diff --git a/.changeset/setup-nav-positions-label.md b/.changeset/setup-nav-positions-label.md
new file mode 100644
index 0000000000..888c870dae
--- /dev/null
+++ b/.changeset/setup-nav-positions-label.md
@@ -0,0 +1,12 @@
+---
+"@objectstack/plugin-security": patch
+"@objectstack/platform-objects": patch
+---
+
+Setup → Access Control nav: the `sys_position` entry is renamed
+`nav_roles`/"Roles" → `nav_positions`/"Positions" (岗位 / ポジション /
+Posiciones) — the last "role" leftover in platform UI copy (ADR-0090 D3;
+the Studio-side relabel already landed in objectui). The framework's
+`.objectui-sha` pin is bumped to pick up the Studio Access-pillar explain
+panel ("why can this user access?", ADR-0090 D6) and the suggested
+audience-binding install prompt (D5/D9).
diff --git a/.objectui-sha b/.objectui-sha
index bc42d3fd10..105544e0ee 100644
--- a/.objectui-sha
+++ b/.objectui-sha
@@ -1 +1 @@
-16e2615f0bbe5d461d9381f1ec31bd2e85089c67
+397dcad73eaf6fdaa1740bff15f9d8faf45c4232
diff --git a/content/docs/permissions/access-matrix.mdx b/content/docs/permissions/access-matrix.mdx
new file mode 100644
index 0000000000..c57482c8ae
--- /dev/null
+++ b/content/docs/permissions/access-matrix.mdx
@@ -0,0 +1,92 @@
+---
+title: Access-Matrix Snapshot Gate
+description: A committed (permission set × object) capability matrix that fails the build on any grant drift, with the semantic diff as the review artifact (ADR-0090 D6).
+---
+
+# Access-Matrix Snapshot Gate
+
+AI drafts permission metadata on this platform; the one thing it must never do
+is *silently* change who can do what. The access-matrix gate makes every
+capability change a **visible, reviewable build event**: the
+(permission set × object) matrix is derived purely from metadata on every
+`os compile`, diffed against a committed snapshot, and any drift **fails the
+build** with a semantic explanation until a human regenerates the snapshot.
+
+## Opting in
+
+The gate is per-app: commit an `access-matrix.json` next to
+`objectstack.config.ts`. Generate the first snapshot with:
+
+```bash
+os compile --update-access-matrix
+```
+
+No `access-matrix.json` → the gate is skipped (not opted in). Both
+`examples/app-crm` and `examples/app-showcase` are opted in.
+
+## What a drift failure looks like
+
+Change a grant — say, giving the showcase baseline set access to the private
+notes object — and the next `os compile` fails:
+
+```
+→ Checking access-matrix snapshot (ADR-0090 D6)...
+
+✗ Access matrix drift (1 change) — capability changes must be reviewed
+• 'showcase_member_default' gains access to 'showcase_private_note' (create, read, edit)
+If intended, re-run with --update-access-matrix and commit the snapshot — its diff IS the review artifact.
+```
+
+The diff lines are **semantic**, not JSON: gained/lost operations, View/Modify
+All changes, depth changes, OWD swings. If the change is intended, regenerate
+and commit — the snapshot's git diff then rides the pull request, where a
+reviewer sees the capability delta in plain language instead of spelunking
+through metadata files.
+
+## The snapshot format
+
+One entry per (permission set × object) grant, sorted for stable diffs
+(`AccessMatrixSchema`, version 1):
+
+```json
+{
+  "version": 1,
+  "entries": [
+    {
+      "permissionSet": "showcase_auditor",
+      "object": "showcase_private_note",
+      "create": false,
+      "read": true,
+      "edit": false,
+      "delete": false,
+      "viewAllRecords": true,
+      "modifyAllRecords": false,
+      "sharingModel": "private"
+    }
+  ]
+}
+```
+
+`read` is also `true` when View/Modify All grants it; `edit`/`delete` are also
+`true` under Modify All — the matrix reports **effective** capability, not the
+raw flags. Each row carries the object's OWD so a baseline swing
+(`private` → `public_read_write`) is a visible diff too.
