diff --git a/.changeset/27722-datasource-create-credentials-ref.md b/.changeset/27722-datasource-create-credentials-ref.md
new file mode 100644
index 00000000000..9dd9091b4ce
--- /dev/null
+++ b/.changeset/27722-datasource-create-credentials-ref.md
@@ -0,0 +1,19 @@
+---
+'@objectstack/service-datasource': patch
+---
+
+fix(service-datasource)!: a datasource create may not name a stored credential reference; it stores only the one its own secret is bound under (#27722)
+
+Clause-②: no (narrowing) — the datasource admin door's create refuses a draft that names `external.credentialsRef`, where it stored the value as given before. Nothing is widened.
+Metadata-protocol: none
+
+<!-- adr-0087: not-required (no-migration-prescription) No key of any schema is added, removed, renamed or re-shaped, and no export or type changes: a create draft value the admin door used to store as given is refused. The fix for a caller is to send the credential as `secret` and leave the key out, which the refusal says; there is nothing for a migration to rewrite and no tombstone. -->
+
+**BREAKING** accept-set narrowing on the datasource admin door's create (`POST /api/v1/datasources`, `IDatasourceAdminService.createDatasource`), the same rule #27582 set for `secret` fields: a write may only seal a new value or keep its own record's stored reference.
+
+- **Before.** A create draft's `external.credentialsRef` was stored as given, beside or instead of the reference a supplied `secret` is bound under.
+- **Now.** A create has no stored reference of its own, so a draft that names `external.credentialsRef` is refused with `400` before anything is written: no record, no secret, no pool. The message names the key and never the value, and the answer is the same whatever the value names. The only reference a create stores is the one its own `secret` is bound under.
+- **Unchanged.** An update keeps the record's own reference unless a supplied `secret` rewraps it, as before. A create with a `secret` and no `external.credentialsRef` binds it as before. The Console's datasource form never sends the key, so it is unaffected.
+- **Who sees it.** A caller of the admin door's create that sends `external.credentialsRef`.
+
+**The remedy.** Send the credential as `secret` and leave `external.credentialsRef` out; the door binds it and stores the reference.
diff --git a/packages/services/service-datasource/src/__tests__/datasource-credentials-ref-own-reference.test.ts b/packages/services/service-datasource/src/__tests__/datasource-credentials-ref-own-reference.test.ts
new file mode 100644
index 00000000000..09d21eb3820
--- /dev/null
+++ b/packages/services/service-datasource/src/__tests__/datasource-credentials-ref-own-reference.test.ts
@@ -0,0 +1,197 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * #27722 — the datasource admin door applies the #27582 own-reference rule to
+ * `external.credentialsRef`: **a write may only seal a new value or keep its
+ * own record's stored reference.**
+ *
+ * The door's callers are the admin routes (`POST` / `PATCH /datasources`), a
+ * signed-in operator every time; nothing system-side writes through this
+ * service, so there is no pass-through to keep here.
+ *
+ *  - **create** — a new record has no reference of its own to keep, so a draft
+ *    that names `external.credentialsRef` is refused, with one answer whatever
+ *    it names, before anything is written. The credential arrives as `secret`
+ *    and the door binds it; that reference is the only one a create stores.
+ *  - **update** — the record keeps the reference it already holds unless a
+ *    supplied `secret` rewraps it. A patch that names any other reference never
+ *    reaches the stored record.
+ *
+ * The harness is the service's own config seam, so each case reads exactly
+ * what the door persisted, bound, removed and registered.
