A worker ends with its children

A gather ends with its children, and a worker’s body is a gather. A gather — a gather { … } form, or a worker’s body — owns every spawn or watch born inside it, a pipeline stage’s included: its brood, in birth order. On exit it applies one rule, exit_brood:

• return: each child still unclaimed is claimed and awaited in birth order, exactly as await would (await-is-the-block-run-here): its bytes join the gather’s own output, the first failure among them is the gather’s, and the rest are cancelled and drained within the cleanup grace. A normal return joins; it never cancels;
• halt — a raise, an escape, a stop: every unclaimed child is claimed, cancelled and drained within the grace; a body that panics cancels them without waiting;
• drain (I4′): on every exit the gather also waits, within the grace, for every child it started whose scope is cancelled and whose thread has not ended, however it came to be cancelled — the halt rule, a cancel in the body, a cancel through worker <id>. So nothing a gather started outlives it by more than the grace.

Claiming is atomic, so a child claimed elsewhere first — an await !{worker <id>}, a cancel — is no longer the brood’s to settle, and of that claimer and the gather’s join exactly one replays the child’s bytes and meets its ending. A child an outside party claimed and is still awaiting, uncancelled, is left to it. A block that starts workers has not finished until they have, so await of a worker is still its block run here, its last implicit step included. A run outside any gather has no brood: its births belong to the session.

Cancellation is hereditary. A gather’s birth hangs under the scope current when the gather was entered — a worker’s own node inside a worker, the run’s scope at a gather in a run — and a session birth under the session root. So cancel $h reaches everything $h started, and an interrupt or a wall on a run reaches its gathers’ children but never a session worker. A worker converts a Cancelled or TimedOut stop owned by any node but the session root into its own worker was cancelled / worker timed out error, so a cancel made inside the session is a failure the awaiter can try, while a stop the host owns passes as the escape it is. A gather that is not a worker converts nothing.

See gather (I3–I5, I4′), await-is-the-block-run-here (I6), cancellation, and docs/SPEC.md §11.1, §11.3.