@@ -0,0 +1,31 @@
+---
+'@objectstack/core': minor
+'@objectstack/objectql': patch
+'@objectstack/plugin-security': patch
+'@objectstack/plugin-sharing': patch
+'@objectstack/runtime': patch
+---
+
+feat(security): the guest's grants channel — an anonymous request at a guest-entry door holds the sets bound to the `guest` anchor, in the one organization the deployment resolves for it (ADR-0138 E1, D3/D4)
+
+ADR-0087 disposition: none. No authorable key, accept set or stored shape moves: no spec schema, metadata type, stored row or published response field is added, removed, renamed or re-shaped. A declared binding that was not enforced becomes enforced (ADR-0090 D9, as ADR-0138 D3 amends it).
+
+**The bindings that start granting.** On the reference apps, none: `app-showcase`, `app-crm`, `app-multi-package` and `app-todo` declare no definition of the `guest` anchor that names a set. `app-showcase` ships `showcase_guest_portal` as a capability an administrator may bind and binds it to no anchor (its `client_portal_user` position is an ordinary position), and `app-crm`'s `guest_portal` is the public form doors' set, which keeps its own posture. No reference app declares a permission set named `guest`, so no grant stops either. A set starts granting only where a deployment holds an environment definition of the `guest` position that names it.
+
+What changes:
+
+- **`@objectstack/core`** — the anonymous branch of `resolveAuthzContext` resolves the guest's grants on a face that takes the explicit guest entry (the new `guestEntry` input). It reads the sets the `guest` position's definition names, through the same position-bound read every position uses, and the activation ledger as for any held set. It resolves them only in the organization the guest entry's organization step derives (`resolveGuestOrganization`), which asks ADR-0131 D9's predicate and no second spelling of it. With nothing bound, the guest holds no set and no read is issued. The predicate itself, `resolveSystemWriteOrganization`, moves to `@objectstack/core` so both of its askers share it. New exports: `resolveGuestOrganization`, `resolveSystemWriteOrganization` (with `SystemWriteOrganizationDecision` and `SystemWriteRefusalReason`), and `GuestOrganizationUnresolvedError` with `isGuestOrganizationUnresolvedError` and its constants.
+- **`@objectstack/objectql`** — `resolveSystemWriteOrganization` and its two types are re-exported from `@objectstack/core` as the same bindings. Nothing a caller imports changes.
+- **`@objectstack/plugin-security`** — the set resolution treats the guest's sets as any requested set, and no longer folds the guest's position into the request. A permission set that merely shares the anchor's name no longer reaches an anonymous caller, and the baseline and `everyone` never did. At the CRUD gate, a guest that reaches a data operation acting in no organization, on a deployment where the organization step refuses, is refused before the operation runs.
+- **`@objectstack/plugin-sharing`** — the read filter answers deny-all for the guest on every object that record sharing scopes, before the sharing-model branch: the guest reaches rows only through share links, never through the object's sharing model (ADR-0138 D3 item 6, as the maintainer's ruling C amends it). `externalSharingModel` is still not read for any caller. Share links are redeemed at their own door and are unchanged.
+- **`@objectstack/runtime`** — the runtime face, which serves the guest, asks for the guest's grants.
+
+What an anonymous caller sees at an `authRequired: false` endpoint of `type: 'object_operation'`:
+
+- **One organization, a set bound to `guest`:** the operation runs as the guest, under that set, in that organization. A read the set grants is admitted and returns no row, whatever the object's sharing model (`private`, `public_read`, `public_read_write` or `controlled_by_parent`): the guest reaches a record only through a share link. A create the set grants lands in that organization with no owner.
+- **Nothing bound:** `403 PERMISSION_DENIED`, as before.
+- **A walled deployment, several organizations, or none:** `501 NOT_IMPLEMENTED`, naming the missing site binding (ADR-0138 D5), where it used to be `403 PERMISSION_DENIED` with nothing granted. Nothing that was served stops being served. The operator's log names the reason once.
