/fix-issue — resolve a GitHub issue, branch → fix → PR

Turns a filed issue into a merge-ready change: understand, reproduce, fix with a test, verify, and open a PR that closes the issue. Never pushes or opens a PR without showing the diff first.

Steps

Load the issue. Resolve the arg to an issue number (bare number or full URL). Read it and its discussion:
```
gh issue view <n> --comments
```
Extract the actual problem, repro steps, acceptance criteria, and linked PRs/commits. If the issue is vague or already closed, say so and ask before proceeding — don't guess at scope.
Confirm scope (one beat). State in one or two lines what you're changing and what "done" means for this issue. If the issue is really several changes, do the smallest coherent one and note the rest. Don't expand scope beyond what the issue asks.