+
+## How it relates to the rest of the defense
+
+- The **[security posture linter](/docs/permissions/authorization#governance-how-declared--enforced-is-kept-true)**
+  (ADR-0090 D7) rejects *individually dangerous* declarations (unset OWD,
+  high-privilege anchor suggestions, retired aliases). The matrix gate catches
+  what the linter can't: a *legitimate-looking* change whose blast radius a
+  human should still sign off.
+- The **[explain engine](/docs/permissions/explain)** is the same evaluation
+  logic pointed at one decision at runtime; the matrix is the build-time sweep
+  across all of them.
+- Both are only possible because grants are **structured data** — the standing
+  argument for the closed authoring vocabulary over freeform predicates.
+
+## See also
+
+- [Authorization Architecture](/docs/permissions/authorization)
+- [Explain Engine](/docs/permissions/explain)
+- [Security Permissions Matrix](/docs/permissions/permissions-matrix) — the human-readable capability tables
diff --git a/content/docs/permissions/authorization.mdx b/content/docs/permissions/authorization.mdx
index 958fe8a035..038d51130d 100644
--- a/content/docs/permissions/authorization.mdx
+++ b/content/docs/permissions/authorization.mdx
@@ -57,7 +57,7 @@ Two orthogonal identity-layer gates run before all of this: the ADR-0069
 session from protected resources while keeping remediation reachable), and
 **anti-escalation** — RBAC tables are read-only for `organization_admin`, and
 since ADR-0090 D12 every RBAC-table write is additionally checked by the
-**delegated-admin gate**: tenant admins pass, delegates are confined to their
+**[delegated-admin gate](/docs/permissions/delegated-administration)**: tenant admins pass, delegates are confined to their
 `adminScope` (BU subtree + assignable-set allowlist, no self-escalation,
 strict containment for scope grants), and everyone else is denied. The
 `everyone`/`guest` audience-anchor bindings reject high-privilege sets at the
@@ -182,6 +182,9 @@ an administrator who can rewire a user's grants may read why they resolve as
 they do. Studio's Access pillar ships a "why can this user access?" panel on
 top of this endpoint.
 
+Full request/response walkthrough, layer vocabulary, and caller-authorization
+details: **[Explain Engine](/docs/permissions/explain)**.
+
 ## Governance: how "declared = enforced" is kept true
 
 Four CI-time mechanisms make the security posture a **checked artifact**
@@ -198,6 +201,7 @@ rather than a belief:
   `os compile` fails on any capability drift with semantic lines
   (`'crm_admin' gains delete on 'crm_lead'`) until the snapshot is updated via
   `--update-access-matrix` — the snapshot's git diff is the review artifact.
+  Opt-in, format, and workflow: **[Access-Matrix Snapshot Gate](/docs/permissions/access-matrix)**.
 
 - **Conformance matrix** (`packages/dogfood/test/authz-conformance.matrix.ts`,
   ADR-0056 D10): every authorization primitive sits in exactly one honest
diff --git a/content/docs/permissions/delegated-administration.mdx b/content/docs/permissions/delegated-administration.mdx
new file mode 100644
index 0000000000..bfe20c6e4e
--- /dev/null
+++ b/content/docs/permissions/delegated-administration.mdx
@@ -0,0 +1,100 @@
+---
+title: Delegated Administration
+description: Administration itself as a scoped grant — a business-unit subtree, an action set, and an assignable-set allowlist, with self-escalation structurally impossible (ADR-0090 D12).
+---
+
+# Delegated Administration
+
+A group with fifty subsidiaries cannot manage every grant from headquarters —
+but handing each subsidiary a full admin is worse. ADR-0090 D12's answer:
+**administration itself becomes a scoped capability**. A delegate can onboard
+their own staff and reshuffle their own positions, but can never grant
+anything outside an explicit allowlist — *including to themselves* — and can
+never touch tenant-level assets.
