@@ -0,0 +1,14 @@
+---
+'@objectstack/cloud-connection': patch
+---
+
+feat(cloud-connection): `GET /api/v1/marketplace/install-local/:manifestId/sample-data` answers how many of an installed app's sample records a purge would delete now
+
+Clause-②: yes (widening)
+Metadata-protocol: none
+
+- **New read-only route.** `GET /api/v1/marketplace/install-local/:manifestId/sample-data` answers `{ success: true, data: { manifestId, count, unidentified } }`. `count` is the number of rows `POST …/purge-sample-data` would delete if it ran now, found by the purge's own matcher with nothing deleted. A record a user added is not counted, and neither is a sample record whose key field (its dataset's `externalId`) was edited, because the purge deletes neither. A sample record edited only in other fields is still a sample row: the purge deletes it and the count includes it. `unidentified` counts the sample records the purge would report in `errors` and leave in place (no usable key value, or a key two rows carry). Before this, the count was known only from the install answer's `data.seeded`, so after a reload no API could say how much sample data was left; the installed-apps listing's `withSampleData` says only whether any is left.
+- **Same rules as the purge.** It requires `manage_metadata`, answers `404` for a package that is not installed and `422 OS_PROTOCOL_INCOMPATIBLE` for an entry this runtime refused to load, and counts in the purge's scope (the caller's active organization under an organization wall, every row without one). A walled session with no active organization gets `count: 0`, the same answer as the listing's `withSampleData: false` for that session. A package with no seed datasets gets `count: 0`. With no data engine or metadata service it answers `500 DRIVER_UNAVAILABLE`, never `0`.
+- **It cannot delete.** It is a `GET` and accepts no query parameter: any parameter (`dryRun`, `confirm`, …) is refused with `400 VALIDATION_ERROR` before any row is read.
+- **Unchanged.** What the purge deletes, its permission and its answer; the listing's `withSampleData`.
+- `@objectstack/cloud-connection` now depends on `@objectstack/rest`, for the shared closed-query-set refusal message.
@@ -30,6 +30,7 @@
     "@objectstack/metadata-protocol": "workspace:*",
     "@objectstack/objectql": "workspace:*",
     "@objectstack/observability": "workspace:*",
+    "@objectstack/rest": "workspace:*",
     "@objectstack/runtime": "workspace:*",
     "@objectstack/spec": "workspace:*",
     "@objectstack/types": "workspace:*"
 
@@ -13,7 +13,7 @@
  *    eight doors refuse on it; `/status` reads it only to decide what it
  *    serves (#24148) and refuses no one.
  *  - `MarketplaceInstallLocalPlugin` reads it in ONE place
- *    (`resolveInstallPrincipal`), and all five doors answer a held session
+ *    (`resolveInstallPrincipal`), and all six doors answer a held session
  *    through the same refusal (`refuseHeldSession`).
  *
  * Each consults `evaluateAuthGate` (`@objectstack/core`) once, with no request
@@ -384,13 +384,14 @@ async function mountInstallLocal(storageDir: string) {
     };
 }
 
-/** The five doors, addressed with what each needs to act. */
+/** The six doors, addressed with what each needs to act. */
 const IL_DOORS = [
     { route: `POST ${IL}`, body: { manifest: APP } },
     { route: `GET ${IL}`, body: {} },
     { route: `DELETE ${IL}/:manifestId`, body: {} },
     { route: `POST ${IL}/:manifestId/reseed-sample-data`, body: {} },
     { route: `POST ${IL}/:manifestId/purge-sample-data`, body: {} },
+    { route: `GET ${IL}/:manifestId/sample-data`, body: {} },
 ] as const;
 
 /** Install the app as the un-held operator, so the follow-on doors have a target. */
@@ -402,15 +403,15 @@ async function seedInstall(storageDir: string) {
 }
 
 describe('ADR-0069 at MarketplaceInstallLocalPlugin', () => {
-    it('census: five routes, none allow-listed, all five covered below', async () => {
+    it('census: six routes, none allow-listed, all six covered below', async () => {
         const { rawApp } = await mountInstallLocal(dir);
         const keys = [...rawApp.routes.keys()].sort();
         expect(keys).toEqual(IL_DOORS.map((d) => d.route).sort());
         for (const key of keys) expect(isAuthGateAllowlisted(key.split(' ')[1]), key).toBe(false);
     });
 
