@@ -0,0 +1,12 @@
+---
+"@objectstack/plugin-sharing": patch
+---
+
+fix(plugin-sharing): a minted share link carries an organization, never a NULL one (ADR-0131 D9)
+
+Clause-②: no
+
+- **What changed.** `ShareLinkService.createLink` stamps `sys_share_link.organization_id`. It takes the organization of the linked record, read under the system context. When the record names none, it takes the acting context's organization (`tenantId`). When neither names one, it applies the system-write rule: under `single`, the Default Organization (the only one there is); under a wall (`group` or `isolated`), the mint is refused with `ERR_SYSTEM_WRITE_ORGANIZATION_REQUIRED` (status 500) and no link is written. The same refusal answers a `single` install that holds no organization or several. Before, every link was written with `organization_id` NULL.
+- **A link on another organization's record.** Under `group`, a member active in one organization can mint on a visible record of another. The link carries the record's organization, not the session's.
+- **What stays the same.** Under `single` nothing a user sees changes. The mint response keeps the `ShareLink` shape and carries no organization field. A composition that registers no `sys_organization` object writes links as before.
+- **Who can meet the refusal.** No in-repo caller reaches it. Both share-link routes need a signed-in caller. Under a wall, an organization-less API key is refused at admission, and an organization-less session cannot see a record that has a tenant column, so its mint is refused before the stamp. The refusal is reached by a walled, organization-less caller minting on an object with no tenant column, or by a system caller that threads no `tenantId`. The fix is to pass the organization on the context (`{ isSystem: true, tenantId }`).
@@ -0,0 +1,135 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [ADR-0131 D9, C8 stage 8b-0h] Every minted `sys_share_link` row carries
+ * `organization_id` — on a REAL engine over a REAL driver, with the REAL
+ * `sys_share_link` object, so the column under test is the one the registry
+ * injects and the row is read back off the driver, never off the response.
+ *
+ * ## Why the service decides, not the engine
+ *
+ * `sys_share_link` is `unclassified` in the #13491 ledger, so
+ * `Engine.resolveSystemInsertOrganization` lets an organization-less system
+ * insert on it through today. The mint used to rely on that and landed NULL on
+ * every link. The organization is derivable at the mint — the linked record
+ * and the caller are both in hand — so the service stamps it, and refuses
+ * loudly where nothing names one, before and after that exemption retires.
+ *
+ * ## The four pins
+ *
+ *  1. walled: the row carries the RECORD's organization — even when the caller
+ *     acts in another one (the link exposes the record, so it belongs where
+ *     the record does);
+ *  2. walled: an organization-less record takes the caller's organization;
+ *  3. `single`: neither names one — the Default Organization (the only one);
+ *  4. walled: neither names one — refused with the engine's ADR-0112 envelope,
+ *     and no row is written.
+ *
+ * The posture is the REQUESTED one, read from `OS_TENANCY_POSTURE`, so each
+ * case stubs the environment rather than injecting an engine provider.