+
+Unchanged: share links, which still serve an anonymous caller the one record they name, with `publicSharing.eligibility` checked at the mint and at every redemption; the public form doors, which keep their own posture and organization; the flow door, which runs under the flow's own declared posture; every surface that answers an anonymous request `401`; and every signed-in caller.
+
+Level: `minor` for `@objectstack/core`, because new exported symbols widen its published index; `patch` for the other four, whose exports do not move.
@@ -0,0 +1,96 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * ADR-0138 D4 — the refusal an anonymous request meets where it needs an
+ * organization the deployment cannot resolve for it.
+ *
+ * ## The rule
+ *
+ * A guest-entry door with no declared organization binding of its own resolves
+ * the guest's organization on the server, never from anything the client
+ * sends: when the deployment holds exactly one organization the guest acts in
+ * it, and otherwise the request is refused, loudly, naming the missing site
+ * binding (ADR-0138 D5) — never answered by a silent pick. The decision is
+ * `resolveSystemWriteOrganization`'s (ADR-0131 D9), asked by
+ * `resolveGuestOrganization` (`resolve-authz-context.ts`), "never a second
+ * spelling of it" (D4 item 2).
+ *
+ * ## Where it is raised, and why not at the entry
+ *
+ * The runtime face assembles the guest envelope for EVERY sessionless request
+ * it serves, before any route is matched — the domains that answer 401 to an
+ * anonymous caller included. Refusing there would turn every one of those 401s
+ * into this refusal on a multi-organization deployment, and would reach the
+ * flow door (D2 class 5), which D4 item 3 leaves untouched: a flow runs under
+ * its own declared posture. So the entry records nothing it cannot use — no
+ * organization, no set — and the refusal is raised where the guest's
+ * organization MATTERS: the CRUD gate the guest's data operation reaches
+ * (`SecurityPlugin.resolveOperationPrincipals`), before any grant is resolved
+ * (D3 item 7: where D4 refuses, D3 is never reached).
+ *
+ * ## The code
+ *
+ * `NOT_IMPLEMENTED` (501), a member of the ADR-0112 standard catalog, as D4
+ * requires. The request is not malformed and the caller cannot repair it — D4
+ * forbids taking the organization from anything the client sends, so no
+ * 4xx-shaped invitation to "supply a precondition" fits — and it is not an
+ * outage: the deployment lacks a capability that is not built yet, the site
+ * binding (D5, "built when demand arrives"). `PERMISSION_DENIED` would make the
+ * refusal indistinguishable from an ungranted guest, which is exactly what the
+ * located refusal exists to stop.
+ *
+ * ## What the caller is told
+ *
+ * The message names the missing site binding and the two ways to serve the
+ * door, and nothing about the deployment: no organization count and no posture
+ * name reach an anonymous caller (ADR-0138: door-level readings stay private).
+ */
+
+/** ADR-0112 standard-catalog member the refusal answers with. */
+export const GUEST_ORGANIZATION_UNRESOLVED_CODE = 'NOT_IMPLEMENTED' as const;
+
+/** HTTP status a transport answers the refusal with. */
+export const GUEST_ORGANIZATION_UNRESOLVED_STATUS = 501 as const;
+
+/** The caller-facing sentence: the missing site binding, and the remedies. */
+export const GUEST_ORGANIZATION_UNRESOLVED_MESSAGE =
+  'This endpoint serves anonymous callers in the organization the server resolves for them, and this '
+  + 'deployment does not resolve one: an anonymous request acts in an organization only on a deployment '
+  + 'that holds exactly one (ADR-0138 D4), and no site binding maps a request to an organization of its '
+  + 'own yet (ADR-0138 D5). Nothing was read or written. Call this endpoint signed in, or serve it from a '
+  + 'single-organization deployment.';
+
+/**
+ * Why the deployment resolves no organization for the guest — the
+ * `refuse` reasons of `resolveSystemWriteOrganization`. Server-side only.
