@@ -0,0 +1,12 @@
+---
+'@objectstack/skills': patch
+---
+
+docs(skills): objectstack-data teaches `external.connector`, the datasource credential channel that borrows a declared connector instance's credential, beside `credentialsRef`
+
+Clause-②: no
+Metadata-protocol: none
+
+- **Before.** A datasource can name a declared connector instance in `external.connector` and borrow that instance's credential (ADR-0015 amendment D7), so one credential serves the connector's flow actions and an API-backed datasource's records. `objectstack-data`'s `rules/datasources.md` taught only `credentialsRef`, so an agent following it bound a second copy of a vendor credential the stack already held, and had no way to know the key exists or where it is refused.
+- **Now.** The rule's credentials section names the two channels and that exactly one is written: `credentialsRef`, a secret-store handle resolved at connect; or `connector`, for a datasource on a plugin driver such as `@objectstack/driver-odata`, naming a `connectors` instance with a `provider` and an `auth` other than `none`, shown as `schemaMode: 'external', external: { connector: 'erp_api' }`. It says where `connector` is refused (beside `credentialsRef`, on a built-in driver, on a `managed` datasource, and naming an undeclared instance, at `defineStack` or else at connect), that a disabled instance or a stack with no automation service leaves the datasource unconnected with the reason, and that a connector credential not set yet answers `503` per request instead of failing the connect.
+- The new text is paid for inside the same file: the `field.columnName` history clause, the auto-connect lead-in and the escape-hatch note are shortened, and phrases that restated their neighbours (the `columnMap` direction the example already shows, the mapping-routing tail, the write-gate tail) are dropped. The file stays under its token ceiling, which does not move. No schema, key or runtime behaviour changes.
@@ -263,6 +263,76 @@ for the datasources listed under [When auto-connect fails](#when-auto-connect-fa
 and degrades with a warning otherwise. (Credential-less drivers such as SQLite
 simply have no `credentialsRef`.)
 
+### Borrowing a connector instance's credential
+
+An **API-backed** datasource, one served by a plugin driver such as the
+[OData driver](/docs/data-modeling/odata-datasources), has a second channel. When a
+[connector instance](/docs/automation/connectors#declaring-a-provider-bound-instance)
+already authorizes the vendor, name it in `external.connector` and the datasource
+borrows that instance's credential (ADR-0015 amendment D7). The credential is set once,
+where the connector's own is set
+([What `credentialRef` resolves through](/docs/automation/connectors#what-credentialref-resolves-through)),
+and it serves both the connector's flow actions and the datasource's records.
+
+{/* os:check */}
+```typescript
+import { defineStack } from '@objectstack/spec';
+
+export default defineStack({
+  manifest: { id: 'com.example.sales', name: 'Sales', version: '1.0.0', type: 'app' },
+  connectors: [
+    {
+      name: 'erp_api',
+      label: 'ERP API',
+      type: 'api',
+      provider: 'rest',
+      providerConfig: { baseUrl: 'https://erp.example.com' },
+      auth: { type: 'bearer', credentialRef: 'ERP_API_TOKEN' },
+    },
+  ],
+  datasources: [
+    {
+      name: 'erp',
+      driver: 'erp',                  // the OData plugin's name, i.e. the `driver.erp` service
+      schemaMode: 'external',
+      config: {},
+      external: {
+        connector: 'erp_api',         // no credentialsRef: exactly one channel
+        validation: { onMismatch: 'warn', checkOnBoot: false },
+      },
+    },
+  ],
+});
+```
+
+The instance's `auth` decides what is sent: a bearer token, basic auth, or an API key in
+its header or query parameter. The rules:
+
+- **One channel.** `connector` beside a `credentialsRef` is refused. Keep the one that
+  should supply the credential.
+- **API-backed datasources only.** `connector` is refused on a built-in driver
+  (`postgres`, `mysql`, `mongodb` and the rest), which takes a database credential: bind
+  that with `credentialsRef`. It is refused on a `managed` datasource too, since an API's
+  schema is never ObjectStack's to manage: set `schemaMode: 'external'` (or
+  `'validate-only'`).
+- **An instance that can lend.** The name must match a `connectors` entry of the stack
+  that has a `provider` and an `auth` other than `none`. A catalog descriptor (no
+  `provider`) or an instance with no `auth` is refused when the stack is validated, and a
+  datasource created or edited under Setup → Integrations → Datasources is judged the
+  same way when it is saved.
+- **Fail-closed at connect.** An instance that cannot lend when the datasource connects
+  (not declared, disabled with `enabled: false`, no `auth`), or a stack with no
+  automation service (`@objectstack/service-automation` is what lends the credential),
+  leaves the datasource unconnected with the reason, the same connect failure as an
+  unresolvable `credentialsRef`.
+- **A credential not set yet does not fail the connect.** Each request is answered
+  `503 ERR_DATASOURCE_UNAVAILABLE`, with the reference named in the server log, until
+  an administrator sets it; the next request after that reads with it, with no restart.
+- **Rotation.** A credential set again in the connector credential store reaches the
+  next request. One the upstream refuses with a `401` is obtained afresh once and the
+  request retried, which also picks up a rotated environment variable; a second `401`
+  answers `503`.
+
 ## 5. Writes (double opt-in)
 
