Render directly onto the window's default framebuffer (FBO 0) via a GL-backed `SKSurface`, then present with the toolkit buffer swap — no per-frame readback, staging buffer, or queue stall. The **default** live present path on the OpenGL backend (feature 119); unblocks feature 118 FR-002/SC-002.

Offscreen render then GPU→CPU readback. On the GL backend this is no longer the live present path; it backs the on-demand evidence/screenshot routine (decoupled from the live present, FR-004) and serves as an explicit fallback.