feat: add module rename support

[scottming]

Context

While AI-assisted renaming is convenient, it's still slower than a native Language Server implementation. This PR ports the module rename feature from Lexical PR #636, which I've been using reliably for almost two years. Given that the Lexical repository is now archived, I wanted to bring this practical and well-tested feature to Expert.

Changes

Core Implementation (engine)

• Add Engine.CodeMod.Rename module with submodules: Prepare, Module, Entry, File, and Diff
• Add Engine.Commands.Rename GenServer for tracking rename progress and triggering reindex
• Add Engine.Commands.RenameSupervisor for managing rename command lifecycle

LSP Integration (expert)

• Add PrepareRename and Rename handlers for LSP protocol
• Extend Expert.EngineApi with prepare_rename/3 and rename/5 APIs
• Register rename_provider with prepare_provider: true in server capabilities

Infrastructure (forge)

• Add RenameFile struct to Forge.Document.Changes for file rename operations
• Add file_changed and file_saved message types to Forge.EngineApi.Messages

Key Differences from Lexical

• Uses :erpc.call via Expert.EngineApi.call/4 instead of RemoteControl.call
• Added reindexing mechanism after rename to keep search index consistent (see "Why These Changes")
• Namespace mapping: Lexical.RemoteControl.* → Engine.*, Lexical.Server.* → Expert.*

Why These Changes

• Progress tracking & reindex (59953157): Without reindexing after rename, the search index retains old module names. This causes subsequent renames to fail - e.g., renaming Accounts → Accounts2 works, but renaming back fails because the index doesn't reflect the new names.

• Temporary document opening (f08fd155): After a file rename, the new URI may not exist in Document.Store, causing "not_open" errors during reindex. Added ensure_open/1 to temporarily open files from disk when needed.

• Expanded test coverage (a38652ef): Added comprehensive tests covering references, descendants, structs, edge cases, and file renaming with realistic module names.

Extra

A demo video is attached showing the smooth rename workflow - renaming a module and then renaming it back. Tested successfully in both VSCode and Neovim.

CleanShot.2026-01-04.at.15.43.19.mp4

[doorgan]

Some notes(I'm testing on a brand new mix phx.new rename_test project:

• If I am on module RenameTestWeb.Router and I rename it to ExpertRenameTestWeb then

  • No other module prefixed with RenameTestWeb is renamed
  • The use RenameTestWeb, :router isn't renamed either

• If I create lib/rename_test/nested/foo.ex defining RenameTest.Nested.Foo and I rename RenameTest in lib/rename_test.ex, then the child modules are renamed and the files are renamed too, but I end up with an empty lib/rename_test/nested folder

• When I try to rename a function(I know this is not supported by this PR, but still) I get this error:

2026-01-14 16:34:27.690 [info] [Error - 4:34:27 PM] ** (UndefinedFunctionError) function XPGenLSP.ErrorResponse.fetch/2 is undefined (XPGenLSP.ErrorResponse does not implement the Access behaviour

You can use the "struct.field" syntax to access struct fields. You can also use Access.key!/1 to access struct fields dynamically inside get_in/put_in/update_in)
    (xp_gen_lsp 0.11.2) XPGenLSP.ErrorResponse.fetch(%XPGenLSP.ErrorResponse{message: "Failed to handle textDocument/prepareRename, {:error, :request_failed, \"Renaming :call is not supported for now\"}", code: -32603, data: nil}, :placeholder)
    (elixir 1.17.2) lib/access.ex:322: Access.get/3
    (xp_schematic 0.2.1) lib/schematic.ex:608: anonymous fn/5 in XPSchematic.map/1
    (elixir 1.17.2) lib/enum.ex:2531: Enum."-reduce/3-lists^foldl/2-0-"/3
    (xp_schematic 0.2.1) lib/schematic.ex:583: anonymous fn/3 in XPSchematic.map/1
    (xp_schematic 0.2.1) lib/schematic.ex:1001: anonymous fn/4 in XPSchematic.telemetry_wrap/3
    (xp_telemetry 1.3.0) /Users/dorgan/dev/expert/apps/expert/deps/telemetry/src/telemetry.erl:324: :xp_telemetry.span/3
    (xp_schematic 0.2.1) lib/schematic.ex:947: anonymous fn/3 in XPSchematic.oneof/1

Also we should have some progress reported, I'm testing on VSCode(it's easier for me to trigger these actions from this editor) and I don't see progress reported there, neither in the status bar nor in the Expert logs there