test(metadata-protocol): the credentialsRef pin's find double holds the caller's bound; record its engine double in the ledger

The stub engine's `find` applies `limit` after the filter, as the ObjectQL
double-limit gate asks of a new double, and the engine-double ledger
records the pin's `findOne` and `update` seams (regenerated with
`check-engine-double-contract.mjs --write`).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016WV4cx2wNeyC4kD8R4P7Ns

Author: claude

packages/metadata-protocol/src/protocol.datasource-credentials-ref-own-reference.test.ts

@@ -70,8 +70,9 @@ function makeStubEngine() {
             assertEngineFindOnePredicate(table, opts);
             return findRow(opts.where)?.row ?? null;
         },
-        async find(_table: string, opts: { where: Record<string, unknown> }) {
-            return Array.from(rows.values()).filter((r) => matches(r, opts.where));
+        async find(_table: string, opts: { where: Record<string, unknown>; limit?: number }) {
+            const hits = Array.from(rows.values()).filter((r) => matches(r, opts.where));
+            return typeof opts?.limit === 'number' ? hits.slice(0, opts.limit) : hits;
         },
         async insert(table: string, data: Record<string, unknown>) {
             writes.push(`insert ${table}`);

scripts/engine-double-contract.pinned.json

@@ -606,6 +606,16 @@
       "verb": "findOne",
       "pinned": 2
     },
+    {
+      "file": "packages/metadata-protocol/src/protocol.datasource-credentials-ref-own-reference.test.ts",
+      "verb": "findOne",
+      "pinned": 1
+    },
+    {
+      "file": "packages/metadata-protocol/src/protocol.datasource-credentials-ref-own-reference.test.ts",
+      "verb": "update",
+      "pinned": 1
+    },
     {
       "file": "packages/metadata-protocol/src/protocol.datasource-delete-prolongation.test.ts",
       "verb": "delete",