Lays the groundwork for WorkspaceEdit/rename (L2+) by making
navigation cross-file-correct.
- Relocate file_path/file_meta from the EditorCore global onto
Buffer itself, so each buffer keeps its own filesystem identity
across cross-file navigation. Accessors + registry/editor/lua/
semantic_render call sites migrated; zero behavioural change for
single-file flows.
- uri->path: project_index::uri_to_path made pub; pmacs.lsp.path_for_uri.
- find-or-open: BufferRegistry::find_by_path + pmacs.buffer.find_or_open
dedups an already-open file instead of spawning a duplicate buffer
(SP-4 Gap A).
- Bounded jump ring on EditorCore (cap 64, oldest-evict, stale-buffer
skip): push_jump/jump_back + pmacs.editor.* bindings + lsp.jump-back
command bound to M-,.
- pmacs.lsp.go_to_definition cross-file branch: decode URI ->
push_jump -> find_or_open -> reposition, with a failure path that
unwinds the pushed origin. ensure_server now passes cfg.env through.
Tests: 5 jump-ring unit tests; m4_12_cross_file_go_to_definition_and_
jump_back end-to-end via a new `defenv` fake-LSP mode. All gates green
(lib 1262/0, m4 67/0, m8_1/m8_9/m8_10, m9_1, m11_5 --features crdt 2/0).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>