@@ -0,0 +1,45 @@
+---
+'@objectstack/service-datasource': minor
+---
+
+fix(service-datasource)!: on `objectstack start`, external validation and the boot gate compare every federated object
+
+**BREAKING (narrowing)** — on `objectstack start` a deployment with real schema drift on a
+federated object can now refuse to boot, as its `external.validation.onMismatch` setting
+declares.
+
+The federation service (`ExternalDatasourceServicePlugin`) read the `metadata` service once,
+in its `init()`, and kept the answer. `objectstack start` composes no metadata plugin: its
+`metadata` service is the kernel's in-memory fallback, which the kernel registers after every
+plugin's `init()`, just before the start phase. So on `start` the federation service kept "no
+metadata service" for the life of the process, and every read behind it answered as if the
+deployment declared nothing. It now asks for the `metadata` service each time it reads it, so
+`start` sees what `objectstack dev` always saw.
+
+| on `objectstack start` | before | now |
+| --- | --- | --- |
+| the boot gate (ADR-0015 §5.2) | logged "all federated objects match their remote schema" with `objects: 0`, having compared nothing, so no `onMismatch` policy ever applied | compares every federated object and applies each datasource's `onMismatch` to every measured mismatch |
+| `POST /api/v1/datasources/:name/external/validate` | `ok: true` with no rows | one row per federated object bound to the datasource, with its diffs |
+| `POST /api/v1/datasources/:name/external/refresh-catalog` | answered the snapshot, never stored it | also stores it as the datasource's `external_catalog` record |
+| `GET /api/v1/datasources/:name/external/tables` | ignored the datasource's `external.allowedSchemas` | leaves out a table whose schema is outside them |
+| draft and import names | never resolved a package namespace: drafts were unprefixed, and an import's explicit `name` was never held to the ADR-0028 prefix rule | resolve the namespace of the datasource's package when the datasource carries package provenance; an import whose explicit `name` lacks that prefix is refused `400 EXTERNAL_IMPORT_ERROR` |
+
+**What to do if a `start` deployment now refuses to boot.** Under `onMismatch: 'fail'` (the
+default) the boot stops with `ExternalSchemaMismatchError`, naming the object, the datasource
+and each drifted column. Either fix the drift (align the object's fields, its
+`external.columnMap` or `external.ignoreColumns`, or the remote table) or set
+`external.validation.onMismatch: 'warn'` on that datasource, which boots and logs the drift
+instead. To see the drift before deploying, call
+`POST /api/v1/datasources/:name/external/validate` on `objectstack dev`, which already
+compared. A remote that cannot be reached still never stops the boot. An import refused for
+its name takes a `name` carrying the datasource package's namespace prefix.
+
+**Unchanged.** `objectstack dev`, and every composition that registers a metadata plugin before
+the federation service, answers exactly as before: measured on the showcase, every federation
+door and the boot gate gave the same answers before and after. What validation judges, what
+each `onMismatch` value does, and the boot gate's skip for a datasource that sets
+`external.validation.checkOnBoot: false` are unchanged.
+
+Clause-②: no (narrowing)
+
+<!-- adr-0087: not-required (no-migration-prescription) No authorable key, spelling, export, config field or stored shape is removed or renamed, and no stored row is read or rewritten: on a composition with no metadata plugin the federation service now reads the metadata service it always declared it reads, so the boot gate and the federation doors judge the objects and datasources the deployment already declares. The handling above is an operator choice between two settings that already exist, not a FROM to TO mapping that objectstack migrate meta could apply. The other categories are closed on facts: the package publishes (not unpublished); no ADR-0087 id covers when a plugin resolves a service (not registered / already-registered); and the change is runtime behaviour, not a declaration (not runtime-interface-only / type-surface-only). -->
@@ -0,0 +1,143 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+//
+// [#21876] On a composition with no metadata plugin — the `objectstack start`
+// shape — the federation service compares every federated object.
+//
+// ## What was broken
+//
+// `ExternalDatasourceServicePlugin.init()` read the `metadata` service once and
+// kept the answer. `objectstack start` composes no metadata plugin: its
+// `metadata` service is the kernel's in-memory fallback, registered after every
+// plugin's `init()`, just before the start phase. So the federation service
+// kept "no metadata service" for the life of the process. Measured on the
+// showcase under `objectstack start`: `POST /datasources/:name/external/validate`
+// answered `ok: true` with no rows, and the boot gate logged "all federated
+// objects match their remote schema" with `objects: 0` — although two
+// federated objects exist, and one of them could have drifted. Under
+// `objectstack dev` (which composes the metadata plugin before this one) both
+// objects were compared. The service now resolves `metadata` when it is used.
+//
+// ## Why this composition
+//
+// The verify harness composes no metadata plugin either, so its `metadata`
+// service is the same kernel fallback, registered at the same moment, as on
+// `objectstack start`. The first case asserts that, so a harness that one day
+// composes a metadata plugin cannot turn this file into a silent pass. The
+// harness does not mount the federation service, so this file mounts it, as
+// `objectstack dev` and `start` do. It does not mount the boot gate either
+// (`createExternalValidationPlugin`, `@objectstack/runtime`): the gate's input
+// is the federation service's whole-farm sweep, `validateAll()`, which the
+// third case reads directly. The gate's own log on a real `objectstack start`
+// is recorded on the pull request that brought this file.
