Follow-ups on the cherry-picked handler:
- a throwing observer can no longer change the decision; the handler returns
an explicit deny regardless of logging failures
- the denied-URL log carries origin only, so query tokens / signed URLs from
attacker-controlled content never reach the persisted desktop log
- the hidden link-title window (loads arbitrary user-linked pages on render,
had no window-open handler at all) now denies too
- tests trimmed to two invariants (proven red against the pre-fix shape)
b51c055a12