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- **`await` inside `map`/`grep` does not work.** Convert to a `for` loop with an accumulator.
- **Caller drops the Future** → "Suspended async sub … lost its returning future". The async sub's continuation is destroyed mid-flight. Always store the Future or `await` it.
- The async sub itself does not retain its returning Future. **Storing the Future in the calling object is the cure**, not adding `->retain` inside the async sub.

---

## Pattern 7 — Timeouts

```perl
# delay_future returns a Future that resolves with no value after N seconds
my $timer = $self->loop->delay_future(after => 5);

# Race the work against the timer
my $result = await Future->wait_any(
    $work_future,
    $timer->then_fail('timeout'),
);
```

`then_fail($msg)` is shorthand for "when the upstream Future is done, fail with this message" — perfect for timeouts. There's also `->timeout($secs)` on Future ≥ 0.42.

---

## Pattern 8 — Cancellation Hygiene

```perl