     for (const { user, gate } of HELD) {
-        it(`HELD (${gate.code}): all five doors answer 403 with the gate's code, before any effect and before the ledger is touched`, async () => {
+        it(`HELD (${gate.code}): all six doors answer 403 with the gate's code, before any effect and before the ledger is touched`, async () => {
             await seedInstall(dir);
             const ledgerBefore = existsSync(join(dir, LEDGER_FILE));
             const { rawApp, effects } = await mountInstallLocal(dir);
@@ -430,6 +431,9 @@ describe('ADR-0069 at MarketplaceInstallLocalPlugin', () => {
         const list = await rawApp.routes.get(`GET ${IL}`)!(makeC(`http://localhost${IL}`, 'u_member'));
         expect(list.status).toBe(200);
         expect(list.payload.success).toBe(true);
+        const counted = await rawApp.routes.get(`GET ${IL}/:manifestId/sample-data`)!(makeC(`http://localhost${IL}`, 'u_member', {}, APP.id));
+        expect(counted.status, JSON.stringify(counted.payload)).toBe(200);
+        expect(counted.payload.success).toBe(true);
         for (const route of [`POST ${IL}/:manifestId/reseed-sample-data`, `POST ${IL}/:manifestId/purge-sample-data`, `DELETE ${IL}/:manifestId`]) {
             const res = await rawApp.routes.get(route)!(makeC(`http://localhost${IL}`, 'u_member', {}, APP.id));
             expect(res.status, `${route}: ${JSON.stringify(res.payload)}`).toBe(200);
 
@@ -250,6 +250,17 @@ export const CLOUD_CONNECTION_ROUTE_LEDGER: readonly CloudConnectionRouteLedgerE
             + '`manage_metadata` (never merely a signed-in session) and driven from the Console. No `@objectstack/client` method builds this URL, and '
             + 'a bulk data-purge door is deliberately not something the application SDK exposes.',
     },
+    {
+        route: 'GET /api/v1/marketplace/install-local/:manifestId/sample-data',
+        family: 'marketplace-install-local',
+        mountedIn: 'marketplace-install-local-plugin.ts',
+        disposition: 'server-only',
+        note:
+            'the read-only count beside purge: how many of the packaged app\'s sample rows the caller\'s scope still holds, '
+            + 'counted by the purge\'s own matcher, so it is the number a purge would delete now. It deletes nothing and '
+            + 'takes no query parameter. Behind `manage_metadata`, the purge\'s gate, since it exists to tell an operator '
+            + 'what a purge would remove; no `@objectstack/client` method builds this URL, for the reason purge has none.',
+    },
 
     // ── marketplace browse passthrough ─────────────────────────────────
     {
 
@@ -15,7 +15,7 @@
  *
  * ## What is pinned, through the booted plugin's own doors
  *
- *  - a key whose owner holds `MFA_REQUIRED` (scope `account`) → all five doors
+ *  - a key whose owner holds `MFA_REQUIRED` (scope `account`) → every door
  *    answer `403 MFA_REQUIRED` with the session's message, before any effect;
  *  - a key whose owner holds only `PASSWORD_RESET_REQUIRED` (scope
  *    `credential`) → served;
@@ -201,13 +201,14 @@ function withKey(body: unknown = {}, manifestId?: string) {
     };
 }
 
-/** The five doors, addressed with what each needs to act. */
+/** The six doors, addressed with what each needs to act. */
 const IL_DOORS = [
     { route: `POST ${IL}`, body: { manifest: APP } },
     { route: `GET ${IL}`, body: {} },
     { route: `DELETE ${IL}/:manifestId`, body: {} },
     { route: `POST ${IL}/:manifestId/reseed-sample-data`, body: {} },
     { route: `POST ${IL}/:manifestId/purge-sample-data`, body: {} },
+    { route: `GET ${IL}/:manifestId/sample-data`, body: {} },
 ] as const;
 
 let dir: string;
@@ -221,7 +222,7 @@ afterEach(() => {
 });
 
 describe('install-local doors — a key answers as its owner\'s session does (#23455, ruling C′)', () => {
-    it('REFUSES a key whose owner holds MFA_REQUIRED on all five doors, with the session\'s 403 code and message, before any effect', async () => {
+    it('REFUSES a key whose owner holds MFA_REQUIRED on all six doors, with the session\'s 403 code and message, before any effect', async () => {
         const postures: Record<string, Posture[]> = {};
         const m = await mountInstallLocal(dir, postures);
         // Installed by the same key while its owner is not held, so the
 
