feat(snapshot): complete concurrent PageBroker staging

[dfeigin-nv]

Adds concurrent PageBroker request handling and bounded terminal transaction retention.

Validation: make -C deploy/snapshot/pagebroker test daemon, go test ./internal/pagebroker, Helm lint/render, and git diff --check.

Concurrent restore E2E (commit c19741ace6): on aws-k3s-eu-north, namespace runai-test, two restore requests were submitted 48 ms apart. Both restore pods became Ready; PageBroker staged and committed separate transaction IDs; agent logs reported CRIU restore completion for both.

[devin-ai-integration]

Devin Review found 4 potential issues.

View 1 additional finding in Devin Review.

[datadog-official]

 

⚠️ Warnings

🚦 3 Pipeline jobs failed

Pre Merge | pre-commit     

🔧 Fix in code. This looks caused by changes in this PR.

Pre-commit hooks made changes that need to be committed.

Docs link check | lychee     

See error

Multiple resources not found returning 404 status codes from several documentation links.

Pre Merge | pre-merge-status-check     

📋 Copy prompt for your agent

CI on my pull request is failing. Help me find and fix the root cause of each failing job below — they were flagged as caused by changes in this PR, so focus on the diff. For each job, explain the failure and propose a fix.

Branch: pagebroker-daemon-concurrency

Pre Merge | pre-commit
Commit: 9d1d91094e9f24fc887537f87e9471a138521fd6
Error (code / build):
Pre-commit hooks made changes that need to be committed.
CI job: https://github.com/ai-dynamo/dynamo/actions/runs/31950955588/job/95174284371

ℹ️ Info

🔄 Datadog auto-retried 3 jobs - 3 passed on retry

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 48.19% (-1.48%)

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[dfeigin-nv]

Moved to ai-dynamo/snapshot#94.