:sig
pid_t task(String key, std::function<void()> exec_func, u64 timeout = 60*10)

:params
key : string uniquely identifying the task across the whole runtime instance
exec_func : function to execute
timeout : maximum run time in seconds; `0` disables the timeout
return value : the process ID of the started (or still running) task, or `0` when the task could not be started

:see
>task
task_pid
task_kill
task_repeat

:content
Starts `exec_func` in a new process and returns that process ID.

If a process with the same `key` is already running anywhere in the runtime instance, `task()` does not start a second copy. Instead it returns the PID of the already-running task. Coordination is through a shared task status file under `BIN_DIRECTORY`, so the key applies across workers, not just the current worker process.

Task keys may contain ordinary user-facing text. UCE hashes the key before using it as an internal lock/status filename so slashes and other path-like characters cannot escape the task state directory.

`timeout` is enforced in the child process with an alarm. The default is ten minutes. Pass `0` only for tasks that have their own shutdown path.

Related:

- PHP: background-process patterns using `proc_open()`, queues, cron, or worker supervisors
- JavaScript / Node.js: Node `child_process`, worker queues, timers, schedulers, and supervised background jobs