+ */
+export type GuestOrganizationRefusalReason = 'walled-posture' | 'ambiguous-organization' | 'no-organization';
+
+/**
+ * ADR-0138 D4's located refusal. Identified by {@link isGuestOrganizationUnresolvedError}
+ * (a `code` and `reason` compare), never `instanceof`, so it survives a package
+ * boundary where two copies of this module can exist.
+ */
+export class GuestOrganizationUnresolvedError extends Error {
+  /** ADR-0112 wire code. */
+  readonly code = GUEST_ORGANIZATION_UNRESOLVED_CODE;
+  /** HTTP status a transport should answer — the spelling the HTTP doors read. */
+  readonly status = GUEST_ORGANIZATION_UNRESOLVED_STATUS;
+  /** The same number under ADR-0112 D5's spelling. */
+  readonly httpStatus = GUEST_ORGANIZATION_UNRESOLVED_STATUS;
+  /** Why no organization resolved — for the server's own log, never the wire. */
+  readonly reason: GuestOrganizationRefusalReason;
+
+  constructor(reason: GuestOrganizationRefusalReason) {
+    super(GUEST_ORGANIZATION_UNRESOLVED_MESSAGE);
+    this.name = 'GuestOrganizationUnresolvedError';
+    this.reason = reason;
+  }
+}
+
+/** True when `err` is ADR-0138 D4's located refusal. */
+export function isGuestOrganizationUnresolvedError(err: unknown): err is GuestOrganizationUnresolvedError {
+  if (typeof err !== 'object' || err === null) return false;
+  const e = err as { code?: unknown; name?: unknown };
+  return e.code === GUEST_ORGANIZATION_UNRESOLVED_CODE && e.name === 'GuestOrganizationUnresolvedError';
+}
@@ -169,6 +169,9 @@ export {
   // security catalog — the `sys_metadata_activation` ledger, never a catalog
   // row's `active` column — shared with the explainer and the security plugin.
   readDisabledCatalogNames,
+  // [ADR-0138 D4] The guest entry's organization step, shared with the CRUD
+  // gate that raises D4's located refusal — one step, two askers.
+  resolveGuestOrganization,
   resolveLocalizationContext,
   type ResolvedAuthzContext,
   type ResolveAuthzInput,
@@ -177,6 +180,28 @@ export {
   type ResolveLocalizationInput,
 } from './resolve-authz-context.js';
 
+// [ADR-0131 D9, ADR-0138 D4] The ONE "which organization does a caller with no
+// organization of its own act in?" decision. Two askers: the engine's
+// system-context insert (`@objectstack/objectql`, which re-exports these same
+// bindings) and the guest entry's organization step above.
+export {
+  resolveSystemWriteOrganization,
+  type SystemWriteOrganizationDecision,
+  type SystemWriteRefusalReason,
+} from './system-write-organization.js';
+
+// [ADR-0138 D4] The located refusal an anonymous request meets where it needs
+// an organization the deployment cannot resolve for it — a standard-catalog
+// code (`NOT_IMPLEMENTED`), naming the missing site binding (D5).
+export {
+  GuestOrganizationUnresolvedError,
+  isGuestOrganizationUnresolvedError,
+  GUEST_ORGANIZATION_UNRESOLVED_CODE,
+  GUEST_ORGANIZATION_UNRESOLVED_STATUS,
+  GUEST_ORGANIZATION_UNRESOLVED_MESSAGE,
+  type GuestOrganizationRefusalReason,
+} from './guest-organization.js';
+
 // [#18783] The EFFECTIVE object-permission map — ONE function behind both the
 // `/auth/me/permissions` `objects` slot and `ISecurityService.getEffectiveObjectPermissions`
 // (the map `current_user.can()` reads). The four folds moved here from