Validate uv package names against PEP 508 before uv pip show

[Copilot]

Sighthound flagged five Critical command-injection findings around exec.Command calls built from dynamic data. Four of the five are already mitigated in the current code; the exception is the uv validation path, which only rejected --prefixed names.

Audit of reported findings

#	Location	Status
2	pip_validation.go — pip index versions <pkg> --pre	Already guarded by validatePipPackageName (PEP 508 allowlist)
3	dependabot.go — npm install --package-lock-only	Fixed argument slice; npmPath resolved via fileutil.ResolveExecutablePath
4/5	poutine.go — docker run -v <volumeMount>	buildDockerVolumeMount canonicalizes and validates host path (absolute, no :) and container path
1	pip_validation.go — uv pip show <pkg> --no-cache	Gap — addressed here

Changes

• pkg/workflow/pip_validation.go: validateUvPackages now applies validatePipPackageName to each extracted package name before the exec.Command call, matching the pip path. Invalid names are collected into the existing errors slice and surfaced as a validation error rather than reaching uv. Added a #nosec G204 justification consistent with the pip call site.
• pkg/workflow/argument_injection_test.go: regression test asserting a malformed name is rejected.

Package extraction is permissive enough to yield names like pkg;whoami from uvx pkg;whoami in workflow custom steps, which previously flowed straight into the argv:

// before: only a '-' prefix check upstream
cmd := exec.Command(uvPath, "pip", "show", pkgName, "--no-cache")

// after
if err := validatePipPackageName(pkgName); err != nil {
    errors = append(errors, fmt.Sprintf("uv package '%s' is invalid: %v", pkg, err))
    continue
}
cmd := exec.Command(uvPath, "pip", "show", pkgName, "--no-cache")

Note on the test guard: it skips when uv is absent, because validateUvPackages then falls back to the pip path where invalid names are warnings rather than errors. Worth a second opinion on whether that fallback should also hard-fail.

• Fixes [sighthound] Security findings in github/gh-aw #51007

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