D703 - The guest-memory window is frame state

Status: decided Date: 2026-09-26

The frontend reads the pipeline window's exact span from guest memory, and the driver sets it on the backend once per frame through set_guest_memory, before the commands. A span that is not wholly mapped reads as empty. Amended by D733: a draw's traced buffers reach the backend as buffers of their own, per draw.

Why: every module in a submission shares one window compiled into it, and the guest never numbered it, so a guest-numbered buffer bind would misrepresent it. The span must equal the mask the module applies, or an index folds to a different word. An empty window is what an unplaced window holds; zero-filling or a partial read would invent memory.

Rejected:

• A BindBuffer command: its slot is the guest's numbering, and this buffer is the translation's.
• A partial or zero-filled window: contents the guest never wrote.