fix(follow-link): resolve+open definitions ourselves on the Vim clients

The Vim follow-link path delegated to the LSP client's jump UI
(:LspDefinition / coc jumpDefinition), which broke two ways for wiki
link-following:

1. **No create-on-follow (vim-lsp + coc).** vim-lsp's location handler
   readfile()s the target to build a quickfix entry; for a not-yet-created
   page that throws E484 and aborts the jump, so <CR> on [[NewPage]] did
   nothing. The server was correct throughout — textDocument/definition
   returns a *synthesised* location for missing pages (verified over
   JSON-RPC).
2. **Wrong window placement (coc).** Without an explicit open command coc
   fell back to coc.preferences.jumpCommand (e.g. a tab command).

Stop delegating: nuwiki#commands#follow_link_or_create() /
follow_link_drop() now resolve textDocument/definition directly and open
the URI themselves via a shared s:open_definition(open_cmd) helper — :edit
for <CR>, `tab drop` for <C-S-CR>. :edit opens a buffer for a missing path
(save creates it, matching vimwiki) and gives exact current-window
placement regardless of the user's coc jumpCommand. Removes
s:jump_definition / s:drop_from_response.

Also fix the coc action name: CocAction('getDefinition') does not exist
(E605 "Action getDefinition does not exist") — the registered action is
'definitions'. Fixed in s:open_definition and badd_link.

coc config delivery: the setup guidance shipped without
initializationOptions, so coc users never sent wiki_root and the server
resolved links against its default root (existing pages flagged broken,
follow-to-create landed in the cwd). The printed snippet
(autoload/nuwiki/lsp.vim) now emits initializationOptions populated with
the resolved settings, and the README coc snippet documents it as required.

Add development/start-vim-coc.sh — a coc.nvim dev launcher (sibling of
start-vim.sh) that wires coc's prebuilt release branch + a generated
coc-settings.json (with initializationOptions), deliberately omitting
vim-lsp so the coc path is exercised; doubles as a reproducer.

Tests: new cr.follow_opens_missing_page_in_current_window case in
test-keymaps-vim.vim (stubs CocAction to a missing page, asserts
current-window :edit). Keymap suite 254+18 green; config-parity (Vim +
Neovim) green. Neovim path unchanged and re-confirmed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