@@ -240,7 +240,7 @@ import {
 import { ConnectionCredentialStore } from './connection-credential-store.js';
 import { readJsonRequestBody } from './request-json-body.js';
 import { MARKETPLACE_INSTALLED_UI_BUNDLE } from './marketplace-ui.js';
-import { matchSeedRows, purgeSeedRows, type PurgeSeedDataset } from './marketplace-install-local-purge.js';
+import { countSeedRows, matchSeedRows, purgeSeedRows, type PurgeSeedDataset } from './marketplace-install-local-purge.js';
 import { planCustomizationPairInstall, type PairInstallItem } from './marketplace-install-local-customization-pair.js';
 import type {
     AuthSessionApi, ConnectorCredentialRef, IAuthService, IAutomationService, IHttpServer, IMetadataService, IObjectQLEngine,
@@ -268,6 +268,7 @@ import { judgeOverrideWrite, overrideWriteIdentityOf, overrideWriteItemsOf, type
 // [ADR-0146 D10, #28564] The `__c` extension-field reservation's one judge, step 1c''.
 import { judgeExtensionFieldSuffix } from '@objectstack/metadata-protocol';
 import { resolveThrownHttpError } from '@objectstack/types';
+import { unknownQueryParamRefusalMessage } from '@objectstack/rest';
 // [#25366] The code the registry's security-catalog refusal carries, compared
 // rather than `instanceof`-tested: the engine keeps the class unexported so a
 // consumer holding the other build realm's copy cannot misread it.
@@ -278,6 +279,13 @@ type SessionRead = Awaited<ReturnType<NonNullable<AuthSessionApi['getSession']>>
 
 const ROUTE_BASE = '/api/v1/marketplace/install-local';
 
+/**
+ * The closed query-parameter set of `GET …/:manifestId/sample-data` (AGENTS.md,
+ * route rule 5): it reads none. An unknown name is refused with a located
+ * `400`, never ignored — the door has no dry-run switch to mistype.
+ */
+export const SAMPLE_DATA_COUNT_QUERY_PARAMS: readonly string[] = Object.freeze([]);
+
 /**
  * [#25366] Whether a `manifest.register` failure is the registry's security
  * catalog refusal (`SecurityCatalogNameConflictError`, ADR-0048 §3.4 narrowed;
@@ -1240,9 +1248,11 @@ export class MarketplaceInstallLocalPlugin implements Plugin {
 
             const reseedHandler = async (c: any) => this.handleReseed(c, ctx);
             const purgeHandler = async (c: any) => this.handlePurge(c, ctx);
+            const sampleDataCountHandler = async (c: any) => this.handleSampleDataCount(c, ctx);
 
             if (typeof rawApp.post === 'function') rawApp.post(ROUTE_BASE, postHandler);
             if (typeof rawApp.get === 'function') rawApp.get(ROUTE_BASE, getHandler);
+            if (typeof rawApp.get === 'function') rawApp.get(`${ROUTE_BASE}/:manifestId/sample-data`, sampleDataCountHandler);
             if (typeof rawApp.delete === 'function') rawApp.delete(`${ROUTE_BASE}/:manifestId`, deleteHandler);
             if (typeof rawApp.post === 'function') {
                 rawApp.post(`${ROUTE_BASE}/:manifestId/reseed-sample-data`, reseedHandler);
@@ -4537,6 +4547,108 @@ export class MarketplaceInstallLocalPlugin implements Plugin {
         }, 200);
     };
 