 Federation is read-only by default. To allow writes, **both** the datasource and the
 
@@ -33,7 +33,8 @@ disagree.
 - **Each entity set you bind has a key.** The key becomes the record's `id`. An entity
   type with no usable key is refused at the first request.
 - **You know how it authenticates.** The driver sends no credential, a bearer token, or
-  HTTP basic. It does not run an OAuth2 flow ([Credentials](#3-credentials)).
+  HTTP basic, or, borrowed from a connector instance, an API key too. It does not run an
+  OAuth2 flow ([Credentials](#3-credentials)).
 
 ## 1. Mount the plugin
 
@@ -61,7 +62,7 @@ export default defineStack({
 | `name` | `odata` | The datasource it serves. It is also the driver name and the `driver.<name>` service suffix. |
 | `serviceRoot` | (required) | The service root URL, http or https, with no credentials and no query string. |
 | `version` | `4.0` | The protocol version. `4.0` is the only value. |
-| `auth` | `{ scheme: 'none' }` | `none`, `bearer`, or `basic` with a `username`. The secret is the datasource's `external.credentialsRef`. |
+| `auth` | `{ scheme: 'none' }` | `none`, `bearer`, or `basic` with a `username`. The secret is the datasource's `external.credentialsRef`. Leave it `none` when the datasource borrows a connector instance's credential ([Credentials](#3-credentials)). |
 | `secrets` | (none) | Where `credentialsRef` is resolved: an object with `resolve(credentialsRef)`. When absent, the host's `datasource-secret-resolver` service is used; `os serve` registers one. |
 | `pageSize` | `500` | Rows asked for per server page (`Prefer: odata.maxpagesize`). |
 | `requestTimeoutMs` | `30000` | The timeout of each request. |
@@ -164,8 +165,17 @@ What each piece does on this driver:
 ## 3. Credentials
 
 ⛔ Never put a credential in the stack, in the plugin options, or in the `serviceRoot`
-URL. The secret is the datasource's `external.credentialsRef`, and the plugin resolves it
-through the host's secret store:
+URL. The datasource names exactly one of two channels:
+
+- **A secret of its own**, `external.credentialsRef`, resolved through the host's secret
+  store. This is the example in step 2.
+- **A connector instance's credential**, `external.connector`, when a connector already
+  authorizes the same service
+  ([Borrowing a connector instance's credential](#borrowing-a-connector-instances-credential)).
+
+### A secret of its own: `credentialsRef`
+
+The plugin resolves `external.credentialsRef` through the host's secret store:
 
 - **`bearer`** sends `Authorization: Bearer <secret>`.
 - **`basic`** takes `username` from the options and the password from the secret.
@@ -197,6 +207,56 @@ the credential: an auth scheme with no `credentialsRef`, a `credentialsRef` with
 `secrets` nor the service, and a handle that does not resolve. The caller is answered
 `503 ERR_DATASOURCE_UNAVAILABLE`, and the cause goes to the server log.
 
