gopls Refactoring

gopls is Go's LSP server. It renames symbols with semantic precision — scope, packages, and interface implementations all handled correctly.

Three blind spots, each with a known fallback to sed:

• CGo files (import "C") — gopls's type-checker cannot parse the C preamble, so it cannot rename inside these files.
• Unexporting (uppercase→lowercase) when other packages reference the symbol — gopls's visibility rules treat this as illegal, so it refuses.
• go:generate comments — gopls renames Go identifiers, not comment text, so lines like //go:generate moq ... DeviceInterface must be updated by hand.

See WORKED-EXAMPLE.md for an end-to-end walkthrough (renaming DeviceInterface→Device in the hgml package).

Phase 0 — Collect facts

Run all four checks. Don't decide the path yet — you need Phase 3's reference list first.

0a. CGo?