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+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#25522 cut 8] The compatibility-API bodies of `ObjectQL` (the methods
+ * that match the legacy `@objectql/core` interface), moved out of
+ * `engine.ts` whole: `registerObject` (a single definition into the
+ * registry, field names filled from their keys), `getConfigs` (the
+ * registered objects as a name-to-config map), `introspectDatasource` (a
+ * datasource's live remote schema, ADR-0015), `syncSchemas` (every
+ * registered object's storage synced to its driver, a federated object bound
+ * without DDL), `syncObjectSchema` (the same for one object, on demand) and
+ * `removePackage` (a package's hooks, actions and objects removed).
+ *
+ * A MOVE, not a redesign. Each exported function below is the body of the
+ * `ObjectQL` method of the same name as it stood, re-indented one level and
+ * otherwise unedited: the same registry calls, the same two refusals before
+ * introspection, the same federated routing, the same durability ERROR when a
+ * schema sync fails, and the same removal order. Each method's docblock stays
+ * on the method in `engine.ts`, which is still the contract.
+ *
+ * What stays in the class: `getDriverByName`, because ADR-0096 cites it by
+ * `engine.ts#getDriverByName`; `create`, a static factory; `createContext`,
+ * which hands the engine itself to `ScopedContext`, a value `engine.ts`
+ * defines (moving it would import the engine at run time); and
+ * `unregisterObject`, `getObject`, `getDriverForObject`,
+ * `dropObjectSchema`, `datasource`, `on` and `close`, whose bodies are no
+ * longer than the host literal moving them would cost.
+ *
+ * ## How the moved bodies reach the class
+ *
+ * The shape #23050 set for `rest-server.ts` (its `data-action-routes.ts`
+ * header carries the full reasoning), applied per method as
+ * `engine-execute-transactions.ts` applies it. The class keeps all six
+ * methods — every one is public, and the published `.d.ts` lists each one's
+ * name, signature and position — and each body is one literal of exactly the
+ * {@link CompatibilityApiHost} members that method reads, plus a `.call`.
+ * The fields the bodies read (`_registry`, `drivers`, `hooks`, `logger`)
+ * go as GETTERS, so each read happens when the body makes it, as it did. The
+ * methods they call (`getDriverForObject`, `removeActionsByPackage`) go as
+ * late-bound closures over the instance, so a double or spy set on the engine
+ * is still the one a call reaches.
+ *
+ * This module imports the engine only as a TYPE, so there is no module cycle
+ * at run time, and nothing re-exports it, so the published surface does not
+ * move.
+ */
+
+import type { ServiceObject } from '@objectstack/spec/data';
+import type { IntrospectedSchema as SpecIntrospectedSchema } from '@objectstack/spec/contracts';
+import { StorageNameMapping } from '@objectstack/spec/system';
+import { isFederatedObject } from './federated-object.js';
+import type { ObjectQL } from './engine.js';
+
+/**
+ * The `ObjectQL` members the functions below read — every one of them, and no
+ * other; each function's `this` is the `Pick` of the members IT reads. Each is
+ * typed AS the class member (an indexed access on the class), so a change to a
+ * member's type on the class is a change here too, and naming a member the
+ * class does not have is a compile error. See the module header for which
+ * members are getters.
+ */
+export interface CompatibilityApiHost {
+  readonly _registry: ObjectQL['_registry'];
+  readonly drivers: ObjectQL['drivers'];
+  readonly hooks: ObjectQL['hooks'];
+  readonly logger: ObjectQL['logger'];
+  getDriverForObject: ObjectQL['getDriverForObject'];
+  removeActionsByPackage: ObjectQL['removeActionsByPackage'];
+}
+
+/** The body of `ObjectQL#registerObject`; the method's docblock there is its contract. */
+export function registerObject(
+  this: Pick<CompatibilityApiHost, '_registry'>,
+  schema: ServiceObject,
+  packageId: string = '__runtime__',
+  namespace?: string,
+): string {
+  // Auto-assign field names from keys
+  if (schema.fields) {
+    for (const [key, field] of Object.entries(schema.fields)) {
+      if (field && typeof field === 'object' && !('name' in field)) {
+        (field as any).name = key;
+      }
+    }
+  }
+  return this._registry.registerObject(schema, packageId, namespace);
+}
+
+/** The body of `ObjectQL#getConfigs`; the method's docblock there is its contract. */
+export function getConfigs(this: Pick<CompatibilityApiHost, '_registry'>): Record<string, ServiceObject> {
+  const result: Record<string, ServiceObject> = {};
+  const objects = this._registry.getAllObjects();
+  for (const obj of objects) {
+    if (obj.name) {
+      result[obj.name] = obj;
+    }
+  }
+  return result;
+}
+
+/** The body of `ObjectQL#introspectDatasource`; the method's docblock there is its contract. */
+export async function introspectDatasource(
+  this: Pick<CompatibilityApiHost, 'drivers'>,
+  datasource: string,
+): Promise<SpecIntrospectedSchema> {
+  const driver = this.drivers.get(datasource);
+  if (!driver) {
+    throw new Error(`[ObjectQL] Datasource '${datasource}' has no registered driver to introspect.`);
+  }
+  if (typeof driver.introspectSchema !== 'function') {
+    throw new Error(`[ObjectQL] Driver for datasource '${datasource}' does not support introspectSchema().`);
+  }
+  return driver.introspectSchema();
+}
+
+/** The body of `ObjectQL#syncSchemas`; the method's docblock there is its contract. */
+export async function syncSchemas(
+  this: Pick<CompatibilityApiHost, '_registry' | 'getDriverForObject' | 'logger'>,
+): Promise<void> {
+  const allObjects = this._registry.getAllObjects();
+  for (const obj of allObjects) {
+    const driver = this.getDriverForObject(obj.name);
+    if (!driver) continue;
+    // [#21777] Same predicate and same treatment as the boot sync. The remote
+    // owns this object's schema, so `syncSchema` would be refused
+    // (`ExternalSchemaModeViolationError` on an external-schema datasource).
