fix(graph): treat cancel_node as control flow, not fatal error#2258

Zelys-DFKH wants to merge 1 commit intostrands-agents:mainstrands-agents/sdk-python:mainfrom

Zelys-DFKH:fix/graph-cancel-node-graceful-skipZelys-DFKH/sdk-python:fix/graph-cancel-node-graceful-skipCopy head branch name to clipboard