+ */
+
+import { describe, expect, it } from 'vitest';
+import {
+  DatasourceAdminService,
+  type DatasourceAdminServiceConfig,
+  type StoredDatasource,
+} from '../datasource-admin-service.js';
+
+/** A reference some other write minted — the kind a caller must not store. */
+const OTHER_REF = 'sys_secret:sec_minted_elsewhere';
+
+function makeHarness(seed: StoredDatasource[] = []) {
+  const records: StoredDatasource[] = seed.map((r) => ({ ...r }));
+  const secrets = new Map<string, string>([[OTHER_REF, 'other-credential']]);
+  const ops: string[] = [];
+  let seq = 0;
+
+  const config: DatasourceAdminServiceConfig = {
+    probe: async () => ({ ok: true }),
+    listDatasourceRecords: async () => records.map((r) => ({ ...r })),
+    getDatasourceRecord: async (name) => {
+      const r = records.find((x) => x.name === name);
+      return r ? { ...r } : undefined;
+    },
+    putDatasourceRecord: async (record) => {
+      ops.push(`put:${record.name}`);
+      const idx = records.findIndex((r) => r.name === record.name);
+      if (idx >= 0) records[idx] = { ...record };
+      else records.push({ ...record });
+    },
+    deleteDatasourceRecord: async (name) => {
+      ops.push(`delete:${name}`);
+      const idx = records.findIndex((r) => r.name === name);
+      if (idx >= 0) records.splice(idx, 1);
+    },
+    writeSecret: async (input) => {
+      const ref = `sys_secret:sec_minted_${++seq}`;
+      ops.push(`writeSecret:${ref}`);
+      secrets.set(ref, input.value);
+      return ref;
+    },
+    removeSecret: async (ref) => {
+      ops.push(`removeSecret:${ref}`);
+      secrets.delete(ref);
+    },
+    readSecret: async (ref) => secrets.get(ref),
+    countBoundObjects: async () => 0,
+    listObjectsBoundTo: async () => [],
+    registerPool: (record) => {
+      ops.push(`registerPool:${record.name}`);
+    },
+    unregisterPool: (name) => {
+      ops.push(`unregisterPool:${name}`);
+    },
+  };
+
+  const service = new DatasourceAdminService(config);
+  const stored = (name: string) => records.find((r) => r.name === name);
+  return { service, stored, secrets, ops };
+}
+
+const DRAFT = {
+  name: 'reporting',
+  driver: 'postgres',
+  config: { host: 'db.internal', database: 'analytics' },
+};
+
+describe('#27722 — a create may not carry a stored credential reference', () => {
+  it.each([
+    ['a reference another write minted', OTHER_REF],
+    ['a reference that names nothing', 'sys_secret:sec_never_minted'],
+    ['a value in no reference shape', 'not-a-reference'],
+  ])('refuses %s, writing nothing', async (_label, ref) => {
+    const { service, stored, secrets, ops } = makeHarness();
+
+    await expect(
+      service.createDatasource({ ...DRAFT, external: { credentialsRef: ref } }),
+    ).rejects.toThrow(/external\.credentialsRef/);
+
+    expect(stored('reporting')).toBeUndefined();
+    expect(ops).toEqual([]);
+    expect(secrets.get(OTHER_REF)).toBe('other-credential');
+  });
+
+  it('answers the same whatever the reference names, and never echoes it', async () => {
+    const messages: string[] = [];
+    for (const ref of [OTHER_REF, 'sys_secret:sec_never_minted', 'not-a-reference']) {
+      const { service } = makeHarness();
+      const err = await service
+        .createDatasource({ ...DRAFT, external: { credentialsRef: ref } })
+        .catch((e: unknown) => e as Error);
+      expect(err).toBeInstanceOf(Error);
+      expect((err as Error).message).not.toContain(ref);
+      messages.push((err as Error).message);
+    }
+    expect(new Set(messages).size).toBe(1);
+  });
+
+  it('refuses it beside a supplied secret too: the door mints the only reference a create stores', async () => {
+    const { service, stored, ops } = makeHarness();
+
+    await expect(
+      service.createDatasource(
+        { ...DRAFT, external: { credentialsRef: OTHER_REF } },
+        { value: 'fresh-credential' },
+      ),
+    ).rejects.toThrow(/external\.credentialsRef/);
+
+    expect(stored('reporting')).toBeUndefined();
+    expect(ops).toEqual([]);
+  });
+
+  it('stores the reference its own secret was sealed under', async () => {
+    const { service, stored, secrets } = makeHarness();
+
+    await service.createDatasource(DRAFT, { value: 'fresh-credential' });
+
+    const ref = stored('reporting')?.external?.credentialsRef;
+    expect(ref).toMatch(/^sys_secret:sec_minted_/);
+    expect(ref).not.toBe(OTHER_REF);
+    expect(secrets.get(ref!)).toBe('fresh-credential');
+  });
+
+  it('still creates a record that names no reference at all', async () => {
+    const { service, stored } = makeHarness();
