Port Features skill

Port Features

Upstream code is the spec for the feature's behavior. Every guard, ordering, timeout, and odd branch in it may be a bug fix someone already paid for. A rewrite from your understanding of the feature drops the ones you didn't notice.

A port doesn't stop at the copy. The result must read as if this project wrote it: the feature is naturalized, in its names and in the environment it runs in.

1. Start from the code. Get a local checkout of upstream with its history, pin the exact commit, and read the feature's real files, not a screenshot, summary, or fetched snippet. Follow imports and callers until you know which files make up the feature.
2. Read the history. Read path-scoped git log, following renames, for those files, and read the fixes. For each piece that looks unnecessary, find out from history why it is there, and sort it: does it serve the feature, or the place upstream runs (its platforms, its install story, its users' machines)?
3. Copy, then edit. Copy the exact files, with their tests, into the destination first. Keep upstream's structure and algorithms for the feature itself, even where you would have written them differently. Never write your own version in their place.
4. Naturalize the names. Convert upstream's product name and naming scheme to this project's everywhere, except names an outside system still depends on. Use the destination's existing names for a concept that already has an owner here. Done when a case-insensitive search for upstream's names finds them only in the license notice and those outside contracts.
5. Naturalize the environment. Map what upstream's host gave or lacked onto what this project's host gives. Logic that existed only because of upstream's environment is deleted, not ported: a fallback for a platform we never run on, provisioning for something our machines already have, a workaround for a constraint we don't share. Touchstone: code that downloads and installs a tool on first use, written for user desktops, ported onto machines whose image already ships that tool. When unsure whether the destination really has it, measure on the real host instead of keeping the machinery.
6. Diff back. Diff the result against the pinned source and justify every change as a rename, a host binding, an environment deletion, or a deletion of upstream code the ported feature doesn't use. When a carried-over test fails, fix the adapter before touching the algorithm or the test.

Rules

• Attribution lives in the repository's single third-party notices file, which carries the upstream license and lists the ported paths. No per-file license headers, no copied license files, no "ported from" comments.
• Names and environment change; feature behavior does not. A difference in what the feature does for the user is a decision to raise, not a port edit.
• Never call a rewrite a port.

Done when the destination is the pinned upstream feature, renamed and fitted to this project, plus a diff you can account for. The handover names the upstream commit and every deliberate difference.