Add a regression test that actually runs the CancelledError branch of
AgentLoop._dispatch end-to-end and asserts the in-flight checkpoint is
materialized into session.messages before the cancellation unwinds.
The three existing tests call _restore_runtime_checkpoint directly, so
they pass even if the cancel-time restore is ever removed from
_dispatch. This new test is the one that actually locks the fix in
place.
Made-with: Cursor
When a user sends /stop to interrupt an active agent turn, the task is
cancelled via CancelledError. Previously, the cancellation handler just
logged and re-raised, discarding any tool results and assistant messages
accumulated during the interrupted turn.
The runtime checkpoint mechanism already persists partial turn state
(assistant messages, completed tool results, pending tool calls) into
session metadata via _emit_checkpoint. However, this checkpoint was only
materialized into session history on the NEXT incoming message via
_restore_runtime_checkpoint — not at cancellation time.
Now the CancelledError handler in _dispatch calls
_restore_runtime_checkpoint immediately, so the partial context is
preserved in session history. This means the next message the user sends
will see all the work that was done before /stop, rather than starting
from scratch.
Fixes#2966
Includes 3 tests verifying checkpoint restoration on cancellation.
