Always preserve recovery and redrive safety invariants

Treat the user’s “never” requirements as strict invariants, especially around ownership changes, lease recovery, retries, interruption cleanup, and competing wakes. Implement fencing before every externally visible side effect so stale execution cannot dispatch providers, publish output, start or fail tools, promote recovery work, or arm wakes. Add focused regression tests that deterministically pause execution at the relevant boundary, mutate ownership or race another operation, resume execution, and assert exact outcomes—including zero forbidden events or requests, unchanged durable state, correct run counts, and cleanup of active coordination state.