+    /**
+     * GET /api/v1/marketplace/install-local/:manifestId/sample-data
+     *
+     * How many of the package's sample rows the caller's scope still holds:
+     * `{ manifestId, count, unidentified }`. `count` is the number of rows a
+     * purge run now would delete — {@link countSeedRows}, the purge's own
+     * {@link matchSeedRows} pass with nothing deleted — so the console can say
+     * "N records will go" after a reload, when the install answer's
+     * `data.seeded` is long gone. `unidentified` is the seed records the purge
+     * would report in `errors` and leave in place.
+     *
+     * A read of its own, not a switch on the purge: a GET can delete nothing,
+     * whatever the request carries, and it takes no query parameter at all
+     * ({@link SAMPLE_DATA_COUNT_QUERY_PARAMS}). Not a field on the listing
+     * either: the listing answers `withSampleData` for every installed package
+     * on every visit, from the FIRST seed row it finds; a count reads every
+     * seeded object's rows, so it is asked for one package, when it is needed.
+     *
+     * Every answer is the purge's for the same request, read-only:
+     *   • the purge's gate, `manage_metadata` ({@link requireInstallCapability}),
+     *     since the count exists to word the purge's confirm;
+     *   • `404` for no install, the unreadable-entry answer, and the protocol
+     *     handshake's `422 OS_PROTOCOL_INCOMPATIBLE` (#21834), in that order;
+     *   • the purge's scope: under an organization wall the caller's active
+     *     organization, table-wide without one. A walled session with NO active
+     *     organization reads nothing and answers `count: 0` — ADR-0123 D2's
+     *     answer for a tenant-scoped READ, the listing's `withSampleData: false`
+     *     for the same session; the purge it would word refuses that session;
+     *   • a package that declares no seed datasets answers `count: 0` (the
+     *     purge's `400 NOTHING_TO_PURGE` is about acting, and nothing is acted on);
+     *   • no data engine or metadata service: the purge's `500
+     *     DRIVER_UNAVAILABLE`, never a `0` that reads as "nothing left".
+     */
+    private handleSampleDataCount = async (c: any, ctx: PluginContext): Promise<Response> => {
+        const admission = await this.requireInstallCapability(c, ctx, 'Counting sample data');
+        if (!admission.ok) return admission.response;
+        const query = typeof c.req?.query === 'function' ? c.req.query() : undefined;
+        const queryRefusal = unknownQueryParamRefusalMessage(query, SAMPLE_DATA_COUNT_QUERY_PARAMS);
+        if (queryRefusal) {
+            return c.json({ success: false, error: { code: 'VALIDATION_ERROR', message: queryRefusal } }, 400);
+        }
+        const manifestId = String(c.req.param?.('manifestId') ?? c.req.params?.manifestId ?? '').trim();
+        if (!manifestId) {
+            return c.json({ success: false, error: { code: 'INVALID_REQUEST', message: 'manifestId path param required.' } }, 400);
+        }
+        if (!this.ledger.has(manifestId)) {
+            return c.json({ success: false, error: { code: 'RESOURCE_NOT_FOUND', message: `No marketplace install for ${manifestId}.` } }, 404);
+        }
+        const { entry, failure } = this.ledger.read(manifestId);
+        if (!entry) {
+            return this.unreadableLedgerEntry(c, ctx, manifestId, failure, 'count sample data');
+        }
+        const incompatible = this.refuseProtocolIncompatibleEntry(c, entry);
+        if (incompatible) return incompatible;
+
+        const answer = (count: number, unidentified: number): Response => c.json({
+            success: true,
+            data: { manifestId, count, unidentified },
+        }, 200);
+
+        const datasets = seedDatasetsOf(entry.manifest);
+        if (datasets.length === 0) return answer(0, 0);
+
+        let ql: IObjectQLEngine | undefined;
+        let metadata: IMetadataService | undefined;
+        try { ql = ctx.getService<IObjectQLEngine>('objectql'); } catch { /* no data engine */ }
+        try { metadata = ctx.getService<IMetadataService>('metadata'); } catch { /* no metadata service */ }
+        if (!ql || !metadata) {
+            return c.json({
+                success: false,
+                error: {
+                    code: 'DRIVER_UNAVAILABLE',
+                    message: 'The data engine (objectql) or the metadata service is not available on this runtime — cannot count sample data.',
+                },
+            }, 500);
+        }
+
+        let organizationId: string | undefined;
+        if (organizationWallActive(ctx)) {
+            const resolved = await this.resolveActiveOrgId(c, ctx);
+            // [ADR-0123 D2] No organization, so no organization's rows to count.
+            if (!resolved) return answer(0, 0);
+            organizationId = resolved;
+        }
+
+        const { SeedLoaderService } = await import('@objectstack/runtime');
+        const loader = new (SeedLoaderService as any)(ql, metadata, ctx.logger);
+        const graph = await loader.buildDependencyGraph([...new Set(datasets.map((d: any) => String(d.object)))]);
+        const { count, unidentified } = await countSeedRows({
+            engine: ql,
+            datasets,
+            graph,
+            organizationId,
+            report: (problem) => ctx.logger?.warn?.(
+                `[MarketplaceInstallLocal] ${manifestId}: the sample-data count could not identify `
+                + `${problem.records} seed record(s) of ${problem.object} (${problem.kind}: ${problem.detail}); `
+                + 'a purge would leave them in place',
+            ),
+        });
+        return answer(count, unidentified);
+    };
+
     /**
      * [#21834] ADR-0087 D1's handshake on the two sample-data doors: the answer
      * reseed and purge give a ledger entry whose declared protocol range