docs(nook): surface tree-sitter as a decision-ready candidate

Author: truffle-dev

docs/nook/roadmap.md

@@ -116,10 +116,28 @@ shipped, so the remaining surface is narrower than it once was.
   single-file editor (a vim replacement for editing a dotfile), so a
   real modal layer is the largest open question. Needs operator sign-off
   before building, not a unilateral start.
+- **tree-sitter highlighting** (design/02) — research is done, this is
+  now a single binary-size decision, not an unknown. Measured: the pure-Go
+  CGO-free backend (odvcencio/gotreesitter) with the `grammar_subset`
+  build tags embeds one grammar in 9.10 MB vs 30.83 MB for the naive
+  umbrella import — the subset escapes the 542 `init()` registrations, so
+  the umbrella is off the table and the subset path holds. The parser
+  runtime is a fixed ~6.8 MB over a bare binary; each extra grammar is
+  ~0.08 MB. Net for nook: adding tree-sitter-go moves ~15 MB → ~21-22 MB
+  before chroma is reclaimed. The one open call is whether that ~6.8 MB
+  one-time add clears the "lightest, fastest" north star — an operator
+  taste decision, not a build unknown. No upstream issue is needed
+  (issue #88 already ships the build-tag matrix). Do not wire the
+  dependency into nook's build before this decision.
 - **Settings/themes surface** — config inheritance and theme hot-reload
   ship; a discoverable settings UI on top does not yet.
-- **Depth passes on shipped panes** — completion ranking, diagnostics
-  presentation, multibuffer ergonomics. Each is a self-contained slice.
+- **Depth passes on shipped panes** — diagnostics presentation and
+  multibuffer ergonomics are each self-contained slices. Completion has a
+  concrete gap: the popup sorts by LSP SortText but has no type-to-filter
+  — typing any rune while it is open dismisses it (main.go, the "any
+  other key" branch) rather than narrowing the list live the way Zed and
+  VSCode do. Closing that is a host keystroke-routing plus live-render
+  change, so it wants a visual loop, not a blind hour.
 
 Pick the smallest finishable slice that advances parity; one capability,
 its tests, its CHANGELOG line, one commit.