Keep Rescue attached through yielded execution

[vitry]

What to build

Keep the named and generic Rescue forwarders attached to the one original companion execution until it reaches a real exit code. Partial stderr, heartbeats, or an outer code-cell completion must not terminate the child turn or leave the companion running after the child stops.

Acceptance criteria

• A companion fixture that runs beyond the initial terminal yield keeps the Rescue child active until the same execution exits.
• The child polls only the original execution handle and never starts a second companion command.
• Named Role and generic compatibility instructions enforce the same terminal-completion contract.
• needs-choice remains terminal with exit code 3 and same-child continuation remains unchanged.
• Installed-role qualification proves no early child completion or orphan companion process.

Blocked by

None — can start immediately.