+
+    await service.createDatasource({ ...DRAFT, schemaMode: 'external', external: { allowWrites: false } });
+
+    expect(stored('reporting')).toBeDefined();
+    expect(stored('reporting')?.external?.credentialsRef).toBeUndefined();
+  });
+});
+
+describe('#27722 — an update keeps its own reference and stores no other', () => {
+  const OWN_REF = 'sys_secret:sec_own';
+
+  it('keeps the record\'s own reference when a patch names another', async () => {
+    const { service, stored, secrets, ops } = makeHarness([
+      { ...DRAFT, origin: 'runtime', external: { credentialsRef: OWN_REF } },
+    ]);
+
+    await service.updateDatasource('reporting', { external: { credentialsRef: OTHER_REF } });
+
+    expect(stored('reporting')?.external?.credentialsRef).toBe(OWN_REF);
+    expect(ops).not.toContain(`removeSecret:${OTHER_REF}`);
+    expect(secrets.get(OTHER_REF)).toBe('other-credential');
+  });
+
+  it('stores no reference on a record that holds none when a patch names one', async () => {
+    const { service, stored } = makeHarness([{ ...DRAFT, origin: 'runtime' }]);
+
+    await service.updateDatasource('reporting', { external: { credentialsRef: OTHER_REF } });
+
+    expect(stored('reporting')?.external?.credentialsRef).toBeUndefined();
+  });
+
+  it('replaces its own reference only with the one a supplied secret is sealed under', async () => {
+    const { service, stored, secrets, ops } = makeHarness([
+      { ...DRAFT, origin: 'runtime', external: { credentialsRef: OWN_REF } },
+    ]);
+
+    await service.updateDatasource(
+      'reporting',
+      { external: { credentialsRef: OTHER_REF } },
+      { value: 'rotated-credential' },
+    );
+
+    const ref = stored('reporting')?.external?.credentialsRef;
+    expect(ref).toMatch(/^sys_secret:sec_minted_/);
+    expect(secrets.get(ref!)).toBe('rotated-credential');
+    expect(ops).toContain(`removeSecret:${OWN_REF}`);
+    expect(ops).not.toContain(`removeSecret:${OTHER_REF}`);
+    expect(secrets.get(OTHER_REF)).toBe('other-credential');
+  });
+});
diff --git a/packages/services/service-datasource/src/contracts/datasource-admin-service.ts b/packages/services/service-datasource/src/contracts/datasource-admin-service.ts
index a62d063af44..d287b3a7876 100644
--- a/packages/services/service-datasource/src/contracts/datasource-admin-service.ts
+++ b/packages/services/service-datasource/src/contracts/datasource-admin-service.ts
@@ -160,7 +160,9 @@ export interface IDatasourceAdminService {
 
   /**
    * Persist a new runtime datasource (`origin: 'runtime'`, environment-scoped).
-   * Rejects when a code-defined datasource of the same name exists.
+   * Rejects when a code-defined datasource of the same name exists, and rejects
+   * a draft that names `external.credentialsRef`: the only reference a create
+   * stores is the one a supplied `secret` is bound under.
    */
   createDatasource(input: DatasourceDraft, secret?: SecretInput): Promise<DatasourceSummary>;
 
diff --git a/packages/services/service-datasource/src/datasource-admin-service.ts b/packages/services/service-datasource/src/datasource-admin-service.ts
index e6cea3eff55..d1ce3f7ad72 100644
--- a/packages/services/service-datasource/src/datasource-admin-service.ts
+++ b/packages/services/service-datasource/src/datasource-admin-service.ts
@@ -649,6 +649,7 @@ export class DatasourceAdminService implements IDatasourceAdminService {
 
   async createDatasource(input: DatasourceDraft, secret?: SecretInput): Promise<DatasourceSummary> {
     this.assertValidName(input?.name);
+    this.assertNoDraftCredentialsRef(input);
     if (!input.driver) throw new Error('A driver is required to create a datasource.');
     this.assertValidConfig(input.driver, input.config);
     // The wizard is a publish door for `pool` too (#5714). Rejected BEFORE the
@@ -1175,6 +1176,29 @@ export class DatasourceAdminService implements IDatasourceAdminService {
     }
   }
 
+  /**
+   * [#27722] The #27582 rule at this door: a write may only seal a new value or
+   * keep its own record's stored reference. A create has no record of its own,
+   * so the only `external.credentialsRef` it stores is the one a supplied
+   * `secret` is bound under, and a draft that names one is refused. One answer
+   * whatever it names: the message names the key and never its value, and
+   * nothing about the reference is looked up. Thrown before anything is
+   * written (a `400` at the route).
+   *
+   * An update needs no such refusal: it keeps the stored reference unless a
+   * supplied secret rewraps it, whatever the patch's `external` says.
