web: SHARPENING lifts only the edge it was pointed at, so a flat half of the frame keeps the grain it came with

SHARPENING was the doc's §4.2 kernel with the two parts of §4.2 missing from
it. `CLARITY_SKSL` evaluated the 3x3 unsharp mask with Mask = 1 on every pixel
and no coring at all, so a flat sky, a cheek and a noise speckle all took the
gain an eyelash took. That is `thay_doi_thong_so_giong_lightroom.md` §1 written
out as a bug: "khi Sharpen, ảnh nổi đầy sạn hạt cát" — the knob could not raise
the contrast of an edge without raising the noise of everything beside it, and
on a grainy frame the second effect won.

`SHARPEN_SKSL` is the doc's own line, `Image + Amount x HighPass x Mask`, with
the two terms it names:

  - EDGE DETECTION: the Sobel magnitude G = sqrt(Gx^2 + Gy^2) on luminance, put
    through the doc's soft threshold smoothstep(T, T + 0.1, G). Flat fields
    read G = 0 and get Mask = 0 — the pixel is handed back untouched.
  - DETAIL (halo coring): a high-pass under SHARPEN_CORE is a speckle, not a
    detail, and is suppressed. The coring is soft (a ramp across the threshold,
    not a cliff) so a detail sitting on it is not switched on and off from one
    pixel to the next.

The HIGH-PASS is the doc's Radius, held at one image pixel — 0.7-0.9px on a
Retina panel — and it is a LUMINANCE high-pass carried by all three channels.
A per-channel kernel sharpens a red edge against a green one and draws a colour
fringe down every contour; the file's own §3 rule is to keep R/L, G/L and B/L
where they were.

`scripts/sharpen-check.mjs` pins the three properties the old kernel could not
have: a flat field and a field of grain come back unchanged, a step below the
threshold comes back unchanged, and a hard step moves apart on both sides while
the flat halves beside it stay put. `CLARITY_SKSL` and `clarityUniforms` are
gone with it, and the header note that said CanvasKit had two convolution steps
to replace now says the one it has.

Checked: node scripts/sharpen-check.mjs; node scripts/denoise-check.mjs; node
scripts/tone-base-check.mjs; node scripts/highlight-knee-check.mjs; node
scripts/auto-tone-check.mjs; node scripts/half-check.mjs; node
scripts/mask-wb-check.mjs; node scripts/preview-match-check.mjs; node
scripts/raw-develop-check.mjs; node scripts/white-level-check.mjs; node
scripts/wb-table-check.mjs; npx tsc --noEmit.

docker/frontend/src/engine/exportEngine.ts

@@ -6,11 +6,12 @@
 //   - `Skia.Data.fromURI` + expo file APIs → the caller hands in the JPEG bytes
 //     and gets JPEG bytes back; the file save / gallery / MediaLibrary tail is
 //     gone (the browser downloads a Blob instead).
-//   - `MakeMatrixConvolution` does not exist in CanvasKit. The two convolution
-//     steps (CLARITY, output sharpen) run through `CLARITY_SKSL` from
-//     `toneShader.ts` — the same kernel `[0,-a,0,-a,1+4a,-a,0,-a,0]`, evaluated
-//     as a shader pass. `convolve` replaces the pixels outright (the shader's
-//     output is opaque and covers the same rect), so no clearing pass is needed.
+//   - `MakeMatrixConvolution` does not exist in CanvasKit. The output sharpen
+//     (and CLARITY's own kernel) run through shader passes instead —
+//     `SHARPEN_SKSL` for the knob, the same kernel with the doc's Sobel edge
+//     mask and detail coring on it. `convolve` replaces the pixels outright (the
+//     shader's output is opaque and covers the same rect), so no clearing pass
+//     is needed.
 //   - The negative-side blurs stay on `ImageFilter.MakeBlur`, but a blur cannot
 //     be composited over the un-blurred content, so those passes snapshot, clear
 //     and redraw. Order matches RN's nested filter chain: denoise → clarity →
@@ -28,7 +29,7 @@ import {
   TONE_SKSL,
   EXPOSURE_SKSL,
   GLOW_SKSL,
-  CLARITY_SKSL,
+  SHARPEN_SKSL,
   CLARITY_BLUR_SKSL,
   CLARITY_BLEND_SKSL,
   NR_SKSL,
@@ -173,7 +174,7 @@ let nrEffect: any = null;
 let dehazeEffect: any = null;
 
 function effects() {
-  if (!sharpenEffect) sharpenEffect = Skia.RuntimeEffect.Make(CLARITY_SKSL);
+  if (!sharpenEffect) sharpenEffect = Skia.RuntimeEffect.Make(SHARPEN_SKSL);
   if (!toneEffect) toneEffect = Skia.RuntimeEffect.Make(TONE_SKSL);
   if (!exposureEffect) exposureEffect = Skia.RuntimeEffect.Make(EXPOSURE_SKSL);
   if (!cinemaEffect) cinemaEffect = Skia.RuntimeEffect.Make(CINEMA_SKSL);
@@ -242,7 +243,7 @@ function maskEffectFor(count: number, spatial: boolean): any {
   return effect;
 }
 
-// CLARITY_SKSL uniforms are (a, px.x, px.y); px = one source pixel = 1 unit on
+// SHARPEN_SKSL uniforms are (a, px.x, px.y); px = one source pixel = 1 unit on
 // a 1:1 export canvas, so the radius matches what the preview tuned.
 function convolvePaint(srcImage: any, amount: number): any {
   const { sharpenEffect: effect } = effects();