads(agent_inst.captured[0].content)
    add2 = json.loads(agent_inst.captured[1].content)
    assert add1["quantity"] == 2
    assert add2["cart"].get("Widget") == 2
    assert add2["cart"].get("Gadget") == 1

Reference files