implement-change

Imported from verdaccio/verdaccio (.agents/skills/implement-change/SKILL.md). Install upstream with npx skills add verdaccio/verdaccio --skill implement-change. Copyright stays with the author.

Implement a change

Apply AGENTS.md. Keep repository policy there; this skill connects implementation to the testing-changes, review-code, and pull-requests workflows.

Understand the problem before adding code

Establish the intended behaviour and concrete success criteria from the request, the issue, or the reproduction. For a bug, reproduce it first when practical: pnpm build, start a registry (pnpm start, or node packages/verdaccio/bin/verdaccio --config <yaml> --listen 4873), and run the client command from the report against it. A reporter's npm install symptom is a registry route plus a client expectation; find both.

Decide which release lines the work concerns:

• A feature lands on master only.
• A bug fix lands on every supported line that has the bug: master first, then a port to 6.x (binary) and/or 8.x (internal modules 6.x consumes). Check whether the code path exists there before promising a port, and say in the PR when it is pending.

Check whether Verdaccio can already do it. Configuration (packages/config/src/conf/default.yaml documents the keys), package-access rules (access/publish/unpublish with groups), uplink options (maxage, timeout, fail_timeout, cache, auth), bundled plugins, middleware and filter plugins, and the web UI settings cover a lot. If an existing capability fully solves the request, the deliverable is an explanation and possibly a documentation change; if it partly solves it, extend the owning feature rather than adding a parallel one. Respect an explicitly requested behaviour that nothing existing provides.

Anything a package manager observes is a contract. Before changing a status code, header, packument field, tarball URL, or auth flow, check what registry.npmjs.org and the npm CLI (npm/cli) do, and remember the e2e matrix runs npm, pnpm, yarn modern (3 and 4), bun, and deno.

Put it in the owning layer

Trace the request through the layers before editing: api/web (routing, status, response shape) → store (local versus uplink merge, filters, stage) → local-storage or the storage plugin (files) and proxy (uplink HTTP); auth for identity and access; config for parsing and defaults; core for pure helpers.

Ask where the behaviour belongs, which abstraction it extends, and what else observes it: a validation added only in an api route leaves the web UI and every plugin exposed; a change in store affects every storage plugin. Changes to interfaces in @verdaccio/types break third-party plugins and are major. Prefer a coherent extension over a local workaround, and keep refactoring bounded to the change.

Reuse before you write

Search packages/core/core/src/*-utils.ts, @verdaccio/config, the store lib helpers, and @verdaccio/test-helper before writing a helper. If the logic exists but is not exported, export or move it and update the callers. Preserve meaningful differences; do not force unrelated behaviour into one generic function because it looks similar. Prefer a maintained package to a hand-rolled parser or escaper, added to the narrowest package that needs it (and older than the workspace's seven-day release-age rule).

Implement and validate

Implement the smallest cohesive change that meets the success criteria. Follow the conventions in AGENTS.md: errorUtils and HTTP_STATUS for errors, the package logger instead of console, streams for tarballs, import.meta.dirname, minimal comments, no swallowed errors.

Add tests that prove the observable contract at the right level: a unit test for a helper, a packages/api integration test for a route, a nocked uplink for store and proxy behaviour, and an e2e scenario only for client wiring. A bug fix ships with a regression test that fails without it.

Add one changeset for the PR, naming every published package it touches (patch for fixes, minor for features, major for breaking config, plugin, or HTTP contract changes), written as a release note without exploit detail. Update docs/migrations-guide.md for breaking changes and docs/warnings.md for a new warning code.

Rebuild the packages you touched, then use testing-changes to run their tests, their dependents' tests, and the client-facing suites the change can affect. Investigate every failure. Then review the complete diff with review-code, fix the verified findings, and rerun the checks the fixes touch.

Report what changed, what existing capability was considered and why it was not enough, the reuse or extraction chosen, the release lines covered and the ports still pending, and exactly what was validated. Commit, push, or open a PR only when the user or the calling workflow authorises it; use pull-requests when taking the change through a PR.