Reworked engine_request_min_interval_ms from start-spacing to a proper
post-completion gap: _rate_acquire holds a per-engine lock for the whole
request, _rate_release frees it only `interval` ms AFTER completion (via
loop.call_later, non-blocking) — so consecutive requests to the engine
are ALWAYS separated by at least that idle GPU time regardless of request
duration. Wired acquire/release into all 3 inference dispatch paths with
release in every finally/early-return. _rate_acquire refreshes config on
mtime change so a value saved in the web UI applies to the next request.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014S8VtAvG499SsCbeESRK7V