diff --git a/apps/server/test/threads/thread-send-dispatch.test.ts b/apps/server/test/threads/thread-send-dispatch.test.ts
index acab5bdc3..98a8ac746 100644
--- a/apps/server/test/threads/thread-send-dispatch.test.ts
+++ b/apps/server/test/threads/thread-send-dispatch.test.ts
@@ -1,5 +1,6 @@
 import {
   archiveThread,
+  updateHost,
   getQueuedThreadMessage,
   getThread,
   listEvents,
@@ -19,6 +20,7 @@ import {
 import { groupHostDaemonEvents } from "@bb/host-daemon-contract";
 import { afterEach, describe, expect, it, vi } from "vitest";
 import type { TelemetryService } from "../../src/services/system/telemetry.js";
+import * as queuedDispatch from "../../src/services/threads/queued-message-dispatch.js";
 import * as threadEvents from "../../src/services/threads/thread-events.js";
 import { runQueuedMessageDispatch } from "../../src/services/threads/queued-message-dispatch.js";
 import {
@@ -344,6 +346,81 @@ describe("user message telemetry", () => {
   });
 });
 
+describe("active thread admission before host readiness", () => {
+  it.each(["stale", "fresh"] as const)(
+    "rejects a start with a %s snapshot without waking a suspended host",
+    async (snapshot) => {
+      await withTestHarness(async (harness) => {
+        const { environment, thread } = seedProviderThreadFixture({
+          harness,
+          value: 3987,
+        });
+        updateHost(harness.db, harness.hub, environment.hostId, {
+          phase: "suspended",
+          suspendedAt: Date.now(),
+        });
+        applyLoggedThreadLifecycleEvent(harness.deps, {
+          event: { type: "run.started" },
+          threadId: thread.id,
+        });
+        const current = getThread(harness.db, thread.id);
+        expect(current?.status).toBe("active");
+        if (current === null) throw new Error("Missing seeded thread");
+        const readiness = vi
+          .spyOn(queuedDispatch, "requestQueuedMachineReadiness")
+          .mockImplementation(() => {});
+
+        await expect(
+          acceptThreadSendRequest(harness.deps, {
+            thread: snapshot === "stale" ? thread : current,
+            payload: { input: textInput("begin another turn"), mode: "start" },
+          }),
+        ).rejects.toMatchObject({
+          status: 409,
+          body: {
+            code: "thread_not_writable",
+            details: { reason: "already_active" },
+          },
+        });
+        expect(listQueuedThreadMessages(harness.db, thread.id)).toEqual([]);
+        expect(readiness).not.toHaveBeenCalled();
+      });
+    },
+  );
+
+  it("keeps the host wait for queue-if-active after a stale idle snapshot", async () => {
+    await withTestHarness(async (harness) => {
+      const { environment, thread } = seedProviderThreadFixture({
+        harness,
+        value: 3988,
+      });
+      updateHost(harness.db, harness.hub, environment.hostId, {
+        phase: "suspended",
+        suspendedAt: Date.now(),
+      });
+      applyLoggedThreadLifecycleEvent(harness.deps, {
+        event: { type: "run.started" },
+        threadId: thread.id,
+      });
+      const readiness = vi
+        .spyOn(queuedDispatch, "requestQueuedMachineReadiness")
+        .mockImplementation(() => {});
+
+      await expect(
+        acceptThreadSendRequest(harness.deps, {
+          thread,
+          payload: { input: textInput("follow up later"), mode: "queue-if-active" },
+        }),
+      ).resolves.toMatchObject({
+        delivery: "queued",
+        queuedMessage: { waitingOn: { kind: "host-offline" } },
+      });
+      expect(listQueuedThreadMessages(harness.db, thread.id)).toHaveLength(1);
+      expect(readiness).toHaveBeenCalledWith(harness.deps, environment.hostId);
+    });
+  });
+});
+
 describe("startup queue waits", () => {
   it("steers provisioning input into the first turn in queue order", async () => {
     await withTestHarness(async (harness) => {