fix(clink): resolve codex CLI from nvm/npm global paths

[syf2211]

Summary

Fix clink failing with codex: command not found when Codex CLI is installed globally via nvm + npm and PAL MCP is launched through uvx, which does not inherit nvm-injected PATH entries.

Motivation

Fixes #442. The MCP subprocess inherits a minimal PATH from uvx, so shutil.which('codex') cannot find binaries installed under $NVM_DIR/versions/node/*/bin.

Changes

• Add clink/path_resolution.py with resolve_cli_executable() and augment_path() to search common user-local install directories (nvm node bins, ~/.local/bin, ~/.npm-global/bin, etc.)
• Update clink/agents/base.py to resolve CLI executables via the augmented lookup and pass an augmented PATH to subprocesses
• Add unit and integration tests for nvm-style layouts
• Update existing agent test fake_which stubs to accept path= (required by shutil.which)

Tests

pytest tests/test_clink_path_resolution.py tests/test_clink_codex_path_resolution.py tests/test_clink_codex_agent.py tests/test_clink_claude_agent.py tests/test_clink_gemini_agent.py -q
# 12 passed

Notes

• Resolution still prefers the inherited PATH; augmented directories are only used as fallback.
• Mirrors the native CLI discovery pattern already used in run-server.sh for Claude/Codex integration.
• Does not cover fnm/volta/asdf layouts; can be extended if needed.

[gemini-code-assist]

Code Review

This pull request introduces a new path resolution utility (clink/path_resolution.py) to locate CLI executables in common user-local installation directories (such as NVM, NPM, and Cargo) when they are missing from the host PATH. The base agent is updated to leverage this utility, and corresponding unit and integration tests are added. Feedback on these changes highlights a potential bug in lexicographical version sorting for Node directories, an opportunity to simplify path deduplication using dict.fromkeys(), and a cross-platform issue in tests where mocking the HOME environment variable should be replaced by directly mocking Path.home.

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[gemini-code-assist]

Sorting version directories lexicographically with reverse=True can lead to incorrect version preference. For example, "v9.0.0" > "v18.0.0" evaluates to True in Python because '9' > '1'. This means an older single-digit major version of Node will be preferred over a newer double-digit major version.

To fix this, we should use a semver-aware sorting key that splits the version string into integers.

    if versions_dir.is_dir():
        def version_key(p: Path) -> tuple[int, ...]:
            parts = p.parent.name.lstrip("v").split("-")[0].split(".")
            return tuple(int(x) for x in parts if x.isdigit())

        version_bins = sorted(versions_dir.glob("*/bin"), key=version_key, reverse=True)
        candidates.extend(str(path) for path in version_bins)

[gemini-code-assist]

In Python 3.7+, dictionaries maintain insertion order. We can simplify the deduplication of candidate paths using dict.fromkeys(), which is more concise and idiomatic.

Suggested change

	seen: set[str] = set()
	unique: list[str] = []
	for candidate in candidates:
	if candidate not in seen:
	seen.add(candidate)
	unique.append(candidate)
	return unique
	return list(dict.fromkeys(candidates))

[gemini-code-assist]

Using monkeypatch.setenv("HOME", ...) to mock the home directory is not fully cross-platform because Path.home() on Windows resolves using the USERPROFILE environment variable (or other Windows-specific APIs) rather than HOME.

To ensure the tests are robust and cross-platform, we should mock Path.home directly using monkeypatch.setattr.

Suggested change

	monkeypatch.setenv("HOME", str(tmp_path))
	import pathlib
	monkeypatch.setattr(pathlib.Path, "home", lambda: tmp_path)

[gemini-code-assist]

Using monkeypatch.setenv("HOME", ...) to mock the home directory is not fully cross-platform because Path.home() on Windows resolves using the USERPROFILE environment variable (or other Windows-specific APIs) rather than HOME.

To ensure the tests are robust and cross-platform, we should mock Path.home directly using monkeypatch.setattr.

Suggested change

	monkeypatch.setenv("HOME", str(tmp_path))
	monkeypatch.setattr(Path, "home", lambda: tmp_path)