vLLM × PyTorch torch-nightly CI root-cause

Read-only root-cause analysis for the vLLM torch-nightly triage cron. The upstream triage job runs the A/B (torch nightly vs same-commit baseline), parses the logs, and hands off artifacts; this skill reads that artifact, root-causes each regressed cluster, groups by shared cause, routes each cause to the right repo, and writes its findings to findings.md / findings.json. It has no Buildkite/ClickHouse access, files no issues, and retries no jobs — tools are Read, Glob, Grep, Write.

Routing knowledge derived from the multi-week triage of vLLM PR #40077 (torch 2.12.0 + triton 3.7.0), which filed 16+ issues under umbrella pytorch/pytorch#180899.

Step 1: Read the cluster logs