Resolve python tools off PATH, not just as importable modules

1.1.0 reported an installed ruff as missing and skipped the lint. Its
resolution order ended at `python -m <tool>`, guarded by an `import <tool>`
probe, but ruff ships as a standalone Rust binary and is never importable.
The probe failed, the check was recorded as skipped, and the gate reported a
coverage gap that did not exist.

This also regressed 1.0.2, which called a bare `ruff` and let PATH resolve it.
Restore that path, ordered after the project venv and uv so a project-local
tool still wins, and before `python -m` so a binary is found even when a
same-named module is not importable.

Verified by injecting an unused import into audit-terraform and confirming the
guard blocks with `ruff check .`. The new regression test fails against the
1.1.0 resolution order and passes against this one.

Tests: 10 passing (bash-guard), 197 (audit-code), 106 (audit-terraform),
ruff clean across both skills.

plugins/guards/hooks/bash-guard.mjs

@@ -220,11 +220,24 @@ function pyTool(dir, tool, args) {
   const venv = join(dir, '.venv', 'bin', tool);
   if (existsSync(venv)) return [venv, args];
   if (existsSync(join(dir, 'uv.lock')) && pyprojectHasProject(dir)) return ['uv', ['run', tool, ...args]];
+  // PATH before `python -m`: ruff ships as a standalone binary and is never importable,
+  // so probing for a module would declare an installed ruff missing.
+  if (onPath(tool)) return [tool, args];
   if (pyModuleAvailable(tool)) return ['python', ['-m', tool, ...args]];
   skipped.push({ dir, tool });
   return null;
 }
 
+function onPath(tool) {
+  try {
+    execFileSync(tool, ['--version'], { stdio: 'ignore' });
+    return true;
+  } catch (e) {
+    // A non-zero exit still proves the binary exists; only ENOENT means absent.
+    return e.code !== 'ENOENT';
+  }
+}
+
 function pyprojectHasProject(dir) {
   try { return /^\[project\]/m.test(readFileSync(join(dir, 'pyproject.toml'), 'utf8')); }
   catch { return false; }

plugins/guards/hooks/test-bash-guard.py

@@ -96,4 +96,11 @@ with tempfile.TemporaryDirectory() as tmp:
     r = run_guard(bash("jj git push --bookmark main"), cwd=tmp)
     check("passing nested test allows the push", decision(r) != "deny", f"got {decision(r)!r}")
 
+with tempfile.TemporaryDirectory() as tmp:
+    skill = nested_repo(tmp, "def test_passes():\n    assert True\n")
+    open(os.path.join(skill, "scripts.py"), "w").write("import os\n")
+    r = run_guard(bash("jj git push --bookmark main"), cwd=tmp)
+    check("lint failure blocks the push", decision(r) == "deny", f"got {decision(r)!r}")
+    check("ruff is resolved off PATH, not skipped", "ruff" in reason(r), f"got {reason(r)!r}")
+
 sys.exit(1 if failures else 0)