fix(cloud-agent-next): recover cold attach after idle stop

[eshurakov]

Release a completed retryable attach proof so the next drain can issue a new session.attach after QUEUE_RETRY_MS, then prompt. Do not retire kilo when session.preparing receipts expire, and allow attach when kilo is not yet ready so retries are not deadlocked.

Stack

Remaining control-plane recovery stack. #5912–#5918 are merged. Merge from the bottom.

1. fix(cloud-agent-next): control-plane recovery follow-ups #5919 eshurakov/recovery-stack → main
2. fix(cloud-agent-next): release unadmitted queued messages on quarantine #5920 eshurakov/recovery-not-ready-retry → eshurakov/recovery-stack
3. fix(cloud-agent-next): recover cold attach after idle stop #5957 eshurakov/recovery-cold-bootstrap-attach → eshurakov/recovery-not-ready-retry
4. fix(web): keep Cloud Agent workspace tabs stable during progress #5958 eshurakov/ca-stable-workspace-tabs → eshurakov/recovery-cold-bootstrap-attach

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (17 files)

• packages/cloud-agent-sdk/src/normalizer.ts
• packages/cloud-agent-sdk/src/normalizer.test.ts
• services/cloud-agent-next/src/persistence/SandboxControl.ts
• services/cloud-agent-next/src/sandbox-control/diagnostics.ts
• services/cloud-agent-next/src/sandbox-control/diagnostics.test.ts
• services/cloud-agent-next/src/sandbox-session/SandboxSession.ts
• services/cloud-agent-next/src/sandbox-session/control-dispatch.ts
• services/cloud-agent-next/src/sandbox-session/control-dispatch.test.ts
• services/cloud-agent-next/src/sandbox-session/recovery/failed-snapshot-uses-terminal-failure.test.ts
• services/cloud-agent-next/src/sandbox-session/session-message-queue.ts
• services/cloud-agent-next/src/sandbox-session/session-message-queue.test.ts
• services/cloud-agent-next/test/integration/sandbox-control.test.ts
• services/cloud-agent-next/wrapper/src/control/control-event-transport.ts
• services/cloud-agent-next/wrapper/src/control/control-event-transport.test.ts
• services/cloud-agent-next/wrapper/src/control/sandbox-control-handlers.ts
• services/cloud-agent-next/wrapper/src/control/sandbox-control-handlers.test.ts
• services/cloud-agent-next/wrapper/src/control/session-operation.ts

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_{Reviewed by grok-4.6 · Input: 190.2K · Output: 31.9K · Cached: 1.9M}

_{Review guidance: REVIEW.md from base branch eshurakov/recovery-not-ready-retry}