Fold demo-build learnings: Swift 2.4 profiles recipe, checkout order-field contract, order-line seeding, update backup gate, MCP no-op rows

[Justinvolved]

Folds eight learnings from two 2026-07 demo runs (a customer build dispatch and a Swift 2.4 profiles key test) into the demo and staged-foundational skills. Version 4.11.0 — 4.9.0 and 4.10.0 are claimed by open PRs #58/#59; the CHANGELOG sequence is independent of merge order.

dw-demo-swift

• customer-center.md §6 (new) — Swift 2.4 sign-in profiles / switch user: profiles (same-username AccessUser rows + AccessUserIsLogin, ListUserProfiles/UserProfilesTemplate, DwSwitchUserUniqueId -> StartSwitchUser) vs impersonation (AccessUserSecondaryRelation + CanImpersonate) — two mechanisms, easy to conflate; the zero-custom-code picker recipe (cloned rows, NEWID() unique ids, distinct customer numbers, master IsLogin=1, one restart; per-profile isolation free via PriceUserCustomerNumber + UseUserID); the ?ShowProfiles=1 sign-in-page picker quirk; and the platform-honesty rule — the documented 10.29+ gate does not bite on a 10.28.1-PreRelease build, so state the platform when a demo shows features the customer's GA lacks.
• checkout-order-fields.md (new reference + routing row) — the stock delivery-date beat needs NO custom order field (EnableDeliveryDate posts into native OrderShippingDate); order-field values live in per-system-name EcomOrders columns, so a definition without its matching column breaks every order read (IndexOutOfRangeException in ExtractOrderFieldValues); MCP create_order_field always violates DW_FK_EcomOrderField_EcomFieldType (upstream bug — SQL contract documented).

Staged foundational (dw-demo-base/references/foundational/)

• commerce-orders.md — order-line price seeding: change default currency -> restart -> THEN seed (pre-restart seeding lands x100 unit-price artifacts); qty-tier EcomPrices rows silently reprice explicit unit prices; add_products writes only unit-price columns, so backfill line/order totals and sanity-sweep in SQL. Pointer added from the dw-demo-pim order-seeding appendix.
• setup-upgrade.md — in-place platform update gate: pre-update SELECT COUNT(*) FROM ItemList + BACKUP DATABASE, post-update counts must match — an in-place update cycle has been observed to empty ItemList/ItemListRelation/child item tables with no error; protective rule only, no root-cause claim. Routing row added in dw-demo-base SKILL.md.
• extend-mcp-tools.md §5 — two silent no-op catalogue rows: patch_products_safe on variant EcomProducts rows echoes its input model while the row stays NULL (SQL sweep is the canonical variant-enrichment surface — canonical-setup-order.md step 14 updated to say so); copy_page with destinationParentPageId=0 lands the copy in area 1 unless areaId is passed.

Gates

• python scripts/validate-skills.py exit 0 (0 errors, 0 warnings)
• Sanitize grep pack: zero hits across staged diff and commit message
• Dedup: profiles content is new (no prior ListUserProfiles/ShowProfiles coverage); order-line rules extend the existing commerce-orders seeding section; no supersedes required