[JacobStephens2]

Summary

Keep concurrent Ticket Runs owned through delivery and teardown, with child salvage finished before Spec worktree cleanup.

Spec run → child_run::Runs
  start       refuse outstanding duplicates → launch and retain
  next ending sweep every child → reap/join → oldest numbered ending
  drop        TERM every child → drain all → Worktree cleanup

Ticket scheduling, Spec PR accounting, progress, and standalone Base fix waiting keep their existing owners.

Closes #475

Evidence

• Before: dropping_a_collection_stops_all_siblings_before_waiting_and_saves_their_work failed with sequential shutdown: sibling salvage never completed within the finite fixture's lifetime.
  After: Ordinary drop and caught unwinding save both siblings' work, deliver one TERM per live child, reap every owned child, and preserve the Command interruption flag.
• Before: duplicate_start_is_refused_before_launch_and_keeps_the_original_child_owned failed because the original handle was replaced.
  After: Active and queued duplicates are refused before launch; delivered identities can be reused.
• 20 child execution tests, 49 Spec module tests, and all 60 end-to-end Spec tests pass, including parent-only sibling interruption/salvage and final drained-Ticket accounting.
• cargo fmt --check, cargo clippy --all-targets -- -D warnings, and full cargo test pass (one existing ignored test). The full suite was rerun after a transient ETXTBSY fixture launch failure; the affected test also passed in isolation.

Test seams

• child_run::Runs: construction, owned launch registration, next numbered ending, and collective cleanup on drop or unwinding, with finite local executables at the existing private launch seam.
• Existing standalone child Run execution and Spec run lifecycle interfaces, including parent-only sibling interruption/salvage and final drained-Ticket accounting.

Merge Danger

Door: two-way

No persistent data or command-policy changes; reverting restores the previous supervision implementation.

Blast Radius: Spec

Concurrent Ticket Run supervision and Spec owner teardown. Standalone Base fix execution continues its existing blocking wait.

Unaddressed findings

Standards

None. The repeated cleanup assertions were consolidated into a fixture helper.

Spec

None. Completed-child setup now waits for process and reader completion at the private launch seam, removing the queue tests' scheduling assumption.

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