Focused TDD build plan for the engine: topology decision baked in (Option 1
standalone fleet as the software model, cluster-per-datacenter as the growth
target — hosts get datacenter + nullable cluster fields, placement filters by
datacenter). Covers data model, DB-state-machine orchestrator, 15 customer steps,
new ProxmoxClient, Stripe idempotent intake, and wiring the existing admin/customer
progress views to real data via Reverb. References the state handoff for workflow.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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