+   */
+  private assertNoDraftCredentialsRef(input: DatasourceDraft): void {
+    const external = input.external as { credentialsRef?: unknown } | undefined;
+    if (external?.credentialsRef === undefined) return;
+    throw new Error(
+      `Invalid datasource '${input.name}': \`external.credentialsRef\` is not accepted on create. `
+        + 'It names a credential already stored, and only the reference this door binds a supplied `secret` '
+        + 'under can be stored on a new datasource. Send the credential as `secret`, and leave '
+        + '`external.credentialsRef` out. Nothing was written.',
+    );
+  }
+
   private toRecord(input: DatasourceDraft): StoredDatasource {
     return {
       name: input.name,
diff --git a/packages/services/service-settings/src/settings-secret-handle-own-reference.pin.test.ts b/packages/services/service-settings/src/settings-secret-handle-own-reference.pin.test.ts
new file mode 100644
index 00000000000..d6ed64f96b9
--- /dev/null
+++ b/packages/services/service-settings/src/settings-secret-handle-own-reference.pin.test.ts
@@ -0,0 +1,98 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * #27722 — the settings write door against the #27582 own-reference rule:
+ * **a write may only seal a new value or keep its own record's stored
+ * reference.**
+ *
+ * Measured, not changed: this door never takes a reference from its caller at
+ * all. For a declared-encrypted key, `setMany` seals whatever value it is
+ * handed and stores the handle that seal minted; the submitted value is never
+ * the stored handle, whatever shape it has. These pins hold that answer, so a
+ * later change that let a caller-supplied value stand in for the stored handle
+ * reds here.
+ *
+ * Each case names a live handle another organization's write minted, so the
+ * pin measures a real stored handle rather than one that names nothing.
+ *
+ * The writer is an enforced caller (the settings routes' context) holding the
+ * namespace's write capability. The in-process caller takes the same path:
+ * the door has no reference-bearing branch for any caller.
+ */
+
+import { randomBytes } from 'node:crypto';
+import { describe, expect, it } from 'vitest';
+import type { SettingsManifest } from '@objectstack/spec/system';
+import { SettingsService } from './settings-service.js';
+import { LocalCryptoProvider } from './local-crypto-provider.js';
+import type { SettingsContext, SettingsSecretStore } from './settings-service.types.js';
+
+const manifest: SettingsManifest = {
+  namespace: 'sms',
+  version: 1,
+  label: 'SMS',
+  scope: 'tenant',
+  readPermission: 'setup.access',
+  writePermission: 'setup.write',
+  specifiers: [
+    { type: 'password', key: 'auth_token', label: 'Auth token', required: false, encrypted: true },
+  ],
+};
+
+const asOrg = (tenantId: string): SettingsContext => ({
+  tenantId,
+  userId: `admin_${tenantId}`,
+  enforced: true,
+  permissions: ['setup.access', 'setup.write'],
+});
+
+function boot() {
+  const rows = new Map<string, Record<string, unknown>>();
+  const secretStore: SettingsSecretStore = {
+    async insert(row) { rows.set(row.id, { ...row }); return { id: row.id }; },
+    async get(id) { return (rows.get(id) as any) ?? null; },
+    async update(id, patch) { rows.set(id, { ...rows.get(id), ...patch }); },
+  };
+  const svc = new SettingsService({
+    env: {},
+    cryptoProvider: new LocalCryptoProvider({ key: randomBytes(32) }),
+    secretStore,
+  });
+  svc.registerManifest(manifest);
+  return { svc, rows };
+}
+
+/** Org A holds a live secret; returns the handle its write minted. */
+async function seedOtherOrganization(svc: SettingsService, rows: Map<string, unknown>) {
+  const before = new Set(rows.keys());
+  await svc.set('sms', 'auth_token', 'org-a-credential', asOrg('org_a'));
+  const minted = [...rows.keys()].filter((id) => !before.has(id));
+  expect(minted).toHaveLength(1);
+  return minted[0];
+}
+
+describe('#27722 — the settings write door stores only a handle its own write minted', () => {
+  it.each([
+    ['the bare handle', (h: string) => h],
+    ['a `secret:` reference to it', (h: string) => `secret:${h}`],
+  ])('seals %s as a new value rather than storing it as the handle', async (_label, spell) => {
+    const { svc, rows } = boot();
+    const foreign = await seedOtherOrganization(svc, rows);
+    const foreignRow = { ...(rows.get(foreign) as Record<string, unknown>) };
+    const submitted = spell(foreign);
+
+    const before = new Set(rows.keys());
+    await svc.set('sms', 'auth_token', submitted, asOrg('org_b'));
+    const minted = [...rows.keys()].filter((id) => !before.has(id));
+
+    // One new seal, under a handle that is not the submitted one.
+    expect(minted).toHaveLength(1);
+    expect(minted[0]).not.toBe(foreign);
+    // Org B reads back exactly what it wrote — never the credential the
+    // named handle holds.
+    expect((await svc.get<string>('sms', 'auth_token', asOrg('org_b'))).value).toBe(submitted);
+    // The other organization's handle and its value are untouched.
+    expect(rows.get(foreign)).toEqual(foreignRow);
+    expect((await svc.get<string>('sms', 'auth_token', asOrg('org_a'))).value).toBe('org-a-credential');
+  });
+});