The full Parsec model: launching a game from a desktop session flips the
client into captured relative automatically, and back — no chords.
- Capture overlay now distinguishes 'hidden' from 'no cursor yet':
CursorOverlay grows a visible flag, overlay() returns Some whenever a
bitmap is known (the encode loop strips invisible overlays after
forwarding so no blend path ever draws one; the CPU composite guarded
on visibility already).
- Host forwarder maps it onto the reserved wire bit: visible ⇒ VISIBLE,
hidden-but-known ⇒ RELATIVE_HINT (an app grabbed/hid the pointer),
never any hint before the first bitmap — a cold start can't flip a
desktop session into capture.
- Presenter: edge-triggered auto-flip on hint changes via the new
Capture::set_desktop (chord semantics untouched); a manual ⌃⌥⇧M sets
an override latch that holds until the HOST's intent next changes, so
the hint never fights the user. Leaving relative warps the local
cursor to the host's last pointer position through the new
content_to_window inverse-letterbox mapping (unit-tested against
finger_to_content) — the hand-back is seamless.
Verified on .21: fmt + clippy -D warnings + tests (presenter 20 incl.
the inverse-mapping roundtrip, host 245).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>