Return benchmark queue correlation ids

Use the triggered activity ID as the benchmark queue correlation handle
so successful trigger responses return a value that is also preserved on
queued fanout and outbox work.

#787 (comment)

Assisted-by: Codex:gpt-5.5

Author: dahlia

docs/manual/benchmarking.md

@@ -153,12 +153,15 @@ A successful trigger returns `202 Accepted`:
 {
   "version": 1,
   "activityId": "https://example.com/activities/bench-1",
-  "queueCorrelationId": null,
+  "queueCorrelationId": "https://example.com/activities/bench-1",
   "recipientCount": 1,
   "inboxCount": 1
 }
 ~~~~
 
+The `queueCorrelationId` is the activity ID preserved on the queued fanout or
+outbox work.
+
 
 Metrics
 -------

packages/fedify/src/federation/bench.ts

@@ -197,6 +197,10 @@ export async function handleBenchmarkTrigger<TContextData>(
     const sender = parseSender(body.sender);
     const recipients = await parseRecipients(body.recipients, context);
     const activity = await parseActivity(body.activity, context);
+    if (activity.id == null) {
+      throw new BenchmarkTriggerError("activity must have an id.");
+    }
+    const activityId = activity.id.href;
     const inboxes = extractInboxes({ recipients });
     const inboxUrls = Object.keys(inboxes);
     if (inboxUrls.length < 1) {
@@ -220,8 +224,8 @@ export async function handleBenchmarkTrigger<TContextData>(
     return jsonResponse(
       {
         version: 1,
-        activityId: activity.id?.href ?? null,
-        queueCorrelationId: null,
+        activityId,
+        queueCorrelationId: activityId,
         recipientCount: recipients.length,
         inboxCount: inboxUrls.length,
       },

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

@@ -677,17 +677,21 @@ test("benchmarkMode trigger endpoint", async (t) => {
     const body = await response.json() as {
       version: number;
       activityId: string;
-      queueCorrelationId: string | null;
+      queueCorrelationId: string;
       recipientCount: number;
       inboxCount: number;
     };
     assertEquals(body.version, 1);
     assertEquals(body.activityId, "https://example.com/activities/bench-1");
-    assertEquals(body.queueCorrelationId, null);
+    assertEquals(
+      body.queueCorrelationId,
+      "https://example.com/activities/bench-1",
+    );
     assertEquals(body.recipientCount, 1);
     assertEquals(body.inboxCount, 1);
     assertEquals(messages.length, 1);
     assertEquals(messages[0].type, "outbox");
+    assertEquals(messages[0].activityId, body.queueCorrelationId);
     assertEquals(messages[0].inbox, "https://sink.example/inbox");
   });
 });