+
+Because the scope lives on an ordinary permission set, it is distributed via
+positions, audited in the same tables, and explained by the same engine as
+every other grant. No parallel admin subsystem.
+
+## Authoring an admin scope
+
+```typescript
+export const FieldOpsDelegate = definePermissionSet({
+  name: 'field_ops_delegate',
+  label: 'Field Ops Delegate Admin',
+  // The scope authorizes WHAT may be administered…
+  adminScope: {
+    businessUnit: 'Field Operations',   // WHERE: this sys_business_unit subtree
+    includeSubtree: true,               // default true
+    manageAssignments: true,            // user ↔ position rows (sys_user_position)
+    manageBindings: false,              // position ↔ set rows (sys_position_permission_set)
+    authorEnvironmentSets: false,       // may they author environment-owned sets?
+    assignablePermissionSets: ['showcase_contributor', 'showcase_manager'],
+  },
+  // …and plain CRUD on the RBAC link tables lets the requests through at all.
+  // Both are required: table CRUD with NO scope is refused outright.
+  objects: {
+    sys_user_position: { allowRead: true, allowCreate: true, allowEdit: true, allowDelete: true },
+    sys_position: { allowRead: true },
+    sys_permission_set: { allowRead: true },
+    sys_business_unit: { allowRead: true },
+    sys_business_unit_member: { allowRead: true },
+    sys_user: { allowRead: true },
+  },
+});
+```
+
+`businessUnit` names the subtree root by `sys_business_unit.name`; a
+misconfigured name resolves to an empty subtree and **approves nothing**
+(fail-closed).
+
+## What the runtime gate enforces
+
+Writes to the governed tables (`sys_user_position`,
+`sys_position_permission_set`, `sys_user_permission_set`,
+`sys_permission_set`) pass through the `DelegatedAdminGate`:
+
+| Rule | Effect |
+|---|---|
+| Tenant admins pass through | The superuser wildcard reaches the ordinary CRUD/RLS checks — delegation constrains *delegates*, not HQ |
+| Subtree anchoring | Assignments a delegate creates must be anchored (`sys_user_position.business_unit_id`) inside their subtree, and the target user must sit inside it |
+| Allowlist, no self-escalation | Every set reached by the write — bound to the assigned position, or granted directly — must be on `assignablePermissionSets`. Granting an un-allowlisted set is refused **for anyone, including the delegate themselves** |
+| Action flags | `manageAssignments` / `manageBindings` / `authorEnvironmentSets` gate their table classes independently; re-composing a position (`manageBindings`) additionally requires every current holder to sit inside the subtree |
+| Strict containment | Granting or authoring a set that itself carries an `adminScope` requires a held scope that **strictly contains** it — handing your own exact scope to a peer is refused (no lateral propagation) |
+| Single-row writes | Delegates write single rows by id only — a broad filter-write cannot be boundary-checked |
+| Audit stamp | Every assignment a delegate creates is `granted_by`-stamped automatically |
+| Tenant-level assets stay tenant-level | The `everyone`/`guest` audience anchors and security-domain publishes are untouchable from any delegated scope |
+| No scope, no admin | Holders of plain CRUD on the RBAC tables with **no** scope are refused: administration is a scoped capability now, not a side effect of table access |
+
+Every rule above is exercised end-to-end by the showcase permission zoo
+(`packages/dogfood/test/showcase-permission-zoo.dogfood.test.ts`): the
+in-subtree allowlisted assignment passes with a `granted_by` stamp; the
+out-of-subtree anchor, the off-allowlist grant (to self), and the
+`manageBindings: false` binding write are each refused.
+
+## The assignment anchor
+
+Positions never bind to a business unit at the *definition* level — that
+would recreate the position-per-department explosion. The **assignment row**
+may: `sys_user_position.business_unit_id` names the unit the person holds the
+position *in* ("张三 is sales_manager **of 华东**"). It does exactly three
+things: anchors that assignment's depth grants to the subtree, provides the
+delegation boundary check above, and makes "manager of what" an auditable
+fact. Capability bits are never BU-scoped.
