Add review-open-issue skill documenting bug-issue triage practices

.github/skills/review-open-issue/SKILL.md

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+# Skill: Review an open issue for TheAlgorithms/Python
+
+Triage an open issue — most often one carrying the `bug` label — **together with
+every pull request attached to it**, and produce a verdict a maintainer can act on
+without re-doing the work. The goal is a review that any triager (human or AI) can
+run the same way every time, and that ends in an explicit list of `Closes #NNNNN`
+lines the maintainer can paste into a merge commit.
+
+This repo exists to **teach visitors to fix bugs by doing**. So the default is to
+merge adequate existing contributor work, not to open a fresh PR that races them.
+Only open your own PR when no attached PR adequately solves the issue.
+
+## How to run this skill
+
+### 1. Reproduce before you trust the report
+
+- Check out current `master` and actually **run the failing case** from the issue.
+- If it reproduces, say so and paste the minimal reproducer (inputs → observed
+  output, e.g. `nan` + a `RuntimeWarning`).
+- If you **cannot** confirm it locally — an optional dependency isn't installed,
+  the failure needs an external service, the report is too vague — **say that
+  explicitly rather than guessing.** "Not reproducible in a vanilla checkout"
+  is a real, useful verdict.
+
+### 2. Classify the issue
+
+Sort each issue into one bucket and act accordingly:
+
+- **Confirmed bug with an adequate open PR** → recommend the specific PR to merge.
+- **Confirmed bug, no adequate PR** → open a new PR yourself (see step 5).
+- **Not a bug / working-as-intended** → recommend closing, and explain why (e.g.
+  binary search returning *an* index of a duplicate is correct, not a defect).
+- **Feature request mislabeled as a bug** → recommend dropping the `bug` label; do
+  **not** close it as a bug.
+- **Too vague / needs reporter info** → comment **on the issue itself** asking for
+  the one concrete thing missing (a file path, a traceback, a reproducer), and note
+  it should be closed if no answer arrives.
+- **Environment / optional-dependency, not an algorithm defect** → note it needs
+  someone with that environment; it is not fixable in a vanilla checkout.
+
+### 3. Examine every attached PR — pick one, name the duplicates
+
+For a bug with several open PRs:
+
+- **Verify each fix's doctest values numerically** against a trusted reference
+  (`scipy`, `numpy.linalg`, `geopy`, or a brute-force check over random inputs).
+  Don't take a doctest's word for it — confirm the number.
+- Prefer the **first-in PR with the smallest correct diff** that follows repo
+  convention (doctests over new test files, `raise` over `assert`, no unrelated
+  reindentation or churn of clean doctests into floating-point noise).
+- **Reject out-of-scope "fixes"** — e.g. swapping a real divide-by-zero for a
+  `1e-15` magic constant makes results implementation-defined. Fix the issue, not
+  more.
+- Identify the byte-for-byte **duplicates** so the maintainer can close them with
+  thanks in the same action.
+
+### 4. Emit the verdict — fixed output shape
+
+Post one comment that a maintainer can act on directly. For each issue give a
+one-line rationale and the exact autoclose line. Two formatting rules matter a lot
+to human maintainers scanning the thread:
+
+- **Start every line that references an issue or PR with a Markdown list marker
+  (`-` or `* `).** GitHub-flavored Markdown only autolinks `#NNNNN` inside a list,
+  and those autolinks are colored — **purple = merged, red = closed, green = open** —
+  so the maintainer can see merge/close progress at a glance. A bare `#14813` at the
+  start of a line does not autolink.
+- **Merging a PR that closes an issue also closes the issue's other open PRs**, so
+  fold the duplicates into one autoclose statement rather than listing the winner
+  alone:
+
+  ```text
+  * #14813 — 3x3 inverse returns the transpose → merge #14821
+    (Closes #14813, Closes #14840, Closes #15045)
+  ```
+
+Recommended shape:
+
+```text
+## Confirmed bugs with an adequate open PR — merge
+* #<issue> — <one-line what/why> → merge #<pr> (Closes #<issue>, Closes #<dupe>, …)
+
+## Not a bug / not merge-ready
+* #<issue> — <feature-request → relabel | needs cleanup | needs a human call>
+
+## Summary — lines to add
+* Closes #<issue> → #<pr>
+```
+
+### 5. When you must open your own PR
+
+If no attached PR is adequate, open one — but let the contributors keep the credit
+where their work was close. Use autoclose keywords in the **commit message body**
+so the merge closes the issue *and* the superseded PRs:
+
+```text
+Fixes #12233
+Fixes #12262
+Fixes #13635
+```
+
+Follow the [`new-pull-request`](../new-pull-request/SKILL.md) skill for the
+mechanics (synced `master`, named branch, checked description box, untouched
+`uv.lock`).
+
+## Tone
+
+Be specific and kind. Name the exact PR and the exact reason, credit the
+contributor by handle, and offer runners-up detailed feedback so they learn — the
+point of the repo is that people come back and fix the next one.