Add lifespan example with ASGI interaction explanations

Author: FloorIsGround

examples/snippets/servers/streamable_simple_lifespan.py

@@ -0,0 +1,55 @@
+"""
+Example showing ASGI route mounting with lifespan context management.
+
+From the repository root:
+    cd examples/snippets/servers
+    uv run streamable_uvicorn_lifespan.py
+"""
+
+import contextlib
+
+from starlette.applications import Starlette
+from starlette.routing import Mount
+
+from mcp.server.fastmcp import FastMCP
+
+# Create MCP server
+mcp = FastMCP(name="My App", stateless_http=True)
+
+
+@mcp.tool()
+def ping() -> str:
+    """A simple ping tool"""
+    return "pong"
+
+
+# lifespan for managing the session manager
+@contextlib.asynccontextmanager
+async def lifespan(app: Starlette):
+    """Gather any session managers for startup/shutdown.
+    See streamable_starlette_mount.py for example of multiple mcp managers.
+    """
+    async with mcp.session_manager.run():
+        yield
+
+
+"""Create the Starlette app and mount the MCP server.
+lifespan ensures the session manager is started/stopped with the app.
+session_manager references must only be made after streamable_http_app()
+"""
+app = Starlette(
+    routes=[
+        # Mounted at /mcp
+        Mount("/", app=mcp.streamable_http_app()),
+    ],
+    lifespan=lifespan,
+)
+
+if __name__ == "__main__":
+    import uvicorn
+
+    """Attach to another ASGI server LIFO
+    ASGI chain: Uvicorn -> Starlette -> FastMCP
+    Route: http://0.0.0.0:8000/mcp
+    """
+    uvicorn.run(app, host="0.0.0.0", port=8000)