Extends SchedulerState with running_overlays / refresh_running /
blocked_servers_by_overlay, and updates can_start with the truth table:
install and refresh_workshop_items are global mutexes; build_overlay
serializes per-overlay; server jobs block on builds for any overlay
their blueprint references.
Adds enqueue_build_overlay coalescing helper that returns an existing
queued job for the same overlay rather than inserting a duplicate.
Adds run_job dispatch for build_overlay (BUILDERS[overlay.type].build)
and refresh_workshop_items (re-fetches metadata, re-downloads on
time_updated/filename change, enqueues coalesced rebuilds for affected
overlays).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>