+
+## Explaining delegated decisions
+
+The [explain engine](/docs/permissions/explain) closes the loop twice:
+
+- explaining **another user** is authorized by `manage_users` *or* a delegated
+  `adminScope` whose subtree covers that user — a delegate can diagnose their
+  own people, and only their own people;
+- contributor attribution plus the `granted_by` stamp answer both *who
+  granted this* and *who could have*.
+
+## See also
+
+- [Permission Sets](/docs/permissions/permission-sets) — the container `adminScope` rides on
+- [Positions](/docs/permissions/positions) — how delegates receive the scope
+- [Explain Engine](/docs/permissions/explain)
+- [Authorization Architecture](/docs/permissions/authorization)
diff --git a/content/docs/permissions/explain.mdx b/content/docs/permissions/explain.mdx
new file mode 100644
index 0000000000..57c8151852
--- /dev/null
+++ b/content/docs/permissions/explain.mdx
@@ -0,0 +1,107 @@
+---
+title: Explain Engine
+description: Ask the runtime why a decision came out the way it did — every pipeline layer, with contributor attribution, over the kernel service or REST (ADR-0090 D6).
+---
+
+# Explain Engine
+
+Authorization here is a nine-layer pipeline, and a nine-layer pipeline nobody
+can interrogate is a support ticket generator. The explain engine
+(ADR-0090 D6) is the first-class answer to *"why can 张三 PATCH 李四's
+leave_request?"* — it walks the **same code paths the enforcement middleware
+runs** (shared permission-set resolution, evaluator, FLS mask, RLS
+composition), so the report is *explained by construction*, never a parallel
+re-implementation that can drift.
+
+## What a decision looks like
+
+Each report carries the final verdict, the resolved principal, and one entry
+per pipeline layer, in enforcement order:
+
+```
+principal → required_permissions → object_crud → fls → owd_baseline
+         → depth → sharing → vama_bypass → rls
+```
+
+| Field | Meaning |
+|---|---|
+| `allowed` | The overall decision for `(object, operation, principal)` |
+| `principal` | Resolved identity: `userId`, `positions[]`, `permissionSets[]`, optional `principalKind` / `onBehalfOf` |
+| `layers[]` | One entry per layer: `layer`, `verdict`, human-readable `detail`, `contributors[]` |
+| `readFilter` | For reads: the composed row filter actually applied — the machine artifact |
+
+Layer verdicts are `grants` / `denies` / `narrows` / `widens` / `neutral` /
+`not_applicable`. **Contributor attribution** names the permission set that
+produced the verdict and how the caller holds it (position binding, additive
+`everyone` baseline, direct grant) — e.g. the showcase auditor's read of
+another user's private note reports:
+
+```json
+{
+  "layer": "vama_bypass",
+  "verdict": "widens",
+  "detail": "View/Modify All Data bypass held via [showcase_auditor] — ownership and sharing checks are skipped.",
+  "contributors": [{ "kind": "permission_set", "name": "showcase_auditor", "via": "position:auditor" }]
+}
+```
+
+## Calling it
+
+**Kernel service** (in-process, plugins/tests):
+
+```typescript
+const security = kernel.getService('security');
+const decision = await security.explain(
+  { object: 'showcase_private_note', operation: 'read', userId: targetUserId },
+  callerContext,
+);
+```
+
+**REST** — same contract, two transports (`ExplainRequestSchema`):
+
+```bash
+# GET, query-string form
+curl -H "Authorization: Bearer $TOKEN" \
+  "$BASE/api/v1/security/explain?object=showcase_private_note&operation=read&userId=usr_123"
+
+# POST, body form
+curl -X POST -H "Authorization: Bearer $TOKEN" -H 'Content-Type: application/json' \
+  -d '{"object":"showcase_private_note","operation":"read","userId":"usr_123"}' \
+  "$BASE/api/v1/security/explain"
+```
+
+`operation` is one of `read | create | update | delete | transfer | restore |
+purge` (defaults to `read`); omit `userId` to explain **yourself**.
