# Ch433 — UV-optimized STQ packing

## Root cause

The repaired Ch432 sampler restored the missing perspective-bilinear samples,
but the f19 base scene still showed granular spatial misregistration against
its independent floating-point reference.  Post-repair isolation rejected a
13-bit reciprocal table and rejected nearest filtering: both worsened the
software-reference and PCSX2 scores.

The remaining fixture path used `--fast-fit-scale`.  That shortcut selected
the largest representable common S/T/Q scale, normally 6144, even though the
scheduler generator already had a per-triangle search that scores packed RTL
UVs against authentic floating-point UVs.  A common scale cancels only at
infinite precision; vertex quantization, integer gradients, and reciprocal
quantization make the choice observable.

## One-variable repair

`zsrt139f43` retains f19's exact 766-draw population, 254 chronological state
groups, 125 capacity epochs, native 12.4 geometry, textures, palettes, fog,
bilinear reference, Z state, and alpha state.  Only `--fast-fit-scale` was
removed.  The optimizer selected scales from 0.375 through 6144 rather than
forcing almost every triangle to 6144.

The coverage planner no longer emits the shortcut by default.  It remains
available through an explicit planner `--fast-fit-scale` option for quick
diagnostic fixture generation.

## Production result

The full registered-gradient f43 replay passed all 125 epochs:

- 282,363 fragments fed and 232,326 passed Z;
- zero drops, color overflows, and AXI errors;
- 125 complete markers and drains;
- final Z mismatch 0/307,200 and color mismatch 0/176,888.

Against its independent software reference, f43 improves from f19's
MAE/RMSE 8.7494/18.7008 to 4.1633/11.9970.  Its mapped PCSX2 score improves
from 18.3393/25.8374 to 17.7172/24.8787.

`zsrt139f44` substitutes the optimized f43 base slices into the complete f42
composition while preserving the chronology-correct PSMT4 character,
direct-color highlights, and alpha/postprocess population.  The production
replay passed all 292 epochs with 2,339,405 fragments fed, 2,285,783 passed,
zero drops/errors, and exact final Z and color scoreboards.  Relative to f42,
87,282 pixels change.  The mapped PCSX2 score improves from
15.0765/21.9717 to 14.8127/21.5567.

## Silicon acceptance

No compile was required.  The timing-clean Ch432 RBF ran both asset-only
fixtures.  f43 passed all 125 runtime gates and matched simulation byte for
byte at SHA-256
`f4ae82153791a66ae8ed7c4b3dd01f609b9706e826e971311c602181f8a08bc7`.

The complete f44 board run passed all 292 texture, palette, staging, drain,
and zero-drop gates.  It reported 240,492 nonzero words, bounds
`(0,0)..(511,479)`, sum32 `0x96f07662`, xor32 `0x0a031310`, and selected the
HDMI line-buffer source.  Its 307,200-word framebuffer is byte-identical to
production simulation at SHA-256
`3f492ab65c12415f4d0cd1aeafc64072870fd43bed237be4a923efbce30d2081`.

The accepted board image is
`captures/gs/silenthill3/extracted/sh3_zsrt139f44_ch433_board.png`; the mapped
comparison is
`captures/gs/silenthill3/extracted/recon/sh3_zsrt139f44_ch433_board_mapped.png`.
Ch433 is accepted, and f44 is the current live HDMI baseline.
