diff --git a/docs/PROJECT_INDEX.md b/docs/PROJECT_INDEX.md
index dcbb6be..21fab47 100644
--- a/docs/PROJECT_INDEX.md
+++ b/docs/PROJECT_INDEX.md
@@ -14,7 +14,7 @@ Every tenant has three surfaces on this one codebase:
## System overview
- **Architecture**: `Component (container) → Facade → Domain Service → Repository/Provider (DI token, swappable mock↔API) → Mock | API`. Enforced by `npm run arch:check` (import boundaries + circular deps), not just convention. Full detail: [ARCHITECTURE.md](ARCHITECTURE.md), governance docs at `docs/architecture/foundation/**` (11 ADRs + 9 standards docs).
-- **Seller Management** (optional, not built): typed foundation only — `modules.sellerManagement.enabled` gate on `BootstrapConfig`, disabled by default, zero effect on existing marketplaces. See ADR-011 and `docs/architecture/foundation/Seller-Management-Diagrams.md`.
+- **Seller Management** (optional, not built): typed foundation + Phase 1 Backoffice placeholder UI only — `modules.sellerManagement.enabled` gate on `BootstrapConfig`, disabled by default, zero effect on existing marketplaces. Full capability doc: `docs/architecture/foundation/Seller-Management.md`.
- **State**: Signals-based facades everywhere, no NgRx (ADR-007).
- **Rendering**: Bootstrap JSON → Section Engine → Page Renderer → Widget Host → registered widget component (ADR-005). 100% lazy-loaded routes.
- **Theming**: CSS custom properties per tenant, 3 theme stylesheets, never hardcoded hex in a component (ADR-008). Design system spec: [`DESIGN.md`](../DESIGN.md) (root of repo).
diff --git a/docs/architecture/foundation/README.md b/docs/architecture/foundation/README.md
index 1a7ca9a..558dc34 100644
--- a/docs/architecture/foundation/README.md
+++ b/docs/architecture/foundation/README.md
@@ -49,6 +49,7 @@ It is a platform runtime that must support unlimited tenants from one Angular ap
### Seller Management (optional, in preparation — not built)
+- [Seller-Management.md](Seller-Management.md) — capability overview, start here
- [ADR-011](adr/ADR-011-optional-seller-management-module.md) — decision record
- [Seller-Management-Diagrams.md](Seller-Management-Diagrams.md) — hierarchy, bootstrap gate, type diagram
- [Seller-Management-Domain-Models.md](Seller-Management-Domain-Models.md) — typed models, optional sellerId fields
diff --git a/docs/architecture/foundation/Seller-Management.md b/docs/architecture/foundation/Seller-Management.md
new file mode 100644
index 0000000..267e752
--- /dev/null
+++ b/docs/architecture/foundation/Seller-Management.md
@@ -0,0 +1,214 @@
+# Seller Management — Capability Documentation
+
+Status legend used throughout this document:
+
+- **Implemented** — exists in source on `feature/seller-management-foundation` today, verified (`tsc`, `arch:check`, or live browser test).
+- **Planned** — has a typed contract or explicit ADR decision, but no code reads/writes it yet.
+- **Future** — a concept named in this document for roadmap completeness only. No shape, contract, or decision exists yet. Do not build against this section without a new ADR.
+
+This document is the entry point. Detail lives in its companion docs:
+[ADR-011](adr/ADR-011-optional-seller-management-module.md) (decision),
+[Seller-Management-Diagrams.md](Seller-Management-Diagrams.md) (hierarchy/bootstrap-gate diagrams),
+[Seller-Management-Domain-Models.md](Seller-Management-Domain-Models.md) (every type, field by field),
+[Seller-Management-UX-Review.md](Seller-Management-UX-Review.md) (Phase 1 UI review).
+
+## 1. Overview
+
+Seller Management is an **optional platform capability** that would let one
+marketplace host multiple independent sellers, each with their own
+inventory/orders/branding, under one centralized administration. It is not
+another tenant — a seller is a child scope beneath exactly one marketplace
+(ADR-011).
+
+**Implemented today:** typed contracts for the whole hierarchy, a disabled-
+by-default feature flag, one Backoffice page that explains the capability
+and collects interest ("Request Access" / "Learn More"). **Nothing else** —
+no CRUD, no backend, no seller-facing UI, no checkout/order behavior change.