+
+## Who may ask
+
+The endpoint is **authenticated-only** — even on `requireAuth: false`
+deployments (an access report is sensitive even about oneself). Beyond that,
+authorization lives in the *service*, so REST and in-process callers share one
+rule:
+
+- **Yourself** — always allowed.
+- **Another user** — requires the `manage_users` capability **or** a delegated
+  `adminScope` whose business-unit subtree covers that user (ADR-0090 D12):
+  an administrator who can rewire a user's grants may read why they resolve
+  the way they do — and *only* a covering administrator. Anything else → 403.
+
+A deployment without `@objectstack/plugin-security` answers 501.
+
+## What it powers
+
+- **The admin simulator** — Studio's Access pillar builds its "why can this
+  user access?" panel on this endpoint.
+- **The [access-matrix snapshot gate](/docs/permissions/access-matrix)** —
+  the publish-time matrix is the same evaluation run over representative
+  (permission set × object) pairs; explain is the per-decision zoom lens.
+- **Delegated-administration audits** — explain reports both *who granted*
+  (the `granted_by` stamp) and, via contributor attribution, *who could
+  have* ([delegated administration](/docs/permissions/delegated-administration)).
+
+## See also
+
+- [Authorization Architecture](/docs/permissions/authorization) — the pipeline the layers mirror
+- [Access-Matrix Snapshot Gate](/docs/permissions/access-matrix)
+- [Delegated Administration](/docs/permissions/delegated-administration)
+- Reference: [Explain schema](/docs/references/security/explain)
diff --git a/content/docs/permissions/meta.json b/content/docs/permissions/meta.json
index 1813d6ffad..c4cdd63793 100644
--- a/content/docs/permissions/meta.json
+++ b/content/docs/permissions/meta.json
@@ -9,10 +9,13 @@
     "profiles",
     "permission-sets",
     "positions",
+    "delegated-administration",
     "sharing-rules",
     "field-level-security",
     "permission-metadata",
     "permissions-matrix",
+    "access-matrix",
+    "explain",
     "access-recipes"
   ]
 }
diff --git a/content/docs/permissions/permission-sets.mdx b/content/docs/permissions/permission-sets.mdx
index 4eb0527336..21fb4b9c59 100644
--- a/content/docs/permissions/permission-sets.mdx
+++ b/content/docs/permissions/permission-sets.mdx
@@ -159,7 +159,8 @@ suggestions after marketplace installs and in the Access pillar.
 ## Delegated administration — `adminScope` (ADR-0090 D12)
 
 A permission set may carry an `adminScope`, making its holders **scoped
-administrators**:
+administrators** (full gate rules and runbook:
+[Delegated Administration](/docs/permissions/delegated-administration)):
 
 ```typescript
 export const EastSubsidiaryAdmin = definePermissionSet({
diff --git a/content/docs/permissions/permissions-matrix.mdx b/content/docs/permissions/permissions-matrix.mdx
index 5d8923905d..cbfb31273c 100644
--- a/content/docs/permissions/permissions-matrix.mdx
+++ b/content/docs/permissions/permissions-matrix.mdx
@@ -307,3 +307,9 @@ flowchart TD
 <Callout type="tip">
 **Performance:** For reads, steps 2–6 are compiled into a query filter (owner-match ∪ materialized shares, AND-ed with RLS) at query time, not evaluated record-by-record. By-id writes are verified with a pre-image check: the target row is re-read through the write-scope filter before the mutation. This keeps security checks efficient even on tables with millions of rows.
