DWM composes a display only when something dirties it, so a session opened
onto an idle desktop never produced a first frame: the host's synthetic-input
"compose kick" (cursor wiggle / sibling-display jump) was the only source, and
it is inherently unreliable — blocked on the secure desktop, defeated by a
fullscreen game's ClipCursor, user-visible, and dead in service contexts. The
field symptom: connect → black stream until something repaints the desktop.
Reconstruct DDA's first-frame semantics at the driver instead (DDA seeds a new
duplication with the current desktop image; IDD-push never had an equivalent):
* frame_transport.rs: new FrameStash — the retained last composed frame, a
driver-private copy-only texture. publish() now reports Published /
DescMismatch / Dropped, and harvest_into() pulls the last-published ring
slot into the stash (keyed-mutex guarded, freshness-checked) before a
superseded publisher is dropped — between sessions the driver keeps writing
the host-side-dead old ring, so that slot IS the current desktop image.
* swap_chain_processor.rs: the worker stashes every frame the ring can NOT
take (unattached, or descriptor-mismatched during a mode/HDR-flip race),
harvests before a supersede, and REPUBLISHES the stash into every freshly
attached ring — the host sees a normal seq=1 publish milliseconds after
channel delivery, no compose needed. Zero steady-state cost: matched
publishes touch only the ring. The frame-channel stash is now polled every
iteration (attach latency = first-frame latency; it was 1-in-30).
* monitor.rs: preserved_stash (LUID-tagged) so the retained frame survives
swap-chain unassign→reassign flaps, alongside the preserved publisher.
* host idd_push.rs: kick_dwm_compose demoted to documented last-resort
fallback for pre-stash drivers; a debug log now fires when a kick actually
runs so field logs show whether the stash path is working.
No proto change: the republish is an ordinary publish, so old host + new
driver and new host + old driver both keep working (the latter via the kick).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
enricobuehler
89a08f83af