GetMemoryFootprint() returned a constant 0 with a stale "PR 4.4 sets this" comment
even though PR 4.4 shipped the SubscriptionRegistry. Replace with a live estimate:
64 bytes × TrackedItemHandleCount + 256 bytes × TrackedSubscriptionCount. A 50k-tag
set now registers ~3 MB with the server's cache-flush heuristic instead of being
invisible. Returns 0 when no subscriptions are active.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
ecc91b0e48