benchkeeper 6.15

• maintaining-repos covers general improvement and cleanup (#274): the pass now starts on a clean tree and adds three parts, each in a file next to SKILL.md that is read only when its part runs: cleanup with a tool table per stack and pinned versions (tools.md: knip, jscpd, dependency-cruiser, with the Python and Rust candidates marked unverified), architecture checks (architecture.md: cycles, forwarding modules, one source of truth, documented against actual structure, and what to do without a GLOSSARY.md or ADRs), and a test audit by mutation testing (test-audit.md: StrykerJS through its command runner, a bound of one module per run, concurrency 4, a memory cap, a heap cap and a per-mutant timeout, survivors sorted into equivalent, unreachable, message and gap, and a test is removed only when the module's mutation result is unchanged without it). The report is one ranked list with a local baseline file, .benchkeeper/maintenance.json, that the next pass compares against. The rule "remove a test only together with the code it covers" now also allows removal with a recorded reason. The description stays a user-started skill (disable-model-invocation), so it costs no context in Claude Code. New eval set skill-maintaining-repos (should-not-load cases; not run). Evidence: the research comment on #274 and evaluations/practices/code-health-pass.md.
• Plugin version 6.15.0.
• Upgrade: npx benchkeeper@6.15.0 apply.