Show the colour mixer as three runs of twelve, each row a colour

The mixer was thirty-six sliders reading "Hue / Sat / Lum" twelve times
over with nothing saying which band any row belonged to. The identity was
there all along — the descriptor declares param.mixer.orange.sat and BANDS
carries orange at 30° — and was discarded on the way out: labels.rs had no
mixer entries, so every key fell through to a derived label that yields the
bare channel name.

A parameter can now say which aspect it adjusts and which subject it
adjusts it on, with the subject's hue where the subject is a colour
(descriptor::Facet). That is data about what the operation does, not a
layout: the mixer genuinely weights pixels around 30°. What to draw from
30°, and in what order to stack the runs, stay in dr-ui (ARCH §4.3a) —
develop.rs brings rows sharing an aspect together and marks the first of
each, and adjust.slint names the run once and draws a swatch, a track and a
readout on one line.

Grouped by channel rather than by band because an edit is almost never
"everything about orange"; it is the saturation of the greens, made by
comparing one channel across neighbouring bands. Twelve band sections put
those twelve rows in twelve different places.

The swatch is the label, which is what makes twelve rows fit where four
did. The band name is not lost: it is the row's accessible label, so the
control is not colour-only, and labels.rs is where the mapping is written
down — including chartreuse as "Yellow-Green" and spring as "Blue-Green",
since nobody hunting foliage scans a list for "Spring".

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/ui-refinement.md

@@ -170,7 +170,7 @@ thirty-six anonymous sliders reading `Hue 0 / Sat 16 / Lum 0` twelve times
 over, with nothing saying which band any row belongs to. Three separate
 defects meet here.
 
-### M1 — Band identity is lost (a bug, not a style issue)
+### M1 — Band identity is lost (a bug, not a style issue) — **done**
 
 `labels.rs` has no `param.mixer.*` entries, so all thirty-six keys fall
 through to a default that yields the bare channel name. The core is not at
@@ -181,11 +181,30 @@ discarded at resolution.
 **Deliverable.** Resolve mixer keys to their band. A row reads `Orange · Sat`,
 or `Sat` under a band heading — M3 decides which.
 
-### M2 — Bands carry their centre hue as capability data
+**Landed** as a `band.*` catalogue resolving the *subject* of a faceted
+parameter (M2), rather than as entries for the thirty-six `param.mixer.*`
+keys. Three bands are catalogued to something other than their key: chartreuse
+reads "Yellow-Green" and spring "Blue-Green", because a photographer looking
+for foliage does not scan a list for "Spring".
+
+### M2 — Bands carry their centre hue as capability data — **done**
 
 **Deliverable.** `ParamDescriptor` gains an optional band hue in degrees, set
 by `band_params!` from `BANDS`. The UI converts degrees to a swatch.
 
+**Landed** as `descriptor::Facet` — a little wider than "a band hue", and the
+width is what M3 turned out to need. A parameter may say which **aspect** it
+adjusts (the channel) and which **subject** it adjusts it on (the band), with
+the subject's hue attached where the subject is a colour. `ParamDescriptor` is
+otherwise unchanged and `faceted()` is a const builder step, so the thirty-six
+descriptors stay `static` and every other operation says nothing at all.
+
+The hue reaches the screen as `Swatch` in `widgets.slint`, which owns the
+saturation and brightness. Those two are *not* in `style.yaml`: it holds
+colours and lengths, and a third section for two floats used in one component
+buys less than it costs. `Theme.swatch` — the square's size — is a length and
+does live there.
+
 **Why this is not a §4.3a violation.** A band's centre hue is a *fact about
 the operation* — the mixer genuinely acts on the 30° band, and that number is
 what it acts on. The core says "this parameter belongs to the band centred at
@@ -202,15 +221,33 @@ exactly as an image is data. That is categorically different from an accent
 decorating a heading, which is what the palette rule forbids. Keep them small
 and let them identify, never dominate.
 
-### M3 — Structure: twelve collapsible bands
+### M3 — Structure: three runs of twelve, not twelve of three — **done**
 
-**Deliverable.** The mixer renders as twelve `Section`s — one per band, titled
-by band name, carrying its swatch — each holding Hue, Sat and Lum. Collapsed
-by default; the modified dot (Workstream C) shows which bands hold an edit
-without expanding them.
+~~The mixer renders as twelve `Section`s — one per band, titled by band name,
+carrying its swatch — each holding Hue, Sat and Lum. Collapsed by default.~~
 
-This needs no new `WidgetKind`: it is Workstream C's sections applied to a
-grouping the frontend derives from parameter ids. Depends on C.
+**Superseded, twice over.** The lids came off the develop column entirely
+(Workstream C's sections are now plain headings), so "collapsed by default"
+had nothing left to mean. And the grouping was the wrong way round: an edit is
+almost never "everything about orange", it is "the saturation of the greens",
+made by comparing one channel across neighbouring bands. Twelve band sections
+put the twelve rows you want to compare in twelve different places.
+
+**Landed.** Three runs — Hue, Saturation, Luminance — of twelve rows each,
+under the operation's own heading. `develop.rs` stacks the rows by aspect
+(`presentation_order`) and marks the first of each run; `adjust.slint` names
+the run once and draws the rest. Each row is a swatch, a track and a readout on
+one line: the swatch *is* the label, which is what makes twelve rows fit where
+four did, and the band name lives on as the row's accessible label so the
+control is not colour-only.
+
+The mixer's declaration order is untouched — it declares band by band, which
+is the order the shader wants. Rearranging it for the panel would have been
+the core laying out a screen (§4.3a); doing it in `develop.rs` is the same
+frontend-side derivation that decides there are groups at all.
+
+Nothing here is mixer-specific: any operation whose parameters carry facets
+groups this way, and one that carries none is untouched.
 
 ### M4 — A single-parameter operation should not cost a heading
 
@@ -222,9 +259,10 @@ parameters number one wants to *be* a named row, not a group containing one.
 row labelled by the operation. Derived frontend-side from the parameter
 count — the core says nothing about it, per §4.3a.
 
-**Done when.** Every mixer row says which band it edits; bands collapse with
-modified state visible while collapsed; Vibrance and Saturation are one row
-each; and no hex colour appears in any descriptor.
+**Done when.** Every mixer row says which band it edits; the rows for one
+channel read as a run rather than as twelve unrelated sliders; Vibrance and
+Saturation are one row each; and no hex colour appears in any descriptor.
+**All four are met.**
 
 ---