fix(nix): install hunkdiff alias so hunk patch works

[schickling-assistant]

Problem and user impact

Since 0.22.0, hunk patch <file> (and other review flows that respawn the TUI) fail under the Nix flake package with:

error: unable to execute '…/bin/hunkdiff': No such file or directory

hunk --version / --help / skill path still work. v0.21.1 works with the identical install layout. Reported as #1106.

Approach

The review flows resolve the TUI through a hunkdiff lookup, mirroring the npm package's dual hunk/hunkdiff bins (same ./bin/hunk.cjs). The Nix installPhase only installed hunk, so the lookup fails. This change installs hunkdiff as a symlink to the wrapped hunk binary (wrapper env, including HUNK_INSTALL_SOURCE=nix, is preserved through the symlink).

Non-goals: no behavior change to any other install path (npm, curl, Homebrew); no new package output.

Tests and manual checks performed

• nix build .#hunk --no-link on x86_64-linux: builds clean.
• hunk patch /tmp/smoke.patch from the fixed package with a clean PATH (package bin only): renders the review TUI, exit 0. Before the fix: the unable to execute …/bin/hunkdiff error.
• hunk --version and hunkdiff --version both report the packaged version.
• Bun unit test suite not run: the change touches only nix/package.nix (no TypeScript), and the failure/success is fully determined by the installed file layout, verified above.

Platforms

• Tested: x86_64-linux (Nix).
• Not tested: aarch64-linux, x86_64-darwin, aarch64-darwin (same derivation shape; relies on CI).

Follow-up

Once merged, downstream Nix consumers can advance past the v0.21.1 hold.

Posted on behalf of @schickling

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[benvinegar]

Thanks!