docs: per-key home cap wording, combined field always present, reset body required

The gates intro promised a task-wide cap the keyed example does not
deliver (a concurrencyKey splits the home queue per key); the combined
object is emitted on every queue with null fields rather than omitted;
and both reset endpoints reject a zero-length body, so the body is
required. Also restores the example that drifted off overriddenAt.

Author: matt-aitken

docs/queue-concurrency.mdx

@@ -183,7 +183,7 @@ The combined limit only applies to runs triggered with a `concurrencyKey`; runs
 
 ## Holding slots in more than one queue (queue gates)
 
-Sometimes one limit isn't enough: a webhook processor should be capped as a task, but each tenant should also have a global cap across every task they run. Queue gates let a run hold a concurrency slot in more than one queue at once.
+Sometimes one limit isn't enough: each tenant's webhook processing should be capped, but the tenant should also have a global cap across every task they run. Queue gates let a run hold a concurrency slot in more than one queue at once.
 
 Pass an array as `queue`: the first entry is the run's home queue (where it waits), and up to two more entries name gates — other queues the run must also have capacity in before it starts, and occupies while it executes:
 
@@ -204,6 +204,8 @@ export const processWebhook = task({
 await processWebhook.trigger(payload, { concurrencyKey: tenantId });
 ```
 
+Because the trigger passes a `concurrencyKey`, the home queue splits per key as usual: `concurrencyLimit: 2` caps each tenant's webhook runs, not the task overall (add a `combinedConcurrencyLimit` to the home queue to bound it across all tenants).
+
 A gate without a `concurrencyKey` uses the run's own key, so the shared `tenant` queue above caps each tenant across every task that names it as a gate. Give the gate a literal key to pin it to a single slot pool instead, for example capping all traffic to one external provider across your whole environment:
 
 ```ts /trigger/sync.ts

docs/v3-openapi.yaml

@@ -3136,7 +3136,8 @@ paths:
           description: The queue ID (e.g., `queue_1234`), or the name of the queue when using the `type` body parameter.
           example: queue_1234
       requestBody:
-        required: false
+        required: true
+        description: At least an empty JSON object `{}` must be sent; a zero-length body is rejected with a 400.
         content:
           application/json:
             schema:
@@ -3190,7 +3191,8 @@ paths:
           description: The queue ID (e.g., `queue_1234`), or the name of the queue when using the `type` body parameter.
           example: queue_1234
       requestBody:
-        required: false
+        required: true
+        description: At least an empty JSON object `{}` must be sent; a zero-length body is rejected with a 400.
         content:
           application/json:
             schema:
@@ -4449,11 +4451,13 @@ components:
               format: date-time
               nullable: true
               description: When the concurrency limit was overridden
+              example: null
             combined:
               type: object
               description: |
                 The combined concurrency cap across all `concurrencyKey` values of the queue.
-                Present when the queue has a `combinedConcurrencyLimit`.
+                Always present; `current` is null when the queue has no combined limit, so
+                check `combined.current !== null` rather than the field's presence.
               properties:
                 current:
                   type: integer
@@ -4480,7 +4484,6 @@ components:
                   nullable: true
                   description: Runs currently in flight across all concurrencyKey values
                   example: 4
-              example: null
             overriddenBy:
               type: string
               nullable: true