MAINT: Triage the pre-2021 issue backlog

Problem

The open issue backlog is 62 items with a median age of 3,688 days — 10.1 years. Forty-six (74%) are older than five years, and the age distribution is bimodal (nothing between 1 and 2 years old): a small live set from the last year, and a 46-issue archaeological layer that predates the current maintainer team.

Not all of it is worthless. #47 — "Refactor matrix equations", open twelve years — is still referenced by a live TODO in _matrix_eqn.py:8. These are unowned rather than invalid, and the distinction matters for how they are closed.

Proposed approach

Work the 46 pre-2021 issues in one campaign, each landing in exactly one of four outcomes: close as wontfix with a one-sentence reason; close as duplicate linking the survivor; adopt with a Type label and a current-state comment; or move to a Someday milestone if it is a genuinely good idea nobody will start soon (what the wishlist label has been standing in for).

Resist mass-closing with a bot comment: 46 issues at a couple of minutes each is a bounded afternoon, and several encode institutional knowledge about the quadrature and matrix-equation code that is written down nowhere else.

Two long-lived open PRs belong in the same pass: #576 (5+ years, type annotations — see the type-hint policy discussion in this milestone) and #702 (3+ years, vectorise lorenz_curve/gini).

Acceptance criteria

• All 46 pre-2021 issues reach one of the four outcomes
• Every close carries a reason and a wontfix or duplicate label
• Every surviving issue carries exactly one Type label; unlabelled items triaged
• PRs #576 and #702 are merged, rebased, or closed with a reason

From the July 2026 technical-debt audit (AI-assisted; claims verified against 28d4b3b on 2026-07-25).

Start by reviewing the 46 pre-2021 issues, with particular attention to the live TODO in _matrix_eqn.py:8 and the institutional context around the quadrature and matrix-equation code. Also inspect PRs #576 and #702 and the type-hint policy discussion. Done means every old issue has one of the four stated outcomes, surviving issues have exactly one Type label, and both PRs are merged, rebased, or closed with a reason.