feat(diff): review a GitHub pull request with --pr

[habakan]

Summary

Implements hunk diff --pr <number|url> [--repo <owner/repo>] — review a GitHub pull request directly, without a manual gh pr checkout.

Closes #465.

Hunk stays a local diff viewer: it shells out to the user's authenticated GitHub CLI (gh pr diff <ref> --patch) and feeds the resulting patch through the existing patch pipeline. A PR is just another patch source, so no new rendering/loader path was needed.

hunk diff --pr 68
hunk diff --pr https://github.com/modem-dev/hunk/pull/68
hunk diff --pr 68 --repo modem-dev/hunk

Changes

• src/core/github.ts (new): fetchPullRequestPatch() wraps gh, with friendly errors when gh is missing (ENOENT), the PR can't be fetched (surfaces gh stderr — not-authenticated / not-found), or the diff is empty.
• src/core/cli.ts: --pr / --repo options on diff; parseDiffCommand returns a kind: "patch" input when --pr is set. --pr combined with a target / --staged / pathspecs errors out.
• src/core/types.ts: PatchCommandInput.label lets an in-memory patch carry a header label (PR #68), since it has no backing file. loadPatchChangeset honors it.
• Docs (generate:docs) + changeset + tests.

Scope (deliberately an MVP)

Per the issue, this is the inbound direction only — open a PR to review it. Left as follow-ups so this PR stays focused:

• Importing unresolved review threads as startup notes (composes with Github PR review comments as annotations #487 / Approve/reject agent notes and publish accepted ones as a GitHub PR review #460).
• Current-branch PR auto-detection (lumen-style).

Happy to adjust the surface (e.g. patch vs diff, flag naming, --repo inclusion) if you'd prefer a different shape.

Verification

• bun run typecheck — clean.
• bun test src/core/cli.test.ts src/core/github.test.ts src/core/loaders.test.ts — pass. New coverage: github.test.ts (success, --repo passthrough, URL label, gh missing, non-zero exit, empty diff) and cli.test.ts (diff --pr → patch input, --pr + target rejected).
• bun run lint — 0 warnings/errors.
• bun run check:docs — clean after regen.
• End-to-end against a real PR via authenticated gh: fetches the patch and parses to kind: "patch", label: "PR #68".

[greptile-apps]

PR author is not in the allowed authors list.

[vercel]

@habakan is attempting to deploy a commit to the Modem Team on Vercel.

A member of the Team first needs to authorize it.

[benvinegar]

Did you try:

 gh pr diff 663 --patch | hunk patch -

If that's too tough to remember (it is), you could make a little shell fn and add it to your .bashrc/.zshrc:

hunk-pr() {
    gh pr diff "$1" --patch "${@:2}" | hunk patch -
}

Usage:

  hunk-pr 663
  hunk-pr 663 --repo modem-dev/hunk

I'd prefer if we documented + shared this workflow vs. coupling hunk to gh and making remote fetches. It really expands the surface area a lot.

[habakan]

That makes sense — keeping hunk decoupled from gh and avoiding remote fetches is a fair call, and the pipe workflow covers the core use case well.

I've turned this into a docs PR instead: #672 documents gh pr diff 123 --patch | hunk patch - and your hunk-pr shell function in the website workflow docs and README. Closing this one in favor of that.