Rewrite the architecture under the no-Magi constraint

Magi and any learned head are ruled out, so every structure comes out of a
gemma prompt field or plain Python over gemma's output. Each section now
carries what exists today and a DoD.

The build order starts at step 0, the measurement spine: eval/chapter-truth.json
plus purity and fragmentation printed by audit_registry.py. Nothing below it is
measurable without that file.

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

NEXT.md

@@ -71,9 +71,15 @@ contain the right person. Coverage is still the `has_face` gate plus those refus
    face touching the bottom edge of one fragment with a textless fragment below. No evidence has been
    gathered yet on how often this chapter does it.
 
-1c. **Three items from `ARCHITECTURE.md` are cheap against the current code.** A `plane` field per
-   detection for art-in-art, same-panel co-presence demoted to a weak cannot-link once the plane exists,
-   and `offscreen` as a fourth `speaker_ref` kind.
+1c. **`ARCHITECTURE.md` was rewritten on 2026-08-13 under the no-Magi constraint.** Every section now
+   carries a DoD. Its build order starts at step 0, `eval/chapter-truth.json` plus purity and
+   fragmentation printed by `audit_registry.py`. Nothing below it is measurable without that file.
+
+   Steps 1 and 2 are independent and cheap: `plane` and `species` per detection, and the
+   face-plus-person embedding already queued in item 1 above. The weak cannot-link is step 3 and depends
+   on step 2, not on `plane` alone. Co-presence as a hard constraint is load-bearing while cosine cannot
+   separate people, so demoting it early regresses purity. `offscreen` as a fourth `speaker_ref` kind is
+   still cheap and independent.
 
 2. ~~**Order the corners in `_bbox_to_pixels`.**~~ **Done 2026-08-12, run and verified on a GPU.** 0
    degenerate boxes over 119 detections (`decisions/identity-bbox.md#bbox-corners-ordered`).