+### Borrowing a connector instance's credential
+
+When a [connector instance](/docs/automation/connectors#declaring-a-provider-bound-instance)
+already authorizes the ERP for your flows, the datasource can borrow its credential instead
+of holding a secret of its own (ADR-0015 amendment D7). One credential, set where the
+connector's is set, then serves the connector's actions and the datasource's records.
+Name the instance in `external.connector`, leave `credentialsRef` out, and create the
+plugin with `auth` left at `none`:
+
+```typescript
+connectors: [
+  {
+    name: 'erp_api', label: 'ERP API', type: 'api',
+    provider: 'rest', providerConfig: { baseUrl: 'https://erp.example.com' },
+    auth: { type: 'bearer', credentialRef: 'ERP_API_TOKEN' },
+  },
+],
+datasources: [
+  {
+    name: 'erp', driver: 'erp', schemaMode: 'external', config: {},
+    external: { connector: 'erp_api', allowWrites: true },   // no credentialsRef
+  },
+],
+plugins: [
+  createODataDriverPlugin({
+    name: 'erp',
+    serviceRoot: 'https://erp.example.com/odata/v4/sales/',   // no auth, no secrets
+  }),
+],
+```
+
+- **The instance's `auth` decides how the credential is sent:** `Authorization: Bearer`,
+  `Authorization: Basic`, or an API key in its `headerName` header (default `X-API-Key`)
+  or, with `paramName`, a query parameter.
+- **The plugin borrows at the first request**, from the `connector-credential-source`
+  service that `@objectstack/service-automation` registers, and keeps the handle. Every
+  request then presents the current credential: one past its expiry is obtained afresh
+  before it is sent, and one the service refuses with a `401` is obtained afresh once and
+  the request retried. A second `401` answers `503`, naming the instance in the server
+  log.
+- **It fails closed.** Each of these refuses the request with nothing sent, answered
+  `503 ERR_DATASOURCE_UNAVAILABLE` with the cause in the server log: no automation
+  service in the stack, an instance that cannot lend (not declared, disabled, no
+  `auth`), a credential that is not set yet, a `credentialsRef` beside the connector,
+  and an `auth` scheme other than `none` on the plugin, which would send a second
+  credential. An instance that cannot lend also fails the datasource's connect, so
+  Setup → Integrations → Datasources shows why
+  ([Borrowing a connector instance's credential](/docs/data-modeling/external-datasources#borrowing-a-connector-instances-credential)
+  has the rules the stack is validated against).
+
 ## 4. What the service is asked
 
 Behind the floor, a list read is one `GET` on the entity set:
 
@@ -460,7 +460,8 @@ So a driver grows in three steps, each correct:
 3. **Skip the floor with a conformance-tested driver.** This is planned for a later
    phase ([#27261](https://github.com/objectstack-ai/objectstack/issues/27261)): a driver
    that passes the platform's conformance kit would be trusted with paging and the cap.
-   It does not exist yet.
+   The kit ships ([Run the conformance kit](#run-the-conformance-kit)); the trust does
+   not exist yet.
 
 **The 1000-row cap.** A read that matches more than 1000 rows is refused with
 `422 EXTERNAL_ROW_CAP_EXCEEDED` rather than answered from a partial set. The fix is to
@@ -492,6 +493,61 @@ configured by the host that composes it, through the options it passes to the pl
 keep the credential in the host's secret handling and out of metadata and the
 repository.
 
