#2520 bench: measure resident lookahead on RX 7900 XTX

Description

## Title

bench: measure resident lookahead on RX 7900 XTX

Issue: Refs #1922. Measurements for #2476.

## Summary

This adds the full performance report for the resident-expert lookahead policy in #2476. On a Ryzen 5 7600X / RX 7900 XTX with IQ1_M, 11 matched English pairs improved decode throughput by **1.67%** (approximate 95% interval: **0.80–2.58%**) and reduced request CPU time by **6.10%** (**5.26–7.06%**).

The run used 12 balanced, randomly ordered ON/AUTO pairs and two ON/ON controls: 28 engine starts, 84 requests and 50,400 generated tokens. Each arm used the same executable, a 600-token warmup, and 600-token English and code requests. All observations are retained, including unmatched work and the startup rejected for partial residency.

## What changed

- A [report](https://github.com/KeyanHu-git/Strata/blob/e4821fe7edb330668c139460b0deb1fe2d50a7f1/bench/results/2026-10-15-rx7900xtx-resident-lookahead/README.md) with hardware, build identity, configuration, method, all-run medians/ranges and each paired result.
- All request timings, output IDs, MTP and expert-tier counters, startup excerpts, fixtures, schedule and exclusion reasons in JSON/CSV.
- Figures in PNG, SVG and PDF, plus plotting, analysis, verification and rerun scripts.
- The earlier five-pair check, kept separately because it used a shorter warmup.

## Extra Notes

The included English pairs have identical output, MTP work and expert-tier counts; nine were faster and all eleven used less CPU time. Code has four matching pairs and remains exploratory under the predeclared minimum of eight.

Validation: the published data reproduces every eligibility decision and statistic; the portable runner's schedule and failure cleanup pass two offline tests. Figures were rendered and inspected. Machine paths and unrelated service metadata were removed. This report changes no engine source.

![English paired effects](https://raw.githubusercontent.com/KeyanHu-git/Strata/e4821fe7edb330668c139460b0deb1fe2d50a7f1/bench/results/2026-10-15-rx7900xtx-resident-lookahead/figures/english.png)