The handoff catch in session-handoff.ts and the /handoff handler in
command-controller.ts mapped any error named AbortError to "Handoff
cancelled" regardless of whether the handoff signal was actually
aborted. Providers throw name-AbortError errors on non-user conditions
(stalls, idle timeouts, nested resolution failures), so a genuine
generation failure surfaced as a user cancellation and hid the cause.
Only report "Handoff cancelled" when handoffSignal.aborted is set;
re-throw the real error otherwise. The controller now trusts the
normalized "Handoff cancelled" message and drops its own AbortError
check so re-thrown provider failures render as "Handoff failed: ...".
Fixes#7903
roboomp
1e6638d8cd