HF 4.16.3

Engine: 4.16.3.

• Avoid copying the retained queue when discovery found no events for the current phase. Discovery and the nonempty removal filter stay unchanged.
• In one instrumented seed-21 aborted 31-day prefix using fresh Node 26.12 Worker isolates, the private prototype was faster in all seven fixed pairs: paired median reduction 1.271188 s; median per-pair relative reduction 9.424452%. Complete native/raw-host values and counts matched in all 17 runs. See the experiment for the method and limits.
• This is a finite prototype result, not browser, full-game, save or two-second qualification. The fixture did not exercise nonempty discovery. Before the version bump, published 4.16.2 and the identity-preserving private prototype both replayed the 777-transaction native checkpoint; that is not a 4.16.3 save.
• Migration: older 4.x saves require a fresh start under the existing exact-engine policy. No legacy continuation, archive repair or retagging is added.