diff --git a/packages/cli/src/bench/scenarios/inbox.test.ts b/packages/cli/src/bench/scenarios/inbox.test.ts
index 57df0e970..ac10a8912 100644
--- a/packages/cli/src/bench/scenarios/inbox.test.ts
+++ b/packages/cli/src/bench/scenarios/inbox.test.ts
@@ -9,6 +9,7 @@ import test from "node:test";
 import { serve } from "srvx";
 import { getContextLoader, getDocumentLoader } from "../../docloader.ts";
 import { buildFleet } from "../actor/fleet.ts";
+import type { Clock } from "../load/clock.ts";
 import { normalizeSuite } from "../scenario/normalize.ts";
 import type { Suite } from "../scenario/types.ts";
 import { spawnSyntheticServer } from "../server/synthetic.ts";
@@ -60,16 +61,17 @@ async function spawnBenchmarkTarget(usernames: string[] = ["alice"]) {
       received++;
     });
 
-  // Record every inbox path that was POSTed to, so a test can confirm that
-  // deliveries were spread across multiple recipients' personal inboxes.
-  const inboxHits = new Set<string>();
+  // Count POSTs per inbox path, so a test can confirm how deliveries were
+  // allocated across multiple recipients' personal inboxes.
+  const inboxHits = new Map<string, number>();
   const server = serve({
     port: 0,
     hostname: "127.0.0.1",
     silent: true,
     fetch: (request: Request) => {
       if (request.method === "POST") {
-        inboxHits.add(new URL(request.url).pathname);
+        const path = new URL(request.url).pathname;
+        inboxHits.set(path, (inboxHits.get(path) ?? 0) + 1);
       }
       return federation.fetch(request, { contextData: undefined });
     },
@@ -192,7 +194,13 @@ test("inboxRunner - reports server metrics scoped past the warm-up", async () =>
   }
 });
 
-test("inboxRunner - rotates deliveries across multiple recipients", async () => {
+// Recipients are allocated round-robin by signing index, so the run makes a
+// fixed number of attempts rather than however many fit in a real-time window:
+// four constant arrivals under a fake clock, each consuming one allocation
+// index, split exactly two per recipient whatever order they complete in.
+async function assertAllocatesAcrossRecipients(
+  signing: "jit" | "presign",
+): Promise<void> {
   const target = await spawnBenchmarkTarget(["alice", "bob"]);
   let fleet: Awaited<ReturnType<typeof spawnSyntheticServer>> | undefined;
   try {
@@ -214,11 +222,22 @@ test("inboxRunner - rotates deliveries across multiple recipients", async () =>
         ],
         // Personal inboxes so each recipient's deliveries hit a distinct path.
         inbox: "personal",
-        load: { concurrency: 2 },
-        duration: "300ms",
+        // 10/s over 400ms schedules exactly four arrivals (0, 100, 200, and
+        // 300ms), which is also the batch size presign signs up front.
+        load: { rate: 10, maxInFlight: 2 },
+        duration: "400ms",
+        signing,
       }],
     };
     const scenario = normalizeSuite(suite).scenarios[0];
+    let now = 0;
+    const clock: Clock = {
+      now: () => now,
+      sleepUntil: (timeMs) => {
+        now = Math.max(now, timeMs);
+        return Promise.resolve();
+      },
+    };
     const measurement = await inboxRunner.run({
       scenario,
       target: target.url,
@@ -226,8 +245,10 @@ test("inboxRunner - rotates deliveries across multiple recipients", async () =>
       contextLoader: await getContextLoader({ allowPrivateAddress: true }),
       allowPrivateAddress: true,
       fleet,
+      clock,
     });
 
+    assert.strictEqual(measurement.requests.total, 4);
     assert.strictEqual(
       measurement.requests.successRate,
       1,
@@ -235,15 +256,10 @@ test("inboxRunner - rotates deliveries across multiple recipients", async () =>
         JSON.stringify(measurement.errors)
       }`,
     );
-    // Both recipients' personal inboxes received deliveries.
-    const hits = target.inboxHits();
-    assert.ok(
-      hits.has("/users/alice/inbox"),
-      `expected alice's inbox to be hit; hits: ${JSON.stringify([...hits])}`,
-    );
-    assert.ok(
-      hits.has("/users/bob/inbox"),
-      `expected bob's inbox to be hit; hits: ${JSON.stringify([...hits])}`,
+    // Each recipient's personal inbox received exactly half of the deliveries.
+    assert.deepStrictEqual(
+      Object.fromEntries(target.inboxHits()),
+      { "/users/alice/inbox": 2, "/users/bob/inbox": 2 },
     );
   } finally {
     try {
@@ -252,7 +268,19 @@ test("inboxRunner - rotates deliveries across multiple recipients", async () =>
       await target.close();
     }
   }
-});
+}
+
+test(
+  "inboxRunner - allocates jit deliveries across multiple recipients",
+  { timeout: 60_000 },
+  () => assertAllocatesAcrossRecipients("jit"),
+);
+
+test(
+  "inboxRunner - allocates presigned deliveries across multiple recipients",
+  { timeout: 60_000 },
+  () => assertAllocatesAcrossRecipients("presign"),
+);
 
 test("inboxRunner.validate - rejects activity options it cannot honor", () => {
   function resolve(activity: Record<string, unknown>) {