Chart builder: intent front door, Heatmap mark, role-aware guidance

docs/chart-builder-enhancement-scope.md

@@ -25,6 +25,49 @@
 Newest first. The at-a-glance build-order tracker is §4; per-item detail is §3. This log is
 the quick "where are we" — read it first.
 
+- **2026-06-13 (guidance: reason over role, not raw type)** — closed a **false-positive class**
+  in `builderWarnings` (eng-council + council consult). A histogram (bar, binned-Q X, count Y)
+  tripped "two measures → scatter" because `isMeasureMapping`/`effectiveType` ignored `bin`.
+  Fix: `isMeasureMapping` is now **bin-aware** (a binned field is a discretized dimension —
+  mirrors Vega-Lite's own `isDiscrete(fieldDef)`); a new `isReorderableCategory` keeps Sort
+  from being offered on a histogram's binned axis (the council-flagged regression); the scatter
+  rule routes through the role predicate + a positive mark list (deletes the `mark !== 'rect'`
+  bolt-on); `stackMeasureChannel` excludes binned. Pinned with regression tests (no
+  scatter/Sort on a histogram; real bar still sorts; two raw measures still nudge). Promoted to
+  **/alignment check #15** ("reason over role, not raw type"). **Not done (deliberately):**
+  intent-gating the taste warnings — verified no current intent layout trips one, so the gate
+  would be dead code; recorded as a standing principle in `builderWarnings` instead. The
+  broader posture (curate good via the front door > enumerate bad via warnings) is the council's
+  recommended bottom for the combinatorial-warning worry. Verified: typecheck + test (913) +
+  eslint + build.
+
+- **2026-06-13 (3A + heatmap mark)** — **the intent-first front door shipped (Tier C), and
+  the mark set gained `rect` (Heatmap).**
+  - **Heatmap mark** — `rect` added to `MARK_TYPES` (six marks; labelled **Heatmap** in the
+    picker, which now wraps to two rows in the 320–360px pane). Guidance rewired: both-axes
+    rule covers heatmaps; a new hint nudges a Colour measure on a two-axis heatmap with a
+    one-click **Colour by count**; `rect` is exempt from the two-measures→scatter nudge (a
+    binned 2-D histogram is valid). Never the auto-default mark; names read "Heatmap of …".
+    Spec §06 mark-type + guidance updated.
+  - **3A intent front door** — a **persistent strip** at the top of the config pane (the
+    interaction model chosen with the user over a replace-on-open screen — "shows all
+    controls + a do-it-for-me", the Tableau _Show Me_ parallel). Core (`chart-builder.ts`):
+    `CHART_INTENTS` (Compare/Ranking/Change-over-time/Correlation/Distribution/Part-to-whole/
+    Heatmap), `intentLayout` (intent × column-roles → mark + channels), `intentApplicable`
+    (Show-Me gating), `applyIntent` (reshape, keep dataset/transforms/title), and
+    `activeIntent` (structural match → the live chart's intent highlights with **no stored
+    state**; lights the smart default on open). Store: `setIntent`. UI: an APG **toolbar** of
+    toggle chips (roving tabindex, arrows move / Enter applies, accent-ring selection,
+    `aria-disabled`+reason on inapplicable intents).
+  - **Council** run on the front-door copy/flow → toolbar (not radiogroup — select-on-arrow
+    would reshape the chart), disabled-focusable-with-reason, intent-framing (Heatmap kept as
+    the one chart-type label, mirroring the mark). Recorded in `architecture/10` §5; spec §06
+    gained an **Intent (the front door)** subsection.
+  - **Verified:** `typecheck` + `test` (909, +17: intent core/store, heatmap guidance/naming)
+    - `eslint` + `build`. **Owed:** a visual pass on the live strip (chips, disabled states,
+      keyboard) + a heatmap rendered from real data. **Open (user's call):** whether the
+      _Heatmap_ chip should read as an intent phrase instead (council's intent-framing point).
+
 - **2026-06-12 (3D)** — **entry points & discoverability shipped. Up next: 3A (the
   front door now has somewhere to be found).**
   - **Library creation surface forked:** primary **Build Chart** (accent, takes the
@@ -557,9 +600,10 @@ Phase 1  1A actionable hints      ✓ done
 Phase 2  2A value-or-field channels (Property model)  ✓ done
          2B field shelf + in-place type cycling       ✓ done (field-first + on-chart shelves)
 Phase 3  3D entry points & discoverability         ✓ done (2026-06-12)
-         3A intent-first front door (Tier C)       ← next; built on 2B; the defining feature
-         3B starter examples
+         3A intent-first front door (Tier C)       ✓ done (2026-06-13); persistent strip
+         3B starter examples                       ← next; pairs with 3C
          3C open in builder (strict hydration)     ← added 2026-06-11; pairs with 3B
+Marks    +rect (Heatmap)                           ✓ done (2026-06-13)
 Phase 4  (gated) theta/facets/styling-overrides/undo/lookup — decide after Phase 3
 
 Also shipped (builder UX/perf, from dogfooding): near-fullscreen modal, internal-scroll