Fallback to new Reaper when reused Reaper is unreachable

[cristianrgreco]

Summary of changes

• Make Reaper reuse best-effort: if connecting to a discovered running Reaper fails, try other candidates and then create a new Reaper in the same lock cycle.
• Update Reaper discovery to return all running candidates and prefer newer ones first.
• Add a regression test that simulates an unreachable reused Reaper and verifies fallback creation of a new Reaper.

Verification commands run

• npm run format
• npm r