diff --git a/tests/sandbox.test.ts b/tests/sandbox.test.ts
index 7cb12a2..853aa95 100644
--- a/tests/sandbox.test.ts
+++ b/tests/sandbox.test.ts
@@ -11,6 +11,36 @@ const sandbox = async (...args: string[]) => {
   return (await $.raw`deno sandbox ${args.join(" ")}`.text()).trim();
 };
 
+/**
+ * `sandbox volumes create` returns the volume id immediately, but the
+ * backend takes a moment to make the volume mountable inside a sandbox
+ * even after it's queryable via `volumes list`. Poll the list endpoint
+ * first, then sleep `postListSleepMs` to let the cluster sync — without
+ * that extra sleep we still hit `VOLUME_NOT_FOUND` when the follow-up
+ * `sandbox create --volume <id>:path` runs.
+ */
+async function waitForVolumeReady(
+  volumeId: string,
+  {
+    timeoutMs = 30_000,
+    intervalMs = 500,
+    postListSleepMs = 5_000,
+  } = {},
+): Promise<void> {
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    const list = await sandbox("volumes", "list");
+    if (list.includes(volumeId)) {
+      await new Promise((r) => setTimeout(r, postListSleepMs));
+      return;
+    }
+    await new Promise((r) => setTimeout(r, intervalMs));
+  }
+  throw new Error(
+    `Timed out waiting for volume ${volumeId} to become visible via 'volumes list'`,
+  );
+}
+
 Deno.test("sandbox create", async () => {
   const sandboxId = await sandbox(
     "create",
@@ -143,15 +173,39 @@ Deno.test("sandbox with volume mount", async () => {
     "--region",
     "ord",
   );
-
-  const sandboxId = await sandbox(
-    "create",
-    "--quiet",
-    "--timeout",
-    "60s",
-    "--volume",
-    `${volumeId}:/data/dataset`,
-  );
+  await waitForVolumeReady(volumeId);
+
+  // The sandbox-side volume lookup hits a different service from the
+  // volumes list endpoint we just polled; that service propagates the
+  // new volume asynchronously, so a one-shot wait isn't enough. Retry
+  // the mount-bearing create a few times.
+  let sandboxId: string | undefined;
+  let lastErr: unknown;
+  for (let attempt = 0; attempt < 6; attempt++) {
+    try {
+      sandboxId = await sandbox(
+        "create",
+        "--quiet",
+        "--timeout",
+        "60s",
+        "--region",
+        "ord",
+        "--volume",
+        `${volumeId}:/data/dataset`,
+      );
+      break;
+    } catch (err) {
+      lastErr = err;
+      await new Promise((r) => setTimeout(r, 5_000));
+    }
+  }
+  if (!sandboxId) {
+    throw new Error(
+      `sandbox create with --volume kept failing: ${
+        lastErr instanceof Error ? lastErr.message : String(lastErr)
+      }`,
+    );
+  }
 
   await sandbox(
     "exec",