Add inline security comments to extra-args validation in setup-python-env action

[Copilot]

The extra-args validation loop in the composite action lacked comments explaining its security intent, and the shellcheck disable directive didn't reference the validation—making the connection between the two implicit and fragile.

Changes

• .github/actions/setup-python-env/action.yml
  • Added comment inside validation block stating the token validation intent
  • Added NOTE documenting that -- (end-of-options marker) is intentionally permitted by the regex; any following positional args would fail validation
  • Updated shellcheck disable=SC2086 comment to include "all tokens validated above", explicitly tying the validation loop to the uv sync call

if [[ -n "$EXTRA_ARGS" ]]; then
  # Validate each whitespace-split token: must start with '-' and contain only safe flag characters.
  # NOTE: '--' (end-of-options marker) is intentionally allowed; positional args would fail validation.
  for arg in $EXTRA_ARGS; do
    if [[ ! "$arg" =~ ^-[a-zA-Z0-9=._:/@+-]+$ ]]; then
      echo "::error::Unsafe extra-args token: '$arg'. Each token must start with '-' and contain only safe flag characters." >&2
      exit 1
    fi
  done
fi
# shellcheck disable=SC2086  # intentional word-splitting for uv flags (all tokens validated above)
uv sync $args $EXTRA_ARGS

Testing

• Not run (why?)
• uv run poe check
• Other: comment-only change; no functional logic altered

Checklist

• Linked issue or task reference
• Added/updated tests where relevant
• Updated docs/README if needed
• No secrets or sensitive data added
• Considered backward compatibility and deployment impact

Additional context

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