docs(wait): separate compute billing from concurrency release (#4405)

The wait docs describe the 5 second compute-billing threshold as if it
were also the suspension threshold. It isn't, and the gap is confusing
when you're sizing a poll interval:

- **Compute** stops being charged for any wait longer than 5 seconds.
- **Concurrency** is only released once the machine has been snapshotted
and shut down. For `wait.for` and `wait.until` that happens 60 seconds
into the wait — a shorter wait stays `EXECUTING` and holds its
concurrency slot for the whole wait, even though the compute is free.

So `await wait.for({ seconds: 30 })` in a polling loop never releases
its slot, which looks like a bug if the docs told you waits over 5
seconds checkpoint.

## Changes

**`docs/snippets/paused-execution-free.mdx`** — rendered on `/wait`,
`/wait-for` and `/wait-until`. Drops "we checkpoint and" from the
billing sentence so it's purely about compute, then adds one paragraph
for the concurrency half.

**`docs/queue-concurrency.mdx`** — the "Waits and concurrency" section
states flatly that waiting runs don't consume slots. Adds a short
subsection for the time-based exception.

**`docs/how-to-reduce-your-spend.mdx`** — "Waits longer than 5 seconds
automatically checkpoint your task, meaning you don't pay for compute" →
the compute claim only. Code comments follow, plus a pointer that
waiting doesn't always free concurrency.

**`docs/how-it-works.mdx`** — the Checkpoint-Resume walkthrough used
`wait.for({ seconds: 30 })` as *the* example of a wait that suspends.
Bumped to 5 minutes and noted the sub-60s exception.

No behaviour change — docs only.

Author: matt-aitken

docs/how-it-works.mdx

@@ -148,7 +148,7 @@ Here's how the Checkpoint-Resume System works:
 
 2. **Subtask Handling**: If a task needs to trigger a subtask, it can do so and wait for its completion using `triggerAndWait`
 
-3. **State Checkpointing**: While waiting for a subtask or during a programmed pause (e.g., `wait.for({ seconds: 30 })`), the system uses CRIU (Checkpoint/Restore In Userspace) to create a checkpoint of the task's entire state, including memory, CPU registers, and open file descriptors.
+3. **State Checkpointing**: While waiting for a subtask or during a long programmed pause (e.g., `wait.for({ minutes: 5 })`), the system uses CRIU (Checkpoint/Restore In Userspace) to create a checkpoint of the task's entire state, including memory, CPU registers, and open file descriptors. A `wait.for()` or `wait.until()` shorter than 60 seconds doesn't checkpoint — see [Wait](/wait).
 
 4. **Resource Release**: After checkpointing, the parent task's resources are released, freeing up the execution environment.
 
@@ -178,9 +178,9 @@ export const parentTask = task({
     console.log("Child task result:", result);
 
     // This will also cause the task to be checkpointed and suspended
-    await wait.for({ seconds: 30 });
+    await wait.for({ minutes: 5 });
 
-    console.log("Resumed after 30 seconds");
+    console.log("Resumed after 5 minutes");
 
     return "Parent task completed";
   },

docs/how-to-reduce-your-spend.mdx

@@ -170,25 +170,25 @@ export const boundedTask = task({
 
 ## Use waitpoints instead of polling
 
-Waits longer than 5 seconds automatically checkpoint your task, meaning you don't pay for compute while waiting. Use `wait.for()`, `wait.until()`, or `triggerAndWait()` instead of polling loops.
+You don't pay for compute during any wait longer than 5 seconds. Use `wait.for()`, `wait.until()`, or `triggerAndWait()` instead of polling loops.
 
 ```ts
 import { task, wait } from "@trigger.dev/sdk";
 
 export const waitpointTask = task({
   id: "waitpoint-task",
   run: async (payload) => {
-    // This wait is free - your task is checkpointed
+    // You aren't charged for compute during this wait
     await wait.for({ minutes: 5 });
 
-    // Parent is also checkpointed while waiting for child tasks
+    // The parent isn't charged either while it waits for a child task
     const result = await childTask.triggerAndWait({ data: payload });
     return result;
   },
 });
 ```
 
-[Read more about waitpoints](/wait-for).
+Waiting saves you compute, but it doesn't always free up concurrency — see [Wait](/wait).
 
 ## Use debounce to consolidate multiple triggers
 

docs/queue-concurrency.mdx

@@ -199,6 +199,10 @@ For example, if you have a queue with a `concurrencyLimit` of 1:
 - When the executing run reaches a waitpoint and checkpoints, it releases its slot
 - The next queued run can then begin execution
 
+### Short time-based waits keep their slot
+
+Checkpointing takes time, so a run doesn't checkpoint the moment it reaches a waitpoint. For [`wait.for()`](/wait-for) and [`wait.until()`](/wait-until) it happens 60 seconds into the wait, so anything shorter stays `EXECUTING` and holds its slot for the whole wait. If you're polling in a loop, use an interval comfortably above 60 seconds so the slot is actually released between polls.
+
 ### Waiting for a subtask on a different queue
 
 When a parent task triggers and waits for a subtask on a different queue, the parent task will checkpoint and release its concurrency slot once it reaches the wait point. This prevents environment deadlocks where all concurrency slots would be occupied by waiting tasks.

docs/snippets/paused-execution-free.mdx

@@ -1,4 +1,6 @@
 In the Trigger.dev Cloud we automatically pause execution of tasks when they are waiting for
 longer than a few seconds.
 
-When triggering and waiting for subtasks, the parent is checkpointed and while waiting does not count towards compute usage. When waiting for a time period (`wait.for` or `wait.until`), if the wait is longer than 5 seconds we checkpoint and it does not count towards compute usage.
+When triggering and waiting for subtasks, the parent is checkpointed and while waiting does not count towards compute usage. When waiting for a time period (`wait.for` or `wait.until`), a wait longer than 5 seconds does not count towards compute usage.
+
+Free compute isn't the same as freed concurrency: the concurrency slot is only released once we've snapshotted the machine and shut it down. For `wait.for` and `wait.until` that happens 60 seconds into the wait, so anything shorter stays `EXECUTING` and holds its slot for the whole wait.