Make Best one network, and retire Medium and the mixture

Best was a mixture of two experts and a gate, 110 GMAC a megapixel;
Medium a single network at 48 that was softer on real edges. fb-combo
(darkroom-denoise, 20 000 steps from fb-edges2, taught by the mixture
with a quarter of its crops from the edge-rich parts of the frames) is
Medium's shape and holds the mixture's edges on real photographs:
edge PSNR within 0.04-0.06 dB at ISO 1600/6400/25600, more sharpness
kept at all three, the chart's edge 0.89 photosites wide against 0.82.
It is 0.27 dB short on smooth areas at ISO 25600. It becomes Best, and
the methods are Bilinear, Fast and Best.

Saved edits keep their numbers: 2, which was Medium, is now Best, and
3, which was Best, is past the end and reads as the default, Best.
The network ships as mosaic-hq, a new name: the result cache keys a
model by name and size, and this one is byte for byte the old Medium's
size. Its tablet form (A16W16) lost 0.00 dB in simulated QDQ at every
ISO and at most 0.09 dB across the noise bracket.

core/dr-pipeline/src/graph.rs

@@ -2216,13 +2216,13 @@ mod tests {
         g.set_param(
             learned_denoise::ID,
             learned_denoise::METHOD,
-            learned_denoise::Method::Medium.index(),
+            learned_denoise::Method::Fast.index(),
         );
         let state = g.state();
         let mut h = EditGraph::default_chain();
         h.set_denoise_available(true);
         let _ = h.set_state(&state);
-        assert_eq!(h.denoise_method(), learned_denoise::Method::Medium);
+        assert_eq!(h.denoise_method(), learned_denoise::Method::Fast);
         assert!((h.denoise_grain() - 0.4).abs() < 1e-6);
     }
 }

core/dr-pipeline/src/learned_denoise.rs

@@ -35,23 +35,27 @@ pub const GRAIN: ParamId = ParamId("grain");
 
 /// TRACES: FR-DEV-3g
 /// The demosaics a photograph can be developed with, in the order the
-/// sidecar numbers them. Three networks that trade time for quality — the
-/// same training, distilled into smaller students (docs/dev/denoise.md §13)
-/// — and the classical demosaic, which is no network at all.
+/// sidecar numbers them. Two networks that trade time for quality
+/// (docs/dev/denoise.md §15) and the classical demosaic, which is no network
+/// at all.
+///
+/// Until 0.24 there were four — Bilinear, Fast, Medium, Best — and the
+/// sidecar keeps their numbers: 2, which was Medium, is now Best, and 3,
+/// which was Best, is past the end and reads as the default, which is
+/// Best. Both land on the network that replaced them, with no migration.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum Method {
     /// The classical demosaic: the noise stays.
     Bilinear,
-    /// The smallest student: a quarter of the medium network's work.
+    /// The smallest student: a quarter of Best's work.
     Fast,
-    /// One network the size of the first release's.
-    Medium,
-    /// Two experts, one for flat areas and one for edges, and a gate.
+    /// One network of the first release's size, taught by the mixture of
+    /// experts it replaced: the mixture's edges at a third of its work.
     Best,
 }
 
 impl Method {
-    pub const ALL: [Method; 4] = [Method::Bilinear, Method::Fast, Method::Medium, Method::Best];
+    pub const ALL: [Method; 3] = [Method::Bilinear, Method::Fast, Method::Best];
     pub const DEFAULT: Method = Method::Best;
 
     /// The sidecar's number for it.
@@ -92,7 +96,6 @@ pub(crate) static DESCRIPTOR: LazyLock<Arc<OpDescriptor>> = LazyLock::new(|| {
                 vec![
                     LocalizedKey("param.learned_denoise.method.bilinear"),
                     LocalizedKey("param.learned_denoise.method.fast"),
-                    LocalizedKey("param.learned_denoise.method.medium"),
                     LocalizedKey("param.learned_denoise.method.best"),
                 ],
             )
@@ -117,3 +120,20 @@ pub(crate) static DESCRIPTOR: LazyLock<Arc<OpDescriptor>> = LazyLock::new(|| {
 pub fn descriptor() -> Arc<OpDescriptor> {
     DESCRIPTOR.clone()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// An edit saved before 0.24 stored Medium as 2 and Best as 3. Both
+    /// now name the network that replaced them, and nothing reads as Fast
+    /// or Bilinear that did not before.
+    #[test]
+    fn the_retired_methods_read_as_best() {
+        assert_eq!(Method::from_index(0.0), Method::Bilinear);
+        assert_eq!(Method::from_index(1.0), Method::Fast);
+        assert_eq!(Method::from_index(2.0), Method::Best, "Medium, before 0.24");
+        assert_eq!(Method::from_index(3.0), Method::Best, "Best, before 0.24");
+        assert_eq!(Method::Best.index(), 2.0);
+    }
+}