Tool cancellation is now cooperative end-to-end: the queue stays busy until compensation completes, cancellation is checked cooperatively across the pipeline, the fallback window is compensated too, and cleanup_failed is surfaced explicitly. Includes a gated delayed-compensation E2E test.
When a borrowed tab's original window is gone, tab_return's fallback
picker called getLastFocused({windowTypes:["normal"]}) and only
excluded the *current* session's Agent Window. Agent Windows are
created with type:"normal", so the picker could move a returned user
tab into *another* session's Agent Window. That session could then
write to the tab (it passes enforceAgentWindow), and the tab would be
destroyed when that session stops and closes its window — a
cross-session sandbox break plus silent user-data loss.
Thread an isAgentWindowId predicate (derived from SessionManager in
the production handlers, mirroring the existing filter in
borrow-confirmation's listConfirmationCandidates) through
returnBorrowedTab -> chooseFallbackWindow so every live Agent Window
is skipped as a fallback target.
Adds two regression tests (both fail on the unpatched code).
Co-Authored-By: Claude <noreply@anthropic.com>
NianJiu