Preserve benchmark defaults for auth loaders

An authenticated document loader only affects authenticated key fetching.  It
should not disable benchmarkMode's private-address default for the regular
document and context loaders, whose local benchmark behavior is still needed.

Keep the explicit allowPrivateAddress and userAgent guard intact while avoiding
that guard for the benchmark default.

#787 (comment)
#787 (comment)

Assisted-by: Codex:gpt-5.5

Author: dahlia

packages/fedify/src/federation/middleware.test.ts

@@ -148,6 +148,19 @@ test("createFederation()", async (t) => {
     assertEquals(federation.allowPrivateAddress, false);
   });
 
+  await t.step(
+    "benchmarkMode keeps private-address default with auth loader only",
+    () => {
+      const federation = createFederation<number>({
+        kv,
+        benchmarkMode: true,
+        authenticatedDocumentLoaderFactory: () => mockDocumentLoader,
+      });
+      assertInstanceOf(federation, FederationImpl);
+      assertEquals(federation.allowPrivateAddress, true);
+    },
+  );
+
   await t.step("benchmarkMode rejects an explicit meterProvider", () => {
     const [meterProvider] = createTestMeterProvider();
     assertThrows(

packages/fedify/src/federation/middleware.ts

@@ -473,8 +473,7 @@ export class FederationImpl<TContextData>
     super();
     const benchmarkMode = options.benchmarkMode ?? false;
     const hasCustomLoaderFactory = options.documentLoaderFactory != null ||
-      options.contextLoaderFactory != null ||
-      options.authenticatedDocumentLoaderFactory != null;
+      options.contextLoaderFactory != null;
     const allowPrivateAddress = options.allowPrivateAddress ??
       (benchmarkMode && !hasCustomLoaderFactory ? true : false);
     const signatureTimeWindow = options.signatureTimeWindow ??
@@ -599,7 +598,7 @@ export class FederationImpl<TContextData>
     this.router.trailingSlashInsensitive = options.trailingSlashInsensitive ??
       false;
     this._initializeRouter();
-    if (allowPrivateAddress || options.userAgent != null) {
+    if (options.allowPrivateAddress === true || options.userAgent != null) {
       if (options.documentLoaderFactory != null) {
         throw new TypeError(
           "Cannot set documentLoaderFactory with allowPrivateAddress or " +