docs(paged): record W4A16 scale broadcast rejection

Record the Phase 3 scale-broadcast experiment, its md5 and MUL_MAT_ID gates, the prefill regression, and the decision to ship no 0050 patch.

Assisted-by: Codex:gpt-5

docs/superpowers/plans/2026-06-30-w4a16-scale-broadcast-phase3.md

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+# W4A16 Scale Broadcast Phase 3 Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development or superpowers:executing-plans. Keep checkboxes current while executing.
+
+**Goal:** Test a minimal W4A16 grouped-kernel body optimization after Phase 2 selected `bm32`.
+
+**Scope:** Fork-first in `/home/mudler/_git/llama.cpp`; mirror into LocalAI only after build, md5, op, perf, and mirror gates pass. Keep patch `0050` incremental on top of `0049`, and keep the source diff small.
+
+## Task 1: Implement Scale Broadcast
+
+- [x] In `ggml/src/ggml-cuda/w4a16-gemm.cu`, replace per-lane duplicate `ggml_cuda_ue4m3_to_fp32` scale conversion with one conversion per 4-lane `n_local` group plus `__shfl_sync`.
+- [x] Keep the existing dequant and MMA order unchanged.
+- [x] Do not add broad diagnostic variants or extra launch shapes.
+
+## Task 2: Gates
+
+- [x] Build `llama-batched-bench`, `llama-completion`, and `test-backend-ops` on DGX.
+- [x] Run canonical default-off paged MoE and dense greedy md5 gates.
+- [x] Run forced W4A16 `bm32` vs `base` md5 gates on the canonical prompt.
+- [x] Run forced W4A16 `test-backend-ops test -b CUDA0 -o MUL_MAT_ID -j 1`.
+- [x] Run W4A16 default `bm32` A/B against Phase 2 at `npp=512,2048`.
+
+## Task 3: Disposition
+
+- [x] Keep only if it improves W4A16 prefill by at least 1% at either `npp=512` or `npp=2048` without regressing the other by more than 1%.
+- [x] If kept, commit fork-first with `Assisted-by: Codex:gpt-5`, generate patch `0050`, verify mirror tree hash, update docs, and commit LocalAI. Not taken: perf gate failed.
+- [x] If rejected, revert the fork experiment and record the result without adding a patch.
+
+Result: rejected, no fork commit and no LocalAI patch `0050`.
+
+Artifacts:
+
+- Build: `~/llama-w4a16-phase3`
+- Logs: `~/bench/w4a16_phase3`
+
+Gates:
+
+- Canonical paged MoE md5: `8cb0ce23777bf55f92f63d0292c756b0`.
+- Canonical dense md5: `5951a5b4d624ce891e22ab5fca9bc439`.
+- Forced W4A16 `bm32` md5: `07db32c2bcb78d17a43ed18bc22705cd`.
+- Forced W4A16 `base` md5: `07db32c2bcb78d17a43ed18bc22705cd`.
+- Forced W4A16 `MUL_MAT_ID`: `806/806` on CUDA0.
+
+Performance:
+
+| Shape | 512 S_PP t/s | 2048 S_PP t/s | Decision |
+|-------|--------------|---------------|----------|
+| Phase 2 `bm32` | 1442.28 | 1471.77 | baseline |
+| Phase 3 scale-broadcast `bm32` | 1392.46 | 1422.74 | rejected |
+| Phase 2 `base` | 1310.13 | 1336.02 | baseline |
+| Phase 3 scale-broadcast `base` | 1201.69 | 1221.25 | rejected |
+
+Disposition:
+
+- Reverted local fork experiment in `/home/mudler/_git/llama.cpp`.
+- Do not retry this exact scale-broadcast approach; shuffle overhead and/or compiler scheduling cost exceeds saved FP8 scale conversion on GB10.