phase 8: navigation — definition, refs, hover, completion, ws/symbol

P8 resolved (SPEC §11): lazy + background indexing with progress.
Initial scan runs in a tokio task spawned from `initialized`; the
server stays responsive immediately and nav features answer with
partial data until the index is complete.

WorkspaceIndex (`index.rs`):
- Per-URI `IndexedPage` keeps name, title, headings, outgoing links.
- Reverse maps: `pages_by_name`, `backlinks: HashMap<page, …>`.
- `upsert` scrubs stale entries first so re-parses don't leak.
- `resolve` handles Wiki + AnchorOnly link kinds against the index;
  other kinds (Interwiki/Diary/File/Local/Raw) fall through.
- `slugify` for anchors (lowercases, collapses runs, drops trailing
  dashes, preserves Unicode), `page_name_from_uri` for workspace-
  rooted names, `walk_wiki_files` for the background scanner.

Backend wiring (`lib.rs`):
- `initialize` captures workspace root from `workspaceFolders` or the
  deprecated `root_uri`; advertises definition/references/hover/
  completion (trigger `[`)/workspace_symbol providers.
- `initialized` spawns the indexer, wrapped in
  `window/workDoneProgress` begin/end notifications.
- `did_open`/`did_change` synchronously update the index alongside
  publishing diagnostics; `did_close` keeps the indexed projection
  (file may still exist on disk and other pages link to it) and
  only clears diagnostics + drops the live document state.

Position lookup (`nav.rs`):
- `lsp_to_byte_pos` translates between LSP encoding (UTF-8 or
  UTF-16) and our byte columns.
- `find_inline_at` descends blocks → inlines → inline containers,
  returning the most specific inline whose span covers the cursor.

Handlers:
- definition: wikilinks resolve to a target URI; anchored links
  return the range at the matching heading.
- references: backlinks of the cursor's link target, or of the
  current page when the cursor isn't on a link. Ranges fall back
  to byte-column LSP positions when the source doc isn't open.
- hover: markdown preview with page title + outline (first 8
  headings), or a "not in index" fallback.
- completion: fires only inside an unterminated `[[ … ` on the
  current line; suggests every indexed page name.
- workspace/symbol: case-insensitive substring over every indexed
  heading.

Tests (20 new): slugify (basic / punctuation / Unicode / trailing
dash), page-name derivation under various roots, upsert / replace /
remove, resolve for Wiki + AnchorOnly, sorted `page_names`, UTF-8
passthrough + UTF-16 conversion, position lookup hits and misses.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

SPEC.md

@@ -1,7 +1,7 @@
 # nuwiki — Project Specification
 
 > Last updated: 2026-05-10
-> Status: Phase 7 (Semantic Tokens) complete — moving to Phase 8 (Navigation)
+> Status: Phase 8 (Navigation) complete — moving to Phase 9 (Editor Glue)
 
 ---
 
@@ -591,6 +591,6 @@ These decisions are required before or during the phase indicated.
 | P5 | **Minimum Neovim version** | Phase 9 | 0.8 (`vim.lsp.start`) · 0.11 (`vim.lsp.config`) | 0.8 = broader compat; 0.11 = cleaner Lua API |
 | P6 | **Minimum Vim version** | Phase 9 | Vim 8.2 · Vim 9.0 · Vim 9.1 | LSP client plugins work best on 9.0+; recommend documenting 9.1 as minimum |
 | ~~P7~~ | ~~**Semantic token type mapping**~~ | ~~Phase 7~~ | ✅ **Custom vimwiki-specific token types** | ~20 types (`vimwikiHeading`, `vimwikiBold`, …) + `level1`..`level6` + `centered` modifiers. Phase 9 ships default highlight groups in `syntax/nuwiki.vim` and the Lua glue. |
-| P8 | **Workspace indexing strategy** | Phase 8 | Eager on startup · Lazy + background | Eager blocks startup on large wikis; recommend lazy with progress notification |
+| ~~P8~~ | ~~**Workspace indexing strategy**~~ | ~~Phase 8~~ | ✅ **Lazy + background with progress** | Initial scan runs as a background tokio task; nav features answer with partial data until complete; progress reported via `window/workDoneProgress`. |
 | P9 | **macOS runner** | Phase 10 | Stay manual · Register macOS runner
 | Revisit if a Mac is available; no action needed now |