+ */
+
+import { describe, it, expect, afterEach, vi } from 'vitest';
+import { ObjectQL, SYSTEM_WRITE_ORGANIZATION_REQUIRED_CODE } from '@objectstack/objectql';
+import { SqlDriver } from '@objectstack/driver-sql';
+import type { ExecutionContext } from '@objectstack/spec/kernel';
+
+import { ShareLinkService } from './share-link-service.js';
+import { SysShareLink } from './objects/index.js';
+
+const OBJECT = 'os15212_brief';
+const ORG_A = 'org_a';
+const ORG_B = 'org_b';
+const DEFAULT_ORG = 'org_default';
+
+const BRIEF_FIELDS: Record<string, Record<string, unknown>> = {
+  id: { type: 'text', name: 'id', label: 'Id', primary: true },
+  name: { type: 'text', name: 'name', label: 'Name' },
+  organization_id: { type: 'text', name: 'organization_id', label: 'Org' },
+};
+
+const ORG_FIELDS: Record<string, Record<string, unknown>> = {
+  id: { type: 'text', name: 'id', label: 'Id', primary: true },
+  name: { type: 'text', name: 'name', label: 'Name' },
+};
+
+const open: SqlDriver[] = [];
+
+afterEach(async () => {
+  vi.unstubAllEnvs();
+  while (open.length) await open.pop()?.disconnect?.();
+});
+
+/**
+ *   brief_a  ORG_A
+ *   brief_p  (null)   <- organization-less; what pins 2-4 mint on
+ */
+async function boot(posture: 'single' | 'isolated', organizations: readonly string[]) {
+  vi.stubEnv('OS_TENANCY_POSTURE', posture);
+  const driver = new SqlDriver({
+    client: 'better-sqlite3',
+    connection: { filename: ':memory:' },
+    useNullAsDefault: true,
+  });
+  open.push(driver);
+
+  const ql = new ObjectQL();
+  ql.registerDriver(driver as never, true);
+  await ql.init();
+  ql.registerObject({ name: OBJECT, label: 'Brief', fields: BRIEF_FIELDS } as never);
+  ql.registerObject(SysShareLink as never);
+  ql.registerObject({ name: 'sys_organization', label: 'Organization', isSystem: true, fields: ORG_FIELDS } as never);
+  await driver.initObjects(
+    [OBJECT, 'sys_share_link', 'sys_organization'].map((name) => ({ name, fields: (ql.getSchema(name) as any).fields }) as never),
+  );
+  for (const id of organizations) await driver.create('sys_organization', { id, name: id } as never);
+  await driver.create(OBJECT, { id: 'brief_a', name: 'A', organization_id: ORG_A } as never);
+  await driver.create(OBJECT, { id: 'brief_p', name: 'P' } as never);
+
+  const service = new ShareLinkService({ engine: ql as never, permissive: true, logger: { warn: () => {} } });
+  const links = async () =>
+    (await driver.find('sys_share_link', {} as never)).map((r: any) => ({
+      record_id: String(r.record_id),
+      organization_id: r.organization_id ?? null,
+    }));
+  return { ql, service, links };
+}
+
+const caller = (tenantId?: string) =>
+  ({ userId: 'u_1', positions: [], permissions: [], ...(tenantId ? { tenantId } : {}) }) as unknown as ExecutionContext;
+
+describe('[ADR-0131 D9] a minted share link carries an organization', () => {
+  it("the real sys_share_link object carries the tenant column the stamp writes", async () => {
+    const { ql } = await boot('isolated', [ORG_A, ORG_B]);
+    expect(Object.keys((ql.getSchema('sys_share_link') as any).fields)).toContain('organization_id');
+  });
+
+  it("walled: the RECORD's organization, even when the caller acts in another", async () => {
+    const { service, links } = await boot('isolated', [ORG_A, ORG_B]);
+    await service.createLink({ object: OBJECT, recordId: 'brief_a' }, { ...caller(ORG_B), isSystem: true } as never);
+    expect(await links()).toEqual([{ record_id: 'brief_a', organization_id: ORG_A }]);
+  });
+
+  it("walled: an organization-less record takes the caller's organization", async () => {
+    const { service, links } = await boot('isolated', [ORG_A, ORG_B]);
+    await service.createLink({ object: OBJECT, recordId: 'brief_p' }, caller(ORG_B));
+    expect(await links()).toEqual([{ record_id: 'brief_p', organization_id: ORG_B }]);
+  });
+
+  it('single: neither names one — the Default Organization, the only one there is', async () => {
+    const { service, links } = await boot('single', [DEFAULT_ORG]);
+    const link = await service.createLink({ object: OBJECT, recordId: 'brief_p' }, caller());
+    expect(await links()).toEqual([{ record_id: 'brief_p', organization_id: DEFAULT_ORG }]);
+    // The mint response keeps the contract's shape.
