fix(desktop): discover bun-installed agent CLIs in ~/.bun/bin

[linxule]

Problem

common_binary_paths() probes mise shims, ~/.local/bin, volta, asdf, and (further down resolve_command_uncached) nvm's default bin dir — but not bun's global bin directory, ~/.bun/bin.

bun's installer appends its bin dir to ~/.zshrc / ~/.bashrc, which are interactive-only. A login shell never sources them, so find_via_login_shell() can't recover the path either. That's the same failure mode already called out in this file for nvm:

// Check nvm's default Node.js bin directory — nvm initializes via
// ~/.zshrc (interactive) which is not loaded by a login shell, so
// `node`, `npm`, and npm-global shims installed there are otherwise
// invisible.

So for a GUI-launched desktop app, every rung of the resolution ladder misses a bun-installed CLI:

1. workspace dev dirs — no
2. command_looks_like_path — no, presets use bare names
3. Buzz-managed npm/node dirs — no
4. current process PATH — launchd's minimal PATH on a Finder launch
5. find_via_login_shell — .zshrc not sourced
6. common_binary_paths() — ~/.bun/bin absent
7. nvm default bin — no

This matters because bun is a common install route for the agent CLIs Buzz targets. Kimi Code in particular ships as an npm package (@moonshot-ai/kimi-code), so bun add -g puts it at ~/.bun/bin/kimi — exactly where discovery doesn't look.

Reproduction

On macOS with codex and kimi installed via bun, launching Buzz from Finder:

• Kimi Code shows "CLI needed"
• both CLIs run fine in an interactive terminal

Probing the way find_via_login_shell does, in a clean environment:

$ env -i HOME=$HOME /bin/zsh -l -c 'command -v -- codex; command -v -- kimi'
(nothing)

Launching the app with the bun dir on PATH resolves both immediately:

$ env PATH="$HOME/.bun/bin:$PATH" /Applications/Buzz.app/Contents/MacOS/buzz-desktop

Change

One entry appended to the home-relative list in common_binary_paths(). It goes last so it cannot shadow a directory that already resolves — the change can only add resolutions, never alter existing ones.

Testing

cargo fmt --check passes.

I was not able to run the full just ci gate locally: ring 0.17.14 fails to build in this environment against the macOS 26.2 SDK (cc error compiling p256-nistz.c), which is unrelated to this change. Relying on CI for the rest — the diff adds one PathBuf to an existing Vec<PathBuf> and introduces no new API.

Notes

• Related to Improve Kimi Code runtime discovery #3084, which adds ~/.kimi-code/bin for the same class of GUI-launch discovery failure. That covers Kimi's standalone installer; this covers the bun/npm-global install route. They're complementary — I've left a note on that PR.
• Only ~/.bun/bin is added. bun's global packages live under ~/.bun/install/global/node_modules but are symlinked into ~/.bun/bin, so the single directory is sufficient.
• Worth noting ~/.bun/bin contains no node/npm/npx, so appending it can't shadow a system Node toolchain.