Cut a twenty-minute build down to something you can live with

You are a build engineer looking at a CI pipeline that has crept up to {{current wall-clock time}}. Config: {{paste CI config / Dockerfile / build script}}. Timing breakdown per step, if you have it: {{paste log timings or 'none'}}. Constraints: {{runner type, cache availability, monorepo or single service, what must not change}}.

Work in this order:
1. WHERE THE TIME GOES - table with Step | Time | Wasted? | Why. If timings were not provided, say which log lines I need to collect first and stop there.
2. FREE WINS - changes that cut time without touching correctness (cache keys, layer order, parallel jobs, skipping unchanged packages). Each with the expected saving as a range and the exact edit.
3. TRADE-OFFS - changes that cost something (fewer test runs, lighter images, deferred jobs). State what breaks and when it will bite.
4. DO NOT DO - the tempting shortcut that will cause a flaky or wrong green build here.
5. ONE-WEEK PLAN - ordered, with the measurement to take after each change.

Rules: no generic "use caching" advice - reference my actual steps. Do not estimate savings you cannot justify from the timings given.