detect_shadowed_dcode

Return the shadowing dcode entry point on the user's PATH, if any.

After a successful uv tool upgrade, the upgraded binary only takes effect on the next launch if the user's PATH resolves to uv's tool bin dir for dcode (and deepagents-code). A pre-uv install earlier on PATH will silently win and report the old version, which looks like "the upgrade didn't work" to the user.

This compares each supported console script against uv's tool bin dir. A mismatch means a different binary will run next launch for that entry point.

Caveat: a dcode symlink that lives in some unrelated bin dir but points into the upgraded tool venv (e.g. a manually-created convenience symlink) is reported as shadowing even though the next launch would actually run the upgraded entry point. Comparing directories rather than resolved targets is intentional — see the inline note below for why — and this edge is rare enough that we accept a benign false positive over a class of false negatives.