Add session-scoped state persistence (#2873)

examples/persistent_state/server.py

@@ -0,0 +1,42 @@
+"""Example: Persistent session-scoped state.
+
+This demonstrates using Context.get_state() and set_state() to store
+data that persists across tool calls within the same MCP session.
+
+Run with:
+    uv run python examples/persistent_state/server.py
+"""
+
+from fastmcp import FastMCP
+from fastmcp.server.context import Context
+
+server = FastMCP("StateExample")
+
+
+@server.tool
+async def set_value(key: str, value: str, ctx: Context) -> str:
+    """Store a value in session state."""
+    await ctx.set_state(key, value)
+    return f"Stored '{key}' = '{value}'"
+
+
+@server.tool
+async def get_value(key: str, ctx: Context) -> str:
+    """Retrieve a value from session state."""
+    value = await ctx.get_state(key)
+    if value is None:
+        return f"Key '{key}' not found"
+    return f"'{key}' = '{value}'"
+
+
+@server.tool
+async def list_session_info(ctx: Context) -> dict[str, str | None]:
+    """Get information about the current session."""
+    return {
+        "session_id": ctx.session_id,
+        "transport": ctx.transport,
+    }
+
+
+if __name__ == "__main__":
+    server.run(transport="streamable-http")