lua-resty-adaptive-limit

Adaptive concurrency limiting for OpenResty: the allowed number of
concurrent requests against a protected upstream adjusts automatically
from observed completion latency and explicit overload signals, so
excess load is shed early instead of piling onto a saturating backend.

O(1) request-path admission on top of atomic lua_shared_dict
operations (~0.25us/op measured), one scheduler timer per worker,
deterministic windows with lease-based single-leader controller
updates, Gradient2 (default) and AIMD controllers, graceful-reload
state preservation, worker-exit reconciliation, stuck-pool
diagnostics, and no runtime dependencies beyond OpenResty >= 1.15.8.1.