Record the primitive render dispatch and how it was measured

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/IRIS_EXTRACTION_HANDOFF.md

@@ -5,8 +5,8 @@ Not a decisions log; delete it when the extraction is done.
 
 ## Read this first
 
-**Pull request #11 has been reviewed seven times; the seventh is answered in
-`79dcc15` and an eighth has not arrived.** Check for one before doing anything
+**Pull request #11 has been reviewed seven times; the last answer is `b9c4856`
+and an eighth review has not arrived.** Check for one before doing anything
 else:
 
 ```sh
@@ -39,7 +39,7 @@ packing images into arrays like atlas pages, and a bindless `binding_array`
 - Agent fork: `git@git.arirex.me:iris-ai/iris.git`. The bot cannot push
   canonical; work in the fork and open PRs into `iris/iris:main`.
 - **#11** `split/11-texture-bindings`, worktree `/home/bob/repos/iris-pr11`,
-  head `79dcc15`, fourteen commits on top of `0f6a28b`. Reviewed seven times,
+  head `b9c4856`, fifteen commits on top of `0f6a28b`. Reviewed seven times,
   all answered.
 - **#12** `split/12-pointer-routing`, worktree `/home/bob/repos/iris-pr12`,
   head `028521b`. A scroll falling through a hovered button. Not reviewed as
@@ -67,10 +67,14 @@ shape:
   for a trait object.
 - **The shared group is what every pipeline gets**: the window and the masks.
   A mask texture would go here too.
-- **`Primitive::SAMPLES` says what a primitive samples and how often it binds**
-  -- `Atlas` once for a list, `Image(fn)` for one instance alone, defaulted to
-  nothing. That is group 2, so a rect's pipeline has no texture or sampler in
-  its layout. Both cases share one layout builder and one group builder.
+- **Each primitive records its own draws.** `Primitive::render` makes a
+  `PrimitiveRender` that states the layout its shader reads, uploads what it
+  owns, and records its draws: `GlyphRender` owns the atlas and binds it once
+  per list, `ImageRender` owns the images and binds one per instance, the
+  default owns nothing. The renderer knows nothing about textures.
+  **Measured**, because dispatch per list was the objection: 6 instructions
+  per list, 0.1% of a frame at 256 and at 1024 layers, against the ~5,400
+  wgpu spends recording one. `tests/draw_cost.rs` is that measurement.
 - **`shader.wgsl` became `shader/prelude.wgsl` plus one file per primitive**,
   because one module cannot declare two types at the same binding. The prelude
   carries only what every primitive uses -- window, masks, vertex shader,