Add Claude Code skills for bug reporting, fixing, PR review, and performance work

[SanderMuller]

Follows the same pattern as the existing regression-test skill: workflow guidance for Claude Code under .claude/skills/, complementing CLAUDE.md.

Four skills, one per stage of contributing to PHPStan:

• bug-reporting: turn an observation into a verified root cause and a reproducible issue.
• bug-fixing: reproduce, write the failing test first, fix the root cause, pass the full gate (tests, self-analysis, coding standard, e2e), then open the PR.
• pr-review-feedback: apply review feedback with critical evaluation, re-run the gate, and confirm CI is green before replying.
• performance-work: decide whether a perf problem is a fix or an issue, measure honestly on real code with the result cache cleared, and frame the change for review.

These are distilled from the workflow behind my recent contributions here (e.g. #6086, #5933, #5992, #5961, #5929), not written in the abstract. Each skill ends with a verification step that runs the concrete gate and reads its output, so "done" means the checks actually passed. That discipline comes from real near-misses these caught during that work: a test fixture committed in the wrong state, a coding-standard slip found only after a push, and an optimization that silently never fired yet still passed byte-identical output.

They lean on CLAUDE.md for the type-system principles instead of repeating them.

[ondrejmirtes]

I will take a look but I'm not sure we need these skills since Claude was able to perform the work without them so far.

[ondrejmirtes]

No, sorry, I don't think this is necessary, there's overlap with regression-test skill and it's something that Claude does very well on its own already.

On the other hand, we have this workflow https://github.com/phpstan-bot/phpstan-src/blob/2.2.x/.github/workflows/claude-fix-issue.yml (notice it's a fork, outside of phpstan org) with a big prompt. If some of that was extracted to a skill that could live here in phpstan-src, that would be useful.