Report expected and current protocol versions through the transport
interface and expose session-independent recovery operations.
Offer recovery from the version mismatch popup, publish requests through
the reserved IVSHMEM channel, and select the validated SPICE fallback.
Track primary and fallback video with source-specific generations, and
publish a source only after its first frame or software surface is
ready.
Route SPICE surfaces and cursors through the generic render queue. Keep
the current image across handoffs, and switch input only after the new
source has been presented.
Move fallback activation to its worker so display callbacks cannot
block or deadlock the render path.
