Sprite batcher — M0.9
100 sprites, all sharing the same texture Arc, rendered in a single draw
call.
This is the M0.9 anti-regression contract. The renderer's collect_batches
walks the scene in pre-order, groups instances by (texture_id, blend_mode),
and emits one instance buffer per batch. When sprites share a texture they
collapse into one batch.
For the recorder this is what makes the cursor-trail-of-100-clicks scenario feasible: even if the cursor effects layer fans out into many sprites in a short window, draw-call cost stays constant.
Texture::id() is Arc::as_ptr(&inner) as usize —
texture-pointer-equality. Cloning a Texture shares the GPU resource and
the batch key.