Owns the :mailglass_rate_limit ETS table and the small amount of work that must be serialized: missing-key admission, the bounded contention fallback, and idle sweeping. Callers use AtomicBucket's compare-and-swap fast path; only a caller that exhausts that finite budget enters this mailbox.

ETS opts (OTP 27+)

• :set — single-entry-per-key bucket
• :public — cross-process read/write without owner-forwarding
• :named_table — caller references :mailglass_rate_limit directly
• read_concurrency: true — hot read path optimization
• write_concurrency: :auto — OTP 27 flag for lock striping
• decentralized_counters: true — OTP 27 flag, per-scheduler counters

Crash semantics

If this process crashes, BEAM deletes the ETS table. The supervisor restarts TableOwner and ensure_table/0 recreates the canonical table before every owner ETS operation, including a caller that deleted the table immediately before admission. Bucket state is intentionally ephemeral across a restart; callers either re-admit through the replacement owner or receive the normal bounded limiter denial, never an ETS exception.

Reserved-singleton note

This module uses name: __MODULE__. It is library-internal machinery (not a user-facing singleton) and documented in docs/api_stability.md as a reserved singleton. NoDefaultModuleNameSingleton has an allowlist entry for this module.