v0.5.0: route the neovim MCP through MetaMCP

mcp-neovim-server no longer runs as a per-session npx stdio child.
It is now a MetaMCP namespace upstream on emmett (one persistent
process), reached over Streamable-HTTP via the mcp-session-pool:

  Claude Code -> pool.localhost:12010/p/neovim/mcp
    -> MetaMCP neovim namespace -> mcp-neovim-server -> nvim socket

- .mcp.json: stdio npx server -> streamable-http pool endpoint
- agents/companion.md + skills: tool names are now 3-segment
  (mcp__neovim__neovim__vim_*) — the MetaMCP aggregation shape; the
  surface description and unavailability runbook updated for the
  three-link path (nvim socket / MetaMCP / session)
- README: connection-path diagram

Host side (servers/emmett, deployed separately): neovim added to
services.mcp-session-pool.upstreams; metamcp.nix seeds the neovim
mcp_servers row + mapping and adds nodejs to the unit PATH.

README.md

@@ -1,17 +1,43 @@
 # nvim-agentic-companion
 
-A Claude Code plugin that turns the user's running Neovim into a first-class collaborator.
+A Claude Code plugin that turns the user's running Neovim into a first-class
+collaborator.
 
 It assumes two things are already wired up:
 
-1. **`mcp-neovim-server`** registered as an MCP server in Claude Code, pointed at the nvim RPC socket (default `/run/user/1000/nvim.sock`). NixVim's `extraConfigLuaPre` starts the server on that socket at editor startup.
-2. **`coder/claudecode.nvim`** loaded inside nvim, with `<leader>a*` keymaps wired (toggle, focus, send, accept/deny diff).
+1. **`mcp-neovim-server`** reaching the running nvim's RPC socket (default
+   `/run/user/1000/nvim.sock`, created by NixVim's `extraConfigLuaPre`
+   `serverstart` at editor startup). The plugin ships a `.mcp.json` that points
+   the `neovim` MCP server at a **MetaMCP namespace** over Streamable-HTTP
+   (`pool.localhost:12010/p/neovim/mcp`) rather than spawning a per-session
+   `npx` stdio child — one persistent server, shared across sessions. Because of
+   MetaMCP's aggregation, the tools surface as `mcp__neovim__neovim__vim_*`.
+2. **`coder/claudecode.nvim`** loaded inside nvim, with `<leader>a*` keymaps
+   wired (toggle, focus, send, accept/deny diff).
 
-This plugin doesn't ship those — it depends on them and ties them together with one agent and three skills.
+This plugin doesn't ship those — it depends on them and ties them together with
+one agent and three skills.
+
+## Connection path
+
+```text
+Claude Code session
+  └─ .mcp.json → http://pool.localhost:12010/p/neovim/mcp   (Streamable-HTTP)
+       └─ mcp-session-pool (:12010, M=1 session pooler)
+            └─ MetaMCP `neovim` namespace upstream
+                 └─ mcp-neovim-server (one persistent stdio child on emmett)
+                      └─ /run/user/1000/nvim.sock           (nvim msgpack-RPC)
+                           └─ the running Neovim
+```
+
+MetaMCP and the pool both run on emmett as systemd services under user `oleks`,
+so the per-user socket is directly reachable. If `mcp__neovim__neovim__*` tools
+are missing, walk the chain top-down: socket exists? `systemctl status metamcp`?
+session restarted since the wiring landed?
 
 ## Layout
 
-```
+```text
 nvim-agentic-companion/
 ├── .claude-plugin/plugin.json    # manifest + userConfig (socket, config path)
 ├── agents/
@@ -24,13 +50,21 @@ nvim-agentic-companion/
 
 ## Agent
 
-`companion` — answers questions about the *running* nvim ("what's bound to `<leader>ff`?", "is lualine actually using catppuccin-mocha?") and acts on it ("open neovim.nix at the lualine block"). It reads the declarative NixVim config as the source-of-truth for *why* things are set up the way they are, and the live editor for *what is actually loaded right now*.
+`companion` — answers questions about the *running* nvim ("what's bound to
+`<leader>ff`?", "is lualine actually using catppuccin-mocha?") and acts on it
+("open neovim.nix at the lualine block"). It reads the declarative NixVim config
+as the source-of-truth for *why* things are set up the way they are, and the
+live editor for *what is actually loaded right now*.
 
 ## Skills
 
-- **`editor-introspect`** — read-only queries against the live nvim (keymaps, buffers, options, diagnostics, plugins, messages, cursor, selection).
-- **`editor-act`** — safe driving: open files, jump to definitions, trigger user keymaps, toggle UI. Does **not** edit buffer contents.
-- **`claude-code-handoff`** — when the work is "change code in this buffer," hand it to the in-editor Claude Code session so the user gets a diff to accept or reject inline.
+- **`editor-introspect`** — read-only queries against the live nvim (keymaps,
+  buffers, options, diagnostics, plugins, messages, cursor, selection).
+- **`editor-act`** — safe driving: open files, jump to definitions, trigger user
+  keymaps, toggle UI. Does **not** edit buffer contents.
+- **`claude-code-handoff`** — when the work is "change code in this buffer,"
+  hand it to the in-editor Claude Code session so the user gets a diff to accept
+  or reject inline.
 
 ## Why split it three ways
 
@@ -38,16 +72,20 @@ The companion's three jobs have different blast radii:
 
 - *Reads* are free; do them eagerly.
 - *Edits to navigation/UI* are cheap to undo; do them when asked.
-- *Edits to code* deserve a diff and human review; route them through the inner Claude that already has the right UX for that.
+- *Edits to code* deserve a diff and human review; route them through the inner
+  Claude that already has the right UX for that.
 
-The skills enforce that separation so the agent doesn't drift into running `nvim_buf_set_text` directly when it should be sending to the Claude Code split.
+The skills enforce that separation so the agent doesn't drift into running
+`nvim_buf_set_text` directly when it should be sending to the Claude Code split.
 
 ## Configuration
 
-| Key             | Default                                                | Purpose                                                     |
-| --------------- | ------------------------------------------------------ | ----------------------------------------------------------- |
-| `nvim_socket`   | `/run/user/1000/nvim.sock`                             | Where the running nvim listens (must match the MCP server). |
-| `config_path`   | `/home/oleks/projects/servers/emmett/nixos/neovim.nix` | The declarative NixVim source the companion cites from.     |
+- **`nvim_socket`** — default `/run/user/1000/nvim.sock`. Where the
+  running nvim listens; must match the socket `mcp-neovim-server`
+  connects to (`NVIM_SOCKET_PATH` in the MetaMCP `neovim` upstream).
+- **`config_path`** — default
+  `/home/oleks/projects/servers/emmett/nixos/neovim.nix`. The
+  declarative NixVim source the companion cites from.
 
 ## License