adopt neovim 0.12 native editing features

LOG.md

@@ -203,6 +203,13 @@ Record every decision here with a short rationale. Append new entries; do not re
 - 2026-10-28: Disabled lazy.nvim's LuaRocks integration because no configured plugin requires LuaRocks. This removes the irrelevant missing-hererocks health error without adding a system dependency. Candidate health otherwise reports only optional missing language runtimes, the pending inline-Copilot migration, and the `copilot-cmp` deprecation that will disappear with that migration.
 - 2026-10-28: Adopted the isolated candidate's reviewed plugin lockfile and compatibility adjustments into the main worktree. Production plugin directories remain unchanged until the 0.12 activation step, preserving the working 0.11 rollback environment.
 - 2026-10-28: Chose the post-activation native-feature direction for 0.12. Keep lazy.nvim because the configuration still benefits from its event/command loading, dependency ordering, and build hooks; do not mix the runtime upgrade with an experimental `vim.pack` migration. After activating 0.12, replace `mbbill/undotree` with the native optional package and trial native insert-mode/LSP completion plus built-in snippets. Copilot will use inline suggestions with a separate accept key rather than appearing in the completion popup; remove the cmp stack only after interactive language and editing validation.
+- 2026-10-28: Activated Neovim 0.12.6 with the user-level selector `~/.local/bin/nvim`, which precedes the older `/opt` PATH entry. The root-owned `/opt/neovim` directory could not be reorganized without an interactive sudo password, so 0.11.5 remains intact at `/opt/neovim/nvim-linux-x86_64/bin/nvim`; rollback is `ln -sfn /opt/neovim/nvim-linux-x86_64/bin/nvim ~/.local/bin/nvim`.
+- 2026-10-28: Implemented the 0.12 native editing trial. Native `nvim.undotree` now owns `<leader>u`; native autocomplete combines LSP omnifunc results and bounded buffer sources after a 150 ms delay, requires explicit selection, accepts with `<C-y>`, and uses built-in snippet tabstops. Copilot now supplies separate inline ghost text accepted with `<M-l>` and hides while the completion popup is visible. Removed the nvim-cmp, cmp source, LuaSnip, copilot-cmp, and external Undotree specs, integrations, lock entries, and highlight groups.
+- 2026-10-28: Refined native completion after the PTY smoke test showed buffer words sorting ahead of a valid PHP method. LSP-attached buffers now autocomplete exclusively from the LSP omnifunc; `<C-x><C-n>` remains the explicit current-buffer word workflow, and non-LSP buffers retain bounded automatic word completion. This makes the first selectable language result predictable without losing native fallback completion.
+- 2026-10-28: Added narrow 0.12 guards around the new `autocomplete` option, source match limits, and optional native Undotree package. The retained 0.11.5 binary can therefore still start the configuration for emergency rollback, although native autocomplete and Undotree are intentionally unavailable until the selector is returned to 0.12.6.
+- 2026-10-28: Final smoke testing found that loading `nvim.undotree` before lazy.nvim setup left its command registered but removed its Lua module path. Moved `packadd nvim.undotree` after lazy.nvim finalizes `runtimepath`. The same test showed nvim-ts-autotag attaching to Markdown despite the intended filetype restriction; global autotag actions are now disabled and explicitly enabled only for HTML/PHP/JS/TS/Vue tag-bearing filetypes.
+- 2026-10-28: Active-runtime validation passed through the normal `nvim` selector: native Undotree opens, netrw and Telescope load, PHP native completion offers and accepts `greetExternal()` with snippet syntax, Copilot's inline client is authenticated, Markdown no longer runs autotag, and HTML autotag exits Insert mode without errors. `vim.deprecated` is clean. Remaining health warnings are optional missing language runtimes and the harmless unknown `markdown.mdx` filetype hint.
+- 2026-10-28: Marked `neovim-migration-guide.md` as historical planning input. Its original Neo-tree, cmp, and plugin assumptions are retained for provenance but no longer compete with the active architecture documents.
 
 ## Project-Local Configuration
 
@@ -242,7 +249,7 @@ Neoconf and the earlier layered JSON proposal were rejected. They remain in the
 
 - `spelllang = en_gb`
 - `listchars` and `showbreak` will reuse legacy values.
-- `completeopt = menu,menuone,noselect` for `nvim-cmp`.
+- `autocomplete` with `completeopt = menu,menuone,noselect,popup,fuzzy` for Neovim 0.12 native completion.
 
 ## Process Reminders