development/start-vim-coc.sh

@@ -0,0 +1,178 @@
+#!/usr/bin/env bash
+#
+# start-vim-coc.sh — launch Vim with a minimal config that loads nuwiki
+# through coc.nvim (instead of vim-lsp).
+#
+# The plugin's Vim path (autoload/nuwiki/lsp.vim) prefers `vim-lsp` and falls
+# back to `coc.nvim`. start-vim.sh exercises the vim-lsp path; this script
+# exercises the coc.nvim path. vim-lsp is deliberately kept OFF the runtimepath
+# so `:LspDefinition` doesn't exist and nuwiki's coc branch is the one that runs
+# (s:jump_definition() → CocActionAsync('jumpDefinition', 'edit')).
+#
+# This doubles as a reproducer for the "<CR> opens a new tab" regression:
+# coc-settings.json sets coc.preferences.jumpCommand to `tabe`, so without the
+# fix `<CR>` on a link opens a new tab. With the fix nuwiki passes 'edit'
+# explicitly and the target opens in the *current* window regardless.
+#
+# It clones coc.nvim's prebuilt `release` branch into the dev cache on first
+# run (no yarn/build needed — it just needs Node.js at runtime).
+#
+# Usage: ./development/start-vim-coc.sh [extra args...]
+#   ./development/start-vim-coc.sh                       # open the scratch wiki's index
+#   ./development/start-vim-coc.sh path/to/note.wiki     # open a specific file
+#   NUWIKI_DEV_WIKI=/tmp/foo ./development/start-vim-coc.sh
+#   NUWIKI_DEV_NO_SEED=1 ./development/start-vim-coc.sh       # use WIKI_DIR as-is (no scratch seeding)
+#   NUWIKI_DEV_SKIP_BUILD=1 ./development/start-vim-coc.sh    # reuse the cached binary
+#   NUWIKI_DEV_COC_JUMP=edit ./development/start-vim-coc.sh   # change coc.preferences.jumpCommand
+#
+# The release binary is rebuilt on every launch so source changes always reach
+# the running LSP. `cargo build --release` is incremental, so this is a fast
+# no-op when nothing changed. Set NUWIKI_DEV_SKIP_BUILD=1 to skip the build.
+#
+# Tested with Vim 9.1+ and Node 18+. State (viminfo/sessions, coc data) lives
+# under $XDG_CACHE_HOME/nuwiki-dev/ so your real Vim install stays untouched.
+
+set -euo pipefail
+
+# Shared paths + helpers (log, ensure_binary, write_sample_wiki, seed_wiki).
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/_common.sh"
+
+VIMRC="$DEV_DIR/vimrc-coc"
+VIM_STATE="$DEV_DIR/vim-coc-state"
+COC_DIR="$DEV_DIR/coc.nvim"
+COC_DATA="$DEV_DIR/coc-data"
+COC_SETTINGS="$DEV_DIR/coc-settings.json"
+COC_JUMP="${NUWIKI_DEV_COC_JUMP:-tabe}"
+
+ensure_node() {
+  if ! command -v node >/dev/null 2>&1; then
+    log 'node not found — coc.nvim needs Node.js at runtime; skipping'
+    exit 0
+  fi
+}
+
+ensure_coc() {
+  mkdir -p "$DEV_DIR"
+  if [[ -d "$COC_DIR/.git" ]]; then
+    return
+  fi
+  if ! command -v git >/dev/null 2>&1; then
+    log 'git not found — cannot clone coc.nvim; skipping'
+    exit 0
+  fi
+  log "cloning coc.nvim (release branch) → $COC_DIR"
+  git clone --depth 1 --branch release \
+    https://github.com/neoclide/coc.nvim.git "$COC_DIR" >/dev/null 2>&1
+}
+
+write_coc_settings() {
+  mkdir -p "$DEV_DIR"
+  # Mirror what the vim-lsp client sends (autoload/nuwiki/lsp.vim s:settings()):
+  # both `initializationOptions` (sent on initialize) and `settings.nuwiki`
+  # (served via workspace/configuration). Without these the server falls back
+  # to its own default wiki_root (~/vimwiki) instead of $WIKI_DIR, so it can't
+  # resolve links (e.g. Notes shows as broken) or create-on-follow correctly.
+  cat > "$COC_SETTINGS" <<EOF
+{
+  "coc.preferences.jumpCommand": "$COC_JUMP",
+  "languageserver": {
+    "nuwiki": {
+      "command": "$REPO_ROOT/bin/nuwiki-ls",
+      "filetypes": ["vimwiki"],
+      "initializationOptions": {
+        "wiki_root": "$WIKI_DIR",
+        "file_extension": ".wiki",
+        "syntax": "vimwiki",
+        "log_level": "info",
+        "diagnostic": { "link_severity": "warn" }
+      },
+      "settings": {
+        "nuwiki": {
+          "wiki_root": "$WIKI_DIR",
+          "file_extension": ".wiki",
+          "syntax": "vimwiki",
+          "log_level": "info",
+          "diagnostic": { "link_severity": "warn" }
+        }
+      }
+    }
+  }
+}
+EOF
+}
+
+write_vimrc() {
+  mkdir -p "$DEV_DIR"
+  cat > "$VIMRC" <<EOF
+" start-vim-coc.sh: generated minimal config for nuwiki development (coc.nvim).
+" Regenerated on every launch; edit start-vim-coc.sh, not this file.
+
+" Confine state to the dev cache so we never touch the user's real Vim
+" install.
+set viminfo='100,n$VIM_STATE/viminfo
+let &directory = '$VIM_STATE/swap//'
+let &backupdir = '$VIM_STATE/backup//'
+let &undodir = '$VIM_STATE/undo//'
+
+" Make Vim look for runtime paths in the dev cache. vim-lsp is intentionally
+" absent so nuwiki dispatches jump-to-definition through coc.
+set nocompatible
+let &runtimepath = '$REPO_ROOT' . ',' . &runtimepath
+let &runtimepath .= ',$COC_DIR'
+
+" Point coc at the generated settings + a private data dir.
+let g:coc_config_home = '$DEV_DIR'
+let g:coc_data_home   = '$COC_DATA'
+
+let g:nuwiki_binary_path  = '$REPO_ROOT/bin/nuwiki-ls'
+let g:nuwiki_wiki_root    = '$WIKI_DIR'
+let g:nuwiki_file_extension = '.wiki'
+let g:nuwiki_syntax       = 'vimwiki'
+let g:nuwiki_log_level    = 'info'
+
+filetype plugin indent on
+syntax enable
+set hidden
+set termguicolors
+set number
+set signcolumn=yes
+set noswapfile
+set nobackup
+set nowritebackup
+let mapleader = ' '
+
+" Auto-detect filetype for .wiki files (the plugin ships ftdetect, but
+" --clean disables those — copy the rule here).
+augroup NuwikiFtdetect
+  autocmd!
+  autocmd BufRead,BufNewFile *.wiki setfiletype vimwiki
+augroup END
+
+" coc starts the server automatically from coc-settings.json once a vimwiki
+" buffer loads — no explicit nuwiki#lsp#start() needed.
+
+echomsg '[nuwiki-dev] ready (coc.nvim) — wiki root: $WIKI_DIR'
+echomsg '[nuwiki-dev] coc.preferences.jumpCommand = $COC_JUMP'
+echomsg '[nuwiki-dev] <CR> on a [[link]] should open in the CURRENT window'
+echomsg '[nuwiki-dev] :CocList services for status, :messages for log'
+EOF
+}
+
+main() {
+  ensure_node
+  ensure_binary
+  ensure_coc
+  write_coc_settings
+  seed_wiki
+  write_vimrc
+  mkdir -p "$VIM_STATE/swap" "$VIM_STATE/backup" "$VIM_STATE/undo" "$COC_DATA"
+
+  log "launching: vim --clean -u $VIMRC"
+  if [[ $# -gt 0 ]]; then
+    exec vim --clean -u "$VIMRC" "$@"
+  else
+    exec vim --clean -u "$VIMRC" "$WIKI_DIR/index.wiki"
+  fi
+}
+
+main "$@"