+
+## 2. Architecture & Hierarchy — Implemented (types only)
+
+```
+Platform
+ └── Marketplace (tenant) — always present, backend-resolved (ADR-001)
+ └── Seller (optional) — 0..N per marketplace, backend-resolved (ADR-011)
+```
+
+Full diagram set: [Seller-Management-Diagrams.md](Seller-Management-Diagrams.md).
+
+Rules (ADR-011, enforced by review, not yet by any lint rule):
+Marketplace is the sole primary tenant. Seller is a child scope, never a
+sibling tier. The frontend never resolves seller identity itself — same
+rule as tenant resolution. All seller-aware behavior must check one
+capability flag, never scattered marketplace/seller conditionals.
+
+## 3. Marketplace — Implemented (existing, unchanged)
+
+The marketplace is the existing `TenantConfig`
+(`shared/models/config/tenant.model.ts`) — resolved by the backend from
+request Host, exactly as before this work started. Seller Management adds a
+new `MarketplaceRef` (`core/sellers/models/marketplace-ref.model.ts`): a
+minimal `{id, slug, name}` view of a marketplace *as seen from a seller
+record*, not a replacement for `TenantConfig`.
+
+## 4. Seller — Implemented (types only)
+
+`Seller` (`core/sellers/models/seller.model.ts`): `id`, `marketplace:
+MarketplaceRef`, `name`, `slug`, `status: SellerStatus`, optional `branding:
+SellerBranding`, `createdAt`/`updatedAt`. No repository, gateway, facade, or
+UI reads or writes this type yet — it exists so future CRUD work has a
+settled shape instead of inventing one ad hoc.
+
+**Planned:** a `SellerRepository`/`SellerGateway` pair following the same
+mock↔API DI-token pattern every other admin domain already uses
+(`BACKEND.md` §8). **Future:** the actual CRUD screens, list/detail pages,
+onboarding flow.
+
+## 5. Roles & Permissions — Implemented (types only)
+
+`SellerPermissionRole` (`core/sellers/models/seller-permissions.model.ts`):
+four values — `marketplaceOwner`, `seller`, `sellerStaff`, `platformAdmin`.
+This is a **separate vocabulary** from the existing `AdminRole` (Owner/
+Manager/Support/ReadOnly, `core/auth/models/permission.model.ts`) — not
+merged, not wired into any guard. **No authentication or authorization
+change exists anywhere in this work.**
+
+**Planned:** once a real permission model is designed, these roles gate
+seller-scoped routes/actions the same way `AdminRole` gates admin routes
+today (ADR-009 capability-guard pattern). **Future:** the actual
+permission-to-action mapping, custom/finer-grained roles per marketplace.
+
+## 6. Future Roadmap
+
+### Feature Flags — Implemented (contract), Planned (real use)
+
+`BootstrapConfig.modules.sellerManagement.enabled`
+(`shared/models/config/platform-modules.model.ts`), default `false`
+(`DEFAULT_PLATFORM_MODULES_CONFIG`). Implemented as a typed contract read by
+the Phase 1 page (`admin-seller-management-page.component.ts`); no backend
+sets it to `true` anywhere today, so it is always `false` in practice.
+
+### Bootstrap — Implemented (contract), Planned (real data)
+
+`BootstrapConfig.modules?` and `BootstrapConfig.seller?` (`SellerConfig`,
+`shared/models/config/seller.model.ts`) — both optional, both absent in
+every real bootstrap response today. When a backend eventually resolves a
+seller scope, it populates `seller`; until then this field simply doesn't
+exist on the wire.
+
+### Future API — Future
+
+No endpoint exists. When built, it should follow `BACKEND.md`'s existing
+mock↔API-gateway pattern (§8) rather than a new convention — this is a
+statement of intent, not a designed contract. No URL, DTO, or status-code
+behavior is decided.
+
+### Seller Storefronts — Future
+
+Concept: a seller-branded storefront view within a marketplace (e.g. a
+seller's own product listing page reachable from the marketplace). **Not
+designed.** No route, component, or URL scheme exists or is decided.
+
+### Seller Branding — Implemented (types only), Future (usage)
+
+`SellerBranding` (`core/sellers/models/seller-branding.model.ts`): logo,
+banner, description, contacts, address, theme overrides — every field
+optional. **Implemented as a type only.** Nothing renders it, nothing falls
+back from it to marketplace branding — that precedence logic is **Future**
+work, not yet designed.
+
+### Seller Ownership — Implemented (schema only), Future (logic)
+
+`sellerId?: string` added to `Item` (storefront), `AdminProduct`, and
+`AdminOrder` — optional, absent means marketplace-owned (every existing
+product/order today). **No code reads or writes this field anywhere.**
+Ownership rules, transfer, and enforcement are **Future** work.
