Chart builder: SelectControl pickers, channel chooser, per-type aggregates

docs/architecture/10-interaction-and-feedback.md

@@ -418,6 +418,34 @@ _(Consulted via /council → NN/g #4 consistency, #6 recognition-over-recall, #8
 WAI-ARIA APG disclosure + menu-and-menubar; Carbon popover/overflow-menu/text-toolbar. This
 bullet is the contract.)_
 
+**Resolved — value pickers are the SelectControl disclosure, not native `<select>`.** A
+native select's popup can't be token-styled and renders differently on every browser/OS — a
+foreign object inside a designed surface — so anywhere a control is part of one,
+`SelectControl` replaces it: the same disclosure primitive as the settings popovers (trigger
+with `aria-expanded`/`aria-controls`; portaled, `fixed`-positioned panel; labelled `group` of
+option buttons — **not** an ARIA menu or combobox; single-open registry; Esc closes and
+refocuses the trigger; outside press closes; open lands focus on the selected option;
+Arrow/Home/End rove). The selected option carries `aria-current` and a visible ✓, never
+colour alone. The same control doubles as an **action picker** (no `value`; e.g. "Add field
+to which channel?"). A custom `triggerClassName` _replaces_ the default trigger styling, so
+chip-styled triggers (the pill's type chip, the shelf's field chips) stay chips.
+_(Consulted via /council → WAI-ARIA APG disclosure/menu-button/radio, Carbon, NN/g #4. This
+bullet is the contract; cite it, not the source.)_
+
+**Resolved — field→channel assignment: explicit choice, visible armed state.** Clicking a
+shelf field with no channel armed opens an explicit **channel chooser** (the channels that
+accept the field; an occupied one is labelled with what it replaces) — never a silent
+first-empty-seat grab (NN/g #3, user control). Arming a channel slot short-circuits the
+chooser (the fast path) and **must be visible where the next click happens**: the shelf
+gains an accent ring plus a polite `role="status"` line naming the target ("Assigning to X —
+choose a field below. Esc cancels"); **Esc disarms** without closing the modal (captured
+before the dialog's own Escape handling). Chart-level properties (title/subtitle,
+width/height) live **on the chart side**, in a strip under the preview — a chart property
+belongs on the chart (NN/g #4; the Tableau/Lyra convention). A link-styled affordance that
+_acts_ rather than navigates is mis-dressed: such actions are **ghost buttons** with
+verb-first labels (Carbon links-vs-buttons; "Use a constant"). _(Consulted via /council →
+NN/g #1/#3/#4, Carbon button/link usage. This bullet is the contract.)_
+
 **Resolved — an error names the right fix, not a boilerplate one.** Don't staple a generic
 remedy onto every failure. A missing dataset reference is **not** a JSON/spec syntax problem,
 so the preview gives it a tailored, fixable line — _"Dataset «X» not found. Create it from