Public way to cancel an invocation without sealing it as aborted (2.14) #8130

Is your feature request related to a problem?

Since 2.14, an invocation cancelled with a plain task.cancel() is sealed: each dangling function call gets a synthetic response with error_code='INVOCATION_ABORTED' ("Invocation was aborted by client."), and on resume a sealed call is not replayed (google/adk/events/_abort_events.py, _run_invocation_lifecycle in google/adk/utils/_runner_utils.py).

That is the right default when a user stops a turn. It is wrong when a service stops an invocation so it can be resumed elsewhere: a worker that loses its lease on a run, or shuts down gracefully, and hands the run to another process that resumes the same invocation from the persisted session. After the seal, the resumed invocation reads the abort error as the tool's result instead of finishing the call.

Today the only way to cancel without sealing is to pass the private sentinel as the cancel message: task.cancel(google.adk.utils._runner_utils._CALLER_CLOSED_EARLY_MSG). That works, but it depends on a private name.

Describe the solution you'd like

A public way to stop an invocation that leaves it resumable (not sealed). For example, a public constant to pass to Task.cancel(), or a parameter on the existing abort mechanism that marks the stop as a detach rather than an abort.

Related: nested runners lose the reason

When the outer invocation is stopped, Runner._cleanup_root_task cancels the root node task with a plain task.cancel(). A runner started inside a tool (for example a custom AgentTool whose nested session is persisted and resumed) therefore sees an unexplained cancel and is sealed, even when the outer cancel was the close-early sentinel. Forwarding the outer cancellation's message to the root node task would let a resumable stop reach nested runners. We understand AgentTool's nested session is discarded by design, so this matters only for callers that persist nested runs, but a public resumable stop would ideally propagate.

Version: google-adk 2.14.1, Python 3.11.