+
+### Checkout Modes — Future
+
+Concept: how checkout behaves when a cart contains items from multiple
+sellers (e.g. single combined checkout vs. per-seller checkout flows).
+**Not designed.** No decision exists on this; today every product is
+marketplace-owned and checkout has exactly one flow, unchanged by this work.
+
+### Unified Orders / Split Orders — Future
+
+Concept: whether one customer purchase spanning multiple sellers becomes
+one order record or splits into one order per seller. **Not designed.**
+This is a real business decision (payments, refunds, and reporting all
+depend on the answer) with no default assumed — explicitly listed as an
+open question for whenever Seller Management moves past preparation.
+
+## 7. Migration & Compatibility
+
+### Why existing marketplaces remain unchanged
+
+- `modules.sellerManagement.enabled` defaults to `false` and no backend
+ sets it — every marketplace today gets identical behavior whether the
+ field is present-and-false or entirely absent from its bootstrap
+ response.
+- `BootstrapConfig.modules` and `BootstrapConfig.seller` are optional
+ fields; no existing field's type changed.
+- `sellerId?` on `Item`/`AdminProduct`/`AdminOrder` is optional; no
+ consumer of any of these three types needed updating, verified by
+ `tsc --noEmit` staying clean after each change.
+- Zero components, facades, services, or routes branch on marketplace or
+ seller identity anywhere in this work (ADR-011 compliance requirement) —
+ there is no conditional to accidentally trigger.
+- Every commit in this line of work was verified with `tsc --noEmit`,
+ `arch:check` (import boundaries + circular deps), and — for the UI
+ commits — a live browser pass, specifically to confirm no regression to
+ existing pages.
+
+## 8. Developer Notes
+
+- All seller domain types live in `core/sellers/models/` (mirrors
+ `core/products/models`, `core/auth/models`). Extend there, not ad hoc in
+ feature folders.
+- When real seller-aware behavior is eventually built, gate it behind
+ `modules.sellerManagement.enabled` in one place (a capability guard,
+ ADR-009's pattern) — never scattered `if` checks on tenant/seller identity.
+- The Phase 1 page (`features/admin/seller-management/`) is disposable —
+ it exists to communicate the capability to merchants, not as a
+ foundation to extend. Real seller CRUD UI should be planned fresh once
+ the backend contract exists, not bolted onto this page.
+
+## 9. Builder Notes
+
+The Project Editor / Marketplace Builder has **zero seller-awareness**
+today. Its draft/publish model (`localStorage`-only, no backend write path
+per `BACKEND.md` §1.10) is entirely marketplace-scoped. If/when a seller
+needs their own builder-like surface (branding, storefront layout), it must
+be designed as its own ADR — do not assume the existing builder can be
+reused as-is for a seller scope without that review, since its facades and
+schema (ADR-005, ADR-007) were built assuming exactly one config document
+per marketplace.
+
+## 10. Backend Notes
+
+No backend implementation exists for any part of Seller Management. When
+work begins, follow `BACKEND.md`'s established pattern exactly: a
+`SellerRepository`/`SellerGateway` behind a DI token, `MockSellerGateway`
+first, `ApiSellerGateway` swapped in later, same convention every other
+admin domain in this codebase already uses (`BACKEND.md` §8). The typed
+models in `core/sellers/models/` are the DTO shapes to implement against —
+treat them as the contract, not a suggestion to redesign.
+
+## Diagrams
+
+```mermaid
+graph LR
+ A["Types & feature flag
(this + prior 3 commits)"] -->|Implemented| B["Phase 1 UI
(Partners > Seller Management page)"]
+ B -->|Implemented| C["Backend contract decisions
(BACKEND.md gaps, own ADR)"]
+ C -->|Future| D["Seller CRUD + real gateway"]
+ D -->|Future| E["Seller Branding rendering
+ Storefronts"]
+ E -->|Future| F["Checkout Modes +
Unified/Split Orders"]
+
+ classDef done fill:#2e7d3222,stroke:#2e7d32,color:inherit;
+ classDef future fill:#6b728022,stroke:#6b7280,color:inherit;
+ class A,B done;
+ class C,D,E,F future;
+```
+
+Rollout is strictly left-to-right — no stage after "Phase 1 UI" has started.
+See [Seller-Management-Diagrams.md](Seller-Management-Diagrams.md) for the
+hierarchy and bootstrap-gate diagrams (unchanged, still accurate).