+When a [connector instance](/docs/automation/connectors#declaring-a-provider-bound-instance)
+already authorizes the vendor your driver calls, the datasource can name it in
+`external.connector` instead
+([Borrowing a connector instance's credential](/docs/data-modeling/external-datasources#borrowing-a-connector-instances-credential)):
+one credential then serves the connector's flow actions and your driver's requests. The
+connect step checks that the named instance can lend, and fails the datasource when it
+cannot, but it hands your already-built driver nothing. Your driver borrows the
+credential itself, from the `connector-credential-source` service that the automation
+service registers:
+
+```typescript
+import type { PluginContext } from '@objectstack/core';
+import {
+  CONNECTOR_CREDENTIAL_SOURCE_SERVICE,
+  callWithBorrowedCredential,
+  withoutBorrowedCredential,
+  type BorrowedConnectorAuth,
+  type ConnectorCredentialHandle,
+  type IConnectorCredentialSource,
+} from '@objectstack/types';
+
+// At the first request: `connector` is the datasource's `external.connector`.
+async function borrow(ctx: PluginContext, connector: string): Promise<ConnectorCredentialHandle> {
+  const source = ctx.getService<IConnectorCredentialSource>(CONNECTOR_CREDENTIAL_SOURCE_SERVICE);
+  return source.borrow(connector);
+}
+
+// Every request: the helper refreshes an expired credential, and on a 401 obtains it
+// afresh once and retries; a second 401 throws a 503 naming the instance.
+async function request(handle: ConnectorCredentialHandle, url: string): Promise<Response> {
+  let sent: BorrowedConnectorAuth | undefined;
+  const response = await callWithBorrowedCredential(handle, (auth) => {
+    sent = auth;
+    return fetch(url, {
+      headers: auth.type === 'bearer' ? { Authorization: `Bearer ${auth.token}` } : {},
+    });
+  });
+  if (!response.ok) {
+    // An upstream may echo the credential in its error text: remove it before throwing.
+    const text = await response.text();
+    throw Object.assign(new Error(sent ? withoutBorrowedCredential(text, sent) : text), {
+      status: response.status,
+    });
+  }
+  return response;
+}
+```
+
+The sketch sends only a bearer token. Present `auth` as its `type` says: `bearer` as
+`Authorization: Bearer`, `basic` as `Authorization: Basic`, and `api-key` in its
+`headerName` header or, with `paramName`, as a query parameter. Refuse the request,
+sending nothing, when the service is absent or the datasource also names a
+`credentialsRef`. The OData driver is the reference implementation
+(`packages/drivers/driver-odata/src/plugin.ts` and `transport.ts`).
+
 ## What your driver receives
 
 Measured on the reference test, request by request, with the engine's floor
@@ -604,6 +660,41 @@ operator from "refused" to a shape case, then teach `OPERATORS` the mapping. To
 same shapes arrive through a booted stack — HTTP door, permissions, formula, hook —
 start from the reference test named at the top of this page.
 
+### Run the conformance kit
+
+The shape test pins what *your* driver sends. The platform's plugin-driver conformance
+kit pins what the *engine* relies on, from outside this repository: a driver in its own
+repository runs it in its own CI, so a platform change to that contract fails there
+before it reaches your users. It ships in `@objectstack/objectql`:
+`definePluginDriverConformanceSuite` registers one test per case under your runner's
+`describe` / `it` (vitest and jest alike), and `runPluginDriverConformance` returns a
+report without a test framework.
+
+```typescript
+import { afterAll, describe, it } from 'vitest';
+import { definePluginDriverConformanceSuite } from '@objectstack/objectql';
+import { createPortScheduleDriver } from './port-schedule-driver';
+import { fakeRemoteHolding } from './fake-remote';   // your fake of the remote's API
+
+definePluginDriverConformanceSuite(
+  { describe, it, afterAll },
+  {
+    // A driver over a remote holding exactly the fixture's rows, served under its object.
+    setup: (fixture) => ({ driver: createPortScheduleDriver(fakeRemoteHolding(fixture)) }),
+  },
+);
+```
+
+The kit's oracle is the spec's driver conformance tables, the standard every built-in
+driver is held to. Each read is checked against the floor: the driver may push all of a
+filter down, part of it or none, and may refuse what it cannot translate, but must never
+return fewer rows than match, invent a row, or answer a failure as rows. Add
+`setupUnavailable` (a remote that is down) for the outage cases and `writeProbes` (one
+write the remote accepts, one it refuses) for the write cases; without them those cases
+report `not-offered`. `tiers: ['floor', 'direct']` adds the stricter tier, where the
+driver answers the whole query itself; the floor does not need it. The OData driver runs the
+kit in `packages/drivers/driver-odata/src/odata-driver.conformance-kit.test.ts`.
+
 ## Five business examples
 
 **Port berth scheduling — computed, real-time.** The worked example above. The