docs(todos): Stoicheia WO entered - encoder-only plane predictor design

TODO.sota-2026/04-stoicheia-diffusion-wo.md

@@ -1,6 +1,36 @@
 # 04 — WO (queued, unscheduled): plane-factorized char-level masked diffusion
 
-Status: QUEUED (2026-10-01) — entry criteria at the bottom
+Status: ENTERED (2026-10-03, owner: "make it work - ultimately the best SOTA") — in build
+
+## Entry design decision (2026-10-03)
+
+Diacritization is a LENGTH-PRESERVING PLANE PROJECTION: the letters
+plane is the given skeleton; the haraqat plane is a per-letter
+classification. So the model is an ENCODER-ONLY plane predictor, not a
+decoder:
+
+- Init: **ByT5-small encoder** (pretrained backbone — the
+  from-scratch-collapse law; byte+3 table reused).
+- Input: byte embeddings of the SKELETON + a diacritic-plane
+  embedding per position (MASK at pass 1; pass k>1 carries pass k-1
+  predictions) — Mask-Predict self-conditioning, trained at random
+  corruption levels; inference with K passes of FULLY PARALLEL
+  prediction.
+- Head: per-position classification over the corpus haraqat-combo
+  inventory (label = canonical combining-mark combo following each
+  letter; non-letter positions labeled none).
+- Why this can beat the seq2seq rungs: the AR students decode
+  left-to-right; iʿrāb (33% of the residual) depends on sentence
+  structure AHEAD. Bidirectional conditioning attacks exactly the
+  residual's largest component. Encoder-only + K parallel passes is
+  also a CPU-latency win vs byte-by-byte KV decode.
+- Corpus: benchmark-convention RUNNING TEXT ONLY (r5-units +
+  arabic-combined + news mix) — the r9 convention-drift lesson
+  applied by design; NO paradigm tables.
+- Gates (pre-registered): windowed zero-skip SadeedDiac-25 — rung
+  gate beat 4.5701 (student tier, on-device class); SOTA-dedicated
+  gate beat 2.2864 (teacher tier); CPU latency benchmark vs
+  ara-diac-small-int8static-2.1.
 Literature basis: Stoicheia (arXiv 2608.07249) — 405M character-level
 masked-diffusion encoder for Ancient Greek; input factors into five
 aligned, independently maskable planes (letters, boundaries,