 </Callout>
+
+## See also
+
+- [Access-Matrix Snapshot Gate](/docs/permissions/access-matrix) — the CI gate that fails the build when this matrix drifts
+- [Explain Engine](/docs/permissions/explain) — the per-decision runtime zoom lens
+- [Delegated Administration](/docs/permissions/delegated-administration)
diff --git a/packages/platform-objects/src/apps/translations/en.ts b/packages/platform-objects/src/apps/translations/en.ts
index 2168e256a0..292390c18a 100644
--- a/packages/platform-objects/src/apps/translations/en.ts
+++ b/packages/platform-objects/src/apps/translations/en.ts
@@ -70,7 +70,7 @@ export const en: TranslationData = {
         nav_invitations: { label: 'Invitations' },
 
         // Access Control
-        nav_roles: { label: 'Roles' },
+        nav_positions: { label: 'Positions' },
         nav_permission_sets: { label: 'Permission Sets' },
         nav_sharing_rules: { label: 'Sharing Rules' },
         nav_record_shares: { label: 'Record Shares' },
diff --git a/packages/platform-objects/src/apps/translations/es-ES.ts b/packages/platform-objects/src/apps/translations/es-ES.ts
index fdb4ede768..ca3c06708d 100644
--- a/packages/platform-objects/src/apps/translations/es-ES.ts
+++ b/packages/platform-objects/src/apps/translations/es-ES.ts
@@ -51,7 +51,7 @@ export const esES: TranslationData = {
         nav_organizations: { label: 'Organizaciones' },
         nav_invitations: { label: 'Invitaciones' },
 
-        nav_roles: { label: 'Roles' },
+        nav_positions: { label: 'Posiciones' },
         nav_permission_sets: { label: 'Conjuntos de Permisos' },
         nav_sharing_rules: { label: 'Reglas de Compartición' },
         nav_record_shares: { label: 'Registros Compartidos' },
diff --git a/packages/platform-objects/src/apps/translations/ja-JP.ts b/packages/platform-objects/src/apps/translations/ja-JP.ts
index b831242b21..aa808a4515 100644
--- a/packages/platform-objects/src/apps/translations/ja-JP.ts
+++ b/packages/platform-objects/src/apps/translations/ja-JP.ts
@@ -51,7 +51,7 @@ export const jaJP: TranslationData = {
         nav_organizations: { label: '組織' },
         nav_invitations: { label: '招待' },
 
-        nav_roles: { label: 'ロール' },
+        nav_positions: { label: 'ポジション' },
         nav_permission_sets: { label: '権限セット' },
         nav_sharing_rules: { label: '共有ルール' },
         nav_record_shares: { label: 'レコード共有' },
diff --git a/packages/platform-objects/src/apps/translations/zh-CN.ts b/packages/platform-objects/src/apps/translations/zh-CN.ts
index 4c04e80758..a0df06a66b 100644
--- a/packages/platform-objects/src/apps/translations/zh-CN.ts
+++ b/packages/platform-objects/src/apps/translations/zh-CN.ts
@@ -52,7 +52,7 @@ export const zhCN: TranslationData = {
         nav_organizations: { label: '组织' },
         nav_invitations: { label: '邀请' },
 
-        nav_roles: { label: '角色' },
+        nav_positions: { label: '岗位' },
         nav_capabilities: { label: '能力' },
         nav_permission_sets: { label: '权限集' },
         nav_sharing_rules: { label: '共享规则' },
diff --git a/packages/plugins/plugin-security/src/security-plugin.ts b/packages/plugins/plugin-security/src/security-plugin.ts
index 3234f28c68..f3f39f3743 100644
--- a/packages/plugins/plugin-security/src/security-plugin.ts
+++ b/packages/plugins/plugin-security/src/security-plugin.ts
@@ -252,7 +252,7 @@ export class SecurityPlugin implements Plugin {
           group: 'group_access_control',
           priority: 100,
           items: [
-            { id: 'nav_roles', type: 'object', label: 'Roles', objectName: 'sys_position', icon: 'shield-check' },
+            { id: 'nav_positions', type: 'object', label: 'Positions', objectName: 'sys_position', icon: 'shield-check' },
             { id: 'nav_capabilities', type: 'object', label: 'Capabilities', objectName: 'sys_capability', icon: 'badge-check' },
             { id: 'nav_permission_sets', type: 'object', label: 'Permission Sets', objectName: 'sys_permission_set', icon: 'lock' },
           ],