Theme Builder: structured color/type controls, scheme catalog, diverging preview

docs/chart-theming-scope.md

@@ -165,7 +165,80 @@ ships, it is an explicit per-font user action, never automatic.
 **Rejected:** per-snippet theme field (2026-06-12 — `spec.config` + merge/extract covers
 it without a second mechanism).
 
-## 5. Status log
+## 5. Structured controls (slice 4b)
+
+The builder today is a raw JSON textarea + one font dropdown + the live gallery. Slice 4b
+adds a strip of structured controls above the editor — accelerators that write into the
+JSON, never replacing it. The JSON stays the source of truth and the full-power escape
+hatch; controls cover the common ~80% (color, type, spacing, grid), not all 72 config
+properties (that is the trap vega-editor deliberately avoids by staying JSON).
+
+**Hard constraint — the builder must preserve unknown keys.** Verified by compiling: the
+vega-themes presets carry Vega-_layer_ keys (`symbol`, `shape`, `path`, `group`) that are
+not in the Vega-Lite `Config` schema, and Vega-Lite forwards the whole config to Vega
+unchanged — they take effect. So a structured control must **merge into** the existing
+config (immutable path-set that spreads siblings), never rebuild it from a closed
+schema-typed model, or it silently drops those keys on a round-trip. Same shape as
+`applyFontToConfig`, which walks and rewrites rather than reconstructing.
+
+**Resolved design points:**
+
+- **Surfacing — inline tab strip** (not popovers, not sub-modals). Tabs (Color / Type /
+  Layout / Axes & grid / Legend) sit between the toolbar and the JSON+gallery, all in the
+  one xlarge modal. No nested overlays/focus traps, no contention with the one-open-popover
+  registry, and panels + JSON + gallery stay visible together.
+- **Color model — scheme picker that materializes to swatches.** A `range` family takes
+  either an explicit color array or a named Vega scheme string (both verified to compile).
+  Pick a named scheme for the quick path; "materialize" expands it to an editable swatch
+  array for brand tuning. Catalog ships 15 categorical + 24 sequential + 10 diverging
+  schemes; categorical schemes resolve to arrays, continuous ones to interpolators sampled
+  into stops for the gradient preview and the materialize action.
+- Structured controls are gated on valid JSON (same as the font control): a parse error
+  disables them and the textarea is the fix.
+- Controls write **minimal** config — clearing a value deletes the key rather than writing
+  a default, so a theme stays a diff against stock, not a full dump.
+
+**Panels:** Color (`range.category` swatches/scheme, `mark.color`, `range.heatmap`/`ramp`/
+`diverging`) · Type (base `font`, title/axis/legend size+weight) · Layout (`background` incl.
+transparent, `padding`, `view.stroke`/`fill`/cornerRadius) · Axes & grid (grid on/off + color
+
+- dash, domain, label color/angle — base `axis` only; the 25 variants stay JSON) · Legend
+  (orient, label/title color+size, symbol size).
+
+**Build order:** (a) core foundation — scheme catalog + immutable config path get/set +
+`schemeColors` materialize, with tests; (b) Color panel (highest payoff); (c) Type, Layout,
+Axes, Legend panels; (d) wire the tab strip into the modal.
+
+**Not in slice 4b:** the house style's own gaps — no `mark.color` (single-series charts stay
+Vega-blue), unset legend/header/padding — are left for a separate house-style redo, not
+papered over here. Minor cleanup noted: `theme-preview-specs.ts` declares `$schema` v5 while
+the app standardizes on v6.
+
+## 6. Status log
+
+- **2026-06-14 (slice 4b, first increment)** — **structured-control foundation + Color
+  panel.** Core `theme-controls.ts`: immutable config path get/set (preserves siblings —
+  the Vega-layer-key guarantee — and prunes on delete) + the named-scheme catalog (15
+  categorical / 24 sequential / 10 diverging) + `schemeColors` resolution (categorical
+  arrays passthrough, continuous interpolators sampled to hex), all tested. `vega-scale`
+  added as a declared dep (focused sub-package, like `vega-expression`) with a typings
+  shim in `vite-env.d.ts` (its package.json `exports` omits `types`). Store gains the
+  generic `mutateDraftConfig(fn)` write path; `applyDraftFont` refactored onto it. Modal
+  gains an APG tab strip — **Color** (categorical scheme/swatches + materialize, default
+  `mark.color`, sequential/diverging gradient pickers) and **Type** (the relocated font
+  control). Tabpanel gated on valid JSON. From first-use feedback, same day: the modal
+  body is now **controls + JSON on the left, gallery as a full-height right rail** (the
+  previews were starved before); `SelectControl` gained an optional per-option `preview`
+  so the scheme dropdowns show swatch strips (categorical) / gradient bars (continuous);
+  every swatch is a reusable `SwatchRow` (color picker + copyable/editable hex field); and
+  sequential/diverging gained **Materialize → editable stops**, so custom gradient colors
+  are possible, not just named schemes. Second feedback pass: the raw JSON is now a
+  **collapsed disclosure** at the bottom of the controls column (it was eating half the
+  first screen), forced open only on a parse error; the structured controls fill the
+  column. `SelectControl` options gained a `labelStyle`, so the **font dropdown renders
+  each name in its own family** (the type analogue of the color swatches) and its trigger
+  shows the current font in-face. Verified: typecheck, lint, full tests (950).
+  Remaining: Layout / Axes & grid / Legend panels; swatch reorder.
 
 - **2026-06-12 (slice 4 close-out)** — **custom themes in the §08 envelope.** The
   workspace export now writes a `themes` array (additive — no format bump; importers