+//
+// ## The drift
+//
+// The showcase's remote is a SQLite file its `onEnable` provisions. The file
+// is the test's own (a temporary working directory), and after provisioning
+// its `customers` table loses the `email` column the code-defined
+// `showcase_ext_customer` declares — a real drift, so "compared" and "skipped"
+// give different answers.
+
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import showcaseStack, { onEnable } from '@objectstack/example-showcase';
+import { ExternalDatasourceServicePlugin, resolveSqliteDriver } from '@objectstack/service-datasource';
+import { bootStack, type VerifyStack } from '@objectstack/verify';
+import { mkdtempSync, rmSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+
+/** The showcase's external datasource (`showcase-external.datasource.ts`) and its remote file. */
+const DATASOURCE = 'showcase_external';
+const REMOTE_FILE = '.objectstack/data/showcase_external.db';
+/** The code-defined federated objects bound to it. */
+const FEDERATED = ['showcase_ext_customer', 'showcase_ext_order'];
+
+interface Row {
+  object: string;
+  datasource: string;
+  ok: boolean;
+  diffs: Array<{ kind: string; column?: string; severity: string }>;
+}
+interface Report {
+  ok: boolean;
+  results: Row[];
+}
+
+const objectsOf = (rows: Row[]) => rows.map((r) => r.object).sort();
+
+/** Rename the remote's `customers.email` away, so the remote no longer has the column the object declares. */
+async function driftRemoteCustomers(): Promise<void> {
+  const { driver } = await resolveSqliteDriver({ filename: REMOTE_FILE, warn: () => undefined });
+  const remote = driver as unknown as {
+    connect(): Promise<void>;
+    disconnect(): Promise<void>;
+    execute(sql: string): Promise<unknown>;
+  };
+  await remote.connect();
+  try {
+    await remote.execute('ALTER TABLE customers RENAME COLUMN email TO billing_contact');
+  } finally {
+    await remote.disconnect();
+  }
+}
+
+describe('federation on a composition with no metadata plugin (the objectstack start shape)', () => {
+  let stack: VerifyStack;
+  let token: string;
+  let prevCwd: string;
+  let dir: string;
+
+  beforeAll(async () => {
+    prevCwd = process.cwd();
+    dir = mkdtempSync(join(tmpdir(), 'dogfood-21876-'));
+    process.chdir(dir);
+    // Provision the remote tables, exactly as the showcase does at boot (the
+    // harness imports only the stack's default export, so `onEnable` never
+    // runs on its own), then drift one column away.
+    await onEnable({ logger: { info() {}, warn() {} } } as never);
+    await driftRemoteCustomers();
+    stack = await bootStack(showcaseStack, { extraPlugins: [new ExternalDatasourceServicePlugin()] });
+    token = await stack.signIn();
+  }, 180_000);
+
+  afterAll(async () => {
+    await stack?.stop();
+    if (prevCwd) process.chdir(prevCwd);
+    if (dir) rmSync(dir, { recursive: true, force: true });
+  });
+
+  it('precondition: the metadata service is the kernel\'s in-memory fallback, as on objectstack start', () => {
+    const metadata = stack.kernel.getService<{ __serviceInfo?: { status?: string; message?: string } }>('metadata');
+    expect(metadata.__serviceInfo?.status).toBe('degraded');
+    expect(metadata.__serviceInfo?.message).toMatch(/^In-memory metadata registry/);
+  });
+
+  it('validate compares each federated object, and reports the drifted column', async () => {
+    const res = await stack.apiAs(token, 'POST', `/datasources/${DATASOURCE}/external/validate`);
+    const body = (await res.json()) as { data?: Report };
+    expect(res.status, JSON.stringify(body)).toBe(200);
+    const report = body.data as Report;
+
+    expect(objectsOf(report.results)).toEqual(FEDERATED);
+    const customer = report.results.find((r) => r.object === 'showcase_ext_customer');
+    expect(customer?.ok).toBe(false);
+    expect(customer?.diffs).toEqual([
+      expect.objectContaining({ kind: 'missing_column', column: 'email', severity: 'error' }),
+    ]);
+    const order = report.results.find((r) => r.object === 'showcase_ext_order');
+    expect(order?.ok, JSON.stringify(order)).toBe(true);
+    expect(report.ok).toBe(false);
+  });
+
+  it('the boot gate\'s sweep (validateAll) counts the real federated objects', async () => {
+    const service = stack.kernel.getService<{ validateAll(): Promise<Report> }>('external-datasource');
+
+    const report = await service.validateAll();
+
+    const onShowcase = report.results.filter((r) => r.datasource === DATASOURCE);
+    expect(objectsOf(onShowcase)).toEqual(FEDERATED);
+    expect(onShowcase.find((r) => r.object === 'showcase_ext_customer')?.diffs).toEqual([
+      expect.objectContaining({ kind: 'missing_column', column: 'email' }),
+    ]);
+  });
+});