Reproduce a GitHub issue as a debug page

Goal: given a link to a public GitHub issue or PR, produce the smallest self-contained debug page at debug/<issue-number>.html that exercises the reported bug. A tired developer should be able to open it, see the bug, and start debugging in under a minute.

Why this matters

• Bug fixes start from a concrete, runnable repro. No repro → no fix.
• Issue reporters often give incomplete code. The repro fills gaps with the smallest viable style, data, and interactions.
• A focused page (one style, few sources, minimal UI) makes it obvious which component misbehaves.
• Future maintainers reopen the same page when regressions recur. Keep it self-describing.

Workflow

1. Read the issue carefully

Use gh issue view <N> --repo mapbox/mapbox-gl-js --comments (or gh pr view for PRs) to fetch the full body and comments. Do not rely only on the title or first paragraph — triage comments, maintainer replies, and attached code snippets usually contain the actual repro recipe.