The composer's global Esc-to-cancel listener (useComposerEscCancel) fires
whenever the turn is busy and the active composer matches — but overlays
(Settings, Command Center, agents, cron, …) cover the chat while the
composer stays mounted and 'active' beneath them, so pressing Esc on any
of those pages interrupted the session the user wasn't even looking at.
OverlayView's own escape-layer Esc-to-close fired too, but the stream was
already dead.
Stand Esc down with composerFocusBlockedBySurface() — the same signal the
type-to-focus path uses (BLOCKING_OVERLAY includes OverlayView's
[data-overlay-surface] marker). Esc on an overlay now closes the overlay
via its escape layer instead of canceling the stream beneath it.
Fixes#82618
53daff0644