Build catalog-backed loadout workbench

docs/DESIGN_SYSTEM.md

@@ -814,3 +814,26 @@ Attribute relationship, one numeric effect value, and one non-negative
 whole-number unlock cost. At narrow widths profile cards and augment editor
 cards reduce from multi-column grids to a single column while retaining
 44-pixel interactive targets.
+
+### Loadout workbench
+
+The builder is a three-rail tactical workbench: compact equipment positions on
+the left, the currently selected item editor in the center, and a sticky live
+calculation summary on the right. At medium widths the summary becomes a
+full-width lower rail; on mobile all three rails stack, with equipment first,
+editing second, and results third. Equipment positions remain explicit even
+when empty so loadout completeness is always visible.
+
+Use the shared `BuilderPicker` for builder catalogs and Attribute pools. It
+combines an always-visible current selection with a searchable overlay, icon or
+tactical fallback mark, classification metadata, selected state, and conflict
+state. Conflicting catalog entries remain visible but disabled so restrictions
+such as the single-exotic-weapon rule are explained rather than hidden.
+
+Numeric instance values display their authoritative minimum and maximum beside
+the field and clamp to that range on completion. Always-on item rolls, fixed
+bonuses, inherited profiles, enabled augments, and activated set bonuses feed
+the live totals immediately. Trigger-dependent talents remain explicitly
+`CONDITIONAL` until the user enables `TRIGGER ACTIVE`; only then may their
+effects enter combined totals. This textual distinction must remain clear
+without relying on color.