+    expect(link).not.toHaveProperty('organization_id');
+  });
+
+  it('walled: neither names one — refused with the ADR-0112 envelope, and no row is written', async () => {
+    const { service, links } = await boot('isolated', [ORG_A, ORG_B]);
+    const refusal = await service
+      .createLink({ object: OBJECT, recordId: 'brief_p' }, caller())
+      .then(() => undefined, (err: unknown) => err);
+    expect(refusal).toMatchObject({ code: SYSTEM_WRITE_ORGANIZATION_REQUIRED_CODE, status: 500 });
+    expect(await links()).toEqual([]);
+  });
+});
@@ -44,6 +44,17 @@ import { materializeDeclaredFields, readInternalColumn } from '@objectstack/obje
 // schema and an engine that cannot answer `getSchema` are one answer, `false`
 // — the same definition `getPolicy` below has always used.
 import { isPublicSharingEnabled } from '@objectstack/spec/data';
+import type { TenancyPosture } from '@objectstack/spec/security';
+// [ADR-0131 D9] The one "which organization does an organization-less write
+// resolve to?" decision (`@objectstack/core`'s, re-exported unchanged), and the
+// engine's refusal for it — see
+// `ShareLinkService.resolveMintOrganization`.
+import {
+  resolveSystemWriteOrganization,
+  resolveTenantFieldName,
+  SystemWriteOrganizationRequiredError,
+} from '@objectstack/objectql';
+import { resolveTenancyPosture } from '@objectstack/types';
 import type { SharingEngine } from './sharing-service.js';
 import {
   hashShareLinkPassword,
@@ -60,6 +71,9 @@ import {
 /** Service-elevated context for the plugin's own queries / mutations. */
 const SYSTEM_CTX = { isSystem: true, positions: [], permissions: [] } as const;
 
+/** The organization object the ADR-0131 D9 decision counts on a `single` install. */
+const ORGANIZATION_OBJECT = 'sys_organization';
+
 /**
  * [#5190] The table whose orphans this service owns. `sys_share_link` is
  * `managedBy: 'engine-owned'` and its object doc states every write flows
@@ -662,11 +676,130 @@ export class ShareLinkService implements IShareLinkService {
       use_count: 0,
     };
 
-    await this.engine.insert('sys_share_link', row, { context: SYSTEM_CTX });
+    // [ADR-0131 D9] The organization the link belongs to rides the stored row
+    // and the write context — the `{ isSystem, tenantId }` shape #8844's
+    // refusal prescribes for a system write. The mint response keeps the
+    // contract's shape (`ShareLink` declares no organization column).
+    const organizationId = await this.resolveMintOrganization(input, context);
+    const stored = organizationId === undefined ? row : { ...row, organization_id: organizationId };
+    await this.engine.insert('sys_share_link', stored, {
+      context: { ...SYSTEM_CTX, tenantId: organizationId },
+    });
     // [#21839] The row as stored carries the hash; the mint response does not.
     return withoutPasswordHash(row);
   }
 
+  /**
+   * [ADR-0131 D9, C8 stage 8b-0h] The organization a minted link is stamped
+   * with — never a NULL row on a tenant-columned `sys_share_link`:
+   *
+   *  1. the LINKED RECORD's organization, read under the system context off the
+   *     column the object is walled by, so field-level masking cannot hide it
+   *     from the decision. It wins over the session's: under `group` a member
+   *     active in one organization may mint on a record of another it can see,
+   *     and the link exposes that record, so it belongs where the record does —
+   *     the direct-grant rule `SharingService.resolveDirectGrantOrganization`
+   *     follows for `sys_record_share`;
+   *  2. the acting context's organization (`tenantId`), when the record names
+   *     none — an object with no tenant column, or an organization-less row;
+   *  3. otherwise `@objectstack/core`'s one D9 predicate: the Default
+   *     Organization under `single` when exactly one exists, and a loud
+   *     `ERR_SYSTEM_WRITE_ORGANIZATION_REQUIRED` refusal under a wall (and on a
+   *     `single` install holding none or several) — nothing is written.
