Preserve test-run dispatch scope

## Parent

#674

## What to build

Apply the dispatch contract consistently to test runs. A draft parent test run must still execute the child's Published artifact, child executions must inherit the parent's run kind, and detached test children must remain independent of parent completion while being cancelled when the enclosing test-run scope expires or is torn down.

Covers parent user stories 30–32.

## Acceptance criteria

- [ ] A draft parent test run resolves and executes the selected child's Published artifact rather than a child draft.
- [ ] Test and production run kind propagates from parent to child and is visible in runtime lifecycle inspection.
- [ ] A detached test child may continue after ordinary parent test completion.
- [ ] Expiring or tearing down the enclosing test-run scope idempotently cancels all still-live detached children created within that scope.
- [ ] Waited test children retain the same completion, fault, and cancellation outcomes as production children.
- [ ] Test-scope cleanup cannot cancel an unrelated production child or a child from another tenant or partition.
- [ ] Groundwork restart and race tests cover scope teardown before and after child materialization.

## Blocked by

- #677
- #680

Start with the parent user stories in #674 and resolve the blockers in #677 and #680 before locating the test-run dispatch and scope-lifecycle entry points. Use the acceptance criteria as the completion checklist, including restart and race coverage for teardown before and after child materialization, and verify isolation across tenants and partitions.

Written by the indexing model from the issue text.