fix(cloud-agent-next): preserve wrapper cleanup backoff

[eshurakov]

Follow-up to #3555

• Preserve the persisted physical-wrapper cleanup deadline while explicit session deletion waits for verified wrapper absence, avoiding one-second retry churn that discards lease backoff.
• Remove the obsolete out-of-band SessionService.interrupt provider-kill stack and stale router-test scaffolding now that interruption routes through Durable Object-owned physical teardown.
• Add integration coverage proving explicit deletion retains the wrapper lease retry deadline.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

All previously flagged issues have been resolved; the new commit removes the redundant expect(result.lease.state).toBe('stop_needed') assertion as suggested.

Files Reviewed (5 files)

• services/cloud-agent-next/src/persistence/CloudAgentSession.ts — no issues
• services/cloud-agent-next/src/router.test.ts — no issues
• services/cloud-agent-next/src/session-service.ts — no issues
• services/cloud-agent-next/test/integration/session/deletion-lifecycle.test.ts — previous SUGGESTION resolved ✓

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_{Reviewed by claude-4.6-sonnet-20260217 · 168,855 tokens}

_{Review guidance: REVIEW.md from base branch main}