+   *
+   * The refusal is the engine's own: the envelope its system-insert rule
+   * raises for this same write once the platform-namespace exemption retires,
+   * so the mint answers alike before and after that.
+   *
+   * The posture is the REQUESTED one (`resolveTenancyPosture()`), the source
+   * and fail-stricter direction `resolveAuthzContext` and the `tenancy`
+   * service's `defaultOrgId()` read: a deployment that asked for a wall is
+   * walled here even while it runs degraded.
+   *
+   * `undefined` means there is nothing to stamp: `sys_share_link` carries no
+   * tenant column in this composition, or the composition registers no
+   * organization object at all.
+   *
+   * A failing record read propagates: the mint fails and nothing is written,
+   * rather than stamping the session's organization on a link whose record's
+   * organization is unknown.
+   */
+  private async resolveMintOrganization(
+    input: CreateShareLinkInput,
+    context: ExecutionContext,
+  ): Promise<string | undefined> {
+    if (!this.tenantFieldOf('sys_share_link')) return undefined;
+
+    const recordTenantField = this.tenantFieldOf(input.object);
+    if (recordTenantField) {
+      const rows = await this.engine.find(input.object, {
+        where: { id: input.recordId },
+        fields: ['id', recordTenantField],
+        limit: 1,
+        context: SYSTEM_CTX,
+      });
+      const value = Array.isArray(rows)
+        ? (rows[0] as Record<string, unknown> | undefined)?.[recordTenantField]
+        : undefined;
+      if (typeof value === 'string' && value.trim() !== '') return value;
+    }
+
+    const acting = context.tenantId;
+    if (typeof acting === 'string' && acting.trim() !== '') return acting;
+
+    let posture: TenancyPosture;
+    try {
+      posture = resolveTenancyPosture();
+    } catch {
+      // An unreadable posture is the boot's to refuse; here it reads walled.
+      posture = 'isolated';
+    }
+    const decision = await resolveSystemWriteOrganization({
+      posture,
+      probeOrganizations: () => this.probeOrganizations(),
+      organizationObjectRegistered: !!this.engine.getSchema?.(ORGANIZATION_OBJECT),
+    });
+    if (decision.kind === 'derived') return decision.organizationId;
+    if (decision.kind === 'no-organization-object') return undefined;
+    throw new SystemWriteOrganizationRequiredError(
+      'sys_share_link',
+      posture,
+      decision.reason,
+      decision.organizationCount,
+    );
+  }
+
+  /**
+   * The install's organization ids, capped at two — only "0 / 1 / several"
+   * decides. A composition that registers no organization object answers `[]`
+   * without a read, as the engine's own probe does: the data door refuses an
+   * unregistered name.
+   */
+  private async probeOrganizations(): Promise<readonly string[]> {
+    if (!this.engine.getSchema?.(ORGANIZATION_OBJECT)) return [];
+    const rows = await this.engine.find(ORGANIZATION_OBJECT, {
+      fields: ['id'],
+      limit: 2,
+      context: SYSTEM_CTX,
+    });
+    return (Array.isArray(rows) ? rows : [])
+      .map((r: any) => r?.id)
+      .filter((id: unknown) => id != null && String(id) !== '')
+      .map((id: unknown) => String(id));
+  }
+
+  /** The tenant column of `object`, or `null` when it has none / the engine cannot say. */
+  private tenantFieldOf(object: string): string | null {
+    if (typeof this.engine.getSchema !== 'function') return null;
+    let schema: unknown;
+    try {
+      schema = this.engine.getSchema(object);
+    } catch {
+      return null;
+    }
+    return schema ? resolveTenantFieldName(schema) : null;
+  }
+
   async revokeLink(idOrToken: string, context: ExecutionContext): Promise<void> {
     if (!idOrToken) throw makeError(400, 'VALIDATION_FAILED', 'id or token is required');
     const filter = idOrToken.startsWith('shl_') ? { id: idOrToken } : { token: idOrToken };