+    // Logging that refusal at the #4632 ERROR below was a false durability
+    // alarm, because nothing was meant to be created. The DDL-free binding
+    // still runs, because an object registered at runtime has no other way
+    // to its remote table: without it every read resolves to a table named
+    // after the object.
+    if (isFederatedObject(obj)) {
+      if (typeof (driver as any).registerExternalObject !== 'function') {
+        this.logger.debug('Driver does not support registerExternalObject, skipping external object', {
+          object: obj.name,
+          driver: (driver as any).name,
+        });
+        continue;
+      }
+      try {
+        await (driver as any).registerExternalObject(obj);
+        this.logger.debug('Federated object is not a DDL target — bound to its remote table without DDL', {
+          object: obj.name,
+          driver: (driver as any).name,
+        });
+      } catch (e: unknown) {
+        this.logger.warn('Failed to register external object metadata', {
+          object: obj.name,
+          driver: (driver as any).name,
+          error: e instanceof Error ? e.message : String(e),
+        });
+      }
+      continue;
+    }
+    const tableName = StorageNameMapping.resolveTableName(obj);
+    if (typeof (driver as any).syncSchemasBatch === 'function' && (driver as any).supports?.batchSchemaSync) {
+      // Already handled per-driver below; skip individual call
+    }
+    if (typeof (driver as any).syncSchema === 'function') {
+      try {
+        await (driver as any).syncSchema(tableName, obj);
+      } catch (e: unknown) {
+        // #4632 — this catch used to be empty, with the comment "log
+        // suppressed to avoid noise on already-synced tables". Suppressing an
+        // already-synced no-op is not what it did: `syncSchema` is required to
+        // be idempotent (see this method's doc comment), so a driver that
+        // reaches this catch did NOT sync. The only callers are runtime
+        // installs — marketplace plugin install, template seeding — which go
+        // on to INSERT into a table this failure means does not exist, and
+        // then report the install as successful. Nothing that claims to be
+        // persisted afterwards is.
+        this.logger.error(
+          `Schema sync FAILED for object '${obj.name}' — its table/collection was NOT created or altered, yet the object is ` +
+            `registered and will be written to: those writes will fail, or drop the columns that were never created. ` +
+            `Any seeding or install step that continues past this point is not durable. ` +
+            `Fix the driver error below, then re-run the install/sync.`,
+          e as Error,
+          { object: obj.name, tableName, driver: (driver as any)?.name },
+        );
+      }
+    }
+  }
+}
+
+/** The body of `ObjectQL#syncObjectSchema`; the method's docblock there is its contract. */
+export async function syncObjectSchema(
+  this: Pick<CompatibilityApiHost, '_registry' | 'getDriverForObject'>,
+  objectName: string,
+): Promise<void> {
+  const obj = this._registry.getObject(objectName) as any;
+  if (!obj) return;
+  const driver = this.getDriverForObject(objectName);
+  if (!driver) return;
+  // Federated (external) object (ADR-0015): register read metadata WITHOUT DDL
+  // (its remote schema is owned externally). This is what an app's onEnable
+  // calls after registering a late external driver so coercion maps + the
+  // physical-table mapping exist for queries. See SqlDriver.registerExternalObject.
+  if (isFederatedObject(obj)) {
+    if (typeof (driver as any).registerExternalObject === 'function') {
+      await (driver as any).registerExternalObject(obj);
+    }
+    return;
+  }
+  if (typeof (driver as any).syncSchema !== 'function') return;
+  const tableName = StorageNameMapping.resolveTableName(obj);
+  await (driver as any).syncSchema(tableName, obj);
+}
+
+/** The body of `ObjectQL#removePackage`; the method's docblock there is its contract. */
+export function removePackage(
+  this: Pick<CompatibilityApiHost, 'hooks' | 'removeActionsByPackage' | '_registry'>,
+  packageId: string,
+): void {
+  // Remove hooks
+  for (const [key, handlers] of this.hooks.entries()) {
+    const filtered = handlers.filter(h => h.packageId !== packageId);
+    if (filtered.length !== handlers.length) {
+      this.hooks.set(key, filtered);
+    }
+  }
+  // Remove actions
+  this.removeActionsByPackage(packageId);
+  // Remove objects
+  this._registry.unregisterObjectsByPackage(packageId, true);
+}