XY-903: Fix terminal finalize lane recovery

[yvette-carlisle]

Summary

• persist durable private completion intent and terminal finalize events before accepting terminal tracker exits
• recover accepted terminal finalize paths when app-server returns an error after the finalize tool call, preserving repo-gate/writeback semantics
• allow forced hard interrupt fallback for lane_not_active soft interrupts only when a recorded live process still exists

Validation

• cargo make test
• cargo make check
• cargo run -p decodex --bin decodex -- probe stdio://
• git diff --check