fix(run-engine,core): non-blocking test polls and document the zero total limit

The waitFor polls dequeued with the default 10s blocking pop, which could
blow past the helper deadline on a slow runner; poll non-blocking instead.
Document that totalConcurrencyLimit: 0 holds every keyed run, matching
concurrencyLimit's zero semantics.

internal-packages/run-engine/src/run-queue/tests/totalConcurrency.test.ts

@@ -286,7 +286,9 @@ describe("RunQueue total concurrency limit", () => {
       });
 
       const r1Admitted = await waitFor(async () => {
-        const next = await queue.dequeueMessageFromWorkerQueue("consumer-1", "main");
+        const next = await queue.dequeueMessageFromWorkerQueue("consumer-1", "main", {
+          blockingPop: false,
+        });
         return next?.messageId === "r1";
       });
       expect(r1Admitted).toBe(true);
@@ -350,7 +352,9 @@ describe("RunQueue total concurrency limit", () => {
         });
 
         const r1Admitted = await waitFor(async () => {
-          const next = await queue.dequeueMessageFromWorkerQueue("consumer-1", "main");
+          const next = await queue.dequeueMessageFromWorkerQueue("consumer-1", "main", {
+            blockingPop: false,
+          });
           return next?.messageId === "r1";
         });
         expect(r1Admitted).toBe(true);

packages/core/src/v3/types/queues.ts

@@ -54,6 +54,9 @@ export type QueueOptions = {
    * ```
    *
    * Only enforced for runs triggered with a `concurrencyKey`, and requires server-side support.
+   *
+   * Omit for no total cap. Like `concurrencyLimit`, a value of `0` holds every keyed run in
+   * the queue rather than removing the cap.
    */
   totalConcurrencyLimit?: number;
 };